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Electronics for the enthusiast iii 0 0. -~iii ... iii :::, < >, .D JULY 1988 FEATURES 4 Amplifier Headroom: Is It a Con? 16 50 70 84 by Leo Simpson Meeting the power demands of CDs Amcron MA-1200 Power Amplifier by Bob Flynn Born in the USA National Semiconductor's LM833 Op Amp by Leo Simpson The heart of the Studio 200 Stereo Preamplifier What is Negative Feedback? by Bryan Maher Pt.3 - Negative feedback and frequency response The Evolution of Electric Railways by Bryan Maher HAVING TROUBLE WITH your TV or FM reception? This booster amplifier may be just what you need to lift those signals up out of the noise. See page 30. PROJECTS TO BUILD 14 Flt a Fuel Cut-Off Solenoid to Your Car by Greg Swain Effective thief deterrent; also works with diesels 30 Booster for TV & FM Signals by Branco Justic Lift those signals up out of the noise 40 Studio 200 Stereo Control Unit by Greg Swain Construction plus troubleshooting 56 Build the Discolight by John Clarke Stage your own light show 74 Tone Burst Source for Amplifier Testing by Leo Simpson Checks out amplifier headroom and music power BUILD THE DISCOLIGHT and stage your own light show. It drives four channels of coloured lights which are modulated by music or an in-built pattern generator. Details page 38. SPECIAL COLUMNS 10 Vintage Radio by John Hill Checking and repairing the valves 18 The Way I See It by Neville Williams Are computers turning us into automatons? 34 Serviceman's Log by the original TV serviceman Sounding out a video recorder 64 Amateur Radio by Garry Cratt All about amplitude companded sideband DEPARTMENTS 2 Publisher's Letter 3 Mailbag 14 Circuit Notebook 89 Subscriptions 91 Product Showcase 92 94 95 96 Back Issues Ask Silicon Chip Notes & Errata Market Centre NO GAS, NO GO - with a fuel cut-off solenoid you'll have 'em snowed. Turn to page 14 to see how it's fitted. DIGITAL ELECTRONICS series: due to severe demands on space in this issue, we have had to hold the Digital Fundamentals article over until next month. JULY 1988 1 SILICON CHIP Publisher & Editor-In-Chief Leo Simpson, B.Bus. Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Advertising Manager Paul Buchtmann Regular Contributors Neville Williams, FIREE, VK2XV Bryan Maher, M.E. B.Sc. Jim Yalden, VK2YGY Garry Cratt, VK2YBX Jim Lawler, MTETIA John Hill David Whitby Photography Bob Donaldson Edltorlal Advisory Panel Philip Watson, VK2ZPW Norman Marks Steve Payor, B.Sc., B.E. SILICON CHIP is published 1 2 times a year by Silicon Chip Publications Pty Ltd. All material copyright (c) . No part of the contents of this publication may be reproduced without prior written consent of the publisher. Kitset suppliers may not photostat articles without written permission of the publisher. Typesetting/makeup: Magazine Printers Pty Ltd, Waterloo, NSW 2017 . Printing: Masterprint Pty Ltd, Dubbo, NSW 2830. Distribution: Network Distribution Company. Subscription rates are currently $42 per year (12 issues). Outside Australia the cost is $62 per year surface mail or $1 20 per year air mail. Liability: Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. Address all mail to: Silicon Chip Publications Pty Ltd, PO Box 139, Collaroy Beach, NSW 2097 . Phone (02) 982 3935 . ISSN 1030-2662 * Recommended and maximum Australian price only. 2 SILICON CHIP PUBLISHER'S LE'l.l'ER The widening scope of activity for electronics enthusiasts Since we started SILICON CHIP it is evident that there has been a certain amount of confusion over what the name means. Some people think it refers to computers because they associate the terms "silicon chip" or "micro chip" with computers. That's not unexpected really, since the media have been rabbiting on for years about the microchips used in these wonderful new beasts, computers. It is also not uncommon to find SILICON CHIP stacked up against computer mags in the newsagents. This, in spite of the banner on the front of the magazine proclaiming the fact that it is "Australia's new electronics magazine''. Some people who are well acquainted with electronics sometimes also associate SILICON CHIP with computers because it has seemed to them that most recent electronic devices have been computer related. That too, is not an unexpected reaction. Over the last ten years or so, the technical media have bored their readers to death with reports of the latest micro whiz-bangs. Even the semiconductor companies themselves have contributed to this impression, with floods of press releases on the subject. In fact, everywhere you read about electronics it has seemed that the mainstream activity has been microprocessors. Well, we're here to tell you that isn't so. Since we started work on this magazine some ten or so months ago, we have been collecting as much data as we could from the major electronic components distributors. The shelves in the SILICON CHIP offices are literally groaning under the weight of these data books and they are being added to almost on a daily basis. We're having trouble keeping up with it all. And the vast majority of this data has little do with microprocessors. . The truth is that the last few years have brought forth an explosion of new devices from the semiconductor companies. There are large numbers of new thyristors, bipolar transistors, power Mosfets and many other discrete devices, optoelectronic devices of all sorts, and thousands of logic and linear devices related to virtually every field of electronic activity: consumer, automotive, telecommunications (telephone, video, radio), military and so on. A few years ago, a colleague of ours predicted that in about ten years' time, there would be little scope for activity by electronics enthusiasts. He was wrong, by a very long shot. Today there is vastly more scope for electronics enthusiasts, thanks to the incredible numbers of new devices continually becoming available. SILICON CHIP is devoted to the electronics enthusiast and to the vast scope of electronics which permeates every facet of our lives. Yes, silicon chips are used in computers but they are also incorporated into or have a vital impact on every other product in use today. Leo Simpson MAILBAG Caution on the Party Light I recently purchased the May edition of SILICON CHIP and on the whole found your magazine very readable. However, I was rather alarmed by your "Party Light" project and felt compelled to write. Whilst the idea and project are fine, an essential warning to your readers has been omitted. High intensity flashes at a slow rate are exceedingly hazardous to people suffering from epilepsy; flashing lights can trigger epileptic fits. This is a serious situation indeed and one which should have been mentioned. S. Verlander Wanneroo, WA We checked the contents of your letter with a medical specialist who has confirmed that flashing lights can trigger seizures in some epilepsy sufferers. Indeed, even the innocuous effect of sunlight flashing through trees as a car drives along a country road has been known to bring on an epileptic attack. However, there are flashing lights everywhere; beacons, advertising signs, car traffic indicators and so on. How do these unfortunate sufferers avoid all these instances? For the record, the Discolight featured in this issue would present a similar hazard. Further questions on the MEN system In the April issue of SILICON CHIP, we published a letter from the NSW Department of Energy which commented on our article entitled "Your House Wiring Could Kill You". As noted there, we were not happy with that letter and wrote to the Secretary of the Department as follows: Dear Sir, I refer to your letter on the subject of our article entitled, "Your House Wiring Could Kill You". As such, the comments in the letter are patronising without really addressing the subject raised by the article. I have asked your Mr A. Mccarroll if he would like to add anything to your letter, since we intend to publish it, but he declined. I cannot understand how you can refuse to admit, as it seems in your point 4, that loss of earth and neutral due to corrosion is not a normal course of events. If metals are dissimilar, they must corrode. Nor can I understand the general attitude of complacency about the safety of the MEN system. Your Mr Mccarroll seems to take the attitude that since this occurence of lost neutral and earth connections has not been commonly reported (to his knowledge), it is not a problem. Correspondence published in SILICON CHIP in the January and March issues indicates that the problem is real and one which officialdom has yet to acknowledge. I would maintain that there are hundreds of thousands of MEN installations which have not been inspected for 20 years or more and which now must be getting to the point where they are becoming hazardous. In view of the fact that all installations must become more hazardous with the passage of time, will you please respond to the following questions: (1). Does your Department have a policy whereby County Councils are required or recommended to inspect consumers' neutral and earth connections on a regular basis? (2). If there is no present policy on this topic, will your Department now develop such a policy? (3). In view of the distinct possibility of a hazard developing with the MEN system, will your Department consider modifying the execution of the MEN system in domestic electrical installations? Leo Simpson Silicon Chip Publications The Department's reply I refer to the letter published in the April issue concerning the article entitled, ''Your House Wiring Could Kill You"and your following letter to this Department. Prior to answering the three specific questions asked in your letter, some general comment on the safety of the MEN system of earthing is necessary. The MEN wiring system is preferred by electricity supply authorities throughout Australia. It has a sound safety record with no recorded SILICON CHIP, PO Box 139, Collaroy Beach 2097. fatalities in NSW that can be solely attributed to the malfunction of the system. The satisfactory performance of the system can generally be attributed to its use of a minimum of two leakage/fault paths. In installations wired since 1976 the number of leakage/fault current paths has been increased to three by the addition of an earth electrode. Other systems of earthing do not offer such a simple but effective arrangement. The MEN system is utilised with the knowledge that a problem of 'nuisance' shocks often detected as 'tingles' on taps and the like may occur if the neutral connection should break or develop a high resistance. The Department of Energy monitors the 'nuisance' shocks that are reported to and investigated by supply authorities. Experience has shown that the number and consequences of such shocks are relatively minor, and if compared to the number of installations connected to supply, it would be difficult to argue that the MEN system is not working satisfactorily. It is important that persons who receive a minor shock recognise it as a warning of a possible hazard and report the instance to their local electrical county council for investigation and repair. Alternatively, the services of an electrical contractor could be engaged to rectify the problem. On the issue of corrosion of connections due to dissimilarity of metals such as copper and aluminium, electricity supply authorities have developed work practices utilising corrosion inhibitors to overcome this problem within their reticulation systems. In regard to connections within the consumer's installation, it is pointed out that copper or copper compatible materials are practically universal. In any other case, the SAA Wiring Rules require that earthing conductors be protected from corrosion by means of suitable insulation or enclosure. In respect to the specific questions asked by you, the following comment is offered: (1). The Department of Energy does not currently have a policy which continued on page 93 JULY 1988 3 IS IT A CON? Amplifier headroom is a subject of considerable debate amongst audio enthusiasts. Is it a legitimate way of increasing amplifier power or is it all a con? Well, it depends. By LEO SIMPSON The compact disc is to blame. If the compact disc hadn't come along some five or six years ago, this controversy probably would never have arisen. Amplifier manufacturers would have gone on in the same old way, gradually refining their designs, lowering distortion, increasing reliability and so on. But all of a sudden, the compact disc changed the rules. No longer were contemporary amplifiers up to the job of coping with the signal quality of compact discs. Nor were loudspeakers up to it for that matter and, indeed, many still aren't. Before CD Let's backtrack a little and consider the pre-CD era, say ten or more years ago. Vinyl discs and cassette tapes ruled supreme and signal dynamics were nice and predictable. Recording engineers knew damn well that the sound quality of vinyl records was nothing 4 SILICON CHIP like as good as that off master tapes and master tapes weren't really able to cope with the signal dynamics of live performance. Everyone knew it but that was life. Then along came direct-cut vinyl recordings. Mixing was minimal, with no taping, no signal processing, no nothing. The recording sessions went straight onto the disc and suddenly vinyl recordings took on new life. They sounded "live" certainly much more dynamic than contemporary recordings. But people persisted in playing them at the same general loudness as they were used to, or even louder, and speaker::, began to "blow". There was one particular direct-cut disc of the 1812 Overture that hifi dealers dreaded. People would buy it, get it home, whack it on the turntable, turn up the wick and let 'er rip. Everything, would be more or less OK until the cannon shots and then the speakers would blow out! Some hifi dealers used to reckon that the record should have been been banned. What was happening was that these new recordings had much more dynamic range than the old ones and when a really loud crescendo came along the amplifier would overload severely. Not only did that sound terrible but, paradoxically, an amplifier in severe overload actually delivers a hell of a lot more power to the : speakers. Not surprisingly, the speakers don't like that. More often than not, the tweeters are the first to croak, giving up without a whimper, in just one short burst of power. Midrange drivers can suffer almost as badly and frequently burn out too. Woofers mightn't burn out but they can be so badly over-driven that one or more turns on the voice coil can be loosened and then they sound as though their voice coils Facing page: NAD's biggest commutating amplifier, the model 2600, has a dynamic headroom of + 5dB, giving it a burst capability of ◄ 500 watts per channel compared with a continuous rating of 150 watts per channel into 80 loads. are "poling". The result is the same as if they were burnt out - they have to be re-coned or replaced. 2 ID :s. . "". 1.75 ~ , ::E = al 2 1.5 :fi :z: ~ 1 1.25 z ► 0 20 50 100 200 500 1000 2000 j!!lc iii ii le~ 1 3000 BURST LENGTH (ms) Fig.1: this diagram shows the "power envelope" for conventional amplifiers. For a 20ms burst, the best "dynamic headroom" these amplifiers can achieve is about + 2dB. After CD Compact discs made the situation even worse. Now the recording engineers didn't have to worry about whether the phono cartridges could actually track the discs (often they couldn't). This meant the dynamic range could be even wider than for direct-cut vinyl discs. Signal "crushing" was a thing of the past. Pianos, percussion instruments, brass and wind instruments, all came through the recording process with their full signal range intact. Speakers were dying all over the place - or being found severely wanting. Mind you, the quietness of compact discs didn't help. At least when you put on a vinyl disc the noise of the run-in groove gave you some clue as to how loud the volume control was set. But not with compact disc. Put the disc in the machine, press a button and then wham, right out of utter silence came this ultra-loud music. People have taken a while to learn that CDs are different in that respect. So the era of the compact disc has made new demands of amplifiers and loudspeakers. It adds up to a much larger dynamic range than ever before - louder peaks and much quieter background levels. This does not mean that the average listening level need be any louder than people have become used to. It is just that, having set the volume control for a comfortable listening level, the normal peaks of the music will be "crushed" (read: clipped, chopped off, overloaded, whatever) unless your amplifier and loudspeakers are out of the ordinary. To produce the same average loudness level as you have become .""== / "". ::E re 3 IHF DYNAMIC POWER FOR TRANSIENTS w :z: w 2 ::E z ► 1 0 20 50 100 BURST LENGTH (ms) Fig.2: commutating amplifiers have much higher dynamic headroom than conventional amplifiers (shaded portion). They can also maintain their very high "burst" power outputs for as long as 500ms. 300 250 200 .......... ...... -- -- 150 """'---. .... __ !_ ------ O'------J----'-----'--__;;;=-=-===:1:.--.....:-.-.,100 20 50 1OD 200 500 1ODO 2000 3000 BURST LENGTH (ms) Fig.3: curve A is for a commutating design such as NAD, curve B is for a conventional amplifier as depicted in Fig.1, and curve C is for a very big conventional amplifier. used to used with vinyl discs, your amplifier must be able to deliver a great deal more power, to safely handle the normal peaks of the music. If it can't, you will be missing out on the full signal quality which the CD system can deliver. (Strictly speaking, you could get the same result by having speakers which were much more efficient but that is not a really easy solution. So more amplifier power is the solution. Lots more.) Unfortunately, with just a few exceptions, amplifiers have not become more powerful. (They have become quite a lot more expensive but that's another story which is all too familiar). The ideal system Given a pair of loudspeakers with typical efficiency of 90dB (at 1 watt, 1 metre) in a typical lounge room, you really need an amplifier which will put out several hundred watts per channel, if you are not to "clip" the music signal on peaks. Troubte is, genuine hifi amplifiers with a continuous rating of several hundred watts per channel aren't cheap. Big transformers, high voltage high capacitance filter capacitors, lots of output power transistors and big heatsinks cost real money. But if you want genuine big power, continuously rated, that's the only way to go. Or is it? JULY 1988 5 Dynamic Envelopes of Various Music Signals 500mS BOmS 250mS These oscillograms show typical signal "envelopes" from today's CD recordings. Fig.4 at left is from the Bee Gees "Paradise" disc and shows a 500ms signal burst. Fig.5, at centre, is from Genesis "No Reply At All" and shows bursts BOms long. Fig.6 at right is from a recording of Bruckner's Symphony No 4 and shows 250ms bursts. (Photos by courtesy of The Fallc Electrosound Group). Quite a few years ago now, at least one amplifier manufacturer realised that there was a way to obtain a great deal of power from a relatively small amplifier, but there was a catch. With this approach, you could obtain several hundred watts per channel from quite a small amplifier but only for very short periods, say for a tenth of a second or less. After that, if high power was still being demanded by the music signal, the amplifier was only able to deliver quite modest power, say 50 watts per channel, on a continuous basis. The reason why this approach works is that music signals are not "steady state". They vary all over the shop with the really loud peaks, say from a cymbal clash or trumpet crescendo, happening along with fairly long intervals between each such event; time enough for the amplifier's power supply to rec,over and be ready for the next burst. Bob Carver (with his "magnetic field" amplifier) is generally recognised as the person who pioneered this approach but there were others before him. Hitachi was probably the first, with "class G" amplifiers. Then there was Soundcraftsman with "class H" and then later in the piece, Yamaha, NAD (with the "PowerTracker"), Proton and Crown produced amplifiers with similiar concepts. Commutating amplifiers Such amplifiers are sometimes referred to as "commutating" 6 SILICON CHIP amplifiers. They are able to deliver such high short term power outputs by varying their power supply rails in response to the signal. When a big input signal comes along, which will require a lot of power output capability if it is not going to be clipped, the amplifier automatically increases the supply voltage to its output transistors. This allows the transistors to deliver very high power. When the music signal drops back to normal levels, the supply voltages to the output transistors are also reduced, so that the average power dissipation in the output transistors is kept at a low level. This allows the designers to get away with a much smaller power transformer, much smaller heatsinks, and so on. Typically, in one of these "commutating" amplifiers, the supply voltages are increased by 50 % or, in some cases, by more than 100%. This can mean prodigious increases in short term power, 400% or more. For example, an amplifier with a continuous power rating of 50 watts per channel can have short term power output of 200 watts per channel or more. Just quoting one example, the 7240PE stereo receiver from NAD has a continuous power rating of 40 watts per channel into 80 loads but a short term power output of 160 watts per channel into 80 loads. Or take the Proton Dl200 power amplifier. It has a continuous power rating of 155 watts per channel into 80 loads but its short term ratings give it over 590 watts under the same load conditions. Headroom, dynamic power and all that Well, there is no doubt that such amplifier design techniques work. In terms of amplifier "bang per buck" they are unbeatable. But how do you measure such amplifiers legitimately? In the past there was music power. This is the short term power delivered by an amplifier with "music" signals. Then there was peak music power which without going into the maths of it, gives a rating which is twice that of music power without giving the slightest bit more sound power. These terms became largely discredited years ago when some amplifier manufacturers were "conning" the buying public with enormous ratings which meant nothing in reality. What stopped this rort was the US Federal Trade Commission (FTC) which ruled that amplifiers had to be sold with a "continuous power" rating. This rating could only be arrived at after the amplifier had been preconditioned for an hour at one-third of its rating. This forced the amplifier designers to be much much more conservative in their ratings and so the public then got amplifiers which really did have genuine power ratings. Even so, high fidelity enthusiasts and designers recognised that virtually all amplifiers could deliver more power on a short term basis. To take note of this, the United States' Institute of High Fidelity (IHF) devised a tone burst test of amplifier power. This was defined as the power output delivered by an amplifier for -a burst of 20 milliseconds at intervals of 500 milliseconds (ie, twice per second). The IHF also came up with a new term called Dynamic Headroom which was expressed as the ratio between the continuous rated power of an amplifier and the power delivered under the tone burst test just defined. Being a ratio, Dynamic Headroom is not specified in watts but in decibels, which is a logarithmic measurement of ratio. Typically, amplifiers designed to meet the FTC conditions deliver not much more power under tone burst conditions than they do under continuous tone conditions. This is because they have well-regulated power supplies which don't vary much, regardless of the power demands. For example, an amplifier with a continuous rating of 100 watts per channel (under FTC guidelines) might have a short term (20 millisecond) power output of 120 watts per channel. This gives a dynamic headroom of only + 0.8dB which is nothing to get excited about. But when one of these newer commutating amplifiers comes up with a dynamic headroom of + 6dB, then it's time to sit up and take notice. There is some controversy however. Some amplifier designers and keen enthusiasts regard the 20 millisecond tone burst test devised by the IHF as having no relation to real music. In their opinion, musical peaks and crescendos last much longer, up to as long as 500 milliseconds. And they offer some compelling evidence in the form of oscillograms of music recorded on today's compact discs. Some of these oscillograms are included with this article. They show that peak program signals can easily last for 250 milliseconds or more. Now you might say, "So what? If the peak demand lasts longer that's easily fixed by setting the volume control so that the amplifier doesn't easily overload". If that is your attitude you've missed the message HIGH VOLTAGE SUPPLY CURRENT _.M.,..ON::.:,ITO..,R_ _ _ II I t SIGNAL MONITOR I I I NORMAL SUPPLY II I I t r_____ . ., _____..,. I I I \ SPEAKER Fig.7: this diagram shows how the NAD PowerTracker circuit commutates. It monitors the audio signal and increases the power supply rails to each hall of the amplifier's output stage, dramatically increasing the short term power capability. about the dynamic range of compact discs. The peaks are much louder than the average signal and, as we have just seen, they last for relatively long periods of time. So either you listen at your accustomed loudness levels and "clip" the music on peaks or you listen at much lower levels and miss out on all the soft bits of the music (or listen on headphones). Clearly, if amplifiers are to cope with these signal demands they need to be very powerful. So you have two choices. One, go the brute force way and get an amplifier with as high a continuous power rating as you can afford; or two, purchase an amplifier with large dynamic headroom. The second choice is possibly the better way to go because then you can spend more on loudspeakers, the more efficient, the better. There remains one question. Some enthusiasts reckon that the " commutating" action of these new high headroom amplifiers leads to audible distortion. On some of the early amplifiers of this type, the sound quality was not as good as it should have been and possibly this was partly due to the action of the power supply switching circujts. These days though, amplifier designs produced by manufacturers such as NAD, Proton, Carver and others are highly respected for their sound quality. They are the new generation of amplifiers, more powerful, more compact and more affordable. ~ Another big commutating amplifier, the Proton D1200 (shown with its companion D1100 stereo preamplifier) has a dynamic headroom of + 6dB and a dynamic power output close to 600 watts per channel. JULY 1988 7 Ain't no good Extra Value Power tor drin~i~'! Transformers! But these bargain priced JI DSE2155 3, 4.5, 8, 7.5, 9 & 12V<at> 300ml Stubbles are Just the thing for those hard to get screws! Flat blade chrome Primary: 240V, 50Hz. vanadium. Secondary voltage: 6.3, Cat T-6020 7.5, 8.5, 9.5, 12 & 15V. 50 Secondary current: 1 . amp. Terminations: Flying leads. Cat M-2155 $1 Probably the most versatile supply you can get! Swltchable output with 6 different voltages from 3-12V. Cat M-9526 Medium '695 duty150MM Blade Stock up the toolbox with DSE2840 one of the handiest screwdrivers you can get. Flat blade (5mm dia .) with 6" shank gives plenty of leverage! cat T-6050 Up to 1/3 LESS than you'd pay anywhere elsel Quality NPO Ceramic capacitors at sensational prices. Stock up now while '°Y; ~-:~-ig~~.: ~~p~ 33~F 47pF 56pF 68pF 82pF R:9038 R-9039 R-9040 R-9041 R-9042 ,:g:r ~::gn 3.9pF 68 2·2PF · PF -~~~~ 560 F 15 F P l R-90 45 ~-ig:~ - ~=~8~ 9 1 R- 9052 R-90S 3 $ 150 · .. ~lllliii~li'!'-==~~:...._ ~ 4516 Presettable up/down counter. Cat Z-5738 $1.95 4526 Counter binary. divide by N Cat Z-5744 $1 .20 74HC08 Quad 2 input and gate. Cat Z-5808 70c 74HC11 Triple, 3 Input and gate. Cat Z-5811 404: 74HC139 1 of8 decoder/multiplexer. Cat Z-5920 .95 74IIC157 Quad 2 input multiplexer. Cat Z-5925 Was $1.95 Now $1.50. 74LS31 Delay line IC. Cat Z-4931 65c. 74Hc165 Par load 8 bit shift register. Cat Z-5930 $1.50 74HC174 Hex D-type flip flop. Cat Z-5935 Save 45c Now $1.50 74HC27 Dual J-K flip flop. Cat Z-5827 50c. •y•• Primary: 240V AC. Extra heavy duty Tapped Secondary screwdriver that's Ideal voltages: 15, 17.5, 20, 24, for tradesman and 27.5 & 30V. Secondary hobbyist alike. Chrome current: 1 amp. vanadium, flat blade. Terminations: Solder ~ l u g s. CatM-6672 74LS1383-8 Perfect for CB, car stereos, small amateur receivers and the like. With screw terminals for easy connection. Makes a computer! The Jable line filter virtually eliminates most mains borne garbage. Rated at 240V, 2 amps. Cat M-9850 ;ii,•149- '295 ' 1195- 74HC85 4bit magnitude comparator. Cat Z-5885 $1.50 All the power you'll need for 2m or small HF amateur transceivers, etc. Ideal for 'auto' equipment or as a bench supply. 3A continuous or 4A continuous <at> 75% duty! Cat M-9547 Computer Regulated. 12V protection Spikes and other garbage <at> 1.5A can spell disaster for your ., . . , :~;;Juty osE&&;2 ·. Blade .. Sa _v_e_o _n_ D-ig-ita - 1-IC...s 4002 Nor gate dual. 4 Input. Cat Z-5602 40c 4015 Shift register dual 4 stage. 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Phone, FAX Telex, Telegram, Mail or Viatel - 6 great ways to get your order through - pronto! s 19es VINTAGE RADIO By JOHN HILL Checking and repairing the valves A good collection of valves is essential for the vintage radio enthusiast. In most cases, these will have to be scrounged or salvaged from derelict chassis. Here's how to check the valves for serviceability. The valves are the heart of a valve radio and must be in good condition if the set is to function correctly. Faulty valves can cause any number of problems, from totally silencing the receiver to intolerable distortion, weak reception and intermittent operation. Therefore, if a valve radio is to be restored, it is essential that the valves be checked and any faulty or suspicious ones discarded. When I'm faced with a valve problem, the first thing I do is to check them with a valve tester. A welldesigned valve tester can perform a number of functions, the most important one being an emission test. Good valves have strong emission whereas poor valves have weak emission. (Emission is the ability of the cathode to emit electrons. If emission is low, virtually no current can flow through the valve). Valve testers usually have a built-in meter which is graduated from 0-100%. Any reading from zero to 45 % is considered poor; 45-55% is questionable; and 60% and above is considered good. The average valve tester is a comparatively simple device, al- A box of old triodes from the 1920s. All checked out OK in the valve tester. A ·good collection of valves is essential for the vintage radio enthusiast. 10 SILICON CHIP though the internal wiring and switching is quite intricate. The usual set-up is to tie all the grids and plates together for a total emission readout. My "Heathkit Tube Checker" has a switching arrangement which allows each valve component to be disconnected one at a time so that every base pin can be individually checked for internal problems. All readings are indicated on the meter which tells the operator if there are internal defects in the valve, such as a broken wire to the base pin being checked. Whilst a valve tester is a handy instrument to have, it is not an. essential piece of equipment for the vintage radio enthusiast. I did quite well without one for several years and I certainly do not put all my trust in a valve tester. Although a valve tester gives the operator every indication that a valve is either serviceable or suspect, one really doesn't know for sure if a valve works or not until it is plugged into a radio set and given a run under actual working conditions. To my thinking, the ultimate test for a valve is an emission test followed by a test in a radio to see if it really does work. If a valve passes both tests there cannot be much wrong with it. When testing a valve it is always a good idea to give it a gentle tap to make sure there are no loose components inside that may vibrate and cause trouble. Tapping a valve with faulty internals can induce arcing as well as intermittent on/off and loud/soft situations. A suitable valve "donger" can be made by fitting a rubb,e r grommet to one end of a pencil. A x2 magnifier is handy for inspecting valve filaments and cathodes. The cathode in a good valve will be coated with a whitish compound. Big was beautiful back in the good old days. Shown is an E406, an early AC output valve. The type number has been scratched into the base for identification. Resoldering the base pin connections will often bring a faulty valve back into service. Remove the old solder and clean the wires and base pins before resoldering. Heater checks A few years ago I bought about 120 secondhand valves (mainly oc- A valve should be gently tapped during iesting to show up any intermittent faults. A rubber grommet fitted to the end of a pencil makes a suitable valve "donger", I now have few problems regarding the testing of any commonly used radio valve. I can either test in the valve tester or in a restored radio receiver and either method will give fairly reliable results. But such a convenient situation takes time and money to develop. On the other hand, anyone just starting_to restore their first radio may face quite a problem in finding out if the valves in the set are serviceable or not. If the set goes, the valves must be working; if it doesn't, there is uncertainty as to whether the problem is a defective valve or some other component. There is really no answer to this dilemma other than to have a selection of known good valves that can be used as substitutes. But getting such a collection of valves together takes time and it is unlikely that a new chum to vintage radio restoration will have them. Similarly, it can take years to collect and restbre enough different radios to test a wide range of valves. tal and pre-octal; ie, having a Bakelite base with eight pins) at a time when I had only one receiver. Naturally, any of the valves that fitted that radio were tested in it, but that still left around 100 or so untested. I made some attempt to test the others by checking the continuity of the heaters and found that about one in every twenty was burnt out. The rest were therefore declared "good" and time has proven that most of them indeed were. There were very few duds among those that checked out OK with the ohmmeter across the heater pins. The above test is not a conclusive one as it only checks out the heaters and no other elements of the valve. However, a burnt out heater is a ]UL Y 1988 11 Loose valve bases can easily be repaired with a few drops of "Super Glue". In some cases, it may also be necessary to resolder the pins. fairly common type of valve failure, so checking heater continuity is a good test when no other means of testing is available. Cathode inspection With the exception of some rectifiers, battery valves and a few early AC valves, most valves have a cathode that is heated by an insulated filament (heater) running through it. Some discussion on this cathode may be of value because it has some bearing on the usefulness of the valve. In most valves, it's possible to inspect the cathode using a x2 magnifier. When the cathode is viewed in this manner, it is clearly seen that the metal tube which forms the cathode is coated with a whitish compound that looks very much like icing sugar. Cathode coatings may vary from one manufacturer to another, but regardless of what it is, its job is to emit copious amounts of electrons when the cathode is heated. Now the reason for mentioning this is that when a valve is totally worn out, the cathode coating has all but disappeared. I have observed a number of such valves where the cathode was almost bare with Bakelite and plastic: what's the difference? A number of readers have taken us to task over the terms plastic and Bakelite, as used in this series on vintage radio . As they have pointed out, Bakelite is a plastic. We'll now set the record straight. Bakelite was one of the first plastic materials to be used on a large scale. The trademark Bakelite is named after the inventor, L.H. Baekeland (1863-1944). There are two broad types of plastic: thermosetting and thermoplastic. Bakelite belongs to the thermosetting type and is made by applying heat and pressure to a mixture of phenol (or cresol) and formaldehyde. Thus, the chemical 12 SILICON CHIP name of Bakelite is phenol formaldehyde. Once moulded and set, a thermosetting plastic like Bakelite is very rigid and stable and was an ideal material for radio cabinets. Later radios were mostly made from thermoplastic materials such as cellulose acetate, polyethylene, polyvinyl chloride (PVC) and polyvinyl acetate (PVA), with fillers and dyes added for rigidity and colouring. These latter materials, as the name thermoplastic suggests, are not as stable; they deform under heat. In practice, they haven't lasted as well as Bakelite either. only a few wispy traces of the original coating remaining. These valves still worked but their performance was weak indeed. This knowledge can help a collector who has no valve tester sort out possible good valves from relatively poor ones. If an inspection of the cathode reveals that the coating has all but disappeared or is cracked or broken away, then the valve is suspect. Unfortunately, not all valves allow you to make a cathode inspection. A similar procedure can be applied to rectifiers such as old 80s and 5Y3s. In this type of rectifier the filament is the cathode and is also coated with an electron emitter. Good rectifiers have well coated filaments while poor rectifiers have near bare filaments. The rectifier valve is a very important component in a valve radio. If it's weak, the set will be starved of high tension current and will perform poorly. A set with a weak output can often be cured by replacing a worn-out rectifier. Bright emitters Early valves, made before 1922, didn't have coated filaments and to obtain sufficient emission, brighter filaments were used, These were similar in brilliance to incandescent lamps. However, it was later found that filaments containing thorium or coated with calcium and other special compounds gave adequate emission at much lower temperatures. These early valves were known as " bright emitters" while the later ones were referred to as "dull emitters" . Dull emitters use considerably less filament current, work at much lower temperatures and last longer. Many valve designs from around 1930 on have a "top cap"; ie, an external connection on the top of the valve. Most top caps are hooked up to a grid but some can be the plate connection, so it pays to be careful where you place your fingers. A common problem with this type of valve is that the top cap can become loose or even fall off. Such a valve is not lost - it only needs repairing. Resoldering and regluing the top cap with "Super Glue" will cure this minor problem. envelope. Once this has been done, the pin connections can be resoldered. Resoldering the base pins will often reclaim a faulty valve and that applies to all base type valves, 1920 models or otherwise. Collecting valves Although not essential, a valve tester eliminates a lot of uncertainty when checking valves. This is the author's Heathkit Tube Checker. Valves can also be tested by direct substitution in a known good chassis. Whilst the above remedy sounds simple, some valves are more difficult to repair than others because the protruding wire sometimes breaks off short. When this happens, it is necessary to nibble away some of the glass and carefully solder on a short extension. In some cases, the valve will have completely lost its top cap. It therefore makes sense not to throw away defunct valves, since the top caps and bases can be salvaged and used to repair damaged valves. The base of an old valve can also become loose and a number of glues (including "Super Glue") can be used to re-attach it to the glass envelope. Pin connections One often troublesome fault in very early valves (1920s types in particular) involves the pin connections. The solder at the joint seems to decompose with age, eventually forming a poor or open-circuit connection. The remedy is to first remove the old solder and carefully clean the wires from the glass Loose or detached top caps can be a problem with old valves. The valve can be saved by carefully resoldering the cap and then re-gluing with "Super Glue". Unfortunately, new valves are no longer readily available for most radios. But if you're in the know and have the right contacts, it's surprising what is available on the secondhand market. If you have any doubts about the scarcity of new valves, then try to buy an old 80, a 2A5 or 6B7 and see how you make out. If you would like a more challenging assignment, how about a B406 or an E415. New or secondhand, some of these oldtimers take a bit of finding. Even if they can be found, they don't always work. The only new radio valves that are likely to be available are the more recent miniature types. As far as earlier valves are concerned, it's usually a case of scrounge or go without. Those who may have doubts about using secondhand valves should not worry unduly because there are a lot of good used valves around just waiting to be collected. It's up to you to start looking and find them. Wrecking radios unfit for restoration is a good source of supply. Next month's vintage radio topic will be on capacitors. ~ Close-up view of the meter on the Heathkit Tube Checker. It gives a readout of total emission in percentage terms. Any reading above 60% is considered good. JULY 1988 13 Interesting circuit ideas which we have checked but not built and tested. Contributions from readers are welcpme and will be paid for at standard rates. Fit a fuel cut-off solenoid to thief-proof your car The fuel cut-off solenoid is supplied complete with two threaded nipples, rubber fuel hose, hose clamps and a DPDT switch. If you're one of those people who is not keen on the idea of fitting a car burglar alarm, what about a fuel cut-off solenoid? You might have thought of using an ignition cut-out instead but that is not much good if your vehicle is diesel powered. The fuel cut-off solenoid is the answer. We have just come across a fuel cut-off solenoid available from Jaycar Electronics (Cat. , No. XC-2050). In the unenergised condition, the fuel is cut off. Current drain when the solenoid is energised is about 650mA. In cars with carburettors, the fuel cut-off solenoid can be installed between the fuel pump and the filter (if there is one). In dieselpowered vehicles, the fuel pump will be a positive displacement type and therefore the cut-off solenoid must be installed before the pump (otherwise damage could result). Note: in cars with electric fuel pumps, a cut-off solenoid is unnecessary because you can stop the fuel flow by switching off the 12V supply. The solenoid is supplied with a pre-wired miniature DPDT toggle ~:iw~ +12V VIA---t-er Fig.1: this circuit activates a dashboard flasher when the fuel is cut off. 14 SILICON CHIP 12V BUZZER S1o--- Fig.2: this circuit sounds a buzzer if you turn on the ignition but forget to also turn on the solenoid. A buzzer could .also be added to the circuit shown in Fig.1. switch plus fittings. These include two threaded nipples with tails for push-fitting 8mm rubber fuel hose (also supplied) and four hose clamps. Installation will vary from car to car but the solenoid assembly can be mounted in a number of ways. It is fitted with a 6mm threaded stud and has two holes drilled in the valve assembly which also could be used for mounting to a panel or bracket. One side of the solenoid coil is connected to the frame so that only one wire needs to be connected to complete the circuit. There are a number of options for wiring in the solenoid. Fig.1 is perhaps the most comprehensive. One pole of the switch feeds + 12V from the ignition switch through to the solenoid while the other pole feeds + 12V to a dashboard flasher (Jaycar Cat. No. KJ-7000) when the switch is in the off position. In this way the flasher gives the impression that a burglar alarm is fitted too. (Cunning, huh?). Naturally, the switch should be concealed, as should the wire to the solenoid. Fig.2 deletes the flasher and substitutes a 12V buzzer. Thus, if you turn on the ignition and have forgotten to turn on the hidden switch for the fuel solenoid, the buzzer will sound. Fig.3 is a more complex option using the buzzer. The drawback with Fig.2 is that if you forget to turn off the fuel solenoid after turning off continued on page 91 I FUEL CUT-OFF S0LENOI[ Fig.3: by adding a diode and a capacitor, the buzzer now also sounds briefly when the ignition is switched off, to remind you to switch off the solenoid. z DAVID REID ELECTRONICS LOW COST 20MHz CRO For the electronics enthusiast Aust. Pty. Ltd. GOOD WILL A basic 20MHz scope with extra features not found on similarly priced units GOS-522 HIGHLIGHTS A maximum sensitivity of 1mV/DIV (x5 magnification) Modes CH1, CH2, Dual, CH1 ± CH2, X-Y Choice of Sweep Displays Auto, Normal and Single shot Vertical Trigger Mode and Variable Hold-Off for ease of use 2 PROBES INCLUDED ■ ■ Auto Trigger Level Lock ■ 20ns/DIV timebase DC Trigger Coupling ■ Vertical Trigger Mode ■ Variable Hold-Off Fluke 73 Fluke 75 Fluke 77 Fluke 23 Analog bar graph 3200 count display 0. 7% basic de accuracy 10A Autorangingonly Three year warranty Analog bar graph 3200 count display 0.5% basic de Analog bar graph 3200countdi~ Safety yellow case Fluke TT features and 0.3%basicdc specs. plus lused lOA Autoranging with Range Autoranging with Range Hold 10A + autoranged mA Hold 1OA + autoranoed mA ranges Three year warranty Continuity and diode test beeper Touch-Hold"" Three year warranty GOS-522 Sensitivity SmV/DIV to SV/DIV, DC to 20MHz Timebase 20ns/DIV to 0.Ss/DIV $ 790 EX TAX s912 INCL TAX High quality Oscilloscope probes, suits all other brands 1 : 1 or 10: 1 Attenuation $ ranges Continuity and diode test beeper accuracy s264.oo INCL. 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Channel e • Range: 100MHz to 1GHz • Resolution: 1OOHz, 1KHz, 10KHz swilch selectable• Gate time: 0.027S, 0.27S, 2.7S switch selectable • Accuracy: ± 1 count ± time base error x frequency. 29 .95 Escort EDM-70H ► 3½ Digit LCD Display 6 functions DC V, AC V, DC A and Ohm Diode forward voltage test Transistor hFE test V DC 200mV to 1O00V, 5 ranges 1OOµV max resolution, ±0.5% V AC 200V and 750V 1 00mV max reslution, ± 1 .2% A DC 200µA to 2A, 5 range_s 1 00nA max resolution, ±0. 75% Ohm 200ohm to 2Mohm, 5 ranges 1 00Mohm max resolution, ±0. 75% ► EDM-708 ONLY VALUE AT: s60.oo ONLY 50 .00 $ Same as EDM-70H, but includes continuity buzzer and excludes hFE test. DAVID REID ELECTRONICS 127 York St, Sydney 2000 Ph (02) 267 1385 Fax: (02) 261 8905 INCL. TAX S499.oo AC/DC CURRENT ADAPTOR The DLC-200 is a handheld, adaptor that may be used with any 200mV Input multimeter. DLC-200 INCL TAX INCL TAX Ranges 200A, 400A AC and DC, ±2% 4 digits Output 1 mV/A: 200mV/200A and 400mV/400A BUSINESS HOURS MAIL ORDERS WELCOME Mon-Fri 8.30-5.30 Thurs 8.30-7.00 Sat 9.00-12.30 P.O. Box 0103 Sydney 2000 $1 - $25: $3.00 P&P $26 & over: $6.00 P&P s106.oo INCL. TAX $92.09 EX TAX VISA wC?lcomC? ni?rC? IMo,,.:~•••\I ]ULY 1988 15 HIFIREVIEW Amcron 1200 professional stereo power amplifier How do professional power amplifiers differ from domestic hifi stereo amplifiers? In the case of Amcron the difference is radical, as we found in our review of the Macro-Tech 1200. "Like a battleship". That's the expression most people would use if they had to come to grips with the Amcron Macro-Tech 1200 power amplifier. That's not entirely appropriate though because the battleship term conjures up something extremely rugged but otherwise lacking in technical refinement. So yes, the Amcron is rugged but that is only a small part of the story. We have seen a lot of power amplifiers in our time but not many intended for professional use. By professional use we are thinking of amplifiers used to drive studio monitors or for sound reinforcement in cinemas and theatres. In most of these applications the amplifiers are bolted into place and once commissioned, are never moved for years afterwards. And then there is the other "professional" application which involves sound reinforcement at indoor or outdoor venues that don't have an adequate PA system. In this situation, the amplifier must withstand the rigours of transport, rough handling and less than ideal installations but still deliver high power under often arduous conditions (read: rock concerts). These two separate applications produce a conflict for the designer. For the static installation it does not matter too much if the amplifier is really large and heavy, so long as it does the job very reliably. But the need to have gear that is move.able means that it really can't be too bulky or too heavy. Gear that is really heavy is often mistreated by "roadies" partly because it is too heavy to handle safely and partly because they just don't like it. So Amcron has evidently tried to satisfy two separate camps. On the one hand, it is a rugged amplifier but it is not all that large since it only occupies a standard two-unit high (88mm) 19-inch rack case. Nor is it outstandingly heavy for a 400 watt per channel amplifier (40 FTC rating) with an all-up weight of around 20kg. In the manner of most professional equipment it isn't all that pretty either. "Functional good looks" would better describe it. The lower half of the front panel is the inlet grille for the ventilation fan. The grille has a foam filter behind it to prevent dust and dirt from being sucked in by the fan. There are two level controls, one for each channel and a number of LED indicators which are much brighter than the subtle illumination found on domestic hifi amplifiers. They are meant to be bright; they dim to indicate overdriving or malfunctions. Internal details Inside the steel chassis is quite radically different from hifi amplifiers, as you can see from our photograph. For a start there is a high velocity fan which pulls air from the front and then blows it out through the honeycombed heatsinks at each side. And note the twelve power transistors on each heatsink: that's 24 in all! Two large power transformers are used, which is how Amcron Amcron use forced-air cooling and two separate power transformers to obtain a low profile in their MA-1200. It actually uses two amplifiers in bridge mode in each channel. 16 SILICON CHIP manages to make such a powerful amplifier with a low profile. Each transformer feeds two bridge rectifiers, a main and subsidiary, with the main bridge feeding a 10,000µF lOOV electrolytic capacitor. From there on the circuit becomes very complicated, although that is not immediately apparent. Removing the bottom panel reveals a whole lot more. One large board across the full width of the chassis accommodates the small signal circuitry while a board running down each side accommodates the power amplifier output stages. These latter boards are interesting because all the components, with the exception of the power transistors themselves, are mounted on the copper side. As you look at the amplifier it becomes appararent why they did it this way. The boards are effectively mounted on one side of the flat heatsink while the power transistors are mounted on the topside, with their base and emitter leads passing through and soldered to the copper side of the boards. As mentioned before, each heatsink has a honeycomb section (on the top, next to the power transistors) through which a lot of air is passed. That keeps it compact and cool. The trouble about looking at the inside of the Amcron though, is that it tells you virtually nothing. It is not until you look at the circuit diagram that you realise how unusual it is. Instead of the Amcron being a conventional stereo design, each channel is actually two power amplifiers with the loudspeaker load being driven in bridge mode. This allows the use of a relatively low supply voltage (90 volts total) which means that the bipolar transistors can deliver a great deal more power into low impedance loads. "Come again?", you say. The problem with bipolar transistors is "second breakdown". This severely limits the amount of current that they can deliver when they are running from a high voltage supply, even though they may have a dissipation rating of up to 250 watts. Amcron have got around that problem by halving the supply voltage and using two power amplifiers in bridge mode, in each This is the Amcron MA-1200 with the top cover removed. Immediately visible are the two power transformers, the 12 bipolar power transistors in each channel and the high capacity cooling fan. channel. So that's four power amplifiers in total. Amcron call it "full bridge" technology. We won't even try to to explain how the amplifiers are powered and connected together while still avoiding earth loops. That's complicated enough, but consider that the MA-1200 has three operating modes, selected by a slide switch on the back panel. The three modes are stereo, paralleled mono and bridged mono. Understanding how the two channels are run in parallel is easy enough, but how do you bridge two channels, that each consist of two amplifiers in bridge mode, to get one super-powered mono amplifier? Figure that one out. (There is no switching of the outputs by the way). Another interesting aspect of the MA-1200 is its protection circuitry, referred to as ODEP - Output Device Emulator Protection. This monitors the heatsink temperature and the power output from moment to moment and produces a signal which is determined by the always- · changing safe operating area of the transistor. If the margin is being ex- ceeded, the drive signal is reduced until the transistor junctions cool back to safe conditions. Power ratings In stereo mode, the MA-1200 will deliver 320 watts into 80, 465 watts · into 40 and 600 watts into 20 (per channel, at 0.1 % harmonic distortion). In parallel mono mode, it will deliver 630 watts into 40, 1000 watts into 20 and 1200 watts into rn. Yep, that's not a mistake and they are continuous ratings too. In bridged mono mode, it delivers 935 watts into 80 and 1200 watts into 40. Quoting the very comprehensive specifications would fill several pages of this magazine. How many manufacturers specify their amplifiers for rn loads? Amcron's manual also details some of the torture tests they do to their amplifiers to check output current capacity, their comprehensive protection circuitry, and their behaviour with inductive loads. We had trouble enough providing loads which could cope with the prodigious power output into 80 continued on page 95 JULY 1988 17 THE WAY I SEE IT By NEVILLE WILLIAMS Are computers turning us into automatons? Computers and computer-related devices are popping up everywhere, breeding like mice in a plague. They're taking over everyday tasks, doing our arithmetic, and defining our options with machine-like efficiency. But the more we rely on them, according to one reader, the more we behave like them; like automatons! So that you'll know what the correspondent is on about, I suggest that you read the letter set out in the accompanying panel. You've read it? Good! "Knickers in a knot", "Oliver Twist"! Get it? At least our correspondent can scarcely qualify as an automaton. That'll be the day when a humanoid can come up with spontaneous one-line gags. A whole generation of TV and radio presenters would become redundant. But what is an automaton? According to my dictionary, it has two principle meanings: (1). A mechanical figure or contrivance constructed so as to act, as if spontaneously, through concealed motive power; (2). A person who acts in a monotonous routine manner, without active intelligence. I imagine that our friend "Oliver" has the second definition in mind. He's fearful for all of us who use computers and computer based devices but his immediate and stated concern is for office workers, people who operate automated supermarket "chuckouts", attendants at self-service petrol stations and employees of the 18 SILICON CHIP Taxation Department. That's a fair cross-section of present-day wage earners! I must agree that, if one wants to ridicule and attack our burgeoning, computer-based society, there is no shortage of brickbats ready to hand. On the very day that I sat down to react in print to Oliver's letter, April 22, the following snippet appeared in "Column 8" of the Sydney Morning Herald. I quote it exactly as it appeared: A Kirribilli reader has been receiving letters for her late father from the Advance Banlc addressed to "Mr John K. R. Donavon Dec'd". The letters to the late Mr Donavon demand payment of his health insurance premiums. Undoubtedly, the above letters are being issued routinely by a computer-based system but again, one can hardly blame the machine for doing what it's been instructed to do. A human operator, a bit short on brainpower, has apparently failed to react correctly to formal notification of a person's death, such that the entry has ended up as a spurious name in the list of defaulters. That sort of thing can happen easily enough but if repeated, it ceases to be an oddity and becomes a source of annoyance. Three people, two addresses! For some time, my wife and I have contributed to a particular welfare organisation, quite routinely, until they were computerised. Then we suddenly found ourselves to be three separate people living at two adjacent addresses - presumably because one or other of us had signed the cheque on different occasions and because, at some other time, a door-knocker had confused our own and a neighbour's address. Concerned that they were wasting two lots of stationery and postage, we sought to bring the matter to their notice by indicating on a particular return slip that the other two were redundant and that, in any case, one had a wrong initial and the other a wrong address. But they didn't react to the information nor, apparently, did their system alert them to the fact that two of the three supposedly different people were consistently ignoring their literature. A similar experience with another organisation served to confirm the impression that their staff had become part of the system unwilling or unable to react outside their new "computerised" routine. As I see it, there is a real danger that the goodwill for a welfare cause will be undermined if the computer is allowed to replace rather than supplement human in- Why do computers inhibit common sense? Dear Mr Williams, Most of us have enjoyed a good laugh, at one time or another, at the expense of the unfortunate clerks in a Dickensian office, with their black coats, high stools, massive ledgers and quill pens. But I wonder whether we've noticed their counterparts in modern offices - young women mostly, in regulation uniform, perched behind plastic counters and seemingly hypnotised by a fluorescent screen. You want to know something, buy something, go somewhere, pay an account, draw money and it's always the same routine. They listen impassively, push a few buttons and intone what appears on the screen. It's the ultimate authority; they don't question it. Neither should you! I'm well aware that computers and their derivatives can speed up, rationalise, mechanise and automate a whole range of human activities but there's a problem: they're also eroding our very humanity. They're slowly turning us into automatons - users and victims alike. The supermarket where we do our family shopping has recently been redesigned, rebuilt and fitted out with all the latest gee-whiz technology. At the check-outs (chuck-outs?) they grab things as fast as you can unload your trolley volvement; if supporters begin to perceive that they are corresponding with a machine rather than a person. Self-service petrol stations? They're OK when you're in a hurry but I enjoy the rare experience of pulling into a country service station and having someone offer to fill the tank, check the oil and clean the windscreen. After three or four hours of pounding down the highway, a little human interest and conversation is welcome relaxation before heading out again onto the bitumen. Bar code "chuck-outs" As for bar code check-outs, I and swish them past a laser gismo. It goes beep-beep-beep, flickerflicker-flicker and you, in turn, have to grab your change and run before the next pile of groceries lands on top of your own. Perhaps it's too much to hope for the return of the friendly family grocer but, before this latest hurryup gadget appeared on the scene, there was at least some opportunity for human pleasantries on the way past the manually operated cash registers. A lot of the cashiers were real people! I don't like self-service petrol stations either - and it's not because I'm shy of pumps. But I find no satisfaction at all in doing all my own chores, finding where things are, and then handing my money to someone whose main function is to compare the amount proffered with that shown in the readout. What stirred me to get down on my butt and write this letter? I'll tell you. A few weeks back, knowing that settlement was due, I sent off a cheque to the Taxation Department, along with the relevant assessment slips and a request for an acknowledgement. None arrived but what I received instead was a pay-up-or-else notice and a statement that the overdue debt was currently incrementing at so many dollars per week. have mixed feelings. They are about as far as one can get from the friendly neighbourhood grocer; efficient but almost totally inhuman and so fast that it's difficult, if not impossible, to compare individual items with the price read-out. Yet technically, they intrigue me no end. I look back to an incident many years ago when an executive I knew in a now-defunct parts manufacturing business confided to me that he had just obtained Australian rights involving the use of bar coding to facilitate automatic identification of products and prices. It would revolutionise retailing, So I phoned my tax agent, who promised to inquire on my behalf. She rang back next day, somewhat incredulous. She was told that the Department had experienced a major computer "crash" and had lost the data covering all money received over a couple of weeks. They were now having to reassemble the information. The trouble was, she said, that another part of the system had kept right on despatching demand letters. My cheque had in fact been received, my file was in order and I should ignore the current correspondence. I may be naive but it seems to me that the automatic reaction of anyone sensing a crash in the "income" side of the system should have been to ensure that the despatch of demand letters was also interrupted. I have little doubt that the black coated-clerks in the Dickensian office would have done just that but what is it about a computer that inhibits human common sense? Could it even be that they're turning un into automatons? Not wishing to invite the wrath of some minor public servant, I would prefer that you did not publish my name and address but, on the grounds that my knickers appear to be in something of a knot, I'll. sign off as: Oliver Twist! he said, by eliminating the need for individual price stickers. Computerised check-outs would itemise, record and charge for purchases automatically, while also up-dating sales and stock records on a realtime basis. Prices could be adjusted instantly, or in as little time as it took to write a new display placard. And so on. While it sounded technically feasible, I failed to generate any instant enthusiasm. He would need to convince a great many people to change their ways and spend their money before he could start to eat. But it's all happened. Optimistic as he was, I doubt that he foresaw the devices that can ]UL Y 1988 19 THE WAY I SEE IT- CTD now read the codes printed on products of all shapes, sizes and colours, as they are whipped past in mid-air. The quickness of the hand may indeed deceive the customer's eye but if the claimed reading accuracy figures are to be believed, it very rarely deceives the laser. And for every "Oliver" who objects there may well be others who respond positively to the "hi-tech" environment. I wonder what happens though, when there's a power failure? Word processors My closest encounters with computers have been in their role as word processors. Until my retirement in mid 1983, all my articles were written on a typewriter, using journalists' copy paper - octavo (half-quarto) sheets. Normal practice was to type one paragraph or two short paragraphs per slip. The idea of doing this was to make subsequent editing easier by making it possible to add, remove, substitute or shuffle individual paragraphs with a minimum of retyping. By mid 1984 however, it became practical to set up a basic word processor and printer for well under $1000 and I did just that, using a VZ-200 (later a VZ-300} computer from DSE. It was subsequently replaced by a more ambitious Apple system, which I've been using ever since. But back in 1984, it needed ,only that first article to convince me that the faithful old Adler had had its day. With a word processor there was less need to analyse every phrase before I typed it; if it subsequently proved to be clumsy or ambiguous, it could changed without mess or hassle. Paragraphs could be deleted, inserted, replaced or shuffled electronically with equal ease. Those Printouts! An effective way of building customer distrust of computerised methods is to economise on ribbons and issue barely readable print-outs. As often as not, the worst offenders are not supermarkets but those poverty ridden banks and other financial institutions! Spare a thought for the aged pensioner who recently complained to me that: "They don't write in your bankbook like they used to. They do it in a machine but you can't read it, even with a magnifying glass". I could just read it; coarse dot matrix letters in the palest grey. As she explained to me: "It's my bankbook and I shouldn't have to ask somebody else to tell me what the figures are". But what really delights the Editor, right now, is when I ring him to say that the next article is ready to "shoot down the line". A few minutes later, the text from my Apple is on his hard disc. He can read, check and encode it, before feeding it down the line to the printer's typesetter, which turns it directly into magazine galley proofs. It's all very convenient and efficient but yes, use of a word processor does modify a writer's approach. Relieved of the need for scribble pads, manual corrections, typing and re-typing, he/she can aim for "perfection" first up, work to a draft format, or attack the task piecemeal, knowing that the result can be tidied up on screen before printout. As for going back to a conventional typewriter: forget it. I've lost the will and, if the truth's known, I've probably lost the skill and the patience to work any other way. At the same time, one must concede that word processors have their own frustrations. It takes a while to get used to reading text on a screen rather than on paper. And you can't really concentrate on what you're writing until the mechanics of the computer have become routine. Some systems are better than others in this respect, because they use easily remembered commands and present text on screen in essentially the same form that it will take when printed out. The jargon term is "wysiwyg" - what you see is what you get (well, more or less). One also discovers that, in most word processors, the text on the screen and accumulating in the memory is distinctly vulnerable. A heavy switching pulse on the power line or even a brief drop-out can clutter a literary gem with garbage or wipe it out altogether. Careless operation can achieve a similar result, especially if the program has insufficient safeguards or the odd built-in "bug". That's why you very quickly learn to save, save, save, even if you have to interrupt the muse. That way, a switching pulse, a blackout or a bolt of lightning can't rob you of more than a few minutes' work. The rest will always be safely tucked away on disc or tape. Computers are really tools The point I want to make is that computer related devices are basically tools which should allow us to perform various tasks more expeditiously, more thoroughly and more economically - like those specifically mentioned: transf erring funds, retailing groceries and petrol, collecting income tax and writing articles. But like all new tools and methods, we have to come to terms with them. The point I want to make is that computer related devices are basically tools which allow us to perform various tasks more expeditiously. 20 SILICON CHIP As a reader of this magazine, "Oliver" is presumably not antitechnology. What he's on about is the tendency to delegate control of our affairs to machines, at the expense of human intervention. I think he has a valid point. It is reinforced by what may well be the ultimate example of such a situation - the reputed role of computers in last year's world stockmarket crash. In the USA, portfolio managers had set up a network of computers which were programmed to buy and sell automatically in response to sharernarket moves in either direction. According to a US Presidental task force report, issued earlier this year, these computers generated selling orders totalling between twenty and thirty billion US dollars during the week of the crash, adding considerable fuel to the "selling inferno". A typewriter problem By coincidence, a reader from Woodend, Vic, draws my attention to a problem of a different kind he has encountered with an electronic typewriter - this in the context of spare parts, or the lack of them. I quote: Dear Mr Williams, I have purchased all the issues of SILICON CHIP thus far and have enjoyed them very much. By way of response, I would like to add my experience to the "They'll sell you anything" file. Less than two months ago, I received an electronic typewriter as a gift - a Casio CW-16 portable machine with about as many features as can be crammed into a typewriter before it becomes a computer. It's quite a change from the old manual machines that we struggled along with for the past 20 years. There is one thing wrong with it, though: the ribbons are virtually unobtainable. You wouldn't believe the amount of time and money I've expended in the last two weeks trying to get ribbons. I've rung the Melbourne agents three times and, only on the third occasion, was I able to get the name of some local agents. I've spent any amount of time on the phone trying to get something done but so far, with no success. And this is a brand new machine. I hate to think what the situation will be in a few years' time. I agree that obtaining parts nowadays for almost anything is difficult (I send overseas for virtually everything). We hate to think what sort of trouble we'll be in when our 3-year old National VCR needs service. At least the National brand seems extremely reliable. Our 14 year old National TV has hardly had the back off since new. Agreed, its use for TV reception is very limited because TV signals in this area are almost non-existent. Keep up the good work. I have enjoyed your writings for about twenty-five years. T. R. (Woodend, Vic). Thanks for your letter, T.R., and for your kind remarks. Your story reminds me of my own stated problem with a computer printer, although it was ultimately resolved - with no thanks to the distributor. Hopefully, yours will have been sorted out by now or publication of this letter will prompt someone to point you in the right direction. As for your National brand VCR and TV receiver, the company does have a good reputation for quality but like most other suppliers, these days, they cop their share of criticism for a slow turnaround in jobs and parts. ~ Problems? ... and you don't have our 112 page catalogue ... you've got real problems! ARISTA ... your one-stop problem solver. Audio leads ... Batteries ... Chargers ... Battery holders ... Cables ... Car accessories ... CD accessories ... Converters ... "Cutec" ... Earphones ... Fuses ... Headphones ... Intercoms ... Knobs ... Microphones and accessories ... Mixers ... Multimeters ... Plugs/Sockets, etc ... Plug adaptors ... Power packs and leads ... PA ... Disc and Tape care ... Security equipment ... Signal modifiers ... Solderless terminals ... Storage boxes ... Switches ... Telephone and TV accessories ... Tools and Technical aids .. . Video accessories ... Wiring accessories ... You name it and we're bound to have It ... Try us ... NOW! RCS Radio Pty Ltd is the only company which manufactures and sells every PCB & front panel published in SILICON CHIP, ETI and EA. 651 Forest Road, Bexley, NSW 2207 Phone (02) 587 3491 for instant prices 4-HOUR TURNAROUND SERVICE Get your catalogue ... it'II solve a whole lot of your problems! Just send $2 + 50c p&h and your return address to: ARIST~ ELECTRONICS PTY LTD PO BOX 191, LIDCOMBE, NSW 2141 JULY 1988 21 This brand new •Top of the Line• UHFNHF TV antenna will really drag In those signals. Suitable for VHF 0-11 and UHF band 4 (SBS). Australian designed and manufactured, 3 year warranty on workmanship. Suitable for all Australian capital cities. High gain with reflector for fringe areas. Powdercoat blue boom with red Insulators. Cat. LT-3151 Capacitor Pack $129.00 HI QUALITY AUDIO LEADS As technology Improves the humble HI FI has really i urned the corner" in recent years with the advent of compact disc players, Mosfet amps., etc. In keeping with these changes we have Introduced three high quality audio connector leads, so all that technology is not lost by using inferior grade connecting cables. We have chosen these leads alter evaluating what's available on the market. The criteria we have used is based on the best quallty we could find, but at a reasonable price. The real audiophile may be able to justny leads priced at $100 plus, but quite frankly, we feel the TECHNICAL HI FI connoisseur will be more than happy with the leads we have selected. ~ GOLD SHIELDED 2 RCA TO 2 RCA PLUGS ~"-., 1 metre long Cat. WA-1045 $16.95 "-."'8.-...;;:, 2 metres long Cat WA-1046 $19.95 ~ '-. OXYGEN FREE COPPER SHIELDED ~ A densely braided oxygen free copper (OFC) audio cable moulded togelher with colour coded '-. UR and centre ground wire. ~~ 2 RCA TO 2 RCA PLUGS ~ 1 metre long Cat. WA-1 050 $35.95 ~ · NEW TRANSISTOR IGNITION Ref: SIiicon Chip May/June 1988 A high energy Ignition system which uses the cars existing ignition coll and points. Unit has extended dwell and Is compalible with bolh our Hall Effect and Opto Sensors. In fact, all components to Interface both these are now included free In the TAI kit. Complete kit wkh dlecast box and all components and Interface components. Cat. KC-5030 FERRIC CHLORIDE Two sizes, conveniently packed In a plastic jar for easy storage with a childproof cap. Use only as you require, and simply store the rest until needed, Supplied with instructions. 200g Makes 1 lltre Cat. NC-4252 $4.95 400g Makes 2 lltres Cat. NC-4254 $7.95 Cat. RZ-6695 $12.50 SAVE OVER 60% ~5l2{_y~I9£RFCHOKEPACK Over 50 pieces supplied I A pack of 30 brand new RF chokes with at least 14 different values I Popular values include: 1.5, 4.7, 12, 15, 18, 22, 68, 100 & 1000uH. Each choke Is resin dipped and colour coded (they look like bead tantalums). A colour coding chart Is supplied so that you can decipher the value. BONUS I Not only do you get 30 useful chokes we will give you at no extra charge at least another 30 more RF chokes! These are genuine chokes but are commonly called 'peaking coils'! They look like a 1/2 wan resistor. (Read the choke value In uH as you would a resistor value). Cat. RC-5600 Less than ATTENTION OWNERS OF SCANDIA DESOLDERING TOOLS We stocked this 240V desolderlng tool last year (see 1987 cat p.88) There are many 'in the field' and they were also sold under other brand names. We have a quantity of tips leftover, and can offer these at a saving of almost 50%. ~ . .· . WAS$9.95 ~ N . Cat. TS-1581 10~ a part! 6 WAY POWER OUTLET WITH MAINS FILTER Iii~ 7/ BREAKERLESS (HALL EFFECT) -_=- ~--~i·,~--~·-~ ~_,·_,_·. , , , ,.,., _ , $59.95 NOTE: tt you require absolute mains suppression don1 forget our Australian made Squeeky Clean Mains Filters. CERAMIC MAINS SUPPRESSION CAPACITOR BARGAIN NEW HEAVY DUTY SPEAKER FLEX 47~F 400V AC ceramic capacitor. Ideal for mains suppression. Limited quantly - - - - ~ , . . . , 1 - - - - Cat. RC-5375 Don1 pay through the nose for heavy duty speaker flex. High quality figure 8 speaker cable 2 x 7910.2mm strands in a white covering with black trace. Cat. WB-1712 ~~ c BARGAIN PRICE 10 for $2.00 0 2~ each $1.50 metre ~ s · $120 par 100m roll PHILIPS GENERAL CATALOGUE ~,··~-;;:¼ s . :i ~~'?':j' ),~ (;:::J ,:s.,,. .e .·, ..... ' ,·, $39.95 . ' OPTION 2 SIEMENS HALL EFFECT CONVERSION Ref: Silicon Chip June 1988 tt you have a car that will not take the very comprehensive KJ-6655 Hall type breaker point set, then this device is for you. German made Siemens HKZ-101 Hall Effect switch. Interface components Included In TAI kit. Cat.Z0-1980 $34.95 ONLY $1.95 Not only is It a 6 way power board, It incorporates a voltage surge and spike protector and noise rejection filter network. Supplied with two metre cord and mains plug, safety shutters on each outlet, illuminated master on/off swkh and even a safety circuit breaker. SPECIFICATIONS Max clamping voltage n5AC<at> 50A ~ Spike dissipation energy BOJ<at> 2ns _ Withstanding surge current 4500A (8 x 20us, 1 time) lifll ,, 1, , ~ 11 Clamping response time <10-9 ns -,, ~ 1 Frequency 1kHz- 100MHz ,, Attenuation 20 to 40dB (variable ratio) 1// Cat. MS-4030 $49.95 A professionally engineered STEM electronic fbreakerless") contact breaker system. Yes, only Jaycar has a complete Hall Effect trlggerhead assembly designed to adapt to an extensive number of cars. Each kit contains the following: • Hall Effect Triggerhead • Magnetic rotors for both 4 & 6 cylinder cars • Over 6 cam-lobe adaptors • Over 12 different adaptor plates for your particular distributor • Other hardware (l.e screws, etc) • You can remove this system and re-equip your car with the original breaker points when you sell thecarl • As easy to Install as a set of points • Instruction (simple to follow) included This set Is designed to fit most European and Japanese cars. In fact, it will also fit many Australian cars fitted with Lucas, Bosch, Motorcraft, AC Delco, or Autollte electrics. If you wish you can check first by sending a SAE for a car/distributor fist. Cat. KJ-6655 We supply a pack with 5 melres of both red and whtte solid core hook-up wire. This Is the Ideal size for bread• boards. All you need to do is cut It up Into whatever lengths you require and strip the ends. Doni pay lots of money for pre-cut wire In a plastic box. Cat. WH-3030 Tantalums are getting more expensive all the time. Duet a very large bulk purchase, we can offer you a mixed pack of over 50 Tantalums. Over 40 of these are tag type, and the rest high quality military spec RT style which are worth up to $5 each. A typical pack wlll Include: TAG STYLE 2 x 0.33135V, 10 x2.2/16V,5x6.816.3V, 1 x0.15/50V,20x4.7/16V, 1 x 4.7/25V, 3 x 68/10V, 1 x 100/16V. RT STYLE 1 x 0.11 35V, 1 X 0.22/35V, 1 X 0.33135V, 1 X 0.68135V, 6 X 15/ 20V, 1 x 32/35V, 1 x 47/20V. We reserve the right to make changes If stock shortages occur. This Is a once only offer. Don't miss out. OVER 50TANTALUMS FOR ONLY $12.50 Over $35 worth of Tag Tantalums alone, without taking into account the expensive Milspec style also supplied. ONLY $10.00 OPTION 1 ~r!~n~~jI; ~ BREADBOARD JUMPER KIT?????? · -~ l ·-· ·.. · ·r . . " .\. -~ 1988 Edition NOW AVAILABLE - Brand newl Just released! Line data Is provided on the full range of preferred Philips products including : Logic, memory, analogue, radio, audio, video, semiconductors, tubes, capacitors, resistors and other materials Including speakers, etc. 1.25 inches thick. Dimensions 210 x 145mm. $ _ 25 00 Cat. BP-4402 5000 POWER AMP "BLACK MONOLITH" RE-BORN WITH TOPOLOGY MODULES • Jaycar proudly re-introduces the fantastic 5000 series power ampllier with the new "state-of-th&art" Topology Power Modules. Get the upgraded module performance for the same price as the old 5000 amp. Cat. KE-4200 PUSH BUTTON WALL MOUNT PHONE WITH AM/FM RADIO! ¥~l~~~©OO~ ~--""'~ ~lUJJ<at> ~ ~~lffi<at>~OOO ~ Scoop purchase price! An AM/FM radio with good tone that mounts on the wall (kitchen or garage ldean. When the phone Is answered the music rrutes out. You can even put the music on the line H you need to put the caller on hold! Requires 3 x AAA batteries, not supolled). Cat. YT-7072 ONL V $1.95 ea This unit Is designed for midrange and tweeter control on mJltlway speaker systems. It is suitable for systems up to 80 watts power handling capacity. It presents a constant B ohm Impedance to the load, and so does not disturb the crossover points. Unit is fully sealed, mounting plates and Is labelled high and mid with rotary controls. Both high and mid are in the one unit and we can offer these far below the normal price. Cat. AC-1683 10 up $1.75 each ONLY $9.95 each Another surplus stock purchase. These are standard type telephone plugs without the cable grommet. NORMALLY $3.95 Limited quantity Cat. PP-1400 WAS$39.95 NOW ONL V $20. SAVE50% MIDRANGE AND TWEETER LEVEL CONTROL BARGAIN TELEPHONE DOUBLE ADAPTOR SENSATION Another jaycar exclusive purchase. Allows you to connect two phones to the one ,ocket. These normally sell for $7.50 uf°""•J li1\ 1 SAVE 47% . Cat. XT-6020 ©~©Wlll.&'lr<at>ill~ ~'lr ~~lLlL<at>WJ'lr )J)ffill©~~ ,-1rl \ \ $3.95 ea Tl-1103 • eight digit, • six function Cat.OC-7172 ONLY $10.95 SAVE$4 Little Professor You would DIE If you knew where we bought this shipment of brand-new genuine US-made NADY wireless PA gear froml Suffice to say that they lost a fortune to liquidate this current model merchandise. ONCE AGAIN their staggering loss la YOUR GAIN. OFFER No1 ~95 $27.50 $19.95 TURN YOUR SURPLUS STOCK INTO CASHII Jaycar will purchase your surplus stocks of COITl)Onents and equipment. We are continually on the lookout for sources of prime quality merchandise. CALLGARYJOHNSTONORBRUCEROUTLEYNOWON (02) 747 2022 ,r _ _ _ _ _ _ - - - _ , TIECHNICAL BOOK CLEARANCE - - IFor full details see our 1988 catalogue. I:::: les-0120 Flbreopticsexperiments&projecls How to read schematic diagrams BS-0406 ~~J~~%nnectlonssolved Understanding microprocessors Macintosh programming techniques Intro automotive solid state Understanding digital electronics 8080/8085 software design BS-0420 C prog. techniqu98 for Macintosh I BS-0453 Basic electrlclty 6 cassettes BS-0732 Complete guide - car audio BS-0703 Crash course dlgltal technology IBS-0456 IBS-0416 BS-0404 IBS-0458 BS-0590 I I I SAVE AROUND $200 Genuine NADY MODEL 201 GT Guitar wireless microphone link which Includes FM "True Diversity" receiver, bodypack transmitter with high irfl)8dance Input (aultablefor guitar pickups, baas, sax, etc). The body pack accepts a standard 6.5mm plug and the audio lead acts as the antenna, neat! The body pack measures 96 x 60 x 203mm and weighs only 70 grams. It requires a 9V alkaline battery. Both transmitter and receiver are crystal locked and offer 20-20,000Hz ±3dB frequency response and 120dB (max SPL A-weighted) dynamic range. Output Is line level 600 ohms. MinlmJm adverse operating range 200 feet, lineEis 'II $800+ f hi I A 11 of-slght_1500feet. ~ereyouwi pay . ort ssystem n ustraa Bui while they last you will be able to get thlS product from us for only $5991 ..._ That's right, you WILL SAVE around $200 over the normal price In \ Australlal (Australian rec. retail $799). (H more than one Is ordered, they will be supplied as separate I frequencies). ~-""""'"""""~~~.....- - - - - - - _ , , , 502 ~f:.95 IC $a T :::~; $27.95 $44.50 $19.95 $27.95 $24.95 $37.95 $26.50 $19.95 $34.95 1.o • ° I 5 9 9 INC tax :~~:: I OFFER No2SAVE AROUND $300 $19.95 Genuine NADY 201 HT microphone wireless system $29.95 I comprising of YD-04 microphone (virtually Identical $14.95 performance to Shure SM-58), Integral antenna (no $19.95 I dangling wires) low battery light and professionally rugged. $14.95 Measures 222(L) x 36(0ia)mm weighs 238 grams. Use 9V $25.95 I cell. Included of course is the 201 "True Diversity" receiver $16.50 matched to the same frequency. System performance and $14.95 I range similar to 201GT above. (You see this system $24.95 used by TV entertainers In the US all the timel) (tt more than one ordered or 1 x 201GT and 1 x 201HT Iordered they will be supplied on different frequencies). ICat. DT-5030 ' $699 ~-------------.,) INC tax FUEL CUTOUT_~i1?:::;;:& SOLENOID / ~ --~> .;::,'~ Whoneedsanolsycaralarm,q:- ~ - - l after you have installed one _ of th989 In your vehicle. /It's operated from a hidden switch. Simply tum It on when you leave your car, and H your car is stolen, It won't go very far without any petrol. Supplied with Instructions, pre-wired switched, hardware and even two alarm stickers. Quality MEO Alarm brand. Add to this our deluxe red light flasher kit - KJ-7000 i~~--i5c:~ho needs an alarm? 69.95 - ,,.;BICENTENNIAL" LIGHTS IN YOUR OWN HOME! ' DUMMY INow 111umlnate your garden, tr998 or windows with this low volatge lighting system! I you can have the same beautttul 'firefly' lighting that Is all CNer the civic squares around Australia. The beautWul lights of Hyde Park and Macquarie I CAMERA Street In Sydney, for example can now be in YOUR front garden. tt you have ever travelled to the USA you see such 1irefly' lighting in trees, around · Imotels, houses etc - all over the place! I BARGAIN Until now weatherproof outdoor low wattage festoon lighting simply has not been available. That Is behind us, because Jaycar has an exclusive Ioutdoor/Indoor lighting kit to enable you to beautny your home or garden. Each festoon set comprises a 6 metre cord with 20 lamp bases moulded In I onto the cord at 300mm Intervals. (At the end of the festoon Is a clear 700mm of cord.) Each lamp base Is fitted with a 12V 50mA globe and Iparallel fortune very year. It has been clear polycarbonate weatherproof cap. The entire festoon draws, of course, 1 amp AC or only. THE RATED LAMP LIFE IS 20,000 HOURS I I demonstrated that television 'Plxlelites' as we call them can be connected in a chain for larger Installations. Each lamp Is In parallel and In the likely event of an Individual bulb Ifailure surveillance cameras In the THE REST STAY ON (unlike cheap series type festoons). All that Is required for larger Installations Is 1 amp eX1ra of power supply capacity for I right environment can discour6 metre festoon. The 'Plxlellte' festoon Is moulded In water clear plastic. This enables you to line home or shop windows with Plxlelltes and only Ievery age this activity. see the lights I The clear plastic makes the wiring almost Impossible to see In foliage as well! I This Is where you come In. one amp per festoon a cheap 2155 type transformer (Cat. MM-2002 $10.95) Is all you need for power. But If you have a trickle battery charger or old IAtCB We have made a great purpower supply you ALREADY have power! The festoon, however, Is NOT CHEAP. It Is a quality made In Australia product designed to last a I chase of realistic-looking IIWetlme. (Maybe for the Tricentenary?) A 6.7 metre 20 lamp f8Stoon will cost you $49.95. You can buy a mixed bag of coloured caps (red, amber, Dummy TV Cameras. They green, blue, 5 of each) to convert the festoon for Christmas use - It wrn last MANY Christmases! D I are Australian made, are ISo act now and partlcpate in Australia's Bicentenary. supplied with adjustable mounting bracket, lcat. SL-2602 $49.95 Festoon Set . I swivel fixing screws, flashing LED ·. I circuit board and 2 flashing lc at. SL-2805 $9.95 Bag of 20 coloured caps. ~l We au know that shopliftin g and vandalism cost a small QC, I 1.- --l~ ~- (1 l~ CLOCK MOVEMENT WITH BUILT-IN PENDULUM DRIVER This module measures 87mm long x 55 wide x 35mm deep and uses 1 x AA battery. Clock movement Is supplied with 3 sets of hands, and pendulum Is a suspended arm within the module which swings back and forth. A suitable pendulum can be attached to the bottom of the arm. Flt your own custom clock face. Great for novel applications. Avallable sometime In June. Cat. XC-0103 $22.95 DIGITAL AUTO· TUNE UP TESTER Not only will this measure RPM & dwell (on 8, 6, 5 and 4 cylinder cars) It measures AC volts, DC volts, points resistance, diode check and even has ohms range. But Its best feature Is the nifty little tacho adaptor supplied. It Is a clamp type unit with coiled lead. Simply connect the inductive pickup to the coll HT lead and the RPM's are displayed. For fu ll specs see our 1988 catalogue. Cat.OM-1573 $139.50 DIGITAL L-C METER Quality Inductance and capacitance digital meter. Capacitance range from 2nF to 200uF In 6 ranges. Inductance range from 2mH to 20H in 5 ranges. For fu ll specs see our 1988 catalogue. Cat.OM-1575 1 $219.00 DIGITAL AC CLAMPMETER Ouallty 400 amp LCD ciampmeter with digital hold facility. High Impact case. Full specs In our 1988 catalogue. Cat.OM-1570 g • LEDs. Also supplied Is the 2 x D cell nylon battery holder to power the flasher circuit. A ------------- ~ fake cable wallplate Is also supplied as well as a very conspicuous 21 O(W) x 160(H) self adhesive sign which says "THESE PREMISES ARE PROTECTED BY TIMELAPSE ANTI-THEFT CAME RAS' The text of the sign Is In orange-red fluores. -- - -~ - - _ _,__ __ _....., 1 cent ink against a black backpulse count for under $100. ground. BUT HURRY! We have Features: around 300 only. • Coverage 12 metre x 12 metre Cat. LC-5310 • Detection angle 1101 - 4 piece• $49.95 • Detection beamls - 38 • Adjustable angle $42.95 • Tamper prool protected • NIC and N/0 output $39.95 Cat.LA-5017 _ ._ Jaycar are proud to announce a new PIA to our range. The Terminator has features found In those really expensive PI Rs. FEATURES • Pulse count which virtually eliminates false alarms • 48 detection beams In 3 ranges • Sliding PC board for pattern adjustment • Optional lens for use In hallways • Tamper proof protected • Plus all the usual features of PI Rs. Cat. LA-5018 $119.00Hallway Lens Cat. LA-5020 $3.95 "PLASTI-DIP" AIR DUSTER HEAVY DUTY FLEXIBLE LIQUID COATING It's pure compressed Inert gas for removal of dust and air borne contamination from very delicate and Inaccessible areas of electronic and electrical equipment. 400ml spray pack - 550g nett. Cat. NA-1018 Plastl Dip Is an air dry liquid plastic coating that produces a tough, thick pllsble finish. It Is virtualy Impervious to the elements and has a good dielectric strength. It Is Ideal for making a pliable coating for the handles of tools, etc. It also provides excellent environ• mental protection for circuit boards, etc. Supplied In a 470mldippingcan. · ~ 1 ' ) ~ · Will do dozens of ~ • -~ · ~ tools. !. ;I ;,· Red In colour. · ' .,.· Cat. NP~1100 NOW AVAILABLE $12.95 MINI MUFF PADS Foam earpad replacements for mini headphones. 27mm diameter - 2 pairs. Cat. AA-2012' $3.75 pair $24.95 $29.95 Replacement Punch Cat. TH-1766 $21.50 ~ . J()l!Ql! ~ I ' ( i ', 13'~ ~..~• ,,- '!'_no.:.;,,,.:::::.::"t I ,,,--, / I \ (~ ; ,,, ii' ,; ~ "\ll o\01,(lll""I- SPRINGVALE STORE OPEN TILL 2 PM SAT Nibbling Tool Born in the USA How things change. You can now purchase from Jaycar the original American Adel nibbling tool. Due to price rises from Asian countries we've been able to dlrec1 Import the original tool (which we sold 10 years ago) and sell It at the same price as the Asian copy. • Cuts holes - any shape over 7/16' • Notches clearance for plugs and wiring • Trims underslze holes to flt parts • Suitable for steel up to 18 gauge, Aluminium 16 gauge, plastic and copper Cat. TH-1765 --/ ( ~:::~~::g:011r1I\ ~ $139.95 BURANDA OPEN TILL 8 30 PM THURSDAY $37.95 ONLY $99.95 CARLINGFORD OPEN TILL 2 PM SATURDAY A'BECKETT ST OPEN TILL 8 30 P M FRIDAY ,/.:.:.:.:.:.:.:.:.:.:::.::::=.=.=.= · · •· =.:===ti:=.:.:.=.=.=.===.=.=-:r · · · · · ·.:.=: ·:::::: :·: :·:::::: :·:: :·: =·===·=·=·==:.:::=···············.....·.·.·.·.·.•.·.·.•.·.•.....•.•.•❖••••••••••••••••••••••••••••••••••••••• 1,:~i~l~,.fi■~l~cc!lll Discolite . fJl!:'.~IP· •ll1t~ STUDIO 200 HI FI PREAMP Ref: SIiicon Chip June/July 1988 The new Studio 200 Preafl'l) offers excellent specifications and features for a very moderale price. Main Features • Very low noise on Inputs - less than many CD players • Very low harmonic and Intermodulation distortion • Up to 7 stereo program sources can be connected · Ref: Silicon Chip July 1988 Build your own light show. More features than the Muslcolor. New d e s l - g n . • 4 light channels controlled by 4 separate audio channels ,. • Forward, reverse and auto-reversing chaser patterns • Slrrultaneous strobe on all four channels NEW' • Alernatlng light patterns • Music modulation available on chaser, strobe and alternate patterns • Adjustable rate for light patterns • Inbuilt microphone for beal triggering or audio modulation of lights Cat. KC-5032 • Direct Inputs for beat triggering or audio modulallon of lights • Sensitivity control • Presettable sensitivity levels for each channel • Front panel LEDs mimic light display The Jaycar kit Includes punched and screened front panel, punched and anodised rear panel and all specified parts. 88 88 : ~=i:n~~~~lity headphone amp NEW' • Headphone socket disables output signal to power afl'l) • Tone and balance controls • Easy to build construction SPECIFICATIONS Frequency Response: Phono Inputs RIAA/IEC ±0.3dB from 20Hz to 20kHz; High level Inputs within ±1dB from 10Hz to 100kHz Total Harmonic Distortion less than 0.005%, 20Hz to 20kHz, at rated output level for any Input or output Signa~to-Nolse Rallo phono (moving magnet) 86dB unwelghted (20Hz - 20kHz) with respect to 10mV input signal at 1kHz and rated output. High level inputs (CD, Tuner, etc) 104dB unwelghted (20Hz • 20kHz) or better, with respect to rated output (with volume at maximum). Separation between Channels -62dB at 10kHz; -81dB at 1kHz; and -93dB at 100Hz with respect to rated output. Cat. KC-5033 $159.50 $229.00 STROBOSCOPIC TUNER $47.50 Ref: EA July 1988 This slfl'l)le circuit provides crystal-locked accuracy for tuning virtually any rruslcal Instrument. It also doubles as a stable frequency reference If you prefer to tune up by ear. Kit Includes box and all parts. Cat.KA-1705 ACTIVE CROSSOVER Ref: ETI June 1988 Short form kit Includes PC board and all on board components. Transformer Is extra Cal. MP-1012 $19.95. Cat. KE-4733 FM RECEIVER Ref: EA June 1988 A simple and Inexpensive FM receiver, using only two chips, one of which Is an audio amp. Kli Includes PCB, box, panel, planetary reduction drive, TDA700 chip and all components. $55.00 Ref: EA May 1988 This simple but very effective RF probe enables you to troubleshoot RF circuits. You can 1race' RF just like audlol Kit Includes all specWled parts except the felt tip pen case. The project must be used In conjunction with the KA-1699 Bench Afl'll ($39.95) descrbed In Aprll 1988 EA. Cat. KA-1701 $13.50 ■ ■ ~Ni NiCad CHARGER Cat.KM-3067 $39.95 SIMPLE TESTER FOR POWER TRANSISTORS Ref: EA May 1988 Kit will nneasure current gain and Vbe of all popular power transistors - even Darllngtonsl All project specWied parts In the kit. Cal. KA-1700 $22.95 BABYMINDER $24.95 Ref: ETI Aprll 1988 Monitor your baby's room for crying. WIii trigger a light or buzzer In another room. Kit Includes box, PCB, and all components except 12V AC plugpack and dynamic mic. Cat. KE-4732 $34.95 BENCH AMP/SIGNAL TRACER LINE GRABBER Ref: Silicon Chip March 1988 Handy gadget cuts out one telephone extension when the other Is picked up. No eavesdroppers. One unit required for each extension. Cat. KC-5025 $19.95 ~,t~:~~~~~1~~)a$4~~~~i MAIL ORDERS ~o~~~~~:~~1~~~~~~l 2137 Cat.KA-1699 $39.95 Ref: EA April 1988 Amplifier offers power output of 5 watts, signal tracer has high Input Impedance and a wide range of Input sensitivities. Complete kit including box, speaker, PCB and all components. Plug pack not supplied. 7 POST & PACKING fi~ l!m Irn 100 1 0 _FA_c_s_1_M_IL_E_(o_2_)_74_4_0_7_6_7_ _ _ _r_o_L_LF_R_E_E_(O_O_B)_02_2_B_BB_ _ _ v_rn_s_ ___ s_ 0._oo_ _~ .._.,_..,iiillii....•..._•....1._.._.. VISA $99 HEAD OFFICE -~~--- 5 Cat. KA-1702 Ref: AEM AprH 1988 WIii fuiiy charge then trickle charge - or trickle charge only. WIii charge up to 1o cells at once. Incorporates own plug pack box. RF DETECTOR PROBE .~~t;• LOW COST 50MHz 4 DIGIT DIGITAL FREQUENCY METER Ref: EA May 1988 A low cost but high sensitivity, high Input Impedance unit measuring to well over 50MHz. Kit Includes case, front panel and all specified parts. $39.95 Cat. KA-1704 240 VOLT LINE FILTER Cat. KA-1703 KIii those clicks and pops from next doors vacuum cleaner or lawn edger etc. Kit Includes 240V socket and plug, PCB, all components and hardWare. MAIL ORDER VIA YOUR !f ROAD FREIGHT ANYWHERE IN AUSTRALIA $13.50 '---------------------------------------' GORE HILL SYDNEY· CITY 117 York St. (02) 2671614 · 188 Pacific Hwy cnr Bellevue Ave (02) 439 4799 Mon-Fri 9 • 5.30 Sat 9 - 4p m Mon-Fn 8.30 - 5.30 Thurs 8.30 pm. Sat 9 . t2 CARLINGFORD Cnr. Carhnglord & Pennant Hills Rd (02) 872 4444 • BURANDA OLD CONCORD 115 Parramatta Rd (02) 745 3077 • Mon-Fn B.30 • 5.30 • Sat 8.30 . 12 MELBOURNE-CITY Shop 2. 45 A'Beckett Si City (03) 663 2030 HURSTVILLE 121 Foresl Rd (02) 570 7000 • Mon-Fri 9 • 5.30 Thurs 8.30 pm. Sat 9 • 12 SPRINGVALE VIC Mon-Fri 9 • 5.30 Thurs 8.30 pm • Sat 9 - 2pm 144 Logan Rd (07) 393 0777 Mon-Fri 9 • 5.30 Thurs 8.30 • Sat 9 . 12 Mon-Fri 9 • 5.30 Fn 8.30 • Sal 9 - 12 887-889 Spnngvale Road Mulgrave (031547 1022 Nr Cnr. Dandenong Road Mon-Fri 9 • 5.30 Fn 8.30 Sat 9. 12 DRY TRANSFER LETTERING CASTORS Quality lettering sets, available in 4 different styles. Can be used on most smooth surfaces Including metal, glass, plastic, wood, cardboard and paper. Ideal for lettering on rack cabinets, control panels, etc. Simply position the letter and nb with the cap of a ball point pen or soft pencil. Made In Holland. STYLE 1 Black lettering 4mm high . Capital letters, lower case letters, numbers. Cat. NL-4100 STYLE 2 Black lettering 6.5mm high. Capltals, lower case, numbers. Cat. NL-4102 STYLE 3 Sliver letters with black shadow 7mm high. C~ital letters and numbers. Cat. NL-4104 STYLE 4 Flourescent yellow on black background. Capitals and numbers. Cat. NL-4106 ,.-, J., ,-, , ALL ONE PRICE $2.99 per sheet ;'PE A E b r2 9 ! TY:~ b3f T Y : ~ r n ~TY:E ,-, 0 ,_, C - Call Into any one of our showrooms for an audition (not Concord) Another scoop surplus stock buy. Set of 4 castors to suit speaker boxes, TV's or anything for that matter. Castors are mounted on a 37mm square metal bracket which Is simply screwed to the speaker box etc. by 4 self tappers. (Screws not supplied) Originally used on colour TVs. Cat. HP-0838 ---- SA-100 Upgraded AEM6102 speaker kit. Uses new design crossover, and they do sound better. Complete kit with cabinets : SA-50 Unbelievable sound from such small speakers. Measures only 26(H) x 17(W) x 195(D)cm. Incorporates a 5" woofer and D19 dome tweeter. See AEM magazine for a full review, May edition. Complete kit with cabinets only : $799 $399 SA-130 Upgraded AEM6103 speaker kit. New design crossovers, new slimmer cabinets, upgraded dome tweeter. Complete kit and new designed crossovers are excellent value at: SA-70 Upgraded EA60/60 speaker kit Incorporating 8" woofer and D19 tweeter. Complete kit with cabinets only: $1199 $499 See our catalogue for full details. 500mW<at>6V Audio Amplifier A six transistor 1/2 watt amp for the cost of two hamburgersl It has two transistor tape preamp which Is NAB equalised and a four transistor power amp. It has facilities to take line level inputs. The (Irregularly shaped) board measures roughly 110(L) x 48(W)mm. Each amp comes complete with schematicand connection diagram. (2 required for stereo). Cat.AA-0290 10 up $3.50 each • ONLY $3 95 HURSTVILLE OPEN TILL 8 30 PM. THURS ur usua eso erwIc Is so In a p astIc spoo an contains 5 feetfor $2.50. That's approximately $1.50 per metre. El cheapo braid is 2mm wide and will take solder off a PCB reasonably well although the braid gets a bit hot because there is no plastic spool to hold . You could easily put some In your old spool. Supplied In a 5 metre length for $2.50. That's SOe metre - or 113rd the price ol normal desolderwick. Cat. NS-3025 5 metre pack Please note: braid is not loaded with flux and will not work quite as well as normal desolder braid. SPEAKER CWTH Up until now, if you wanted speaker cloth you had the choice of black or blackl We now have available brown speaker cloth. Top quality, acoustically transparent. Cat. No Colour Size Price CF-2761 Black 1mx1m$9.95 CF-2762 Black 1mx1m $13.50 CF-2766 Brown 1mx1.7m $13.50 6.3 VOLT MES GLOBES Don1 rnss this bargain. OEM's contacl Bruce Routley (02) 74 7 2022 NORMALLY 50e ea THIS MONTH ........... - · $2 4 for $1 10 for TELEPHONE DIVERTER This professional quality product will automatically transfer incoming calls to another telephone number, anywhere. Your business will not lose any Important calls Wyou move, as Incoming calls can be diverted to your new office address. Two telephone line are required while the YT-6510 Is not Telecom approved It Is a very well made product. A 7.5V AC adaptor Is provided. Cat. YT-6510 1988 JAYCAR ENGINEERING CATALOGUE Have you got your copy yet? It has 132 pages and over 4000 products for the electronics enthusiast and professional. Two easy ways to get yours: (1) Call Into any Jaycar store. Only $1 (2) Send $2 to PO Box 185 Concord 2137 and we will send you one. TWEETY PIE This Incredibly little piezo screamer measures 57(L) x 33(H)mm emits a 116dB wall. It's deafening! As used In the screecher car alarm kit. Cat. LA-5255 $17.95 "Spy in the Sky" Sensor The Pyroelectric infra red sensor element is the 'eye' of a passive Infra red detector. It measures 10mm high, 9mm wide and only 6.2mm deep. The IRA.Foo1-P comes complete with full technical data including performance graphs. Information on the operating principle and two typical application circuits I Typical applications: • Burglar alarms • Proximity detectors • Automatic door/shutter switch • Toys, robotics DIAL DRUM/CORD PACK BARGAIN This will probably be your first and last chance to ever buy assorted dial drums. As used In the old day tuners, they are Ideal for the hobbyist who likes experimenting. This pack contains $37.75 worth of dial drums and dial cord and you can have one for only $5. You will not see dial drums again - especially at this clearout, once In a lifetime price. Your junkbox needs some dial drums for the future. WHAT YOU GET 108mm dial drums x 2 54mm dial drums x 1o 57mm dial drums x 2 40mm dial drums x 10 2.5 metres dial cord Value $5.50 $15.00 $3.00 $12.50 $1 .75 $37.75 ALL FOR ONL V $5.00 Cat. HM-3130 DON'T MISS OUT LAST CHANCE - EVER • Accident prevention/machine guard • Electronic appliances • Automatic lighting (in toilet?) Cat. ZR-9500 $19 95 • TURN YOUR SURPLUS STOCK INTO CASH!! Jaycar will purchase your surplus stocks of components and equipment. We are continually on the lookout for sources of prime quallty merchandise. CALL GARY JOHNSTON OR BRUCE ROUTLEY NOW ON (02) 747 2022 23250 NEW LITHIUM BATTERY No. CRD As used in IBM and other computer clocks. 3volt. Cat. SB-2530 $7.95 ·_ . . GREAT MULTIMETERS FOR THE HOBBYIST AND PROFESSIONAL • B • TRANSISTOR TESTER • CENTRE ZERO ADJUST • PEAK TO PEAK & RMS Cat. QM-1050 • 10,000 OHMNOL T • 19 RANGES Cat. QM -1015 $26.50 ECONOMY POCKET $79.95 20,000 OHMSNOLT • SIZE 80 X 50 X 30mm Cat. QM -1001 $17.50 Night Security Sensor This brilliant new product uses a built-in passive infra red (PIR) detector that reacts instantly to body heat, and activates a light when a person approaches your home. The light is automatically turned off when the person leaves. The sensor will swnch up to 600 watts and when set will only operate at night. After triggered, the lights can be adjusted to remain on anywhere between 5 seconds and 1O minutes. FOR FEATURES SEE OUR 1988 CATALOGUE 10 A DIGITAL 4.5 DIGIT 10A • TRANSISTOR TESTER • VINYL CASE Cat. QM-1530 • TRANSISTOR TESTER • DIODE TESTER • DATA HOLD Cat. QM-1550 $89.95 $179 DON'T PAY $199 use existing lights Cat. LA-5130 ONLY $115 The Sunvent is a high capacny solar cell and DC motor powered fan in a well designed cowling. The cowling has been cleverly designed to keep waiter out and back draughts out. It will move about 35 cubic metres of air every half hour in good conditions. Supplied with cover to turn off cells and stop all airflow. • Boats "Hots tick" • Caravans • Port-a-Loos • Greenhouses • Sheds • Holiday homes • Backyard dunnies • Knehans • Weekenders etc Cat. YX-2500 Ideal for the hobbyist and handyman . Our lowest price 240 volt qualny iron has a stainless steel barrel and is supplied with free solder. Spare tip Cat. TS -1453 $4.95 Cat. TS-1450 $49.95 $16.95 ......................... Rover Negative Ion • Low Cost 25 Watt Iron Generator ,. $29.95 : SAVE $50 •• 12" GUITAR SPEAKER Has extended frequency response. Especially suited for not only Bass gunar but Rylhm and Lead as well. FOR FULL SPECS SEE OUR 1988 CATALOGUE. Cat.CG-2380 SAVE $10 ONLY $79.50 •• • • • WITH FREQUENCY COUNTER • CAPACITANCE TESTER • TRANSISTOR TESTER • 20 AMP CURRENT • HIGH IMPACT CASE Cat. QM-1555 $159 Solar Powered Exhaust Ventilator Yes, we've made another scoop purchase. The importer contacted us with his dilemma and we purchased a quantity of these fully imported fully guaranteed air purttiers. These units are 240 volt operated , draw about 1/2 watt, deliver abou1 250 billion ions per second, and cover about 25 square metres. It's even supplied with a Tester PC board and spare needles. If you've ever wondered about negative ion generators, this MUST be the time to buy one. These were selling for about $80. Jaycar has a limned quantity available for: Cat. YX-2905 TOP DIGITAL •• • • AT LAST - Probe Cases We have finally secured a reliable supply of RF probe cases These are constantly used in kits. Size: 200 x 24 x 20mm HUGE 3WAY RANGE OF Crossover Networks • Crossover freq. 800Hz, 5,000Hz • 6dB attenuation • 40 watts rms • 8 ohms Cat. CX-2615 2WAY $15.50 ea 3WAY • Crossover freq. 3,500Hz • 6dB attenuation • 40 watts rms • 8 ohms Cat. CX-2614 • Crossover Freq. 2,800Hz, 8,000Hz • 12 dB attenuation • 50 watts rms • 8 ohms Cat. CX-2617 $9.95 ea 2WAY $18.50 ea 3WAY • Crossover freq. 5,000Hz • 6dB atten uation • 40 watts rms • 8 ohm Cat. CX-2613 • Crossover freq. B00Hz, 5000Hz • 12dB attenuation • 65 watts rms • 8 ohms Cat. CX-2616 $9.95ea 2WAY $28.95 ea 3WAY • Crossover freq. 3,500Hz • 12dB attenuation • 50 watts rms • 8 ohms Cat.CX-2612 • Crossover freq. 600Hz, 3500Hz • 12dB attanua1ion • 80 watts rms • 8 ohm Cat. CX-2619 $13.95 ea 2WAY $32.95 ea 3WAY • Crossover freq. 2,000Hz • 6dB attenuation • 65 watts rms • 8 ohms Cat. CX-2611 • Crossover freq . 500, 3500Hz • 12dB attenuation • 200 watts rms • 8 ohm Cat. CX-2621 $18.95 ea $69.50 ea DPM400 30+30 STEREO AMP INCLUDING PREAMP 3·5 Digital Display Fully built and tested with separate bass, treble, balance and volume controls. This superb amp has less than 0.1 % distortion. There are Inputs for microphone, phono and auxiliary (line) and all power supply components are on board. Just connect a transformer, speakers and a signal - and away you gol Requires 36-38V AC x 2. Size: 186 x 145 x 40(H) mm. Cat. AA-0300 Auto zero, auto polarity, programmable decimal points and 200mV are standard features. At present th is is the world's smallest off-the-shatt DPM . • 10mm character height • Ultra low profile• Ultra compact• Ann unciators • Snap-In bezel • Can plug into a 28 pin IC ski• Surlace mount technology Cat. QP-5502 $79.95 ea $69.95 Transformer to suit Cat. MM -201 0 $24.95 10 or more $75.00 each 1I'©'i!WIEm~ ~IEMII©<at>JR!IIJ)iJJ©1I'©m JE©©JE~ OP-Amp and Linear IC Transistor Selector Over 5,000 American, British, European & Japanese linear IC's with electrical and mechanical spacs, pinouts, manufacturers names, recommended substitutes, ate. Cat. BM-4556 Hardcover edition. Over 27,000 (YES TWENTY SEVEN THOUSAND) transistors listed with electrical, mechanical applications, lead connections, manufacturers names and recommended substitutes. Cat. BM-4554 $29.95 Diode and SCR Index TURN YOUR SURPLUS STOCK INTO CASHII Jaycar will purchase your surplus stocks of components and equipment. We are continually on the lookout for sources of prime quality merchandise. CALL GARY JOHNSTON OR BRUCE ROUTLEY NOW ON (02) 747 2022 It lists 10's of thousands of SCR's, Triacs, Diacs, Diodes of all kinds (including Zanars) and gives descriptions of device, Its main parameters, mechanical details and manufacturers information. 512• pages, 220 x 150mm, softbound. Cat. BM-4560 $29.95 $29.95 $35.00 Digital IC Selector This book supplies over 13,000 digital integrated circuits , with electrical and mechanical specs, manufactures names and pinouts. Size: 178 x 247mm, softcover Cat. BM-4558 $29.95 PORTASOL A BRILLIANT NEW CONCEPT IN SOLDERING IN THE FIELD • No Cords, batteries or bottles • Heavy duty, tip temperature up to 400"C • Adjustable temeprature - equivalent to 10-60 watts • Hard working, up to 60 minutes continuous use • Refills In seconds, uses standard Butane gas lighter fuel • No leakage current to sensitive circuits • Made In Ireland = · it; I' . ,, ., Cat. TS-1420 National Linear Data Books Vol. 1, 2 & 3 $39.95 e!Q./JI'", .. ~ ~ ~(UJQ:{ , 4'.; .'.,,;ri~'j 5 - - ~ IC Index An ideal single reference book for both linear AND digital integrated circuits. Cat. BM-4562 . ~ _ We have managed to obtain a small quantity of the definitive National Li near Data Books . Th h tb ·1 bi f th:;: ~~ok:.en ava1 a e or many years . Se_~~f We don't expect these to iast very long - so be ·=··----.. .. _ quick. ;~:;;•OOK· CD HEADPHONE AMP Ref: Silicon Chip April 1988 Ref: EA December 1985 One of our best selling kits. Needs no auto coil. Uses special output transformer. Cat. KA-1660 Add a headphone socket to any CD player. Has volume control. suits low and high impedance phones, THD less than 0.001%, requires 9Vto 12V AC plugpack. Cat. KC-5029 $24.95 $59.50 pH METER OPTICAL TACHOMETER Ref: Silicon Chip April 1988 Easily measure the pH level in your pool, fishpcnd, garden, etc. Case and all components supplied. Probe extra. Cat. KC-5027 pH Probe and Buffer solutions Cat. QP-2230 $79.95 $49.95 BATTERY MONITOR Ref: Silicon Chip May 1988 Check out engine RPM on your model airplane and---r~~~~~~~~~~~~~~~~~~:, measure the speed of fans and rotating shafts. Cat. KC-5031 Ref: EA May 1987 Monitor your cars battery. 10 rectangular LEDs tell you its condition. PC board and components. Cat. KA-1683 RAILPOWER WALK AROUND CONTROLLER $49.95 $14.95 Ref: Silicon Chip April/May 1988 Incorporates pulse power, inertia (momentum), braking and full overload protection. Kit includes mains transformer, PC boards, hand controller box and components. Box for main controller Cat. HB-6240 $27.95. Cat. KC-5028 3 BAND SHORT WAVE I RADIO '--- Dual Tracking Power Supply $129.95 Ref: EA February 1987 Will supply from Oto ±21.5 volts at currents up to 2 amps. Also features overload protection, a fused +5V<at> 1A output and metering. Cat. KA-1682 ;~::NIN~ / FOR FULL SPECS ON ALL OF THESE KITS SEE OUR 1988 CAT. BUILT VERSION $379.00 Ref: AEM July 1985" ' Cat. KM-3015 $39.95 Protector Car Alarm Ref: Silicon Chip December 1987 Will control the speed of electric drills, fans, electric blankets, lamp dimmers and soldering irons. PC board partially assembled. Cat. KC-5016 Extras not included in kit Ref: Silicon Chip February 1988 Back up battery Cat. SB-2480 $22.50 About every feature you could ever want Piezo Siren Cat. LA-5255 $17.95 in a car alarm. See our 1988 catalogue fo 12 volt Siren Cat. LA-5700 $26.50 full details. Cat. KC-5021 $79.50 Remote Control (NEW FULL KIT) Ref: Silicon Chip Mach 1988 We are now selling this kit in a full form version. Kit includes all components except box for receiver, piezo siren and piezo transducer and banery for transmitter. These Items are available separately: Trasnducer Cat. AB-3440 $2.75; Piezo LA-5255 $17.95; Battery (pkt 2) Cat. SB-2420 $3. 75. $18.95 - $79.50 Ref: EA September 1985 Run 240 volt appliances from 12 volts up to 300 watts. Features auto start, current limiting and overload protection. Cat. KA-1610 $269.00 SPEED CONTROL - Ref: EA January 1987 Tuneable from 0.48MHz to around 17MHz. Quality kit with silk screened and punched panel. Cat. KA-1681 ~ · \ • . Metronome Ref: EA November 1987 Variable beat from 42 to 208 beats/second. Second, third, forth or all beats can be accented. Short form kit no woodwork. Cat. KA-1693 $19.95 $79.50 Cat. KC-5034 ------------------------------------- ?Zr Pf. __________________________________ HEAD OFFICE 4 MAIL ORDERS 0 137 0 0 4 3 POST & PACKING t_::_i_i_2_~~_ti_;_~_:_:a_;_,:_:_~:_:_r:_:______~-~-~-~-t_~_(s_ :~_~_I_I:_:_~_2:_~:_:_8__~_~_EA_$_1o_o_l!_f_li_i_J_al_l____, ,.__,iiliiiifllliiiillr-'11._•11i11_w~...... • ... I ~._.~-• ■ 5 VISA .._MAIL ORDER VIA YOUR ROAD FREIGHT ANYWHERE IN AUSTRALIA $13.50 SYDNEY · CITY 117 York St. (02) 267 1614 · GORE HILL 188 Pac1f1c Hwy cnr Bellevue Ave (02) 439 4799 . Mon-Fri 9 . 5.30 Sat 9 • 4pm CARLINGFORD Cnr . Carlingford & Pennant Hills Rd (02) 872 4444 . BURANDAQLD 144 Logan Rd (07) 393 0777 · Mon-Fri 9 . 5.30 Thurs 8.30 • Sat 9 . 12 CONCORD 115 Parramatta Rd (02) 745 3077 Mon-Fri 8.30 · 5.30 · Sat 8.30 - 12 MELBOURNE-C1TY Shop 2. 45 A'Beckett St City (03) 663 2030 HURSTVILLE 121 Forest Rd (02) 570 7000 Mon-Fri 9 · 5.30 Thurs 8.30 pm• Sat 9. 12 SPRINGVALE VIC Mon-Fri 8.30 . 5.30 Thurs 8.30 pm• Sat 9 • 12 Mon-Fri 9 - 5.30 Thurs 8.30 pm. Sat 9 . 2pm MaslefCard ff Mon-Fr, 9 · 5 30 Fri 8 30 · Sat 9 · 12 887-889 Sprmgvale Road Mulgrave (03) 547 1022 Nr Cnr 0andenong Road Mon-Fri 9. 5 30 Fri 8 30 Sat 9 . 12 __, For best results, the masthead amplifier should be mounted high on the mast, near the antenna terminals. The plastic conduit case makes a neat weatherproof assembly which is easily attached to the mast using an automotive-type hose-clamp. MASTH. . . . .. ~ c AMPIJFI~ FOR TVAND'" This unit can be used as a masthead amplifier or as a distrioution amplifier. It's simply added to yoµr exjsting a.t'lt~nl'la feeder system and can gr~atfy i1tiprov~.- , your television or FM ,r adio reception~ · By BRANCO JUSTIC You can put this masthead amplifier together for less than $30.00. It's easy to install and is suitable for amplifying both VHF and UHF TV signals, and FM signals. Quite often, a signal which is otherwise quite acceptable at the antenna terminals produces poor results when fed to a TV or FM receiver. This occurs because of signal losses in the signal distribution system; in the feeder cable, in matching transformers or baluns and in splitters. Such losses can severely degrade picture quality. 30 SILICON CHIP The best way around this problem is to amplify the incoming signal at the antenna terminals (ie, right at the masthead) to make up for signal losses occurring later in the distribution system. Alternatively, the amplifier can be installed ahead of a splitter system to ensure adequate signal level at each outlet. A splitter is used when you want to connect two or more TV sets to the same antenna. The circuit of the masthead amplifier is based on an OM350 thick film hybrid IC which gives around 18dB of gain from 40MHz to 1GHz. This means that there is plenty of gain right across both the VHF and UHF TV bands, as well as across the FM band (88-lOBMHz). To make the unit easy to build, all the parts are installed on a small printed circuit board. Apart from the IC itself, the circuit uses just three diodes, five capacitors and a small RF choke. The completed assembly slides into a 150mm x 32mm O.D. piece of plastic conduit which is fitted with end caps for weatherproofing. The plastic conduit certainly makes for a very neat and effective assembly. And it's easily mounted on the mast using a large automotive type hose clip [see photo on facing page). 03 1N4004 .----.a------+-1i.-+-+12v SUPPLY Transmission losses Before moving on to the circuit description, let's take a closer look at the losses that occur in the signal distribution system. By understanding what these losses are, you'll know when and where to employ the masthead amplifier. • Feeder cable loss: this is simply the loss that occurs in the cable that connects the TV set to the antenna. It depends on the length and quality of the connecting cable being used and, for good quality coaxial cable, is typically about ldB per 10 metres at VHF. Unfortunately, losses are much higher at UHF so a masthead amplifier can make a big difference to your UHF TV reception. Note that you should always use good quality coaxial cable for TV signal distribution, particularly at UHF, to minimise signal losses. Coaxial cable is also less prone to ghosting and noise pickup than 300-ohm ribbon cable. • Balun loss: a matching transformer or balun is normally used to match the feeder cable impedance (75 ohms) to the antenna impedance (300 ohms). Good quality baluns exhibit losses of less than ldB at VHF but have slightly higher losses at UHF. Don't use a cheap balun if you want to watch UHF channels. It may be OK at VHF but could introduce unacceptable losses if used at UHF, particularly if followed by a long cable run or in marginal signal areas. • Splitter loss: this is the loss that occurs between the splitter's input and any one of its outputs. Of course, the more outputs the splitter has, the greater will be the signal loss. Typical 2-way and 4-way splitters have losses of 3.5dB and 6.5dB respectively at VHF, but again losses at UHF are somewhat higher. So should you use a masthead amplifier to solve your TV reception problems or not? The answer is yes, depending on the circumstances. C1 680pf INPUT 07-i1---+----a~11---t OUTPUT 2xBAW62 01 02 ":' TV MASTHEAD AMPLIFIER 02-1-0788 Fig.1: the circuit is based on an OM350 thick film hybrid IC which gives around 18dB of gain from 40MHz to 1GHz. D1 and D2 protect the IC from excessive input voltages. INPUT ----i l-t ---- ~01 ~~ 68~;F/& 02~ e C• • • • o-:;Opf IC1 ~ <::)J ..C 1----=x ....... ~ 03 L1 1-L OUTPUT ---- Fig.2: the parts layout on the PCB. Be sure to keep all component leads as short as possible and take care when installing polarised components. This view shows the fully assembled PCB. The board is powered from separate supply leads which are run up the mast adjacent to the coaxial cable. Your installation will benefit from a masthead amplifier if: • reception is poor on one or more stations and you are using a fairly simple antenna system; • reception is poor due to signal losses in the cable or in splitters; and • one or more channels i s borderline in quality and you intend adding splitters for additional TV sets to the system. How it works Fig. l shows the circuit details. All the required gain is produced in !Cl (OM350). The input signal is coupled to !Cl via capacitors Cl and C2, while diodes Dl and D2 protect the IC from excessive input voltages [eg, from close RF transmitters, nearby lightning strikes, static build-up, etc). Note that BAW62 diodes are specified here because they are a JULY 1988 31 PARTS LIST 1 PCB, code OE12 (from Oatley Electronics) 1 150mm length of 32mm O.D. plastic conduit 2 32mm I.D. end caps 1 prewound RF choke Semiconductors 1 OM350 wideband amplifier IC 2 BAW62 silicon diodes 1 1 N4004 silicon diode Capacitors 1 1 00µF 16VW PC electrolytic 1 .01 µF ceramic 3 680pF ceramic Miscellaneous Cable clamps, screws, nuts, washers, coaxial cable. high-speed switching type with very low capacitance. This means that they offer good protection to the OM350 without significant signal loss. The amplified output signal from IC1 appears at pin 5, which is also the supply pin for the OM350. From there, the signal is coupled to the feeder cable via capacitor C3. Inductor 11 presents a high impedance at signal frequencies and thus ensures that IC1 's output is not loaded by the supply rail. Power for the circuit is derived from an external plugpack supply and is applied to pin 5 of IC1 via D3 and 11. D3 is there to protect the IC against reversed supply connections while C4 and C5 provide supply decoupling. The PCB has been specially designed to slide into a 32 x 150mm length of plastic conduit which is then fitted with end caps for weatherproofing. The input, output and power supply leads are fed through boles drilled in the bottom end cap and secured to the mast using cable ties. Where to buy the parts Parts for this project are available from Oatley Electronics, 5 Lansdowne Pde (PO Box 89), Oatley, NSW 2223. Telephone (02) 579 4985. Prices are as follows (mail orders add $3.00 p&p): Complete kit (includes PCB, on-board parts, cable clamps, screws and nuts, conduit and end caps) ..................... $27 .95 9V plugpack supply to suit ............ ...... ... .... .... .. ....... .... ..... ... . $10.50 4-way splitter .................... .......... ........................................ $8.50 Power supply/signal combiner ................................................ $4.50 Note: copyright for the PCB artwork associated with this project is retained by Oatley Electronics. 32 SILICON CHIP Construction A kit of parts for this project is available from Oatley Electronics (see panel). The kit is supplied complete and includes the printed circuit board, all on-board components, cable clamps, screws and nuts, and the plastic conduit case. Fig.2 shows the parts layout on the PCB. Be sure to mount the ceramic capacitors and the IC as close to the board as possible, and note that D1 and D2 are the BAW62s. The inductor is supplied prewound on a ferrite core and can be installed either way around. The coaxial cable leads are secured to the copper side of the PCB using the clamps, screws and How to Combine the Signal and Power Supply 1N40Q4 .---..-~H--0+ L1 TO II II .01I 11 .,. 0 0 12V Q- ~~~ftr7 ~ + 680pf MASfliEAD--=-"=I~~~~~~:·~~:J-.,.;;=;;;;.z,.,.,_TO TV/SPLITTER AMPLIAER - + It is easy to eliminate the need for a separate supply cable between the masthead amplifier and the plugpack supply. This simply involves modifying the physical construction of the unit so that the DC supply is fed to the amplifier via the coaxial cable. Fig .3 shows the relevant circuit of the power supply/signal combiner while Fig.4 shows how the circuit can be built onto the lid of a small plastic case. Most of the nuts provided (see photograph). Solder the inner and outer (shield) conductors to the PCB as shown in Fig.2 and note that these leads should be kept as short as possible. Installation If you intend using the unit as a masthead amplifier, it should be installed on the mast adjacent to the antenna terminals as shown in one of the photographs. This arrangement will provide the best signal to noise ratio although a short length of high-quality coaxial cable between the antenna terminals and the masthead amplifier shouldn't make too much difference. 12V Fig.4: here's how to wire the power supply/ signal combiner circuit. Keep all leads as short as possible. parts used here are simply transferred from the main PCB. To modify the PCB, delete C3, C4, C5, D3 and L1, and connect a wire link in place of C3. The leftover parts can then be used to wire up the combiner circuit as shown in Fig.4. Be sure to keep all leads as short as possible and note that the 100µF capacitor (C4 in Fig. 1) is no longer required. The only additional items required are the plastic case, a The coaxial cable leads are secured to the rear of the PCB using small clamps and machine screws and nuts. Use good-quality coaxial cable. SPLITTER 0 + Fig.3: this simple circuit allows the DC supply to be fed to the masthead amplifier via the coaxial cable. TO TV OR 2-way terminal strip, two cable clamps, and screws and nuts. Installation of the combiner is quite straightforward. It is simply positioned next to the plugpack supply and inserted into the coaxial cable between the masthead amplifier and the TV set or splitter. Power will now be fed to the amplifier via the coaxial cable which means that you no longer have to run DC supply leads up the mast. This alternative version of the board is used with the power supply/signal combiner circuit shown in Figs.3 & 4. D3 appears in this photograph but can also be deleted. To install the unit, the completed board assembly is simply pushed into the plastic conduit and the end caps fitted to provide a weatherproof assembly. Note that both the input and output leads, along with the power supply leads, emerge through holes drilled in the bottom cap. These holes can all be sealed with silicone sealant after the assembly has been installed and tested. If used as a distribution amplifier, the unit should be placed as close as practicable to the point where the coaxial cable enters the building. The only proviso here is that you must have a noise-free signal to feed into the amplifier. The output of the amplifier is connected to the splitter input and the splitter outputs then run to the TV receivers. For best performance, the amplifier should be powered from a 10-14V DC supply. Before connecting the supply, check the output voltage with your multimeter. The OM350 has a maximum supply voltage of 15V DC so take care not to exceed this figure. The prototype was powered from a 9V plugpack supply which actually gave an output voltage of 11.5V with the low current drawn by the amplifier (approx. 30mA). ~ ]ULY 1988 33 . Sounding out a video recorder For the most part, TV equipment sound sections tend to be taken for granted; they don't give a great deal of trouble and we don't think much about them. Which is a far cry from the pre-TV days when restoring sound was the main exercise. But modern sound circuits do fail and when they do, they can be quite tricky. machine on that occasion. I had it in the workshop for several days and put it through many recording and replay cycles, without the slightest sign of any problem. The only clue I had was a faulty tape brought in with the machine and this carried a background of the previous sound track at a reduced but still annoying level. Nothing I could do would produce the fault. And since there seemed to be an urgent need for the school to have it back, I simply gave it a routine service, explained the situation and advised them to give it another try and bring it back if or when the fault was more predictable. And that was the last I heard of the device until a couple of weeks ago. I can only assume that it This story concerns a National NV-300 video tape recorder. It belongs to a local private school and had first come to me with the sound fault some two years previously. The complaint then was that it would not always erase the previous sound when a new recording was made, although there seemed to be some doubt in the mind of the staff member as to how serious it was. Some users complained that there was no erase action at all, while others described the effect as a faint background of the previous sound. The NV-300 is one of the older top loading machines but has been a very reliable model. It is also easier to work on than some more modern designs. I didn't have much luck with the • R4038 5~0 TO VIDEO AUDIO OJT l4001 GNO . 470uH BPGOO; ®c,026 Q033 - ____ i I - TP-i001PLAY . 0.5 VI0.5msec . div . : '/ FE H(AO P6005- l GNO P6001-1 __-_ , /,/ . r ' TP<:001 AEC. 0.5VI0.5 msec. d1v. Fig.1: bias/erase oscillator circuit for the National NV300 video recorder. Although a simple arrangement it developed a very tricky fault. Note the missing chassis symbol on pin 8. 34 SILICON CHIP operated normally or, at least, acceptably during that time. Then it was back, brought in this time by another staff member who wasn't even aware that there had been a previous problem. This time the complaint was rather more specific. Granted the failure was still unpredictable but at least when it occurred now, it was complete; there was no attempt to erase the previous signals. I set the machine up at one end of the bench, connected to a monitor and made a half-hour recording over a previous recording. The machine behaved perfectly. So it was going to be one of those faults. I went through this exercise, at approximately half-hour intervals, over the next couple of days, without even a hint of trouble. Then just as I was beginning to wonder whether there was some environmental factor involved, the fault appeared. The previous sound was there at full blast and, just as important, there was only a shadow of the new sound which should have been recorded; just some brief distorted bursts of the louder passages. Well, at least I now knew that the fault was real enough. I had not delved very deeply into the machine at this stage, simply, removing the top cover but avoiding moving anything else for fear of disturbing the fault and causing it to lie doggo. But now I had to go on the attack. I began by removing the bottom cover which provides access to the copper side of the main board. Access to the component side of the board involves removing the front panel and unclipping the sub-boards carrying the clock display and various operating buttons which are on flexible leads. About six screws secure the main board and removing these allows the board to be swung up and propped open. ~f\~'t \ , •• 1-r SU..Or-.l6S TO A 1-OCAl- PR\VAT& SC~OOl-- • .,. The section I was seeking was the audio circuitry and in particular, the bias and erase oscillator, the circuit of which is reproduced here (Fig .1 ). It was fairly obvious that the system was suffering from loss of erase signal but remembering that there had been little of the new signal recorded, it appeared that it was suffering loss of bias signal as well. And since both signals come from the same oscillator, it seemed reasonable to suppose that this was where the trouble lay, rather than, in a lead or plug feeding the erase head. Circuit details As can be seen from the circuit, the oscillator is a simple arrangement; one transistor, two resistors, three capacitors, a choke and a tapped winding forming one side of a transformer, T4001. I decided to put this section under observation and the easiest place to connect the CRO was at pin 1 of plug BP6005, which connects to pin 7 of the secondary of T4001. This tapping supplies the "FE HEAD", or full erase head. This was not the section of interest but it was a convenient monitoring point. The audio erase head is supplied from pin 9, while pin 5 supplies the bias for the audio recording head, this being adjustable via variable resistor R4048. One other point to note is that there appears to be an omission from the circuit, in that pin 8 is shown floating, whereas it is a chassis connection and a vital one. With the CRO hooked up, I set the machine going again in the record mode and observed that there was approximately 45V p-p at the monitoring point, at about 63kHz. And as before, the machine performed perfectly for the next few days. · However, I adopted a routine of recording for periods of about 30 minutes, then shutting the machine down long enough for it to cool, before making another test. My hunch was that the fault was most likely to occur at start-up from cold, rather than while running. And in fact, it proved to be. Suddenly, at one start-up, I had no oscillator signal at pin 7 and a quick check with the CRO at other points gave the same result. But the mere act of making those measurements triggered the circuit back into oscilla- tion. It came up part of the way first, dithered for a second or so and then rose to normal level. From then on it behaved more or less normally but having been alerted, I observed the pattern more closely. Sure enough, it was exhibiting a dithering characteristic whereby the amplitude would vary over a range of about five volts. Then suddenly, it began dropping lower and lower, down to about 10 volts, then failed completely. · Well, that seemed straightforward enough. All I had to do was find out why the oscillator was intermittent and with so few components involved, I didn't imagine it was going to be particularly difficult. My first suspect was the transistor, Q4014. I pulled it out and replaced it but it wasn't long before the machine began dithering again and I knew that I had drawn a blank. That seemed to leave only the two resistors, R4049 and R4050, and the three capacitors, C4010, C4025 and C4024. The resistors were fairly easily checked, in situ and came up spot on. What was more, they showed no indication of any intermittent characteristics in spite of some vigorous pushing and prodding. The capacitors were not so easily checked and I was on the point of pulling them out and replacing them when it occurred to me to try some freezer spray on them. This had no effect on C4010 or C4025 but brought a swift reaction from C4024, the 10,-iF electrolytic; oscillation stopped immediately. So, I was getting somewhere at last. I pulled the capacitor out and replaced it but this produced a strange result. This capacitor no longer responded to the freezer but the original fault was still there! That put me almost back to square one. I pulled out the other two capacitors, tested them, found them to be well within tolerance but replaced them anyway. This achieved exactly nothing; the fault still persisted. Rescued by a drunk By now, there wasn't much else left to suspect; just the transformer in fact and then only by default. The snag was that I had no such device in stock, this being the first time one JULY 1988 .35 issued some two or three years previously and how I missed out on it is rather a mystery. The gist of it was that, in the event of unreliable operation of this oscillator, the 4.70 resistor in the emitter circuit of Q4014 (R4049) should be removed. In fact, the suggestion was that this resistor should be removed anyway, as a routine mod whenever this model was encountered. SERVICEMAN'S LOG A new theory had ever been suspect. But I did have another NV-300 machine on hand an unfortunate victim of a wild Saturday night party during which someone had upset a tankard of beer over it. It's been in the workshop for months and I've been working on it during odd slack periods; the only basis on which any kind of economical repair is possible. In fact, I am close to saving its life and that should make another story. In the meantime I was happy enough to rob the transformer from the drunken machine and try it in the sober one. And that was it. The problem vanished and has not been seen since, in spite of prolonged bench testing and several follow up calls after it went back into service. But that's not the end of the story. For one thing it left several questions unanswered. What was wrong with the coil anyway? Careful testing failed to reveal any obvious faults; certainly nothing in the way of abnormal or varying winding resistance, such as one might expect. It is a small device, apparently of pot core construction, and one thought was that it might have suffered from cracked or chipped ferrite material, a condition which can seriously upset the behaviour of the associated windings. Well, that was one to go on with. 36 SILICON CHIP And what about the freezer upsetting one capacitor but not the one that replaced it? I was still turning these questions over in my mind when I encountered one of my colleagues at a social gathering and during the inevitable shop talk, I related this story. He was suitably impressed but commented that he seemed to recall some kind of modification sheet dealing with cranky bias oscillators in that model. He promised to try to find it and let me know. He rang me the next day to say that he had found it. It had been TETIA TV TIPS HMV 12613 (Braddon) Symptom: No distinct red and somewhat dirty greens. Colour bars look vaguely normal but careful inspection shows red is really a muddy brown . The monochrome picture is perfect. Cure: R541 (4700 0.5W) open circuit. This resistor supplies Vee to IC503, one of two reference oscillator chips in this unusual circuit. In this fault, IC502 (the 8-Y oscillator) probably supplies some drive to the red and green circuits but it's phase is wrong, hence the weak and bad colour. Well, that threw a whole new light on the situation. After mulling it all over for a few hours, I finally came up with what I feel is the most likely explanation. My theory is that the design of the original oscillator circuit was a bit dicey; that is, while it would maintain oscillation under ideal conditions it was only just making it, and was on the verge of dropping out at any time. It was the reference to the emitter resistor which gave me the clue. The use of an unbypassed resistor in the emitter circuit of a transistor oscillator - or the cathode circuit of a valve oscillator in olden days was a favourite trick to improve the oscillator waveform. Because it is unbypassed, it is a simple way of providing a degree of negative feedback, thus holding down the strength of oscillation and reducing the tendency for the transistor (or valve) to be driven to cut-off and saturation, two conditions which seriously distort the waveform. And it can be very effective, the only snag being that it is a compromise arrangement; the negative feedback provided by the emitter resistor is fighting the positive feedback which is fundamental to the oscillator circuit. So, if the idea is carried too far, the whole arrangement can turn cranky. So, was the original oscillator coil faulty or not? It's hard to say. All I know is that it would not work in a circuit which was otherwise fault free. It's possible, of course, that the "fault" in the suspect coil may have been nothing more than a normal spread within otherwise acceptable tolerances. Along with other component spreads it could easily have been the last straw which sank the camel's hump (to mangle a wellknown phrase). UHF REMOTE KEY SWITCH (EA, JAN.87) This proven and reliable unit is *guaranteed* to work. It has countless applications, 40-50 metre range, multiple outputs, and is available at a fraction of the cost of the other equivalent unit. Beware of "short form" kits that include little more than the PCB! <at>;;;~1~ ... ••• IN Tlt£ tl\E.AN"r\W\E., I WAS HAPP'{ "'rO "ROB "n\e:. Ttlt.1-\1\lSFORIV\e:R FROM 11\£ ~UNKeN MACHl>J£ ••• As for the original machine, I'm keeping my fingers crossed. But if I can contrive to get my hands on it again, for any reason, I'll whip that resistor out, just to make sure. In the meantime, I suggest you make a note of that mod which, I understand, also applies to the model NV370. Let's hear it from J.L. To change the scene, here is a story from my regular contributor, J.L. of Tasmania. It is one which is not only intriguing technically but also emphasises that when all else fails, it is important to be able to analyse how a circuit is supposed to work. This is how J.L. tells it. The set was a 63cm National, model TC2652, which was completely dead. However, the owner had observed that it made a brief noise when switched on. When I tried it I found that there was a five second burst of normal sound before the set shut down. This kind of overload is often caused by a faulty tripler and disconnecting it will let the set run normally. Unfortunately, this chassis uses a diode split output transformer rather than a tripler, which rules out this trick. A CRO check of the horizontal output transistor, Q502, showed that it started up OK but died as the waveforms approached full value. And there was not even a flicker of EHT, even while the transistor was running, briefly, at about two thirds its normal voltages. I wired a 60W lamp in series with CHOPPER T801 0801 +111V Our kit includes all the parts needed to make a working link. Even the transmitter battery is included! ON SPECIAL UNTIL END OF THIS YEAR AT ONLY $41.95 Plus $2.50 pack & post For a complete Remote Controlled Car Alarm, combine the UHF Remote Key with our Ultrasonic Car Burglar Alarm (SILICON CHIP, May 1988) or our Shock Detecting Car Alarm Module (ETI, March 1988); or perhaps with both of them. Interconnecting diagrams available from us. For more information, see our advert on page 96. * If upon completing any one of our kits you cannot get it to operate correctly, we will repair it for a maximum fee of $1 0. 00. This offer applies only to properly constructed individual kits which haven't been overloaded in incorrect supply voltages. OATLEY ELECTRONICS ERROR AMPLIAER 0803 8809 Fig.2: simplified circuit of the National TC2652 power supply, as drawn by J.L. T801 and Q801 form a ringing choke oscillator, with regulation provided via Q803 and Q802. 5 Lansdowne Pde, Oatley West, NSW 2223. Phone: (02) 579 4985. Bankcard, Mastercard and Visacard accepted with phone orders. Send mail orders to PO Box 89, Oatley, NSW 2223. JULY 1988 37 e 1'HE.. (\\\f\\111 se., w~s C.OM?L.E."i"EL"'( t>EA'O•••. the collector of Q502 and ran the set for about five minutes. By that time the output transformer was quite warm and giving off a typical sour "brown" smell. I ordered a new transformer. This duly arrived and was fitted but resulted in a set which was even deader than before; there was not even the five second burst of sound. As before, the set would run with the lamp in series with the output transistor but the 111 V HT rail was up to 120V. Without the lamp the voltage shot up to 120V before the power supply shut down. By feeding the set from a Variac I found . that 120V HT resulted from only 100V Philips Tuners ECL 2060 $17.00 Exchange or repair. Three months warranty . Send cheque or money order plus $2.00 pack and post anywhere in Australia. J.V. Tuners, 216 Canterbury Road, Revesby, Sydney, NSW 2212. Telephone (02) 774 1154. 38 SILICON CHIP AC input. Clearly the power supply was not regulating. This power supply is a self oscillating chopper circuit, which controls its ouput voltage by varying the chopper "on" time via an error amplifier. The trouble was that the three transistors and the reference zener diode involved all checked OK. Also, the HT ( + B Adjust) control worked in a seemingly normal way, varying the voltage by about 20V a not unreasonable range. At this point I put on my thinking cap and reviewed what I knew about the problem. (1). The set worked OK when fed with low AC input. This restricted the fault to the power supply circuits. (2). The chopper transistor Q801, regulator transistor Q802, error amplifier Q803 and reference diode D811 were all OK on static test and gave the proper responses under load. (3). The HT ( + B) adjusting trimpot worked over a logical range but at a higher than normal level. Correct HT output should occur with the chopper operating at about 50% duty cycle but in this case it was on for close to 90% of the time. This suggested that the error amplifier was delivering the wrong information. There are not a lot of parts in this circuit but I found its operation difficult to follow. In fact, I could make no sense of it at all until I redrew the circuit in simplified form, omitting every component that was not vital to its operation. Fig.2 shows my simplified diagram. As far as I can see, it works as follows: Q801, T801, D806 and their associated components form a ringing choke oscillator, with voltage regulation via Q802 and Q803. Imagine that Q802 is turned on. This will tie the base of Q801 to its own emitter and thus turn it off. In normal circumstances, Q802 is held in dynamic conduction by error amplifier Q803 using zener D811 as a reference. When the supply rail rises above a preset level, Q803 and Q802 turn on and Q801 turns off. So much for my theory. I already knew that all the transistors and diodes were OK. I also knew that C809 and a number of other capacitors were, at least, not shorted. They might have been open but that would not produce these symptoms. At this point I should have been able to find the fault with just a little logic. With hindsight, I can see it sticking out a mile. In fact, I decided to try an experiment. I removed Q802 and switched on. There was absolutely no difference in behaviour whether the transistor was in or out of circuit. Since it wasn't Q802 it had to be the only other component in this part of the circuit, R808. Sure enough it was open circuit and a new resistor restored normal operation. One final point. Why did I get some output adjustment when the regulator was patently not working? This was the result of Q803 varying its resistance, as part of a divider chain also involving R803/820, R809 and R810. It was only a superficial action but was enough to mislead me in the early stages. Well, that's J.L.'s story and I think we should thank him for the trouble he has taken to set down his analysis of the system and provide a simplified circuit. While this is not the kind of approach we can afford to adopt with every tricky set that lands on the bench, it is one we should be prepared to adopt whenall else fails. ~ Years of continuing research and development means Crown is always one step ahead of the competition. The introduction of the Macro-Tech™ Series is further proof of Crown's commitment to bringing products to the field that make sense and enhance the music industry. The Macro-Tech 1200 - a miniaturized, high-technology stereo amplifier designed.specifically for professional sound reinforcement and studio monitoring. This premium line Crown amplifier can deliver 1000 solid watts of continuous average power in mono mode (1 or 4 ohms), 4 70 watts per channel in stereo mode into 4 ohms or 320 watts per channel into 8 ohms. Very low distortion with extremely high dynamic range, the Macro-Tech Series amplifiers meet the critical demands of digital audio. A major feature of the Macro-Tech 1200 is the PIP panel for plug-in accessories - a variety of optional plug-in circuit cards that tailor the amplifier to the user's needs by adding functions in series with the amplifier input, such as XLR balanced inputs, electronic crossovers, etc. A three-position switch selects stereo, bridge mono, or parallel mono modes _- versatility available only from Crown. Patented Crown circuitry allows extreme voltage swings without putting output transistors in series, thus lower distortion and greater reliability. The Output Device Emulator Protection Circuit (ODEP) simulates the output transistors, and detects and compensates for overheating and overload. Efficient heat sinking and forced-air cooling system prevent overheating to protect your investment. The Macro-Tech 1200 - a high-powered package with a low-profile, only 3½ inches of vertical rack space. Pure sonic quality and legendary Crown dependability - the elite Macro-Tech 1200. Hum and noise: At 26dB gain: 105dB below rated output (A-weighted), 105dB below rated output (20Hz-20kHz), Phase response: +/- 10 degrees 10Hz-20kHz at 1 watt Input Impedance: Nominally 20K ohms, balanced, Nominally lOK ohms, unbalanced, Turn on: No dangerous transients, approximately four second delay, Front panel controls: Thro position ENABLE (on/ offi pushbuttcin switch, Channel 1 and Channel 2 input-level controls, Rear panel controls: Stereo-mono switch (stereo, parallel mono, bridge mono), Internal controls: Sensitivity switch (0,775 for full output or 26dB gain), Display: Amber LED ENABLEHght Is driven by low voltai:(e power supply, 1\vo amber multifunction ODEP LEDS Indicate tfie status of -the high-voltage supplies: thermal shutdown or blown line fuse, The ODEP indicators also monitor the protection circuit The ODEP light normally stays on, but goes out or dims proportionally to the ODEP limitin~A dual-function green SIGNAL LED verifies signal presence, IOC status, and front-end overload, This LED flashes in sync with the signal to indicate signal presence, and flashes veiy brightly if for any reason the output waveform differs from that of the input by a factor of0,05% or greater (IOC), Connectors: input- balanced ¼" phone jacks on chassis (and XLR. type connector on the standard PIP panel), output-color-coded dual binding posts on standard¾" centers; spaced ¾" apart for bridge mono (balanced) output connection, AC line - three-wire, 20A 120V male connector with 5 ft cable, Dimensions: 19" standard rack mount (EIA Std, RS-310-B). 3½" height 16" behind mounting surface, Center of gravity is 6" behind the fron t panel, Heat slnklng: Forced-air cooling through internal heat spreaders, Chassis: steel with specially designed flow through veqtilatlon system Weight: 44 pounds, 10 ounces net weight lkHz power: (see power matrix chart) Frequency response: + / -OJdB 20Hz-20kHz at 1 watt into 8 ohms, Harmonic distortion: less than 0,05% from 20Hz - lkHz and Increasing linearly to OJ% at 20kHz delivering rated power into 8 ohms, each channel, (see power matrix chart) I.M. distortion: less than 0,05% from 10 milliwatts to rated power into 8 ohms, each channel at 26dB gain, (see power matrix chart) Slewing rate: greater than 13 volts per microsecond, · Damping factor: greater than 1000, lOHz to 400Hz into 8 ohms, Output impedance: less than 10 milllohms in series with less than 2 mlcrohenries, DC output offset: (shorted input) 10 millivolts, Load impedance: rated for 8, 4, and 2 ohm usage, but safe with all loads, Voltage gain: fixed 26dB gain or ,775V for full output Input sensitivity: 0,775 volt unbalanced for rated output or 26<1B gain, Amplifier output protection: Macro-~h uses an "Output Device Emulator Protection" (ODEP) circuit which simulates the output transistors internal characteristics, The amplifier can then detect and compensate for overheating and overload, The unit also protects against output shorts, open circuits, mismatched loads, overall overheating, and high-frequency overloads, Overall protection: If unreasonable operating conditions occur. the protection circuitiy limits the drive !we! to protect the output transistor stages, particularly In the case of elevated temperature, 'Transformer overheating will result In temporaiy shutdown of that particular channel, Controlled slew rate voltage amplifiers protect the unit against RF burnouts, Input overload protection Is furnished at the amplifier Input to limit current INTERNATIONAL, INC. Distributed by BOSE AUSTRALIA INC, 11 Muriel Ave, Rydalmere 2116. (008) 02 3367 Toll Free. JULY 1988 39 Studio 200 Stereo Control Unit, Pt.2 Last month, we introduced our new high performance stereo control unit and described the circuit operation. This month, we present the construction and troubleshooting details. By GREG SWAIN & BOB FLYNN Because the circuit of the Studio greatly reduces the possibility of 200 control preamp is so simple, it wiring errors. So the Studio 200 is follows that the construction is also easy to build. straightforward. Most of the work involves mounting components on Collecting the parts three printed circuit board assemWhile some constructors will blies. These are for the power supp- prefer to buy the parts separately, ly, the phono preamplifier, and the most will elect to buy a complete kit tone control and headphone • of parts. Because all the parts are amplifier circuitry. readily available, there is nothing There is very little wiring inside to stop you from adopting either the chassis. This is because all the approach. pots, the headphone socket and the Buying a complete kit is probably pushbutton switches (but not the the easiest option. We understand mains switch) are mounted directly that at least two kitset suppliers, Altronics and Jaycar Electronics, on the tone control board. Similarly, the rotary input selector switch is will be selling kits for this project. mounted On a small PCB which is Both the Altronics and Jaycar kits then soldered at right angles to the will come with pre-punched chassis and the front panel labelling will be phono preamp board. Mounting the switches and pots silk-screened. If you do elect to go it alone, you in this way eliminates the tedium of running separate leads to the tershould have little difficulty in buying the parts separately. The only minals of these components. It also 40 SILICON CHIP parts that might cause constructors some problems are the extension shaft (1/4-inch rod) and shaft coupler for the selector switch and the accompanying 1/4-inch ID x 3/8-inch bush. This latter component mounts on the front panel. If you have difficulty locating this bush, it's quite easy to salvage one by wrecking a potentiometer from your junkbox. The PCBs will be available separately from RCS Radio in Sydney, Jemal Products in Perth, and from Marday Services in Auckland, New Zealand (see page 96 for addresses). Alternatively, you may choose to etch your own boards using the patterns published with this article. To simplify matters, we'll assume that you've purchased a complete kit of parts and that you have the standard one-unit rack case as supplied by Altronics. Starting construction The first job is to partially assemble the rack mounting case. This is supplied as a kit and consists of four rails, the top and bottom panels, and the front panel. Note that the top and bottom panels are 8'1)?= Iii I coJfRoL BOARD ):?RIGHT t\88i30 - t -t0~8 Fig.4: parts layout for the phono preamplifier board. Note that all the resistors in the phono preamp, except for the 1000 and 1MO values, should be 1% metal film types. Take care with the orientation of the IC. swapped over for this project, so that the slotted panel becomes the base and the solid panel becomes the top. To assemble the case, first attach the front and rear rails to the base. These two rails are secured by means of screws which screw into captive nuts on the flanges. Note that the captive nut in the centre of one of the flanges has been drilled out to provide clearance for the tone control PCB. This flange goes towards the top, front of the case. Once the front and back rails are in position, the side rails can be attached using the screws and nuts supplied (slotted screws towards the rear, countersunk Allen screws towards the front). Leave the front panel off at this stage and note that the side rail that carries the switch bracket is mounted on the right hand side of the chassis. The 18 insulated RCA sockets and the binding post terminal can now be installed on the rear panel. Orient the earth lugs on the RCA sockets as shown in Fig.9 and don't forget the solder lug on the binding post terminal. A multimeter should be used to check that each RCA socket is correctly isolated from the chassis. Incidentally, although we used screw-linking gold-plated RCA sockets in our prototype (which_you may have noticed from last month's cover photo), we recommend the use of standard nickel-plated insulated chassis mounting sockets. We suggest Arista RCA3I sockets which are supplied with white nylon insulators. You can now place the chassis to one side and turn your attention to the PCB assemblies. Phono preamplifier PCB This board is coded 01106881 and carries the parts for the phono preamplifier. It also carries five sets of stereo tracks which run between the RCA input sockets on the rear panel and the selector switch JULY1988 41 SOURCE SWITCH Sl 1mm DIA. PCB PINS (SHORTEN PINS CONNECTING TWO LOWEST SWITCH TERMINALS) ---- LOCATING PIN MOULDED IN SWITCH BODY Fig.5: the selector switch should be mounted on its PCB with the locating pin towards the bottom. Check the PCB pattern carefully to ensure that none of the input pads are shorted together. at the front of the board. An additional set of stereo tracks run from the selector switch back to the Tape Out socket. Before mounting any of the parts, it is a good idea to carefully check the copper pattern on the underside of the board. You should especially check for shorts between the long parallel tracks to the selector switch. Don't just rely on a visual check here - switch your multimeter to a high ohms range and use it to confirm that the tracks are isolated from each other. This test will quickly locate faults on any board that has not been correctly etched. Fig.4 shows the parts layout for this PCB. The first job is to install the 21 PC pins. Fourteen of these support the selector switch assembly and these should be installed from the copper side of the MOUNT PCB PINS WITH COLLARS ON COPPER SIDE OF BOARD SILICON CHIP BRACKET Fig.6: mounting detail for the selector switch assembly. Note that the PCB pins must be installed with their collars on the copper side of the phono preamplifier PCB. PCB (see Fig.6). Another three PC pins are required for the power supply connections near the centre of the board ( + 15V, OV and -15V), while the four remaining pins are located at the left and right channel outputs (adjacent to the 1k0 resistors). No particular order need be followed when installing the remaining parts on the board but it's best to start with the smaller parts {resistors and wire links) first. Note that all the resistors in the phono preamplifier, except for the 1000 and 1MO values, are closetolerance 1 % metal film types (see circuit). They have been specified for low noise and their close tolerance values. Check the values on your multimeter before installing them on the board - it's all too easy to misread the colour codes. The switch assembly is soldered at right angles to the phono preamplifier PCB and supported by an L-shaped bracket secured to the side rail. The switch shaft is lengthened using an extension shaft and coupler. 42 SWIT,CHMOUNTING You should also note that four of the capacitors (two in each channel) are marked with an asterisk. These capacitors are in the feedback network of the phono preamplifier and should be close tolerance (5 % or better) types in order to obtain accurate RIAA equalisation. If you have a capacitance measuring function on your digital multimeter you can specially select these capacitors. If you are buying a kit, the kitset suppliers may elect to supply 5 % capacitors or may also hand select the capacitors. Be warned that some closetolerance capacitors may not fit the board unless you bend their pigtails. Don't feel cheated if you are supplied with hand-selected greencaps instead of 5% close tolerance types. The hand selected types will work just as well. Take care with the orientation of the IC and the electrolytic capacitors. The two input inductors are Above: rear view of the selector switch PCB. You may have to shorten two of the PC pins to stop them fouling the switch terminals. each made by winding 4-1/2 turns of 0.6mm enamelled copper wire on an FXl 115 ferrite bead. Scrape the enamel from the ends of the leads before soldering the inductors to the PCB. Construction of the phono preamplifier PCB can now be completed by soldering 28 40mm lengths of tinned copper wire to the input pads along the back of the board. These input leads will later be soldered to the RCA input connectors along the rear panel. I I OUTPU~T RIGHT I LEFT HEADPHONES 02 E• Ce Be 02 E• C• Be 01 ........ 02 . . . . . . -- gf;18 (J][Je -c::illJe 01 E• ~::i :!'l - ce e.- e(Ili) Selector switch assembly Figs.5 & 6 show the mounting details for the selector switch. Position the switch with the locating pin towards the bottom and push the body of the switch all the way down onto the board before soldering the terminals. The pads along the bottom edge of the switch board can now be soldered to the 14 PC pins on the phono preamplifier board (see Figs.6 & 9). It will be necessary to shorten two of these pins to stop them from fouling the two lowest switch terminals. At this stage, you're ready to mount the phono preamplifier assembly in the case. This assembly is supported at the front by the switch mounting bracket and at the rear by the tinned copper wire connections between the PCB and the RCA sockets. Together, these provide ample support for the assembly and eliminate the need to secure the board via mounting pillars to the bottom panel. It also means that the bottom panel can be easily removed for inspection of the underside of the PCB or for other work. To mount the assembly, slide the L-shaped bracket over the switch shaft (see Fig.6), then position the PCB inside the case and fasten the switch bracket to the right hand rail with machine screws and nuts. This done, attach the extension ,shaft to the switch shaft using the shaft coupler. The extension shaft must now be centred in the hole in the front panel. You will find that the mounting hole in the L-shaped bracket has been slotted so that the PCB assembly can be slid sideways to locate the centre position. Check 01 E• C• e. -EID . . . . . . 02 . . . . . 01 BALANCE -cTI[]e 10k - : 6.BµF I e[ill[Je : ! R:====lcoi'\!/i~Ls 4 : O+ <at>[), 100pF - BASS .010 Im ~ • •I e[filJt 22k tQE) 10pF~1B)) .,., 10pF 9®<at>, Si!~ - TREBLE -cm} -r:::ID 180pFA -c!D18i<:ill:) ~i -do~ •I e[ffiJe c. e[E]e .0047 Cll .0047 18DpFA 0 .0047 _. -00 ,...1l!L., L!._!J e[illD ,...ll!L, VOLUME l!_!.f / T\PE ~ ' G D ~- I I ~ R INPUT/RIAA PREAMPLIRER BOARD R I 81 • •S3 • ••• • •S2 • ••• HI H IMODE !MONITOR Fig.7: follow this layout diagram when wiring up the tone control board. The circuit diagram published last month shows the pinouts for transistors Ql and Q2. JULY 1988 43 This is an underside view of the control unit with the bottom panel removed. The links between the pots are not necessary but make sure that they are electrically in contact with the chassis. that the preamplifier PCB is parallel to the bottom of the case before doing up the switch mounting nut to lock the assembly into position. · Before wiring up the RCA sockets, it will be necessary to provide some sort of temporary support for the left hand side of the board. A 5mm drill bit is ideal for this purpose. Slide the drill bit under the board, then wire up the RCA sockets as shown in Fig.9. Bend the leads as shown in the photograph so that they are well clear of each other and don't forget to remove the drill bit when you have finished. Tone control PCB Fig.7 shows the parts layout on the tone control PCB [code 01106883). Commence assembly by installing PC pins at the external wiring points, then install the wire links, resistors, capacitors and semiconductors. Check the orintation of polarised parts carefully when installing them on the board. These parts include the three ICs, four diodes, four transistors and electrolytic capacitors. The 6.8µ,F and 22µ,F 44 SILICON CHIP capacitors are bipolar types and can be installed either way around. The headphone socket, pots and pushbutton switches should be left till last. Be sure to push them all the way down onto the board but don't solder all the leads at this stage. Instead, tack solder diagonally opposite pins at either end of each component. The tone control assembly can now be tested in the front rail to ensure that everything aligns properly. To do this, it is best to remove the bottom panel so that you will have access to both sides of the board. Adjust the alignment of the pots and switches as necessary before removing the board and soldering the remaining pins. Note that it may be necessary to shorten the front row of pins on each pot to prevent fouling of the top flange. It may also be necessary to snip off the top of the Bakelite insulating section of each pot using a pair of sidecutters to give clearance for the bottom flange. Be careful doing this. You don't want to butcher the pot and damage its carbon tracks. That completes the tone control board. It can now be permanently mounted on the front rail and secured using the pot nuts and lockwashers. But before mounting the tone control board to the front rail, take a round file and lightly remove the anodised coating around each potentiometer hole. The idea of doing this is to make sure that the metal case of each pot is electrically connected to the chassis. If you don't do this you may end up with a slight background hum or buzz which may worsen when you touch the control itself. When all pot nuts are secured, use your multimeter to check that all the pot cases are electrically connected together, via the front rail. Check also that there are no shorts between the top flange and soldered connections on the PCB. You should also check that the headphone socket, pots and switches are centred correctly in the clearance holes in the front rail. If everything is correct, you can go ahead and run the shielded cable leads as shown in Fig.9. These leads go to the phono preamplifier board and to the TAPE IN and OUTPUT sockets on the rear panel. Finally, connect the two sets of power supply leads to the + 15V, 0V and -15V terminals. We suggest that you use red cable for the + 15V lead, green for the 0V lead and black for the - 15V lead. Twist the leads together as shown in the photographs before making the connections to the phono preamplifier board. The other set of leads are later connected to the power supply board. Make the leads about 100mm long and leave them floating for the time being. Power supply PCB This PCB is coded 04106881 and is used to provide the ± 15V rails for the circuit. Fig.8 shows the location of the various parts. The main thing to watch out for here is the orientation of the diodes and the two 3-terminal regulators. Be careful not to confuse the regulators and check that their metal tabs both face in the same direction. Install PC pins at all external wiring points. The supply PCB can now be mounted on the bottom panel, along with the power transformer, mains terminal block and earth solder lugs (see Fig.9). The supply board is mounted on 6mm standoffs and secured using machine screws and nuts. Two brass nuts, one on each mounting screw, are used to stand the transformer off the chassis. Once all the items of hardware have b_een mounted, the bottom panel can be re-attached to the chassis. . .l ..... ....... Q vl ...... Q ..ga..e 15 I ov-- F 03-06 F 7915 ••• i!~!:; .. = 100pFQ 1DDµF(S\ \a) o,-+ ~~s I flr-15V ;.·lov ~--+15V ••• --H® I LE01 Fig.8: this is the parts layout for the power supply board. Make sure that you don't transpose the 3-terminal regulators. wiring - you may get a hum loop if you do. The primary leads of the transformer are connected to the mains terminal block while the 15V secondary and centre-tap leads are soldered to three PC pins on the power supply board. Final assembly The front panel can now be mounted but be careful - one scratch and you'll ruin the appearance of the whole project. Secure the front panel at both ends using the Allen screws then install the power switch, the LED and the bush for the switch shaft. The bush is secured using locking nuts installed on both sides of the front panel. Be sure to use mains-rated 240VAC cable for the connections to the power switch. We used heat- shrink tubing to cover the switch lugs and then covered the whole switch body up to the threaded section with a larger piece of heatshrink tubing. The other ends of the leads from the mains switch go to the terminal block, along with a .0lµF 250VAC "anti-thump" capacitor. Make sure that this capacitor is rated at 250VAC. The connections to the LED were also covered with heatshrink tubing. The LED is secured to the front panel by means of a small plastic bezel. Connect the leads from the LED to the power supply board but don't connect the leads to the supply pins ( + 15V, 0V and - 15V) until the supply has been fully tested. Testing Check your power supply wiring Mains wiring Take great care with the mains your personal safety depends on it. Fig.9 shows the mains wiring details. The mains cord enters through a hole in the rear panel and is securely clamped using a cordgrip grommet. Strip back the outer sheath of the mains cord by about 35mm before connecting the active (brown) and blue (neutral) leads to the mains terminal block. The earth lead (green/yellow) is soldered to one of the adjacent solder lugs. The second solder lug terminates an earth lead which is run along the rear panel from the binding post terminal adjacent to the phono input sockets. Don't alter the earth wiring - This is a close-up shot of the power supply components. Note the .01µF 250V AC capacitor connected across the mains switch, at the 3-way insulated terminal block. The transformer is spaced off the chassis using brass nuts. ]ULY 1988 45 The new control unit has very little point-to-point wiring. This has largely been made possible by running the input signals via copper tracks on the phono preamplifier board at top right. The rear panel carries the RCA input and output sockets, an earthing terminal and the mains cord grommet. carefully, then switch on and use your multimeter to check the + t5V and - t5V outputs on the power supply board. The LED should also be lit; if not, you may have connected its leads the wrong way around. If these checks are OK, the supply leads from the tone control board can be connected to the power supply board. A number of voltage checks can now be made. Connect the negative lead of the multimeter to the OV terminal on the power supply board and check that + t5V is present at pin 8 of each of the four LM833s. Similarly, check that - t5V is present at pin 4 of each IC. That being the case, measure the voltage at pin t and pin 7 of each of the !Cs. In each case, it should be within ± 10mV of the OV rail. 46 SILICON CHIP You can also check that + t5V is present at the collector of Qt and that - t5V is present at the collector of Q2. Finally, there should be almost OV at the junction of the emitters of Qt and Q2 (ie, within ± 10mV of OV}. Troubleshooting If the above measurements are not OK, the most likely causes are broken tracks or solder bridges between IC pins. For example, if you have the correct supply voltages on an IC but its output is close to + t5V or - t5V, it is most likely that there is a break in the feedback network or the inputs to that IC. . You can follow this up by measuring the voltage at the input pins of the ICs. Again, these should all be very close to OV. If not, check for breaks in the copper track or poor solder joints; or that the IC is in the wrong way around. Note: if you've put the IC in the right way around, it is most unlikely that any malfunction will be due to a faulty IC. Put the knobs on now and we're ready for the next test. Listening tests No, we're not going to listen to music - yet. The idea of the next few checks is to make sure that everything is really working as it should. You'll need a pair of headphones. Plug 'em into the headphone socket, turn on the power and listen. With the Volume control at minimum setting you shouldn't be able to hear anything. If you now select the phono input and wind up EXTENSION SHAFT RIGHT LEFT \ INPUT/RIAA PREAMPLIFIER BOARD 1 - - - - - - - - - 1 SOURCE +15V DV - 15V S2 MONITOR S3 MODE GND LEFT RIGHT CONTROL BOARD Ill VR2 BASS ----l,.,.+15V ,......-c:;__--i. •-15V _---,_ ___,,..•DV S4 TONE -~ ::,...--...,---_______ ____......----=----=---.__.cy-----------------~----=---....,c<at> MAINS CORD CLAMP GROMMET S6 POWER GREEN/YELLOW E EART BROWN Fig.9: the complete wiring layout of the control unit. Note that there is no direct connection between the signal earth and the mains earth. This is done to avoid hum loops. the Volume to maximum, you will .h ear some hiss and quite a lot of hum. That is normal (because the phono inputs are floating). Turn off the power and connect a short jumper lead between the solder lug of the binding post terminal and the earth lug of one of the phono inputs. This connects all the control unit's circuitry earth to the chassis. Normally, there should be no connection at this point otherJULY 1988 47 wise there will be an earth loop when the power amplifier is connected (assuming that the power amplifier itself is earthed). Now turn on the power again, and wind up the Volume control, still with the phono input selected. There now should be no buzz or hum but there will be some hiss. Again, this is normal. If you now switch to the other inputs (CD, tuner, etc) the noise should drop to extremely low levels (we doubt you'll be able to hear anything, even in a very quiet room). If you now plug a pair of shorting plugs into the phono inputs, the noise on the phono inputs should drop to much lower levels. Good. Pull the shorting plugs, wind up the Volume control and then check the action of the Bass and Treble controls. The Treble control should boost and cut the hiss and the bass control should boost and cut the low frequency phono noise. The Balance control should also shift the noise from left to right and the Mono/stereo switch should also work; when in the mono setting the noise should appear from right in the centre of your head. Switching to Tape Monitor should kill the noise and the Tone Defeat switch should kill any boost and cut effect of the tone controls. Now if all of these things don't check out, it is pretty easy to localise the fault to a particular section. For example, let's suppose that there is no noise on the phono inputs, but very faint noise on the CD and other inputs. OK, that means a fault in the ph9no preamplifier but provided the voltage measurements here were correct, then you probably have an open circuit between the phono LM833 output(s) and the selector switch. In the event that the headphone outputs don't work at all, meaning you don't get to first base, you can connect the headphones to the main control unit outputs. You'll need some jumper leads or a pair of RCA plug to 6.5mm socket adaptor leads to do this. However, don't let the foregoing procedure give you the impression that this control unit is hard to get going. On the contrary. At the time 48 SILICON CHIP SC01-1-068E i'l _ _sC04-1-0688/1 ~ 00 (0 0I .,.. .,.. I 0 (.) . Cl) !J Fig.10: these are the full size patterns for the four printed circuit boards of the control unit. of writing we had built two prototypes and they both worked perfectly, first time; If you haven't made any wiring errors, your's will too. With all checks complete, remove the earth jumper lead from the phono socket and attach the lid of the case. You are now ready to connect the power amplifier and speakers. You can stack the control unit on top of or below the power amplifier but for the absolute lowest noise figures, keep the control unit as far away from the power amplifier as is practical. For lowest noise and hum, the power amplifier should be earthed back to the mains earth via a conventional 3-core power flex and 3-pin mains plug. If you have built the Studio 200 power amplifier this will already be the case. Your system will be quiet, really quiet. And it will sound great. Footnote: 100mm of 0.6mm enamelled copper wire should be added to the parts list published last month. ~ /\fir u ----act"g - F"2 0 0~ r1•__ u 3/3 O '1 ' 0 ...--.... ~ .... --- l~O--- 0~ 9 6 _J ,- co" 00 (0 0 I ,- ,-1 0 (J en 0 0 0 _J JULY1988 49 National Semiconductor's LM833: a new dual low noise operational amplifier National Semiconductor describe the LM833 as a "dual general purpose operational amplifier with particular emphasis on performance in audio systems". It is largely responsible for the outstanding performance of our Studio 200 stereo control unit. By LEO SIMPSON Although not strictly new, the LM833 is a new device to most audio enthusiasts and the latest available data (1988 edition) on it from National Semiconductor is still classed as preliminary; so it is new. However, it is already being used in large numbers, in the audio output stages of several compact disc players sourced from Japan. National Semiconductor claim that the IC uses new circuit and processing techniques to deliver low noise, high speed and wide bandwidth, without increasing external components or decreasing stability. It is therefore ideal for use in the preamplifier and high level audio stages of hifi equipment. As shown in the schematic diagram, the LM833 is a bipolar input op amp (as shown by the PNP bipolar differential input stage). Its input bias currents are actually higher than with run-of-the-mill op amps (such as the 741), being 500 nanoamps (typical) and lmA (maximum). It has low input offset voltage (0.3mV) and low input offset current (20nA). Its open-loop voltage gain is typically 11 0dB and it is intended for operation from the usual ± 15V supplies. The internal 15pF capacitor compensates it for all closed loop gains (presumably down to unity gain) but it has a relatively high slew rate of 7 volts per microsecond which is more than ten times that of the 741. Its gain bandwidth product is +Vcc-----1-------------8 Fig.1: the schematic diagram, showing one op amp in the LM833 package. 50 SILICON CHIP Fig.2: the pinout diagram for the LM833 dual op amp package. typically 15MHz (10MHz minimum) while its power bandwidth is 120kHz. Its outstanding parameter is its low input noise voltage which is typically 4.5nV/root Hz. This compares very favourably with the familiar Signetics 5534 low noise op amp with an input noise voltage of 4nV/root Hz (the 5534A input noise voltage is typically 3.5nV/root Hz). As a further comparison of specs, the LM833 is slightly better than the Signetics 5532 dual low noise op amp and slightly inferior to the 5534 single op amp. Just in case we seem to be making unfair comparisons with the 5534 and its kin, the LM833 does not have the 5534's ability to drive a 6000 load. Instead, its performance is characterised for the more usual minimum load of 2k0. Other parameters which are significant in making the LM833 an important newcomer to audio equipment are its high power supply rejection ratio (PSRR) of 100dB and also its common-mode rejection ratio (CMRR) of to0dB. Again, these are typical figures. Crosstalk between the two op amps in the package is quoted as - 120dB from 20 to 20kHz, which is excellent. Harmonic distortion is quoted as .002 % , from 20Hz to 20kHz. Our DC Electrical Characteristics (TA= Symbol 25•c. vs = ±15vJ Parameter Conditions Min Vos Input Offset Voltage los Input Offset Current Is Input Bias Current Av Voltage Gain RL = 2 kn, Vo = ± 10V VoM Output Voltage Swing RL = 10kD. RL = 2 kD. Typ Rs = 10D. Max Units 0.3 5 mV 10 200 nA 500 1000 nA 90 110 dB ±12 ±10 ±13.5 ± 13.4 V V VcM Input Common-Mode Range ±12 ±14.0 V CMRR Common-Mode Rejection Ratio V1N = ±12V 80 100 dB PSRR Power Supply Rejection Ratio Vs = 15-5V, -15- -5V 80 100 dB la Supply Current Vo = 0V, Both Amps AC Electrical Characteristics (TA = Symbol 8 mA 25•c, vs = ± 15v, RL = 2 kn) Conditions Parameter 5 Min Typ Max Units SR Slew Rate RL = 2 kD. 5 7 V/µs GBW Gain Bandwidth Product f = 100kHz 10 15 MHz Design Electrical Characteristics (TA = 25•c, vs = ± 15VJ The following parameters are not tested or guaranteed. Conditions Symbol Parameter t:.Vos/t:.T Average Temperature Coefficient of Input Offset Voltage THD Distortion RL = 2 kD., f = 20 - 20 kHz VouT = 3 Vrms, Av = 1 en Input Referred Noise Voltage Rs = 100n, f = 1 kHz Typ Units 2 µVl°C 0.002 % 4.5 nV/,/Hz pA/,/Hz in Input Referred Noise Current f = 1 kHz 0.7 PBW Power Bandwidth Vo= 27Vpp, RL = 2kD., THD,;; 1% 120 kHz fu Unity Gain Frequency Open Loop 9 MHz 60 deg -120 dB </>M Phase Margin Open Loop Input Referred Cross Talk f = 20-20 kHz Note 1: If supply voltage is less than ± 1SV, it is equal to supply voltage. Note 2: This is the permissible value at TA experience with the Studio 200 indicates that typical devices easily meet these specs and we would not be surprised to find that, when National Semiconductor finalises its data on the device, it will be effectively upgraded. Fig.3 shows National Semiconductor's RIAA preamp application circuit for the LM833 and it is very close to that used in the Studio 200. Our performance results were also very close to those claimed by National. The main difference in the Studio 200 circuit (presented last month) is in the RF suppression components at the input and the manner of provision of the 50k0 load for the cartridge (using a 100k0 resistor either side of the bipolar input capacitor). National's LM833 is not the s:: 85°C. 10 µF ·i1 1"100µF Fig.3: National Semiconductor's suggested circuit for a phono preamplifier with standard RIAA equalisation. Voltage gain is 35dB at 1kHz and claimed signal-to-noise ratio is 90dB A-weighted with respect ot 10mV input at 1kHz. quietest, fastest, lowest distortion or most stable op amp released in recent times but considering its overall performance, it must stack up as one of the best value op amp packages available. We predict that it will become extremely popular. ~ JULY 1988 51 Altronics End Of Financial Year Sale - You Save Up To 50% I Famous lnphone Brand Cordless Phones $125 mazing Offer - Top Sellln nal Semiconductor Data B ½ Price $17 .50 Data Aquisit ion B 1015 High Speed CMOS B 1020 National Logic B 1025 MOS Memory B 1045 Hybrid Product 13.50 12.95 39.50 12.95 12.95 meter $8.75 6.75 6.50 19.75 6.50 6.50 '\ ('<1 ,.\i Single Gang Miniature 16MM R 2040 500 Ohm Linear R 2048 20 K Linear Normally Normally $3.20 rn~~;~~\\~a 1111111111111111111111111II : :•:i :: !:-·=·. y·-·:: ::::lI.:• 1/2 Price \ .. \f:JO ~o<'\°<' i ~°<',. M9009 sB This unit magnifies any object under a clear,cool,fluorescent light Fantastic for Door, Window or Cupboard - this great little alarm simply fixes to one surface (usually fixed surface) with the : reed switch magnet screwed to the moving door window sash etc. Arm the 1y1tem by ■Imply ,witching on - battery drain is minisule! Operates from 9V Battery (not supplied) Normally Thl1 Month s 5315 sB ::m s229 A0980 Croc Clip Jumper Leads 10 Way Attention Speaker System Constructors Save $2 Polypropylene Passive Radiators ~~::tf_'l=._,,':'::.-1 ~ et 1:: :!:1:· :: $25 • : : : : ,: ;:~ : ;: 12" $39 50 Save A Bundle On These Four Popular Size, Of llllllllllntllllllllllllllllilJ I JI IJII I I IJ Racks, Frames & Panel Seta 111::::Jllll:\\\i: Rack Frames for the Home Stereo System <at>:aar:: 11 :i:f;~=~~r;~;t;;;~t~,~~~dr;':~=ho~ . , ;~f~l7'!~:J~~i.~i~i~;;;i;~~;~;;; ■ ·:_ ·,.,', .::,, ,1', , :':_1', , ,',.1', , ,·,.1,.·, , ,.·_1,,.-, ,,,::,_1,,,,.:,,,1:,,,,,.:,!,, 1, , ,·,,,.,,,,·_1, ,,,.,,,i ,,,,, , ·.,,,,,,1 , ,, ,,,,,1, ,,:,,1,,,1 ,•• ,,:,_1, ,, ,,,,1 ,: .,,,.· _1, ,:,,_· _:,,, ,,, _: •. • .• ~ . : . · .· · I 6 Unit (370mm H) 18 Unit (907mm) 30 Unit (1450mm) and 38 Unit (1804mm) Racks Available - All 450mm Deep Now Normally Normally Now H 0365 Rack Frame 6 unit (370MM) H 0367 Panel Set for H 0365 H 0370 Rack Frame 18 unit (907MM) ~ m~ ~=~~?i¥f:~~)!I{~ 145 ,.,.,.,,,,.,:':':':':"' ·. 'i?"" )0. Mini Alarm 15V 100mA AC/AC Adaptor Find Circuit Faults In a Jiffy 110"" gOc; $1.60 JW' ~ Save $74 On This Great Portable Phone ~, r \ Desk Mounted Magnifier Lamp ~ Shop soiled and Demo Stock Cordless Telephones an Incredible $125 - All guaranteed in perfect working order - and even better any marks or scratches are quite minor (barely noticeable in most cases) . Normally Thl1 Month Interface Date ~=_ ,=_=~;J!J. ,.., $ 99.50 $ 15.00 11 0382 Panel Set for H 0380 $149.00 $1111.00 49.00 311.00 H 0385 Rack screw MS PK12 Natural 2.95 2.00 129.50 1111.00 H 0386 Rack screw M6 PK100 Natural 19.95 17.00 i;:5 ::E~gm==~~ ~~~~2e;u~~~~:~~ik t5 {E 0MM) H 0380 Rack Frame 38 unit (1804MM) 199.95 1 1 175.0l' H 0396 Rack captive nut MS PK100 28.50 25.00 -:-:-:-:-:-:-:-· .. .......... .. :.:.:.i.:.::.1.:.i.:.i.:.::.i.· 1:.::,:. .:::_:_:.:.,.::.:.,;.::_:•.:.:. ·.·. ... . .. .. ~~~:_ .>::;,~ ~ ~ ~ - - ~ ~§>~! Greai,laiueAl$139·- This Month Save Up To 50% On Top Quality { D Series Connectors! ,,, Only $119 Fantaat/c Value D Serles Computer Connectors. Gold Plated tt t Professional Serles :· Micron Electronic Temperature Controlled Temperature Selectable Item, Marked• are 1/2 Price or LeH :'' Solder~ } Exhilarating Sound Perlormanca Brilliant Digital Headphones lncredlbly Comfortable • Utilizes newly developed flat disk vibrator copper clad aluminium wire voice coil and samarium cobalt Magnet. The resultant reproduction is outstanding• lmpedance45Ohms • Maximum input 400 mW• Frequency Respon se 20Hzto20KHz. ··•i•::•l\l !i\\ii II ;.~~:;.~?."h~~.r::,~;:;::;"l',l'~:~"3~:;·::: ff ( ( ( ] .. ':"'' /'\ .,,,,,,,,. ,~;r.~•,:,"g'.'""M 41 0 deg. C. (608 deg : F. 662 deg.F, 716 deg.F, 770 deg. F and 824 deg.F) 1 19 Fixed temperatures are selectable by rotating the detained rotary switch freely without changing heater or tip. Temperature Readout via lead baragraph instantly visable . Patented Heating Element. The specially insulated NICHROME wire heating element is compressed between two layers of stainless steel for ruggednes and is located at the end of the barrel to insure instant heat. Temperature Readout via lead bargraph instantly visable. Patented Heating Element. Heat Capacity. Full 48 watts of het energy availab le for heavy duty work . Zero Voltage Switching The revolutionary electronic "Zero Voltage" switching, protects voltage and current sensitive devices such as CMOS against transient voltage spikes caused in stations. Grounded Tip. The soldering tip is grounded thro ugh the power unit to ensure the tip leakage is less than 0.4 millivolt or 0.03 microampere. Low Voltage Element.24V. Chrome Plated Iron Plated Tip. p 3040 Male PCB mnt. 2.95 p 3050 Fmale PCB mnt. 3.95 p 3090 Ba;;h;~ cover 1.95 C 901 D $ .50 High Quality UHF p 3100 P3110 P 3120 P 3130 p 3140 P 3150 p 3190 14 Element YAGI Le11 Than 1/2 Price! These high grade Yagi Antennas are from DX Antenna Co of Japan and originally sold for over $701 1 ~:: ~i~!:;~: ~~ Male 15 Pin Fmale15Pi n Male PCB RVL Fmale PCB RVL Male PCB mnt . Fmale PCB Backshell cover 2.50 2.25 _95 /fM( .. \0.\ , , Ii•il.\J:J•i 3.25 3.85 4.35 5.50 3.85 4.85 2.20 D825 :..l.!_l_l_l_~_;.:,_~_:~_t_.~_~_;:_;;_:Y_~~--_j_l_J_.:.~;.:f.:;;,;.:, , ~ Dlgltal Multimeter With Bullt-ln Capacitance Meter ::: : Not only do you get all the normal ranges of current, resistance and voltage - but also a convenient and simple to use capacitance meter in five ranges. And as if that's not enough, you also get a transistor tester. Check the features of this top quality new addition to the labtech range. General: ,,,, Dlaplay: 3½ digit LCD, 0.5" height, ( [~~~~:~;;; i,1, ?iJf/ Odeg to 50 deg. C; less than relative ;,: humidityfrom35degCto50deg.C \,,:: . Features: • Non-Microphone Measurement System • LCD Readout • Blood Pressure Monito • Pulse Rate Monitor Carry Case s12.so · ,,,, s Cost Altr or Studio 200 Stereo Control Unit (SIiicon Chip June/July'88) Out-Performs Commercial Units Costing $600 Plus tor (EA May'88) Gain Matched, Power Transistors for Ampllfler Output Stages l ne ;:,1ua10 .!W ::;tereo L;Ontrol Unit is companion to the studio 200 stereo power amplifier (or other power amps). It features slim 1u rackmount profile, treble, bass, balance, input selector, tape monitor switch, stereo/ mono switch and volume control. Inputs include phone: tuner, CD, VCR and tape loop. K5015 s229 Super simple circuit, enables evaluation of current gain and Vbe of power transistors & Darlingtons. K 2532 s24 .95 oa t ry Ch r (ETI Dec'87) Charge Your Batteries Free From The Sun Controls the charge of 12V lead acid batteries hooked to a solar cell Ideal for use on boats & caravans. 13 .99 Calling All Audio Purists This Great New Amp From Silicon Chip Is For You Studio ?.00 Serles 10 Watts Per Channel Power f K 5010 s399 Feature,, • In-Built speaker protection • Toroidal Transformer (low hum)• Black Satin Finish• Low leakage power supply capacitors • Housed in Rugged Custom Chassis. Speclflc1tlon1: • Output Power 100W into 8 Ohms Freq. RH.(111W) 20Hz-SOKHz + or - 1db Input Sen11tlvlty 870mV Harmonic Dl1tortlon (20Hz-2DKHz) 0.1% Signal To Nolie Ratio 100db or Better Protection Fantastic for installing at home, behind your car dash or for interfacing with alarm systems, control systems etc. Requires enternal 12V DC supply. Kil includes 27128 eprom. ~~- .............. K 9500)':t{ y s85 00 .,.,.,....... ~~~,....~91&-•;;= K 1680 $ i~l~~:~ch~s) ~~J°f1~~ ~~:~::::~~e~)~~n:t::fi:f; 0~~~~~1tional. \ ,lililii :,:,,·'\b,:,,;,,:···:,,.,...•.·.·.,. . .•.,, .......,. :::,= ;::,.,=.' '= ' '··======== Car Security System (See ETI Aprll'84) Uses Vibration Sensors To Guard Against Tampering Ii Vandall1m FEATURES: Auto Arming with Exit and Entry delays e Dash Mount status indicator e Remote Protection of bolt-on accessories e Inc. circuitry to monitor any failure of dash warning lights e Protects your expensive stereo from unauthorized removal. Moafet Power Amp Module 150 Watt VIBRATION SENSOR PACK lnc.Mic Cable & Connectors I 4341 s22 .50 RESONANCE MICROPHONE ONLY 14342 s7.so Bench Ampllfler (See ETI Aprll'80) One of the most useful pieces of equipment in an Electronic work-shop is a simple Amplifier Module to test circuits. e 250 Milliwatts output into 4 Ohms e Runs off single 9V supply e Can give0.5wattswhen run on 12V plus heatsink. I 2105 s22.70 (See ETI Jan'81) Studio Specifications The Protector Car Alarm {Slllcon Chip Feb'88) Save Over $100 On An Equlvalent Commerclal System Feature,: e Internal & External Sirens e Dash lamp flasher e Battery back up e Delayed & Non delayed inputs e Ignition killer e Easy to build and install. 14310 s129.oo Here Is general purpose power Amplifier module suitable for Hi Fi, guitar and PA applications employing sturdy reliable MOSFET'1 in the output. Power Output 150W RMS into 4 Ohms 100W RMS into 8 Ohms (At onset of clipping) Frequency RHponH 20Hz to 20KHz +0-0.5db 10Hz to 60KHz +0-3db Measured<at> 1W & 100W levels Input Sen1ltlvlty 1 Volt RMS for full output NolH 114db below full output 15120 C.D. Headphone Ampllfler s79.oo (Slllcon Chip Aprll'88) Adds Headphone Faclllty To Your C.D. Player 24V To 12V DC (Slllcon Chip Dec'87) Suits any C.D. player - suitable for for all headphones - low or high impedance, very low noise and distortion, does not hinder the CD performance. Simple plug in connection. Requires external 12V AC plug pack. Enables 12V appliances like stereos, 2 way radios, CB's etc. to operate from a 24V battery. e Operates from 18V-30V. Output is 13.6V at 5 amps. I 5350 s59.oo Manufacturers, Contractors and Bulk Users Please Contact Our Wholesale Sales Dept. Sydney (NSW Only) Colin Fobister 436 0422 Perth Fred Bloffwitch 09 328 2199 174 Roe St. Perth W.A. 6000 PHONE TOLL FREE 008 999 007 Perth Metro & After Hours (09) 328 1599 ALL MAIL ORDERS P.O. Box 8350 Perth Mail Exchange W.A.6000 AL TRONICS RESELLERS Chances are there is an Altronics Reseller right near you - check this list or phone us for detai ls of the nearest dealer. PleaH Note: Resel lers have to pay the cost of freight and insurance and therefore the prices charged by individual Dealers may vary slightly from this Catalog ue - in many cases, however, Dealer prices will sti ll represent a significant cost saving from prices charged by Altronics Competitors. Don't forget our Exprea1 Mall and Phone Order Service - tor the coat ot e local call, Bankcard, Vlu or Ma1tercard holdera can phone order tor ume day de1patch. STANDARD DELIVERY & PACKING CHARGE $4.00 to 1 Kg $7 over 1Kg AUSTRALIA WIDE - We process your order the day received and despatch via. Australia Post. Allow approx 7 days from day you post order to when you receive goods $7.00 OVERNIGHT JETSERVICE - We process your order the day received and despatch via. Overnight JetHrvlce Courter for delivery next day Country areas please allow additional 24-48 hours. Weight limit 3Kgs (3Kgs covers 95% of Orders). $10.00 HEAVY HEAVY SERVICE - All orders of 10Kgs or more must travel Express Road - Please allow 7 days for delivery. INSURANCE - As with virtually every other Australian supplier, we send goods at consignees risk. Should you require comprehensive insurance cover against loss or damage please add 1% to order value (minimum charge $1). When phone ordering please request "Insurance". TOLL FREE PHONE ORDER - Bankcard,Visa, Mastercard Holders can phone order toll free up to 6pm Eastern Standard Time. Remember with our Overnight JetHrvlce we deliver next day. COUNTRY ALBANY BP Electronics ■ 412681 ESPERANCE Esperance Communications 713344 GERALDTON K.B.Electronlcs & Marine 212176 KALGOORLIE Todays Electronics ■ 212777 KARRATHA Daves Oscltronic 854836 MANDURAH Lance Rock Retravlslon 351246 WYALKATCHEM D & J Pease 811132 NT ALICE SPRINGS Ascom Electronics 521713 F-armer Electronics 522967 ACT CANBERRA Bennett Commercial Electronics 805359 Scientronics 548334 VICTORIA CITY All Electronic Components 6623506 SUBURBAN CHELTENHAM Talking Electronics 5842386 CROYDEN Truscott Electronics ■ 7233860 PRESTON Preston Electronics 4840191 COUNTRY BENDIGO KC Johnson ■ 411411 MORWELL Morwell Electronics 346133 QUEENSLAND CITY Delsound P/L 8396155 SUBURBAN FORTITUDE VALLEY Economic Electronics 2523762 WOODRIDGE David Hall Electronics 8082777 COUNTRY CAIRNS Electronic World ■ 518555 BUNDABERG Bob Elkins Electronics 721785 GLADSTONE Supertronlcs 724321 MACKAY Phlltronlcs ■ 578855 ROCKHAMPTONAcceas Electronics (East St.) 221058 Electron World 278988 TOOWOOMBA Hunts Electronics ■ 329677 TOWNSVILLE Solex ■ 722015 SA CITY Electronic Comp & Equip. 2125999 Force Electronic ■ 2125505 SUBURBAN BRIGHTON Force Electronics ■ 2963531 CHRISTIE& BEACH Force Electronics ■ 3823366 ENFIELD Force Electronics ■ 3496340 FINDON Force Electronics ■ 347 1 188 COUNTRY MT . GAMBIER South East Electronics 250034 WHYALLA Eyre Electronics ■ 454764 TASMANIA HOBART George Harvey ■ 342233 LAUNCESTON George Harvey ■ 316533 Nichols Radio TV 316171 NSW CITY David Reid Electronics ■ 2671385 CARINGHAH Hlcom Unltronics 5247878 LEWISHAM PrePak Electronics 5699770 SMITHFIELD Chantronlcs 6097218 COUNTRY COFFS HARBOUR Coifs Habour Electronics 525684 GOSFORD Tomorrows Electronics ■ 247246 NELSON BAY Nelson Bay Electronics 813685 NEWCASTLE Novocastrlan Elect.Supplies ■ 621358 NOWRA Ewing Electronics■ 218412 RAYMOND TERRACE Alback Electronics 873419 WOLLONGONG NeW1ek Electronics ■ 271620 WA BhM Ribbon Deal■ ,. are highlighted with a ■. These Dealers generally carry a comprehensive range of Altronic products and kits or will order any required Item tor you. STAGE YOUR 0 LIGHT SHOW These days when you go to hear your favourite band or disco there is always a top light show. Now you can have many of these exciting light show effects - with the Discolight. By JOHN CLARKE & LEO SIMPSON The Discolight is a compact and affordable unit which drives four channels of coloured lights to produce an exciting and highly varied light show. It can be driven directly from your stereo system's loudspeakers or it can be triggered from live music picked up by an inbuilt microphone. It can also produce all sorts of light patterns on its own, with or without modulation by the music. With the Discolight you don't need to go to the trouble and expense of hiring a disco system and disc jockey - you can put on your own light show and do it better. In fact, we reckon that as soon as disco operators find out about SILICON CHIP's Discolight, they'll all be building them. The Discolight has a great many 56 SILICON CHIP features which are summarised in an accompanying panel. The Discolighf turns sound into light. Feed music from your stereo, Walkman or whatever into its rear terminals and it then drives four sets of mains-powered coloured lamps. The brightness of the lamps is directly proportional to the loudness of the music signal. In fact, the Discolight divides the audio signal from your stereo into four frequency bands and then uses each of those frequency bands to modulate the brightness of the lamps. Most people will have seen such set-ups on TV shows, in discos and in hotels. The lights may be coloured 100W floodlamps or banks of smaller coloured lights. Typically, four differently coloured floodlamps or sets of lamps would be connected, one set to each channel. You might use red for the lowest frequency band, then yellow, green and blue for the highest band. Not only does the Discolight turn music into fascinating light patterns but it also generates its own light patterns, for when the music stops. If you're operating a disco show and the band stops for a rest break or the music has to stop for some reason, the Discolight generates its own light patterns: chaser, strobe and alternate patterns (we'll describe these later). Understanding how to use the Discolight may be best explained by briefly describing its various front panel controls and rear panel features. On the rear panel are four 3-pin mains sockets to which you connect your banks of coloured lights. There is also a set of four spring-loaded terminals so that you can connect the audio outputs from your stereo amplifier. These are connected in parallel with your speakers and cause negligible loading of your amplifier's outputs. On the front panel are two knobs, a fuseholder, large power switch and five miniature toggle switches, three of which are 3-position types. There are also four LEDs (light emitting diodes), one for each of the light channel outputs. Let's look at the function of these miniature toggle switches first. Right next to the SENSITIVITY knob is the SOURCE (microphone/ speaker) switch. This selects the audio from your stereo system (via the 4-way terminals on the back panel) or the sounds picked up by the Discolight's inbuilt electret microphone. If you have a live band, you can simply place the Discolight nearby and switch to Microphone mode, thus eliminating the need for cable connections. As you might expect, the adjacent SENSITMTY knob adjusts the audio signal levels for the best light switch. The speed at which the display. lights chase each other is set by the In the centre of the five toggles is RATE control knob. the DISPLAY switch. This 3-position In the Strobe mode, all four sets switch is the key to the Discolight's of lights flash on simultaneously, as functions. In its top position, set by the RATE control. In the Alter"4-Band Modulated", you get the nate mode, two pair of channels basic Discolight function whereby flash on and off alternately, at a the audio signal is split into four speed set by the RATE control. separate frequency bands (low The DIRECTION switch controls bass, upper bass, mid-treble and the Chaser mode. You can have the upper treble) and each of these bands control their respective lamps chase in one direction or the other or change direction autolights. The brightness of the lamps at matically, every minute or so. any instant is directly proportional Finally, the BEAT switch gives to the sound level in the respective beat triggering from the music for audio frequency band. the Chaser, Strobe and Alternate In the Modulate (MOD) position pattern modes. In the Oscillator setof the DISPLAY switch, the audio ting of the BEAT switch, these funcsignal both modulates the lights and tions are controlled by the RATE . triggers the various modes selected knob. by the PATTERN switch. Finally, the The four LEDs on the front panel Unmodulated setting of the DISPLAY mimic the behaviour of the four switch allows the light display to be light channels, so that even if you set by the pattern switch. can't see the lamps directly (say The PATTERN switch gives three you are acting as disco operator), light displays: 4-light chaser, strobe .you can tell what they are d9ing by and alternate. The Chaser mode is looking at the LEDs. The LEDs will self explanatory; the four lights also come in handy during any chase each other in one direction or troubleshooting which may have to the other, as set by the DIRECTION be done. DISPLAY SELECTOR CHANNEL 1 CHANNEL 2 CHANNEL 3 CHANNEL 4 RAMP REFERENCE SIGNAL (C) MOOULATEO 1 INPUT MAINS (\ INPUTV 2 3 4 MAINS PAmRN GENERATOR PHASE ZERO DETECTOR t----1CROSSING INPUT Fig.1: the audio signal is split into four frequency bands, rectified and compared with a 100Hz ramp reference signal. The Triacs are then triggered either by the comparator outputs or by signals from the inbuilt pattern generator. ]ULY 1988 57 I / COMPARATOR OUTPUT (B) II "' TRIAC "ON" PERIOD T MAINS VOLTAGE LOW/ BRIGHTNESS Fig.2: when the rectified filter output is greater than the ramp voltage, the comparator output is high and the associated Triac turns on. If the Triac turns on early in the mains half cycle, the lamp will be bright; if it turns on late in the half-cycle, the lamp will be dim. How it works The circuitry for the Discolight consists of four quad op amp ICs, five CMOS ICs, four opto-isolated Triac triggers, four isolated tab Triacs, four LEDs, two 3-terminal regulators and 21 diodes. And that's just the semis. Add in the resistors, capacitors, inductors, switches, pots and all the other hardware bits and it comes to a stack of components. Our total component count comes to over 230, so depending on how you look at it, it is the most complicated circuit we have presented in SILICON CHIP to date. Fig.1 shows the block diagram of the circuit. Switch S1 selects ·the audio signal, either from the internal microphone or from the loudspeaker terminals (which connect to your stereo). The audio signal is then fed to four filters which split it into four distinct frequency bands: Low Bass, Upper Bass, Mid Treble and Upper Treble. The Low Bass frequency band is provided by a 200Hz low pass filter - this means that only signal frequencies below 200Hz are allowed to pass. Then there is the Upper Bass band which passes signals between about 200Hz and 700Hz. This is actually a bandpass filter centred on 440Hz. The Mid Treble band, from about 58 SILICON CHIP 700Hz to 2kHz, is another bandpass filter, centred on 1.5kHz. Finally, the Upper Treble band is from 2kHz to 20kHz and is provided by a 2kHz high pass filter (ie, everything a hove 2kHz passes). The audio signal from each of the four filters is rectified and smoothed to provide a varying DC level, which is then fed to one of four comparators. The comparators compare the varying DC signal to a 100Hz ramp reference signal which is derived from the 240VAC mains supply (via the power transformer). Phase control The next part is messy. We vary the brightness of the lamps, in Warning! The Discolight is not a project for beginners. Unless you have already successfully built a number of mains-powered projects we advise you to leave this one strictly alone. Part of the circuitry is powered directly from the 240VAC mains supply and therefore must be regarded as potentially dangerous. We have designed it to comply with SM regulations but if it is not wired correctly and tested out properly it could be lethal. response to the loudness of the audio signal, by using "phase control". This is a method whereby a Triac (a semiconductor switch) is turned on earlier or later in each mains half-cycle. If the Triac turns on early in each half-cycle, the power delivered to the lamp is high; if the Triac turns on later, the power delivered to the lamp is low. The four comparators shown in. Fig.1 each determine whether their associated Triac turns on early or late in each mains half-cycle. They therefore determine the brightness of the lamps at any instant, depending on the loudness of the audio signal, as represented by the varying DC levels referred to earlier. Fig.2 shows how each corn.parator controls its associated Triac. It looks as "clear as mud" but be patient and all will be revealed. First, look at Fig.2c. This shows the 50Hz mains supply waveform and also the time at which the Triac switches on in each each mains half-cycle. As before, when the Triac turns on early in the half-cycle, the lamp will be bright; when the Triac turns on late in each half-cycle, the lamp will be dim. Fig.2b shows the DC output from the comparator, corresponding to the Triac " on" times. The DC output from the comparator actually turns the Triac on (although not directly, as.we shall see later). Fig.2a shows the interaction of the varying DC, from one of the audio filters, with the 100Hz reference signal (note how this signal is synchronised to the mains waveform in Fig.2c). Whenever the slowly varying DC signal is above the 100Hz reference signal, the output of the comparator goes high and triggers the Triac. So that's the basic process of how the audio signal,is rectified and then controls the Triac to vary the respective lamp's- brightness. But, as you might have guessed, there's a lot more to it than that, otherwise the overall circuit of the Discolight (which you've probably looked at and shuddered) would be a lot simpler. Now refer back to Fig, 1. Instead of the four comparator outputs going directly to trigger the Triacs Main Features Operating features Four light channels controlled by four separate audio channels. Forward, reverse and autoreversing chaser patterns. Simultaneous strobe on all four channels. Alternate light mode. Music modulation available on chaser, strobe and alternate modes. Adjustable rate for chaser, strobe and alternate modes. Inbuilt microphone for beat triggering or audio modulation of lights. Direct inputs for beat triggering or audio modulation of lights. Sensitivity control. Internal presettable sensitivity levels for each channel. * low pass rectified output which uses a 2.2µF capacitor. The larger capacitor provides a somewhat slower response time for the low frequency band. The varying DC output from each filter stage is fed to a 50k0 preset potentiometer (VR1-VR4). Thus the sensitivity of each channel can be set to provide equal brightness of lamps for typical music signals. Following the presets, the DC signals are fed to comparators IC3a, IC3b, IC3c and IC3d. These compare the varying DC for each frequency with the ramp reference signal from IC4d. By the way, ICt, IC2, IC3 and IC4 are all standardised as LM324 quad operational amplifiers. These are cheap and readily available. * Front panel LEDs mimic light display. * * Electrical features 2400W maximum lamp load. 600W maximum lamp load in each channel. Fused mains supply to lamps. Isolated tab Triacs for extra safety. Opto-coupled Triac triggering for complete isolation of control circuitry from 240VAC mains supply. RF interference suppression components on each light channel. Zero voltage switching of Triacs used for unmodulated chaser, strobe and alternate modes for minimum radio interference. Ramp reference resistor. The electret's signal is coupled by a .047 µF capacitor to the non-inverting input of ICtb which boosts the signal by about 31 times. After SOURCE switch St, the signal is fed to the SENSITIVITY control (VR5) and then to op amp ICta (a stage identical to IClb) which again provides a gain of 31 times. ICla's output is then fed to the four filter stages to provide the four frequency bands mentioned previously when we described Fig.1. IC2a and associated components form the 2kHz high pass filter. This is a third order (three RC timeconstants) filter which means that signals below 2kHz are rolled off at 18dB/octave. IC2d and associated components form the 200Hz third order low pass filter for the Low Bass channel. IC2b and IC2c and their associated components form twin-T filters. These are the 440Hz and 1.5kHz bandpass filters for the Upper Bass and Mid Treble frequency bands (as shown on Fig.1). Each of these four filter stages has a gain of about unity. The output of each filter is rectified using diodes Dt, D2, D3 and D4 and smoothed with l µF capacitors except for the 200Hz As mentioned above, each of the four comparators in IC3 use a common ramp reference voltage derived from the 240VAC mains. A 50Hz signal is picked up from the secondary of the 2851 mains transformer via a 100k0 resistor, clamped to ± 0.6V by diodes D14 and D15 and fed to IC4b which functions as a Schmitt trigger to "square up" the waveform. IC4b's 50Hz square wave output is then fed to Schmitt triggers IC9a and IC9b to obtain complementary signals. These signals are then fed to two differentiating networks, each consisting of a .022µF capacitor and 470k0 resistor. The spiky outputs of these two networks are fed via diodes D16 and Dl 7 to the inverting input of IC4c. IC4c thereby delivers a 100Hz pulse train, with each pulse synchronised to the zero voltage points of the 50Hz AC mains waveform. The pulse output from IC4c then feeds a 0.15µF capacitor via D18 with the discharge path being via two 22k0 resistors in series and a 5.6V zener diode (Dl 9). The result is the ramp curve depicted in Fig.2a, delivered from the ouput of IC4d, to the inverting inputs of quad op amp IC3. The outputs of the four comparators connect to ICB which is the Display Selector depicted in Fig.1. ICB is a 4019 quad AND/OR gate which can be regarded as a ** * * * ** they go via a block labelled as the Display Selector. This can be regarded as a four pole switch which selects either the signals from the comparators or a pattern generator. Signals from the pattern generator drive Triacs and hence the lamps in the chaser, strobe or alternate modes. Well, that's probably as far as we can go with block diagrams in describing the basic operation of the Discolight. Now, we have to stop dithering about and get into the circuit description proper. Circuit description Let's start at the extreme top lefthand corner of circuit. This shows an input attenuator consisting of two 10k0 resistors, one for each speaker lead from your stereo amplifier. The 10k0 resistors connect via a common 1.8k0 resistor to ground. This network mixes the two stereo channels together as well as attenuating them. From there, the signal goes to the SOURCE switch S1. Op amp ICl b provides gain for the signal from the electret microphone . The electret is powered via a network consisting of a lkO resistor and lO0µF capacitor which provide decoupling from the main + 12V supply while bias current is fed via the 4.7k0 * * * * * * * JULY 1988 59 +12V SPEAKER INPUTS lDk LEFT0-'W',11,-, + 2kHz HiGH PASS FILTER .,. COM~ COM 220k 3300. +12V 1k r--~HNfl,....-+12v 100 + 16VWI .,. 220k +12V .,. 14 +12V 70k +12V 200Hz LOW PASS ALTER +12V 74C14,40106 9 12 13 15 CK f"\..J'-__ +12V 01 IC& 70k .,. 6 4029 +12V 60 SILICON CHIP J ... S2 10 U/D REVERSE--c>------'AUTO DIRECTION D19 4giJS.:w FORWARl Fig.3: the circuit diagram. IC2a, b, c & d are the audio filters; D1, D2, D3 & D4 the audio rectifiers; IC3a, b, c & d the comparators; and ICB the display selector. IC5, 6 & 7 make up the pattern generator. RAMP 5 8 .,. 1M DISCO LIGHT SC10·1·0688 +12V LED1 16 10 A 680ll K A2 7 11 3 IC8 4019 12 l +12V DISPLAY S4b 1 2 12 13 A 30 10k CHANNEL 4 S4 : 1 : 4-BAND MODULATED 2 : MODULATED 3 : UNMODULATED -:, +12V S3 : 1 : ALTERNATE 2 : STROBE 3: CHASER 10k L1-L4 : 29T, 0.63mm ENAMELLED COPPER WIRE ON NEDSID 17n32/22 IRON DUST TDRIIII S3b 2 3f PAmRN .,. IC7 4051 +12V ! 1 S3a 7812 +12V ,;ITT,.;~ .~ i 10 2 3 11 10k IIH 6 .,. 7912 . A2 GNU 22k +12V 470k S4a 2 '? 020 1N4002 JUUL OU +12V 470k POWER S6 2851 10A I A I I 10 -16VW 470k ..,. + - I I 240VAC I I CASE -12V N 4.7 + 1 16VW _ 16VW - ii JULY 1988 ,- E 61 PARTS LIST 1 plastic instrument case, 262 x 1 90 x 83mm (Altronics Cat. No. H-0482) 1 aluminium rear panel, 251 x 76mm (Altronics Cat. No. H-0488) 1 Scotchcal front panel label, 251 x 76mm 1 PCB, code 10106881, 218 x 172mm 4 1 OA panel-mount mains sockets 1 4-way spring-loaded speaker terminal panel 1 2851 12.6V mains transformer 1 panel mount 3AG fuse holder 1 10A 3AG fuse 1 electret microphone insert 4 Neosid 17 /732/22 toroids 1 DPDT 240VAC toggle switch 2 DPDT centre-off toggle switches 2 SPOT toggle switches 1 SPOT centre-off toggle switch 2 knobs 1 cord grip grommet 1 mains cord and moulded 3-pin plug assembly 3 solder lugs 34 PC stakes 4-pole 2-position switch. This is controlled by S4b, which is one half of the Display Selector switch. When pin 14 is high and pin 9 is low, the comparator outputs are switched through (when switch S4 is in the 4-band modulated position) and thereby control the Triacs. On the other hand, when pin 14 is low and pin 9 is high, the signals from the pattern generator circuitry are switched through (position 2 of switch S4) to control the Triacs in Chaser, Strobe and Alternate modes. Pattern generation The patterns are generated by IC5, IC6, IC7, three op amps and a bunch of diodes, D6 to D13. IC6 is a 4029 up/down counter which drives the one-of-eight decoder IC7. To make the Chaser run in the forward direction, IC6 is made to count up; to run in the Reverse direction, IC6 is made to count down, as set by DIRECTION switch S2 (via pin 10). 62 SILICON CHIP Semiconductors 4 LM324 quad op amps 1 4051 1-to-8 analog multiplexer/demultiplexer 1 4030 quad XOR gate 1 4029 4-bit up/down counter 1 4019 quad 2-input AND/OR selector 1 7 4C14, 40106 hex Schmitt trigger 4 MAC218A8FP or SC142-M or BT137F-600 isolated tab Triacs 4 MOC3021 optically isolated Triac drivers 1 7812 3-terminal +12V regulator 1 7912 3-terminal -12V regulator 2 1N4002 1A diodes 18 1N4148, 1N914 signal diodes 1 5.6V 400mW zener diode 4 5mm red LEDs 4 LED bezels Capacitors 2 470µF 25VW PC electrolytic 2 1 OOµF 1 6VW PC electrolytic 3 1 OµF 1 6VW PC electrolytic 1 4. 7µF 16VW PC electrolytic 1 2.2µF 16VW PC electrolytic The clock signal for IC6 is fed via IC5 from one of two sources, selected by the BEAT switch S5. With S5 in the Music setting, the clock signal is derived from the Low Bass filter via comparator ICtc, which converts the bass signal into a squared up waveform. With S5 in the Oscillator setting, the clock signal comes from ICtd which is wired as a Schmitt trigger oscillator. The oscillator speed is set by the RATE control, VR6. The clock signal selected by S5 is fed to diode D5 and then to exclusive-OR gate IC5. This is connected to give a short positive pulse output whenever the clock signal from S5 makes a positive transition. IC5 thus ensures that the pattern generator circuitry is clocked by every bass beat in the music signal. Back to the one-of-eight The Qt and Q2 outputs from IC6 are connected to IC7; Qt directly to the A input while Q2 goes via PAT- 6 1 1 4 1 2 4 5 4 1 1 1µF 1 6VW PC electrolytic 0.15µF metallised polyester 0.12µF metallised polyester 0.1µF 250VAC capacitors (Wima MP3 or Philips MKT-P 2222 330 40104) .056µF metallised polyester .047µF metallised polyester .033µF metallised polyester .022µF metallised polyester .01 µF metallised polyester .0068µF metallised polyester .001 µF metallised polyester Resistors (0.25W, 5%) 2 x 1MO, 10 X 470k0, 4 X 220k0, 2 x 180k0, 6 x 1 OOkO, 3 X 47k0, 6 X 22k0, 1 X 18k0, 8 X 11 kO, 15 x 1OkO, 2 x 4. 7k0, 2 x 3.3k0, 1 X 2 . 7k0, 1 X 1 .8k0, 2 x 1k0, 4 X 6800, 4 X 3300, 1 X 1 000, 4 x 50k0 miniature vertical trimpots, 1 x 1 MO linear pot, 1 x 1 OOkO log pot Miscellaneous Screws, nuts, self-tapping screws, rainbow cable, 0.63mm enamelled copper wire (ECW), tinned copper wire, mains rated cable, insulating sleeving, solder etc. switch S3a to the B input. The C input of IC7 is connected via the wiper of S3b. Depending on the code fed to the A, B and C inputs, the common input of IC7, pin 3, is connected through to one of the eight outputs, 0 to 7. One of the 0, 1, 2 and 3 outputs can be selected when the C input is low, and one of the 4, 5, 6 and 7 outputs selected when the C input is high. The B input when low can select the 0, 1, 4 or 5 outputs. When high the 2, 3, 6 and 7 outputs can be selected. The A input selects either the 0, 2, 4 or 6 output when low and the 1, 3, 5 or 7 outputs when high. When switch S3 is set for Chaser mode, IC6 counts (up or down) and connects IC7 outputs 0, 1, 2 and 3 to the common input (pin 3; + 12V) in sequence. These outputs connect to the four inputs of ICB (the Display Selector, described above and shown in Fig.1) to drive the Triacs. When S3 is set for Strobe mode, TERN Despite the circuit complexity, the Discolight is easy to build with most of the parts mounted on a single PCB. Note that part of the circuitry is powered directly from the 240VAC supply, so take care when working on the board. the B input of IC7 connects to OV (via S3a) while the C input is connected to + 12V via a 10k0 resistor. Thus outputs 4 and 5 of IC7 a:re selected in sequence. When output 4 is high, it is bridged to outputs 0, 1, 2 and 3 via diodes D6 to D9 so all four Triacs are driven. (Output 5 is connected to + 12V and plays no active part). So all four channels flash on and off in unison. Finally, when S3 is set to Alternate mode, both B and C inputs of IC7 are connected to + 12V. Thus, as IC6 counts, outputs 6 and 7 of IC7 go high alternately. Then, as output 6 goes high, diodes DlO and Dl 1 pull outputs O and 1 of IC7 high also. Similarly, as output 7 goes high, diodes D12 and D13 pull outputs 2 and 3 of IC7 high also. So two channels flash on alternately. To modulate or not to modulate Now for the messiest part; how to obtain the modulated Chaser, Strobe and Alternate modes. Normally, when DISPLAY switch S4 is set to the unmodulated mode, the input to inverter IC9e is pulled low via a 10k0 resistor. This feeds signal from the pattern generator circuitry through to the Triacs. Similarly, when S4 is set the Modulated mode, IC9e's input is still pulled low and the pattern generator signals are fed through to the Triacs but - and here is the tricky bit - have a look at S4a in position 2. Signal from the Low Bass audio comparator feeds via inverter IC9d and a 22k0 resistor, to the INHibit input of IC7. This allows the Low Bass channel to modulate the lamp brightness even though the normal mode would be for zero voltage switching of the Triacs and thus full brightness of the lamps. That is really tricky. Isolation IC8, the Display Selector (depicted on Fig.1), does not drive the four Triacs directly. It does so via four MOC3021 optically coupled Triac drivers. Between pins 1 and 2 of each MOC3021 is an internal LED and when this is driven, the emitted light turns on an optically triggered Triac. This, in turn, feeds the gate of the relevant power Triac and turns it on. continued on page 83 JULY 1988 63 ii I AMATEUR RADIO By GARRY CHATT, VK2YBX Amplitude companded sideband: a new technique for greater spectrum efficiency New technology is always of interest to the radio amateur. This month, we take a look at a new technique called amplitude companded sideband. It offers greater spectrum efficiency, improved speech quality and the ability to add selective calling from the base station. Many countries are now having problems catering for the growing demand for radio communications within a limited frequency spectrum. And although it has a much smaller population than the USA or Europe, Australia will also reach a situation in the near future where spectrum congestion becomes a real problem. A possible answer to this problem is a new mode of transmission called "amplitude companded sideband" , or ACSB for short. The technique promises greatly improved spectrum efficiency. In fact, ACSB will offer up to six times the number of discrete radio channels over existing FM 2-way systems. For this reason, it will be 10d8 PER DIVISION VERTICAL 2kHZ PER DIVISION HORIZONTAL Fig.1: frequency spectrum for a typical ACSB transmission. The 3.1.lcHz pilot tone is 1.3.lcHz above the channel frequency. 64 SILICON CHIP of interest to both commercial users and amateur operators alike. Basically, ACSB is a form of SSB (single sideband) transmission with speech compression and frequency pre-emphasis during transmission and speech expansion and deemphasis on reception. A further refinement is the use of a pilot tone. The basic disadvantage of SSB is that no carrier is broadcast to act as a frequency or amplitude reference in the receiver. This means that the SSB receiver must regenerate a carrier to the exact frequency produced by the transmitter in order to demodulate the incoming signal. This is no problem at HF but becomes increasingly difficult at VHF and above. Assuming reasonable transmitter and receiver fre-quency stabilities of plus and minus two parts per million (ppm), each could be off centre frequency by ± 300Hz at 150MHz, resulting in a worst case (and unacceptable) 600Hz frequency mismatch between transmitter and receiver. ACSB eliminates this problem by transmitting a low-power, fixedfrequency pilot tone. Current ACSB equipment uses a 3. lkHz pilot tone transmitted at a power level of 10% of the total PEP output. This pilot tone is generated accurately to within 1Hz in both the transmitter and receiver. At the receiver end, automatic frequency control (AFC) circuits adjust the synthesiser frequency so that the received pilot tone matches the internal 3. lkHz reference. As a result, the recovered audio is reproduced within 1Hz of its original frequency. DD~~~~RWCf:CND J::ssT AMPLIFICATION/ PRE-EMPHASIS/ COMPRESSION/ LIMITING A:OIO \ UPPER CENTRE ,r:i"'D, % 5. '/E1 VOICE 10.2369 MHz 3100Hz l0 •241MH z 10.2431 MHz 10 4 MHz 10MHz 2431 RF BAND PASS FILTER 10.24MHz LOW PASS ALTER USB CRYSTAL FILTER -----t / MliR 152MHz 0038 RF LINEAR AMPLIAERS 'X, 10.24MHz ~------------1 PILOT OSCILLATOR 3100Hz SYNTHESISER 10.24MHz ALC DETECTOR REFERENCE I"\., ALC CHANNEL SELECTOR CHANNEL DISPLAY Fig.2: block diagram of an ACSB transmitter. The audio filter limits the audio bandwidth to about 2.5kHz so that audio components are kept well clear of the pilot tone. Only the upper sideband is transmitted. The pilot tone also serves as a signal strength reference at the receiver. This enables the AGC (automatic gain control) circuitry to keep the gain at the desired level over a wide range of signal strengths, regardless of pauses in speech. This eliminates listener fatigue due to the "gain pumping" produced by voice-actuated AGC systems used by conventional SSB systems. Squelch The presence or absence of the pilot tone is also used to operate the receiver squelch system. This eliminates random opening of the squelch circuits by noise. In addition, low deviation phase modulation can be added to the pilot tone for signalling purposes. The most common application of this is the use of CTCSS which allows selective calling by the base station. The frequency spectrum of a typical ACSB transmission is shown in Fig.1, along with the standard emission limitations for a 12.5kHz channel. In this case the centre frequency is 152.0025MHz. Only the upper sideband is transmitted. The suppressed carrier is 1.BkHz below the centre frequency at 152.0007MHz, while the 3.lkHz pilot tone is 1.3kHz above the_ channel frequency at 152.0038 MHz. The top line of the graph corresponds to 25W PEP (peak envelope power). The amplitude linearity of the final RF amplifier is the key element in determining the amount of occupied bandwidth which occurs as a result of intermodulation distortion. This means that all amplifier stages must be linear enough to reproduce variations in signal amplitude. All power amplification stages in ACSB must therefore operate in either class A or AB. Although there are some pronounced differences between some of the circuits used in FM radio systems and those used in ACSB, there is nothing mysterious about the circuitry used. Basically, all the receiver IF (intermediate frequency) and RF circuits operate in their linear regions. Most of the audio circuits also operate linearly. Strictly speaking, the audio compressor, limiter and expander circuits are the only circuits not operating in the linear mode. However, these circuits are designed to produce minimal harmonics and intermodulation products. The modulation signal is trans- lated to or from the RF channel frequency using mixers (including a balanced modulator and product detector). Frequency multipliers cannot be used in a modulated signal path due to the non-linear effect on the modulation. However, the local oscillator system can use multipliers since it does not carry modulation. The ACSB transmitter Fig.2 shows the block diagram of an ACSB transmitter. Let's see how it all works. Low level audio from the microphone is first applied to an amplifier/compressor circuit. Compression amplifiers have more gain at low input levels than at higher levels. In this circuit, the gain selfadjusts quickly enough to increase the level of weak voice syllables, so that the average voice level at the output of the compressor is increased relative to the peak level and the overall dynamic range is reduced. For example, a 2:1 compressor would reduce a 60dB dynamic range at the input to a 30dB dynamic range at the output and increase the average voice level by as much as 15dB. Thus, the major benefits of amplitude compression JULY 1988 65 CENTRE 1E 152.0038MHz AUDIO POWER ~ vie-v-t.J.,J 10.24MHz SQUELCH LOGIC SQUELCH CONTROL LOCK CT 10.24MHz _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ____, SYNTHESISER REFERENCE AFC CHANNEL DISl'LAY Fig.3: block diagram of the receiver circuit. A bandpass filter separates out the pilot tone which is then compared with a locally generated 3.1kHz pilot tone to derive AFC information. As well, the separated pilot tone drives the AGC circuits. are reduced dynamic range (which allows easier control of amplitude linearity), improved modulation efficiency (which allows maximum RF power output over a wider range of audio input levels), and improved signal to noise ratio in the receiver when an expander is used. Audio peak limiting may also be used to ensure that a desired peak audio level is not exceeded. An audio peak limiter tends to increase the compression ratio at higher voice input levels and has some affect in increasing the average modulation level. Audio peak limiters must be preceded by audio pre-emphasis to minimise in-band harmonics. Audio pre-emphasis is used to boost the level of high frequencies compared to the bass frequencies which are more predominant in speech signals. This tends to flatten the average output across the passband of the transmitter, helps reduce intermodulation spreading at the RF output, and improves the recovery of high frequency voice signal at the receiver. The preemphasis in an ACSB transmitter is typically between 6dB and 12dB per octave across the audio band. The compressed speech signal is 66 SILICON CHIP fed to a sharp cut-off low pass filter, which limits the audio bandwidth to about 2.5kHz. This ensures that the audio components are kept well clear of the 3. tkHz pilot tone. The pilot tone, which is crystal generated, is then added to the filtered audio. A technique called "pilot pumping" is usually used to reduce the pilot level when the voice power exceeds the maximum pilot power level. This reduction in pilot level during voice peaks helps reduce intermodulation spreading at the transmitter output, and allows the ACSB receiver to detect the level of pilot tone and increase its gain proportionately. This serves to expand the voice dynamic range at the receiver and keeps the receiver quieter during gaps in received speech. Pilot pumping can be achieved by using another audio compressor and/or as a result of feedback ALC (automatic level control) action. Transmitter IF stages The balanced modulator mixes the processed audio plus pilot tone and the IF carrier oscillator together. The resultant output from the modulator includes a DSB (dou- ble sideband) signal "wrapped" around the carrier oscillator frequency. Because the circuit is balanced, this carrier is suppressed by about 30dB. The upper sideband is produced from the sum of the carrier oscillator and the audio frequencies. The lower sideband is produced from their difference. The DSB (double sideband) signal is passed through a buffer amplifier which is also used as an ALC control point. The IF filter is typically an 8-pole unit with steep skirts. This has low ripple and a narrow bandwidth since it is only required to pass frequencies from 300Hz to 3.3kHz above the IF. Thus, the output of the filter contains only the USB (upper sideband) ACSB signal which is then amplified to drive the RF mixer. RF stages The ACSB IF signal is combined with the local oscillator (LO) at the mixer. The mixer is usually a double balanced type so that little output occurs at either the IF or LO frequencies. Among the signals present at the RF mixer output are the sum and the difference of the IF and LO frequencies. The desired This mobile ACSB transceiver features 16 channels and a power output of 25 watts PEP. that as the PA output reaches its compression point, any further increase in drive level reduces gain in the previous stages. The ACSB receiver output is the sum of the IF and LO frequencies, which is an USB ACSB signal. The lower sideband is discarded. The Local Oscillator is generated by a frequency synthesiser, similar to those used in synthesised FM equipment, and has a resolution of 5kHz. As in most commercial and amateur equipment these days, frequency selection is made by a channel switch and PROM (programmable read only memory) circuitry. A stable master reference oscillator is essential, and typical circuits use 10.240MHz as the reference frequency with a stability of ±2ppm. After some amplification, the mixer output is fed to an RF bandpass filter which removes all undesired mixer products. Several gain stages are then used to increase the amplitude of the signal to about lO0mW to drive the RF power amplifier. After linear amplification, the RF output is passed through a low pass filter to suppress any harmonics which may be present, and then fed to the antenna socket. Safety circuitry in the form of ALC protects the power amplifier (PA) from being overdriven. The PA output is sampled, rectified, filtered, and fed back to one or more of the earlier IF or audio stages. The ALC threshold is set so Fig.3 is a block diagram of the receiver circuit. The received signal first passes from the antenna to a selective RF amplifier. The tuned circuits in this amplifier reject the input signal at the image frequency (twice the IF below the desired frequency) and pass the correct input signal. The same synthesiser local oscillator and mixer circuit used in the transmitter is operated in reverse for the conversion of the RF input frequency to the IF (intermediate frequency). From there, the signal is fed to the first IF amplifier which in turn feeds an IF delay circuit and noise blanker. A separate IF amplifier is used to magnify noise pulses and these are used to trigger a noise gate during strong impulse noise periods. The IF delay circuit ensures that the noise pulse arrives at the blanking gate at exactly the same time the gate is turned o'n. The IF signal then passes through a crystal filter (as used in the transmitter) and two subsequent amplifying stages. The IF amplifiers have AGC applied to them so that the average signal level at the product detector is held fairly constant for a wide range of input signals. This AGC is derived from the recovered pilot tone. The product detector uses the carrier oscillator to mix with the IF to produce baseband audio. The baseband audio contains both the audio passband and the 3. lkHz pilot tone. Two separate audio circuits are used here to process these signals. The pilot tone bandpass filter strips the pilot tone from the baseband audio. It is then used to drive the AGC circuits. The pilot tone filter output is also fed to an amplitude limiter which preserves the pilot phase and frequency. This signal is compared with the locally generated 3. lkHz pilot tone and is used to derive AFC information. This AFC is routed back to the synthesiser, where the first local oscillator frequency is adjusted so that the recovered pilot tone is set exactly to 3. lkHz. This guarantees that the recovered speech will be correctly demodulated. In repeater systems, the received pilot tone may have CTCSS phase modulation applied to it. An additional discriminator or phase locked loop can be used to demodulate this information which can then be used for repeater control or squelch control. The voice audio is sent to a fast acting AGC amplifier which has its gain controlled by the pilot tone amplitude. This AGC almost entirely eliminates amplitude fluctuations caused by multipath propagation and vehicle movement. The AGC circuit also acts to reexpand the amplitude compression encoded at the transmitter in the form of pilot amplitude pumping. The fade-corrected signal passes to an amplitude expander which restores the dynamic range of the voice signal. This audio is then subject to de-emphasis. Both deemphasis and amplitude expansion provide a great reduction in channel noise and help to improve the overall signal to noise ratio. The expanded and de-emphasised audio is then fed to the squelch circuit, which feeds the receiver volume control and audio amplifier. Footnote: most of the developmental work on ACSB has been carried out by Stephens Engineering Associates Inc, 7030 220th Street, S.W. Mountlake Terrace, WA 98043, USA. The author wishes to acknowledge the use of public domain information provided by Stephens Engineering, USA. ~ JULY 1988 67 WINTER: A GREAT TIME TO BUILD A KIT AND $AVE! AEM's new Mini Mixer Fantastic! A 4 Input audio mixer for the amateur with specs good enough for the prol Use It for mixing various audio sources - mlcs, tapes, guitars, organs, etc etc. Easy to build, easy on the pocket! Cat K.,'3039 VCR KITS llllataxtYesl A big $70 off last year's ~ Sound Processor free - all you need Is a decoder to get it! Works through virtually any VCR. enjoyment to your videoing. ONIY s2996 Most VCR's have sound that's, well, pretty , - - - - - - - - - - - - - - - - - - - - . . , pedestrian. This great kit fromEAallowsyou totai IASTYEAR :~ .95$ 5 9 control over your VCR sound. 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Cat K-3448 WAS $129.95 NOW S - . 11995 Transformer to suit: M-2010 (gives 14A cont) $64.95 M-2000 (gives 6A cont) $34.95 (j}. tij . , · Need a Keypad? Put together this onel For all situations requiring digital entry, It's superb. And look at the ridiculously low prlcel Cat K-3600 $ COMPLETE WITH CIRCUIT 325 5 Discolight Line Filter/ Conditioner 165 Move over, Musicolour: the Disco Light is here! An incredible array of spectacular lighting functions Is at your fingertips with this new design from SIiicon Chip. Features 4 channels with sound to light, chasing, beat chasing, stroblng, beat stroblng, reverse, forward, up, down, sideways ... you name it, your lights will do It! Cat K-3150 ~~~=~~~:::-~ s45 ~==.--u· Megafast Nicad Charger If you race cars or boats, you'll know what a hassle charging the 7.2V NiCad Is. And you'll probably also know (to your cost) that most chargers aren't worth a cup of c~ld tea! 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Cat K-3248 Strobo Tuner Tuning forks are passel With this new tuning aid from Electronics Australia you'll be able to accurately and professionally tune musical lntruments in seconds. It's fully self contained and Is quite an easy kit to build . If you're into music - get into this! Cat K-3550 That 'thump" you get when you turn your amplifier on is more than annoying: it's dangerous! You could end up blowing the cones from your speakers - and possibly damaging the amp as well. Protect your Investment with this kit: It's easy to build, and stops that massive overload hitting your speakers. You'll find it in this month's Electronics Australia, Cat K-4008 3ges Want to build a ~!l!!!Is ! ! , ! ! c a n n o t supply that kit (the tuning capacitor is almost impossible to obtain!) But we can help you with a kit for a crystal set! Did you know that in Fun Way Into Electronics there's a crystal set to build - along with 19 other great projects including the famous Beer Powered Radio! 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TV Cro Adaptor Near ½ Price Neg Ion Generator Nothing negative about this onel Spare Transmitter: Save $6 Just In case you lose one (or to give someone else control tool) Same transmitter as In above kit. Cat K-3429 WAS$,:,: Just for the fun of it! Build yourself a great performing little AM Headphone Radio. And this month you'll save $2.00! Cat K-2720 ~ sges s24es ~I --- I ' e''- f ior,i c;,o•t:::'°" p,1fGA:1:.,...-"" ..... I i Turn that old b&w (or colour if you're affluent) TV into a great audio oscilloscope with this nifty kit. Up to 300kHz bandwidth - so Its great for audio! Cat K-3060 SAVE1s, What a saving! And what a kit! Build your own negative ,on generator: find out for yourself if the fantastic claims are true! Price Includes safe, low voltage plug - pack. Cat K-3333 WAS S49 NOW We'll LED you make Check your Microwave! s34es s19es LED Laval Meter Add this to your hi Ii for a mini lightshowl It's useful, too - peak level display can warn of danger! Cat K-3370 WAS $19.95 NOW s17es . NOW AVAILABLE AT ALL STORES - OR CALL TOLL FREE: (008) 22 6610 FOR HOME DELIVERY! . 5 NOW s1&es Pl.3: Negative feedback and frequency response WHAT IS NEG~I'IVE This month we look into why open loop amplifiers suffer poor frequency response and we investigate how negative feedback increases the bandwidth. By BRYAN MAHER Analog amplifiers form such an important part of electronic circuitry, that we find them in almost every piece of equipment. Though many signals may be digitized these days, you will always find linear amplification being performed. For example, the ultimate hifi capabilities of CD players can only be .realised by using high quality amplifiers in the final stages. Though feedback concepts can be applied to almost anything electrical, mechanical, hydraulic or others - our interest here is in electronic systems only. So let's start at the beginning, with an (allegedly) linear electronic amplifier without any feedback at all. Frequency dependence Last month we made the bald +15V statement that the open loop gain of an amplifier is different at differing frequencies. Why is that so? All open loop amplifiers have reduced gain at the high end of the frequency range and possibly at the low end too. First, let's look at the reasons for such loss of gain, then we can investigate how negative feedback improves the situation. Fig.1 shows a simple "linear" amplifier stage. We call it "linear" simply to distinguish it from deliberately non-linear digital or logic circuits. By "linear circuits" we mean those with an output voltage which is supposed to be an enlarged but otherwise identical copy .of the input voltage waveform. Strictly we ought to say " roughly linear" because we know that all simple amplifiers have output voltages which are a distorted larger version of their input voltages. Last month, we told the story of an enthusiastic young lady called Krystie who had built a simple transistor amplifier to play her favourite music. But the results were disappointing. The amplifier not only exhibited excessive distortion but the frequency range was also much less than expected. In fact, the high and low frequency notes were so weak they could barely be heard. At this point we can find out how negative feedback can be an almost magical cure for all amplifier ills. Looking again at Fig.1, let us consider in detail what should be happening at each point in the circuit and what is actually happening. First, the signal source (CD player, tape deck or whatever) generates some signal V(in), which we apply to the input, and we expect that same signal waveform V(in) to appear at the base of the transistor. And it does too - more .or less. But why isn't the signal on the base identical to the input? Well, we observe that the signal V(in) has POSITIVE RAIL hreor==----------.:::-----r 1 hreo-3dB-r------------~ .Flg.1: this simple common-emitter amplifier bas no negative feedback .and suffers from harmonic distortion and deficient low and ·high (requency response. 70 SILICON CHIP h r e = 1 - - - - - - - - - - - - + - - - - - -- ---l<- LOG FREQUENCY Fig.2: all transistors suffer from loss of gain at high frequencies. At a really high frequency, FT, the gain drops to unity. FEEDBACK? to pass through Cl which has an appreciable impedance, so there is inevitably some signal loss in Cl. The effect is worse at low frequencies. But by making Cl sufficiently large, up to 1.0µF, very little low frequency response is lost. DC coupling? Why not just DC-couple the whole thing? DC coupling means using no coupling capacitors at all, and indeed that is the ideal. Circuit gain remains undiminished no matter how low the frequency, right down to OHz (ie, DC). But there are drawbacks to DCcoupling right from the input terminals, so common practice is to employ only one coupling capacitor, Cl right at the input. Thereafter, most feedback amplifiers are DCcoupled throughout. Now what about high notes? Why is the simple amplifier also deficient in the top frequencies? There are two main causes and again Fig.1 gives us some answers. Loss of hre Last month we made some comments about the way the hre or current gain of any transistor chang~s at different collector currents and at different temperatures. But current gain is also different at various frequencies. At a constant collector current and room temperature, the hfe holds constant right down to DC. (It may even be a little higher at DC for the secondary reason that large steady DC currents tend to heat the transistor junction more than AC currents of the same peak value). However, at high frequencies the value of hre decreases as shown in Fig.2, and at some very high frequency called fT the value of hre has dropped to 1.0. On the curve Fig.2 we define another point fhfe, the frequency at which the hre has fallen to 0. 707 of the DC value. If the frequencies of interest extend up to fhfe or beyond, the current gain of the transistors will reduce, hence the circuit gain must be less than it is at low frequencies. In practice, we never use transistors anywhere near their upper frequency fT; that frequency is quoted in transistor data sheets only to enable us to draw the curve Fig.2. True, we could go out and buy different transistors having higher values of fhfe and fT, and that is a good idea for the small "front end" transistors in an amplifier. But high frequency large power transistors cost a fortune, so we have to make do with lower frequency types in power transistors. Shunt capacitances Though Fig.1 is all you see if you look at the physical circuit of such an amplifier first stage, there are many "stray capacitances" all around the circuit, which we show dotted. These are due to the natural effects of capacitance which exists between all separated conductors and semiconductors. As well as the stray capacitance Cs from wiring and components to ground, there is the base-emitter capacitance Cbe in the transistor itself. Also there is a capacitance Cm from the transistor's collector back to the base. This Cm is called the "mutual" or the "Miller" capacitance. Cm is the most important of the stray capacitances. It is due to the. collector-base capacitance Ccb, but as the voltage across it is the input voltage plus the stage output voltage, the capacitive current flowing is equivalent to it being much larger capacitance Cm, where Cm = Ccb(l + A), where A is the stage gain. The total input capacitance Cin is the sum: Cin = Cm + Cs + Che· The source resistance (in parallel with Rl and R2) forms a low-pass filter with Cin, reducing the amplitude of high frequency signals. This happens in every gain stage of an amplifier. But there is more. At the output side of the transistor stage we have a number of parallel paths: (1). The equivalent collector output resistance. (2). The collector-emitter capacitance. (3). The collector load resistor. (4). The input resistance and input capacitance of the following stage. (5). The wiring stray capacitance. Those capacitances tend to reduce the high frequency response of the stage, but the lower the parallel resultant of the resistances mentioned the less this reduction. Therefore, while higher collector a r------------+15V y. STAGE 2 STAGE 3 STAGE 4 a--+--- OUTPUT RA FB Fig.3: this four-stage amplifier, with all stages identical to Ql, has negative feedback applied via RA from the output back to the emitter of the first stage. JULY 1988 71 - - - - - - - -- T = 100 - -- -- - - - - i ERROR SIGNAL E Vln 1DmV X DIFFERENCING ACTION BETWEEN BASE ANO EMITTER VOLTAGES K ,___o_F _sT_AG_ E 1_ _ r •---G = 10000-----•-1 \E ...------, 1 __,____ _ _ STAGE 1 - GAIN OF STAGE 1 FB --- y STAGES 2,3,4 i---+---ouwT r- :7 I I I Kl I I : RB t-H R Some names = 1/101 L _.,._I Fig.4: this is a block diagram of the four-stage amplifier shown in Fig.3. RA and Re set the proportion of the output voltage fed back to input K. load resistors may result in higher low-frequency gain, they also cause the gain to drop off badly at higher frequencies. As most amplifiers have two or more stages, the reduction of gain at higher frequencies will occur in every gain stage. The Miller capacitance will have its greatest effect in the front end high-gain stage (because stage gain A is high), while the frequency dependence of hre will be responsible for the poor high frequency response in the final high-power stage (because fT is low). Enter negative feedback Fig.3 shows the outline of a fourstage amplifier where Ql and its sundry components form stage 1. Each stage is inverting, meaning that positive-going inputs produce negative-going outputs, but four stages of phase-inversion result in overall non-inversion; ie positivegoing signals at X result in a positive-going output at Y. In previous episodes we showed some negative feedback block diagrams. Now in Fig.3 we show one possible way to actually apply the feedback voltage from the output back to the input stage. Input signals from the voltage source applied at X naturally increase the output voltage. But you will recall that the negative feedback must be applied In applying negative feedback to our whole amplifier we have reduced its voltage gain. But as we will see, we have improved the amplifier's characteristics in about the same proportion as the reduction in gain. to the front stage in such a way that the feedback voltage reduces the output. As you probably know, a positivegoing signal at X causes an increase in Ql 's collector current, which in turn produces greater voltage drop across R3, hence greater stage output at the collector. In Fig.3, resistors RA and RB form a voltage divider across the stage 4 output, from Y to ground. Do not be confused by the presence of R4, as it is bypassed by C2. The impedance of C2 (at all audio frequencies) is much lower than the resistance of R4, hence there is little or no signal volt~ge drop across R4. As far as AC signal voltages are concerned, point W (junction of RB and R4) is at ground or zero potential). Hence at the emitter K of transistor Ql we have applied some feedback called "FB", a signal which is some fraction of the output voltage. Let us call that fraction "H". So the fraction H will be given approximately by: H = RB + (RA + RB) K is the point where we have applied feedback signals to the emitter of Ql, and you will observe that we now have a "closed loop system" from Ql collector C, through stages 2, 3 and 4, to Y, through RA, back to K, through transistor Ql to C. (1). The gain of the whole amplifier (measured from the input terminal X to the output terminal Y) before any feedback is applied is called the "Open Loop Gain". This is given by the symbol "G". (2). The gain of the whole amplifier (measured from X to Y) with feedback applied is called the "Closed Loop Gain". This has the symbol ''T''. (3). Because of negative feedback, T is always smaller than G. (4). The fraction of output used as feedback is called "H" In Fig.3, H = RB + (RA +, RB). (5). The feedback signal derived from the feedback voltage divider H is (naturally enough) called "FB". FB is simply equal to H x Output. (6). The gain around the loop (from C through stages 2, 3, & 4 to Y, through the voltage divider to K, and through the transistor gain back to C) is called the "Loop Gain". As the Loop Gain is clearly the product of G and H, we simply refer to the Loop Gain as "GH". (7). The input signal at X is to be amplified. So we would like the output signal at Y to be an enlarged replica of the signal at X. (8). As the feedback signal at K is a smaller copy of the output signal at Y, by (6) above we would want the signal at K to be exactly like (but a little smaller than) the input signal at X. If it is, we have succeeded. If not, then we ask the circuit to take corrective action. (9). The difference between the signals at X and at K is called the "Error Signal". This is given the symbol "E". (10). It is the error signal E which is amplified by the amplifier. (11 ). As the error signal is small, we The difference between the signals at X and K is the error signal and it is this signal that is amplified by the amplifier. 72 SILICON CHIP ---ET-----, T = 99.99 Vln 10mV -----T = 99 - - - - - - , 6 = 10000 ----OU11'11T E = Yin - FB 999.9mV E = 0.09999mV _ _ __, K r-RA -1 I FB FB = Y/101 = 9.90000991nV 10k E K I I I 1 r,-.H = 1/101 6 = 5000 ' E = 10mV - 9.80199mV E = 0.198mV r; 10k I -1 I I 11~!0 L_..:...J will need considerable gain in the amplifier. Fig.4 is a block diagram of the circuit of Fig.3. In Fig.4 we have split the action of the first stage Ql into its two functions: (a) The differencing action between the input signal at X (the base) and the feedback signal FB at K (the emitter); and (b) The action of transistor Ql which (as in all transistors) amplifies the difference between the signals at base and emitter. Also we have labelled Fig.4 to point up three facts: (1). It is the error voltage E (not the input voltage at X) which is multiplied by the amplifier gain G. (2). H is simply a fraction, set by the voltage divider ratio. (3). FB is a signal which is some set fraction of the output signal. So just how does all that jazz cure amplifier ills? One thing at a time, please. Consider first the poor response to high frequencies we noted earlier. If, for any reason, the output is not be as high as it should be, then the feedback will be smaller. This means that less will be subtracted from the input signal in forming the error signal E, so E will be a bit larger. This will increase the output to (nearly) the right signal level. Keeping the same amplifier circuit, we redraw Fig.3 and Fig.4, grouping parts of similar function, giving us the simpler Fig.5, where we have written a possible set of conditions; ie resistances of RA and RB, together with gains, and voltages which might be measured 990mV FB I FB = 990mV/101 = 9.801999mV I I ·Fig.5: the signal E, which is the difference signal applied between X and K, is multiplied by 10,000 to give the output signal. Note that Vin is relatively large but signal E is extremely small. ____ Y--OUTPUT I I I I 188 RB Yin 10mv---"' I I 1-H = 11101 L_...:_I Fig.6: even though the open-loop gain of the amplifier has dropped to 5000, the negative feedback ensures that the output signal is still very close to 1 volt by making the difference signal E larger. in a typical four-stage amplifier at low and middle frequencies. Low and middle frequencies We have chosen the amplifier open loop gain G = 10,000, as four stages each having various gains could easily multiply up to that figure. We choose the following values as typical for such an amplifier: input voltage V(in) = lOmV; RA = 10k0; .RB = 1000; G = 10,000 (at low/middle freqencies). From these values we can calculate that: H = RB + (RA + RB) = 100 + (10,000 + 100) = 100 + 10,100 = 0.00990099. Alternatively, 1/H = 101. By this means we can calculate signal voltage values all around the circuit. Without all the calculation details, we have written the results on Fig.5, so if you don't want to bother with calculations, just look at the diagram. Fig.5 shows that at low and middle frequencies, the gain stages of the amplifier give an open loop gain G = 10,000. (a) An input of lOmV gives an output of 999.9mV, so the closed loop gain T (measured from input X to output Y) is T = 100 (approx). (b) The feedback network divides the output by 101 to give a feedback voltage FB = 9.9mV (approx), which is subtracted from V(in) to give an error signal E = 0.099mV (approx). This is multiplied by 10,000 to give an output V(out) = 999.9mV. At high frequencies we must ex- pect the gain G of the amplifier to be less than 10,000 (because of the shunting effect of stray capacitances, the Miller capacitance and the fall-off in hre at high frequencies as discussed earlier). At some high frequency, the open loop gain G could be down to half; ie, G = 5000. For this condition, as illustrated by Fig.6: (c) The same input V(in) = lOmV gives an output of 990mV, so the closed loop gain (measured from X to Y) is approximately 99. (d) The feedback divider fraction is not subject to frequency, so H still divides the new output by 101, giving a feedback voltage FB = 9.8mV (approx), which is subtracted from V(in) to give an error signal E = 0.198mV (approx), which multiplied by the reduced value G = 5000 gives the new output V(out) = 990mV. (e) We observe (with joy) that even though the gain stages only had half gain (G = 5000 at high frequencies), we still found an overall gain only 1 % down (T = 99) at high frequencies; ie, T = 990mV + 10mV = 99. Conclusion From all the above we conclude that negative feedback automatically compensates for at least one amplifier shortcoming; the fact that the open loop gain falls at high frequencies. What about those other deficiencies, like distortion, hum and noise?. Can it be that negative feedback will cure those ills too? That will be our topic for next month's episode.~ ]ULY 1988 73 Check out amplifier headroom & music power Tone burst source for amplifier testing This self-contained test instrument generates the required signals to measure amplifier headroom and music power. It only needs a multimeter to read out the result. By LEO SIMPSON & JOHN CLARKE Whether or not you regard Music Power and Dynamic Headroom as a joke, hifi equipment manufacturers are quoting music power and headroom figures these days. This means means that these parameters should be confirmed when appraising a hifi amplifier. At SILICON CHIP we regularly test commercial amplifiers and our own designs so we wanted to have our own test set-up. Trouble is, we know of no commercial equipment that will do the tests. We also wanted to be able to go further than the standard IHF Music Power tests. We wanted to do longer pulse testing as advocated by manufacturers such as NAD. So what do you when there's no instrument available? You design and make your own - which is just what we did. This strange-looking instrument provides all the facilities needed to perform measurements of music power, dynamic headroom and amplifier overload recovery time. 74 SILICON CHIP We are presenting the resulting design here, not because we think the design will be produced in large numbers (although there are many organisations which could use such an instrument), but because it features a number of interesting circuit techniques. Defining terms Alright, what are the required test signals for the IHF Dynamic Headroom and Music Power? Well, the Dynamic Headroom of a power amplifier is the ratio of the Music Power to the Continuous Power expressed in decibels. So to measure headroom you first have to measure music power. The required signal conditions are set out exactly in the specification IHF-A-202 1978, as published by The Institute of High Fidelity, Inc, USA. While it is common to refer to the signal as being a tone burst, in reality it is a continuous lkHz sinewave which increases in level by 20dB for a duration of 20 milliseconds, twice a second. Or to put it another way, the amplitude of the lkHz sinewave is modulated by a pulse waveform with an "on" period of 20 milliseconds and an "off" period of 480 milliseconds. Further, the transition in level is required to occur at the zero voltage crossing of the sinewave signal. The problem with such a pulse signal is that it is difficult display on most oscilloscopes (because of its very short pulse duty cycle). Second, once the signal is displayed, it is quite difficult to judge when the onset of clipping occurs (which is the level at which the music power is measured). Then, once the exact onset of clipping is established you OSCILLOSCOPE © SYNC~ <at> © VOLTMETER Fig.1: this diagram shows how the Tone Burst Source is connected to a stereo amplifier. The DC reading on the voltmeter is squared and divided by the load resistance to give the amplifier's music ·power output. have to measure the peak-to-peak voltage displayed on the oscilloscope screen. This is difficult to do with any real accuracy since, for a high power amplifier, say with 300 watts music power, the waveform may be 140 volts peak-topeak or more. Once the peak-to-peak voltage is known, it needs to be divided by a factor of 2.828 to convert it to RMS value, then squared and divided by the load resistance to find the music power output. Clearly then, measuring music power output of an amplifier is a fiddly business. Which is why most magazines reviewing high fidelity equipment don't bother to do it.' (Either that, or they don't know how!) And when you want to measure with even longer pulse durations, say up to 300 milliseconds, you really need a storage oscilloscope to do · the job. What we wanted was a selfcontained instrument which would generate the required modulated sinewave signal, measure the power amplifier's output signal and convert it to a DC voltage which can be measured by any voltmeter, digital or analog. The voltage reading is then squared and divided by the load resistance to get the music power output. The result is our IHF Tone Burst Source. Features The IHF Tone Burst Source has a sinewave output which can be switched for continuous or modulated output, in eight burst lengths of 20, 30, 44, 66, 94, 136 and 200 milliseconds. The duty cycle for all burst lengths is fixed at 24: 1. The pulsed or continuous sinewave signal is variable in output level from zero to 2 volts RMS. So that the output waveform of the amplifier under test can be displayed on an oscilloscope, a 15V square wave sync pulse is provided. Fig.1 shows how an amplifier would be connected to the Tone Burst Source to perform a measurement of Music Power. The oscilloscope is desirable but not absolutely mandatory for the test, as we shall see later. Besides the oscilloscope and Tone Burst Source, you need a DC voltmeter (which can be a digital or analog multimeter) and a switchable dummy load which can be set to provide the rated load resistances for the amplifier under test. For most amplifiers, this means that the dummy load will have to provide 4 and 8-ohm loads at the very least, as well as 2-ohm loads for more stringently rated amplifiers. Naturally, the resistive loads need power ratings to cope with the amplifier's full output power. Depending on which channel of the amplifier is being monitored, the left or right channel output is connected to a pair of binding post terminals on the Tone Burst Source, as well as to the dummy load. JULY 1988 . 75 PARTS LIST 1 PCB, code SC4-1 -488, 130 x 103mm 1 Scotchcal front panel, 195 x 1 10mm plastic utility case, 198 x 113 x 60mm (Altronics Cat No H-0 102 or equivalent) 1 15V or 12 .6V mains transformer (see text) 1 push-on/push-off mains switch 3 DPDT miniature toggle switches 1 single-pole 8-position rotary switch (Jay car SR-1 21 0 or equivalent) 1 stereo 6. 5mm jack socket 4 banana jack sockets (two red, two black) 4 panel-mount RCA sockets 1 mains cord and plug 1 cordgrip grommet 3 knobs Inside the Tone Burst Source, the amplifier's output signal is fed to the internal signal monitoring circuitry and to an RCA socket for oscilloscope monitoring. This signal is divided down from the amplifier signals by a factor of 10 or 100, to enable the oscilloscope to correctly display the signal. We have provided this order of signal division because we are assuming that the signal will be connected directly to the CRO instead of via a 10: 1 divider probe and because most CROs have a minimum (calibrated) sensitivity of only 5 volts/div. In addition, the amplifier output signal is fed to a headphone socket which has an associated volume control. With practice, you can judge the onset of clipping "by ear" to within one or two percent. This means that it is possible to dispense with the oscilloscope although, ideally, you should have it anyway to do the test properly. The DC output voltage from the Tone Burst Source is calibrated to provide the DC equivalent of the RMS voltage for two ranges. These are the x3 and x10 ranges. To calculate the IHF power the DC voltage is multiplied by the range, then squared and divided by the load resistance for the amplifier: 76 SILICON CHIP 1 4 1 4 5mm LED and bezel 6mm standoffs solder lug rubber feet Semiconductors 2 555 timers 1 401 3 dual D flipflop 1 4066 quad analog switch 1 TL07 2 dual JFET op amp 1 CA3130 op amp 1 7815 3-terminal regulator 5 1N4002 diodes 1 1N4148, 1 N914 diode Capacitors 1 470µ,F 25VW PC electrolytic 1 4 7 µ,F 1 6VW PC electrolytic 1 15µ,F 1 6VW PC electrolytic 3 1Oµ,F 16VW PC electrolytic 1 6.8µ,F 16VW PC electrolytic 1 4 . 7 µ,F 16VW PC electrolytic 1 3 .3µF 16VW PC electrolytic 2 2. 2µ,F 16VW PC electrolytic PmF = (V x Range) 2/R1 The DC output is also available when the tone burst is disabled so that continuous RMS power can be measured at 1kHz. Using it Having connected the Tone Burst Source as shown in Fig.1, the test for Music Power is straightforward. Feed the burst signal to the amplifier and display the output waveform on the oscilloscope screen. Increase the signal amplitude until the waveform just begins to flatten at the peaks (this is the clipping point) and then back off slightly to obtain an undistorted waveform. Take the meter reading and do the power calculation as outlined above. It's as easy as that. One other test which this instrument can perform is the overload recovery time of an amplifier. The same signal is used but this time it is set so that the amplifier is overloaded by 10dB during the burst times. Most amplifiers will then take a number of cycles (at 1kHz) to recover their equilibium. The overload recovery time is then measured simply by counting the number of cycles at 1kHz so the time can be quoted in milliseconds. 1 3 4 1 1 1 1. 5µ,F 16VW PC electrolytic 1µF 16VW PC electrolytic 0 .033µ,F metallised polyester 0 .01 µF metallised polyester 0.00 1µ,F metallised polyester 22pF ceramic Resistors (0 .25W, 5%) 1 x 1.5MO, 1 X 620k0 , 2 X 4 70k0 , 3 x 220k0 , 1 x 180k0, 1 x 1 OOkO, 1 x 68k0, 1 x 4 7k0, 1 x 39k0, 1 x 27k0, 1 x 24k0, 1 x 20k0, 2 x 18k0 1W, 1 x 15k0, 3 x 1 OkO, 4 x 4. 7k0, 1 x 3.3k0 1W, 1 x 1.8k0 , 1 x 1k0, 1 X 22k0 miniature vertical trimpot, 1 x 5k0 linear potentiometer, 1 x 1kO log potentiometer Miscellaneous Hookup wire, rainbow cable , insulating tubing, solder, screws, nuts etc. Circuit features The circuitry for the Tone Burst Source consists of two 555 timers, one 4013 dual D flipflop, one single and one dual op amp package, one 4066 analog gate package plus assorted diodes, passive components and the power supply components. First of all, the circuit is required to generate a clean stable sinewave at precisely 1kHz. We do this in an unconventional way, using 555 timer IC1, D-type flipflop IC3a, and twin-T filter stage IC4a. IC1 is set to produce a 2kHz square wave. This is fed to D-type flipflop IC3a to produce a 1kHz square wave with a duty cycle of exactly 50%. The square wave is then fed to the twin-T filter stage which then produces a clean sinewave with harmonic distortion of less then 2%. That might not sound like a particularly low distortion value but it is low enough for this purpose. The output signal from IC4a is then fed to output level control VR2 and then to output amplifier IC4b. The amplifier either feeds the signal straight through with fixed gain, as for the continuous signal mode, or with gain switched between two levels, for the burst mode. c W!]OD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR CHIPS .. . WOOD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR Call Geoff for all your instrument needs 20MHz GOS-522 popular Features low cost scope •Sensitivity: SmV/div to SV/div • Bandwidth : , de to 20MHz. • Timebase : 20nS/div to 0.Ss/div $863.10 ex tax $1006.95 inc tax 20MHz GOS-523 with delay and alternate tri ~ 8et: 0 ~ C) 0 ~ Features • Sensitivity : SmV/div to SV/div • Bandwidth : de to 20MHz • Timebase A : 20ns/div to 0.Ss/div (Main) • Timebase B : 20ns/div to 0.Sms/div (Delayed) $1037.60 ex tax $1210.55 inc tax Common Features 40MHz GOS-543 top of the line • Max sensitivity : 1mV/div Features •Modes : Ch1, Ch2, Dual, Ch1±Ch2, • Sensitivity : SmV/div to SV/div X-Y • Bandwidth : de to 40MHz • Swee : Auto, Normal, Sin le • Timebase A: 20ns/div to 0.Ss/div (Main) $1285.10 ex tax • Timebase B : 20ns/d iv to 0.Sms/div (Delayed) $1499.30 inc tax Frequency Counter GFC 801 OF Just In! EPROM Eraser Model LER-121 ~ et: 0 ~ Cl 0 ~ Features • Short Circuit Protected • Auto Constant Voltage • Constant Current Indication • 0.01 % +3mV (typ) Line & Load Regulation • High Quality 4mm Binding Posts • 0.SmV or 1mVrms (typ) Ripple & Noise • Class 2.5 Analog Panel Meters GPR3030 . 0-30V, 0-3A Single Output • V & A analog meters • Fine & Coarse Voltage Control • Hi and Lo Current Ranges $237.60 ex tax $2n.20 inc tax Function Generator GFG-8019 • Multi-Function with BUILT-IN 10MHz Counter • AM, FM Modulation internal or external • Auto/Manual Sweep • 0.2Hz to 2MHz Frequency Range • Sine, Triangle, Square, Pulse and Ramp Waveforms • >20Vp-p open Circuit output, 10Vp-p into son • Variable duty cycle and de offset • VCF gives 1000:1 frequency ratio for 0-1 0V input $554.95 ex tax $643.80 inc tax • Frequency Range from 1Hz to 120MHz • Sensitivity <20mV, 10 to 100MHz, <30mV 100MHz to 120MHz • 8 digit display • 0.1 s, 1s and 10s gate times $307.85 ex tax $359.20 inc tax ~ Reliable Bench Power Supplies Capacity : 9x 24pin or 6x 28pin or . 6x 40pin UV Source : 2537°A, S000µW/cm 2 Tube Life : 3000hours approx Size : 260mm x 86mm x 70mm $95.35 ex tax $110.60 inc tax 23-Pin 'D' Connectors No it's not a misprint - there are now 23-pin connectors on some of the PC's. Geoff of course has 'em! Plugs, sockets and backshell. All $3.50 each GPD3030 2x0-30V, 0Dual Output • Series, Parallel, Independent or Dual Tracking • Four Analog Meters (V & A for both channels) $563.90 ex tax $657.90 inc tax GPQ3030 2x0-30V, 0-3A Dual Output plus Fixed SV • As above but with additional dual fixed +SV, 1A and 3A .supplies • Fixed outputs have LED overload indication $636.77 ex tax $742.90 inc tax Fans We have a furt her small quantity of those quality ITT tangential fans. Made in Germany. High throughput at low pressure across the whole width of the impeller. Noise level is less than a whisper! Self-lubricating sintered bronze sleeve bearings. 240V ac operation . Delivers 341itres/second. $49.50 (P&P $10 due to their bulk!) GPQ3030D Dual Supply with Digital Meters • As above but with two 3 1/2digit panel meters with 0.5%+2 digit accuracy $696.95 ex tax $813.12 inc tax IBM Printer Cables 1.75m and with quality connectors on both ends. You couldn't make them for this price! $14.95 GEOFF WOOD ELECTRONICS PTY LTD 229 Burns Bay Road, (Corner Beatrice St.) INC IN Nsw Lane Cove West, N.S:W. P.O. Box 671, Lane Cove N.S.W. 2066 Telephone: (02) 4271676, Fax: (02) 428 5198. 8.30am to 5.00pm Monday to Friday, 8.30am to 12 noon Saturday. Mail Orders add $5.00 to cover postal charges. Next day delivery in Sydney add $5.00. All prices INCLUDE sales tax. · Tax exemption certificates accepted if line value exceeds $10.00. BANKCARD, MASTERCARD, VISA , CHEQUES OR CASH CHEERFULLY ACCEPTED ~ 0 .,, C) 0 )J (") l: ~ +15V is~ti + 1 16VWI: 47k .,. 8 10k 2kHz ADJUST VR1 22k 3 2kHz IC1 555 .,. 11 CK IC3a 4013 ··· 1 1kHz 13 ..n... ':' J'\J\f\Jv''-..._ + 10 16VWI- 14 ,J\J' OUTPUT LEVEL VR2 5k 10k .01l ">'- - - ' - I LEFT RIGHT k .,. 220k ':' 4.7k OUTPUTS .,. .,. 4.7k ...--....--t---.....,_+15V 01 ~ . _,,,, IC3""' b- QF-2_,;;;;-1l......JL=.::;:+::;:15:.:V=-----4...,_-----------~ .,. BURST PERIOD S1 DC OUT TO VOLTMETER + 10 16VWI 22pF T FROM AMPLIFIER OUTPUT 18k 1W f..,. 3.3k 1W OUTPUI VOLUME VR3 1k LOG. HEADPHONES ~ ~ 1k .,. IHF TONE BURST SOURCE SC4·1-488 470 25VW E-~ CASE -~"' I GND The circuit of Tone Burst Source is essentially a pulse modulated oscillator with selectable pulse times, combined with an AC rectifier (D6) and a sample-and-hold circuit (IC6b, IC5) to produce the DC output signal for the external voltmeter. Amplifier monitoring is via headphones or oscilloscope. In the continuous mode, the gain of IC4b is fixed at 2.2 by the associated lOOkO and 220k0 resistors. In the burst mode, the gain is switched between 2.2 and 0.22 by analog switch IC6a. For 480 milliseconds out of each 0.5 second, IC6a shunts the 22okn feedback 78 SILICON CHIP resistor with a 24k0 resistor and thereby reduces the gain of IC4b to 0.22. Thus the required step up in gain of ten times ( + 20dB) is obtained whenever analog switch IC6a closes, in reponse to a pulse signal. The required pulse signal is generated by IC2, another 555 timer which generates a train of pulses with the required 24:1 duty cycle. This is determined by the 620kn and 27k0 resistors which charge and discharge the capacitor connected to pin 6 of the 555. The 24:1 duty cycle is obtained by dividing the sum of the two The wiring inside the Tone Burst Source is a bit of a bird's nest but is fairly straightforward if rainbow cable is used. Don't bind the wires together as this could create crosstalk problems. resistors (ie, 620k0 + 27k0) + 27k0); this gives a result of 23.963 which is within a gnat's whisker of 24:1. Switch S1 changes the capacitor connected to pins 6 and 2 of the 555, to change the pulse duration from a minimum of 20 milliseconds to a maximum of 300 milliseconds. Note that the duty cycle remains constant no matter what pulse length is selected. This means that for a pulse length of 300ms, the time between the end of one pulse and the beginning of the next is 24 x 300ms = 7.2 seconds. Now the pulse signal could have been fed directly to pin 12 of IC6a to control the gain switching of IC4b but this would mean that the transitions in level would not take place at the normal "zero axis points" of the lkHz sine wave. To ensure that this requirement is met, D-type flipflop IC3b is used. The pulse signal from IC2 is fed to IC3b's D (data) input while the CK input is clocked with the 2kHz square wave signal from ICl. This ensures that the pulse signal fed to This is the full-size artwork for the printed circuit board. JULY 1988 79 ____,...-------_______,_~~-2~~ <at> \ POWER TRANSFORMER MAINS CORO CLAMP GROMMET ~ ~ ~ SS K 0 ~LED1 A/ A .__.._ _,.,,-a,.• C OUTPUTS LEFT .7µF 3.3uF .2uF 0 . 1p . OC OUT TO + VOLTMETER - 0 o:1~J P S3 ~ OUTPUT FROM AMPLIRER OUTPUT TOCRO T HEADPHONES S ~ II \ ~ If I The wiring diagram of the Tone Burst Source uses letter coding to show the various interconnections. Note that eight capacitors are wired around switch S1. Take care with the mains wiring and use plastic sleeving to cover exposed mains connections. pin 12 of IC6a is exactly synchronised with each positive edge of the 2kHz square wave and therefore with the zero axis points of the sinewave from IC4a. Switch S2 disables flipflop IC3b so that its Q output is permanently low. This maintains IC6a in the open-circuit condition so that the gain of IC4b is fixed at 2.2. The output of IC4b is fed via a lµF capacitor to a pair of RCA sockets, for the left and right inputs of a stereo amplifier. IC4a and IC4b are biased to half the supply voltage by a voltage divider con80 SILICON GHIP sisting of two 10k0 resistors bypassed with a lOµF capacitor. The half-supply output of this divider is fed to the non-inverting inputs, pins 5 and 3, of IC4a and IC4b, respectively. The Q-bar output of flipflop IC3b provides the sync signal for an oscilloscope. Well, the description so far has detailed how the sinewave is generated and how it is switched between two levels with a duty cycle of 24:1. Now let's have a look at how the output signal from the amplifier under test is processed. Power amplifier output As noted above, the (left or right channel) output from the amplifier under test is connected via attentua tors to provide monitoring signals for headphones and an oscilloscope, as well as the signal to be measured and processed. VR3 provides the headphone signal, with quite a lot of attenuation in consideration of the high power levels likely to be involved, while the oscilloscope signal comes from the voltage divider associated with switch S3. This gives two division ratios, + 10 and + 100, so the 111, 1.11 -==:-:.:::=-=--• 10 I .. ...... Normally $7.95 ,a ~ 1.9 2s 1 $4.95ea $4.25ea $3.95ea QUALITY 3mm LEDS Cat. No . Col. 1-9 Z 10140 Red $0.1 5 Z 10141 Grn $0.20 Z 10 143 Ylw $0.20 z 10145 o,a $0.20 10 100 I 1 $0.12 $0.15 $0.15 $0.15 $0.10 $0.12 $0.12 $0.12 Equiv (Bourns 3540S, Beckman A14100 R14 110 R14120 A 14 130 R14 140 R14080 1K R14090 1·9 2K SK 10K 20K SOK 100K 10 + $9.95 $9.50 100 + $ 3.50 $ 4.95 $ 5.50 .... $ 7.90 .. . $ 8.90 .. .. $ 9.95 .. $1 0.95 ... $10.95 ... $11 .95 ... $12.95 .. . $26.95 $0.09 $0.08 $0.12 $0.10 $0.1 2 $0.1 0 H10525 105 x 75mm .. .. .. H 10529 105 x 100mm .... H 10534 105 x 140m m H 10535 105 x 150mm x 170mm H 10542 105 x 195mm ---,==r·- - - - i::a-cn--- Dials to suit 16-1-11, 18-1-11, 21-1-11. SOR 100R 200R S00A ~ !!li~~~l~Hi~i:~;~nts of heat for Designe~ by Rod Irving . H10538 105 7256) A14050 R14055 R1 4060 A1 4070 I [l' I H 10543 105 x 200mm H10546 105x 225mm H 10549 105x300mm H10560 105 x 600mm I I I . !'I RCA GOLD PLATED PLUGS AND SOCKETS ' WIRE WRAP IC SOCKETS Black anodised with a thick base plate, this radial fin heatsink can H 10520 105 x 30mm ..... QUALITY 5mm LEDS 10 + HIGH EFFICIENCY RADIAL FIN HEATSINK (!., ~ <%H::l ~ <%H ~ --====at Cat. No . Col. 1-9 Z 10 150 Red $0.10 Z 10151 Grn $0.15 Z 101 52 Ylw $0.15 10 TURN WIRE WOUND POTENTIOMETER Spec:trol Model 534 ¼ " shaft. J ~ \ ... ~ .., These quality 3·1evel wire wrap sockets are tin-plated phosphor bronze. Cat.No. Description 1-9 1O+ P10579 8 pin $1.50 $1.40 P10580 14 pin $1.85 $1 .70 P10585 16 pin $1.95 $1.80 18 pin $1.95 $1.80 P 10587 P 10590 20 pin $2.95 $2.70 P 10592 22 pin $2.95 $2.70 P10594 24 pin $3.95 $3.50 P10596 28 pin $3.95 $3.50 P 10598 40 pin $4.95 $4.50 We have m llllons of d iodes In stock! + 100 + 1000 + IN4148 Small signal Cat. 21 01 35 Je 2½e 3½e Overall : 63mm across, Srnm high . 2e LEDs: 10 x Smmx 1mm Cat.No. 1-9 3e Z101 80 IN4004 400V 1A Cat. 2 101 07 4e HIGH INTENSITY RED LED BAR GRAPH Dimension s: $2.95 10 + $2.75 Save a fort~f~~~~ nalve throw away batteries w ith t hese quality Nlcad s and Rechargers l Size Oes c. 1·9 10+ 100+ AA 450 mA.H. $2.95 $2.75 $2.50 C 1.2 A. H. $9.95 $9.50 $8.95 D 1.2 A .H . S9.95 $9. 50 $8.95 WELLER WTCPN SOLDERING STATION DIODE SPECIALS 1-99 For those who need the ultimate in connection. Essential for laser disc players to get that fantastic sound quality. Plug Cat. P10 15 1 $2.95 Socket Cat P1Qt 50 $2.25 ELECTRET MIC INSERTS With pins for easy board insertion. Cat. C10170 1·9 10+ 100 + $1.20 $1.00 S0.90 The WTCPN Features: • Power Unit 240 V AC • Temperature controlled iron , 24 VAC • Flexible silicon lead for ease of use • Can be left on without fear of damaged tips! The best is always worth having. Ca1. T1 2500 .... .... .. ... R.R.P. $149 SPECIAL, ONLY $129 THIS MONTH ON LY! SUPER DELUXE BATTERY CHARGER • Charges from 1 to 10 O, C, AA, AAA, N, and up to 3 x 9V batteries at the same time . • Dual-colour LED in first three compartments to designate 1·SV or 9V. • 240V AC/SOHz. • Approval No. N10637 Cat. M23525 ROD IRVING ELECTRONICS IS AUSTRALIA'S COMPLETE ELECTRONICS STORE. □- · ··• ~ TRIGGER TRANSFORMERS .. .. .. .... .. ... ..... $1.45 • SAVE$30 O,ECAST ,o,es D1ecast boxes are excellent for RF shleld lng, and s1'ength. ~~re ~rii;o v6dxeg ~~ eaih 14 5 5 H1 1452 110 x60 x30mm . S 6.50 H114531 20 x65x40mm $ 6.95 H 11461 120 x9 4 x53mm $11 .50 H11462 188 x 120 x 78mm ... $13. 50 H11464188x 188 x 64mm .. . $29.50 g~;S 5~ 09,s CO•NECTOR SPECIALS! • W e have just lmpoeed 50,000 . So you get to save a small fortune ! DB25 MALE (P109001 1-9 10 + $1 .00 160 + $0.90 $0.80 DB25 FEMALE (P10901) 10 + 1-9 $1 .20 l OO + $1 .00 $0.90 CANNON TYPE CONNECTORS MULTIMETER Thi s instrument Is a compact, ruaged, battery operated, hand held 31".12 digit multimeter for measuring DC and AC voltage, DC and AC current. Resistance and Diode, for 1-9 10 < P10960 3 PIN LI NE MALE . $3.90 ...................... $3.50 P10962 3 PIN CHAS IS MALE ~~:~i~i~ t~~g~~~ ~~~t~~~r.:i~~e $3.00 ...................... $2.50 CORDLESS RECHARGEABLE SOLDERING IRON • Built in solder point illumination • Easy replacement of solder tip • Protective stand which also functions as chargi ng unit • Sponge pad attach to stand • Plug pack power adaptor • Includes Nicad battery • lnstructtion manual • 12 months warranty Cat. Tt 2480 ....... Normally $79.95 P10964 3 PIN LI NE FEMALE $4.50 ...................... $3.90 P10966 3 PI N CHASI S FEMALE $4.95 ...................... $3.95 n SPECIAL, $69.95 "NO'E!RAND" DISKS !! .!~~to~.t~1~? Now you can buy absolute top qu~lity disks that are also the cheapest 1n Australi a! They even come with a lifetime warranty! So why pay 2-3 times the pnce for the same quality ? Packs of 10, DIS DID without boxes, or brand name, just their white paper jacket, and index labels. (5 V 4 " disks includes write protects) . • t ~t~a~~ti~ r~~~es without short circuit except 200 ohm Range which shows " 000 or 001 ". • ~ ~~~~Jle/oltage protection • Diode testing with 1 mA fixed current. • Audible Continuity Test. • Transistor hFE Test. SPECIFICATIONS .Maximum Display: 1999 counts SPECI AL$79 • MELBOURNE : 48 A 'Beckett St . Pho ne (03) 663 6151 NO RTHCOTE:425High St. Pho ne(03) 4898866 CLAYTON : 56 Renver Rd . Pho ne (03) 543 7877 SOUTH AUSTRALI A: Elec1, o nl c Dlscou nte,s PIL , 305 Morphett St, ADELAID E ~g~~:~~~~Js2~~/Ja~Jin1e1sta1edue 10 3800 ~Jritgi~l :i~~~ automatic Indication Method : LCD display. Measuring Method : Dual-slope in A-0 converter system . Over.range Indic ation: " 1 " Figure only in the display . Temperature Ranges: Operating OoC to +40oC Power Su pply: one 9 volt battery (006P or FC- 1 type of equivalent) Cat. 091530 Normally $109 • Rod Irving Electronics lretght costs) METEX A-D Converter uses C-MOS technology for auto-zeroing, polarity selection and over-range indication. Full overload is provided. It is an ideal instrument for use in the field, laboratory, workshop, hobby and home applications. Features ... • Push-button ON/OFF power switch . • Single 30 position easy to use rotary switch for FUNCTION and RANGE selection. • 1.12" high contrast LCD. • Automatic over-range indication with the " 1" displayed. • Automatic polari ty indication on DC ranges . . . · .. . r1:e · 5¼" DISK STORAGE 5¼" "NO BRAND" DISKS DOUBLE SIDED/DOUBLE DENSITY 10+DISKS 100+DISKS 1.000 +DISKS Efficient ant~Pa~,~ ~otect your disks from being damaged or lost ! Features ... • 100 x s ·1; 4" disk capacity • Smoked plastic hinged lid • Lockable (2 keys supplied) • High impact ABS plastic base. • Contemporary design c1so20 .. .. .... ... .. .. only $17.95 $8-95., $8·50°0 $7·80°0 (ALL PR IC ES PER 10 DIS KS ) 3½" "NO BRAND" DISKS DOUBLE SIDED/DOUBLE DENSITY 10+DI SKS 100 +DISKS 1.000+0ISKS $27 $26 $24 (ALL PRICES PER 10 DISKS) MAIL ORDER : Loca l Orders : (03) 543 7877 Interst ate Orders: (008) 33 5757 All Inquiries : (03) 543 7877 CORRESPONDENCE : P.O. B ox 620, CL AYTON 3168 Telex : AA 151938 Fax: (03) 543 2648 - MAIL ORDER HOnlNE 008 335757 ITOLLFREEJ (STRICTLY O RDERS O N LY) LOCAL ORDERS &INQUIRIES (031 543 7877 POSTAGE RATE S: $1 S9.99 .. ... $10 $24.99 $25 $49.99 $50 $99.99 $ 100 $199 $200 $499 $500 plu s $2 .00 S3.00 $4.00 $5.00 $7.50 $10.00 $1 2.50 The above postage rates are for b asic postage only. Road Freight, b ulky and f ragile Items w ill be cha rged at different rates. All sa les tax exempt orders and wholesale inquiries to : RITRONICS WHOLESALE , 56 Renver Rd , Clayton . Ph. (03) 543 2166 (3 tines) Errors and omissions excepted. Prices and specifications sub1ec1to change :~~:-:a~~s~T;n~;r~a~~en~~~~~~~~s Machines · Apple 1s a registered trademark · Deno1es registered tr admarks of th eir respective owners llla3Z rlndNI 1:131:1l1dWV 1nd1no o~o 7 en w z 0 :::c Q. C") >< 0 0 ,.... 0 ~ >< :::::, ,.... >< 0 0 C >< :::c <( ,.... 0 w Q. ~ :::::, 0 C -o/ ' 0 0 (.) w (.) + z > en :ii! :::::, ...I 0 > 0 a: (.) ~ ~ LL LL ...I :::c C, -o, ii: / ~ LL w ...I ~ :::::, cc C") Q. ,.... ~ :::::, 0 ~ 0) cc cc • • 0 0 w > w ...I z en 0~ al ,,, 0 0 N ....... 0 0 C") --//\ 0 ~ ~ 0 C") 0 N en E C 0 ii: w Q. ~ en a: :::::, a:i w 0 a: ::::, 0 a: w 3:: en Ien 0 Q. ::::, a: m w z 0 I- L LL - :c This is the full-size artwork for the front panel of the Tone Burst Source. resulting display on the CRO needs to be multiplied by 10 or 100 to give the true value. Diode D6 rectifies the signal from the amplifier and feeds it via switch S4 and its associated resistors to analog switch IC6b which, together with IC5, forms a 82 SILICON CHIP "sample and hold" circuit. Each time the sinewave signal from IC4b increases in value by 20dB, analog switch IC6b closes and feeds the rectifier output from D6 to the lOµF capacitor at pin 3 of IC5. The lOµF capacitor stores and holds the charge until the next time IC6b closes, when it takes a new voltage sample. IC5 is a CA3130 Mosfet input op amp arranged as a voltage follower. This op amp has an extremely high input impedance which means that the 10µF capacitor experiences virtually no loading at all from the op amp input. IC5 feeds the voltage from the 10µF capacitor to the output for the DC voltmeter. Diode D5 is a voltage clamp which prevents input voltages to IC6b and IC5 from exceeding + 15.6 volts. This means that for output voltages of more than about 12 .volts or so, the attenuator switch S4 should be switched from the x3 range to the xlO. The resistor values associated with DC output switch S4 are arranged so that the DC voltage at the output terminals is equal to the RMS value of the AC voltage from the amplifier's speaker terminals, when in the continuous mode. For example, in the continuous mode (ie, switch S2 set to disable the burst mode), if 20 volts RMS is fed into the AC input terminals and the DC output switch is set to xlO, the voltage across the DC output terminals will be 2.00 volts. Similarly, for the same input conditions, if the DC output switch is set to x3 , the DC output will be 6.67 volts. In the burst mode, the DC output voltage is equivalent to the music power output voltage from the amplifier. The circuit is powered from a small 15VAC transformer which feeds a bridge rectifier, Dl to D4, and a 470µF filter capacitor. The smoothed DC is regulated to + 15 volts with a 7815 3-terminal regulator. Construction We housed our Tone Burst Source test set in a standard black plastic case measuring 198 x 113 x 60mm, with most of the circuit components mounted on a printed circuit board measuring 130 x 103mm (code SC4-1-488). The power transformer and the printed board is mounted on the metal lid of the plastic case. The lid then becomes the baseplate of the instrument. All the controls are then mounted on the top of the case while most of the input and output terminals are mounted on the sides. We used a 15V 1A transformer but since the current drain of the whole circuit is low, you could save a few dollars by going to a 12.6V 150mA transformer (such as the Altronics Cat. No. MM-2006). Asse_mbly of the PCB is a straightforward job. Install the links, resistors and diodes first, followed by the capacitors and integrated circuits. All the connections to the board are made via lengths of ribbon cable. The capacitors for the burst period switch are wired around the switch itself. Note that the wiring diagram shows most of the interconnecting wires with letter codes. For example, point K on the printed circuit board is joined to point K on VR3, the headphone level control. The case can be drilled for all the controls using the Scotchcal panel as a template. Then it is simply a matter of installing all the hardware and completing the wiring. Setting up You will need a frequency meter or oscilloscope to set up the instrument. After applying power and checking the 15V supply rail, adjust trimpot VR1 to obtain a frequency of 2kHz from pin 3 of IC1. This done, check that tkHz is obtained from pin 13 of IC3, then check the sinewave at pin 7 of IC4. Trimpot VR1 can be tweaked to obtain the cleanest sinewave but make sure the lfrequency is still close to tkHz. dheck that the continuous and burst modes can be obtained at the appropriate settings of switch S2. Check that the burst length varies in accordance with the setting of switch St. Finally, the DC output at pin 6 of IC5 can be adjusted to equal the continuous RMS AC voltage (with burst disabled) from the amplifier output. This can be done by trimming the resistor values associated with switch S4. To trim the xto setting, the 1.5MO resistor can be changed or shunted with higher values to obtain the correct reading. Similarly, the x3 setting can be trimmed by changing or shunting the 20k0 resistor with higher values. ~ T-2500MFP, Philips BT137F-600 or General Electric SC142M. The Discolight ctd from page 63 So the MOC3021s provide very high voltage isolation between all the low voltage control circuitry and the 240V AC circuitry to the Triacs. In series with each IC8 output to the MOC3021s is a LED and these are mounted on the front panel so that they give an indication of the behaviour of the Triac driven lamps. Associated with each Triac is an inductor (Lt to L4) and a 0.tµF 250VAC capacitor. These two components form an RF suppression network for each Triac so that radio interference is reduced when the Triacs are in the phase control mode (for the 4-Band Modulated and Modulated settings of S4). Note that we have specified Triacs with an isolated tab so that they can be mounted directly onto the rear panel without any need for mica washers, insulating bushes and so on. The types specified are Motorola MAC218A8FP, Motorola ~~ Power supply Power for the low voltage circuitry is provided by a 12.6V transformer feeding two half-wave rectifiers, D20 and D21, and two 470µF capacitors. The resulting unregulated positive and negative rails are fed to 3-terminal regulators to give ± 12V DC supply rails. The additional toµF and 1µF capacitors connected at the output of the regulators provide decoupling and bypassing of high frequency "hash". Note that the power switch (S6) connects mains power to the transformer only and not to the Triac output circuitry. The Active AC supply lead to the Triacs is fed directly to their anodes via the 10A front panel fuse. That completes the circuit description of the Discolight. Next month we'll present the constructional information, set-up routine and troubleshooting procedure. ~ SPECTACULAR ELEASE ..-- vifci NEWSA-100 SPEAKER KIT f,:t:i1il~ Since the introduction of VIFA speaker kits in Australia in 1985, thousands of speakers have been built with superb results. VIFA is now proud to release four new speaker kits ranging from a mere $399 to $1199 per pair including cabinets. Never before have speaker kits been so popular in Australia than after the heavy devaluation of the dollar. Similar fully imported quality loudspeakers are today typically 2-2½ times more expensive. And these speakers may very well be using Danish VIFA drivers anyway, as VIFA supply more than 50 of the world's most respected loudspeaker manufacturers with drivers. But why the big savings? Because fully imported speakers suffer from 25% import duty, 20-30% freight, 30% sales tax and 28% handling charges (typically). So if you would rather put your money into better quality than in other people's pockets, VIFA 1 sp::~~:~sd~:1::~t~: ~:~~;o;~·the kits are supplied with all parts needed including fully built crossovers and pre-cut flatpack cabinets ready to assemble. No soldering or carpentry skills are needed, just a Phillips head screwdriver, some simple hand tools and a few hours of your leisure time. Are they as good as people say? Read the reviews, listen and compare with any other speakers twice the price or more. Need we say anymore? VIFA for the quality conscious audiophile. For full details please contact Sole Australian Distributor: SCAN AUDIO Pty. Ltd. P.O. Box 242, Hawthorn 3122. Fax (03)4299309 Phone: (03! 4292199 (Melbourne) (02 5225697 (Sydney) (07 3577433 (Brisbane) (09) 3224409 (Perth) Stocked by leading stores throughout Australia :-:-:-:❖:•:•:•:-. JULY 1988 83 PT.9: 15kV 16.6Hz AC IN NORTHERN EUROPE THE EVOLUTION OF ELECTRIC RAILWAYS Following the success of the Swiss with their BLS railway, Northern European countries such as Sweden and Norway began to follow suit. One notable undertaking was the electrification of the Lappland Railway. By BRYAN MAHER The Lappland line was built originally in 1885-1902, specifically to haul iron ore to the ice-free Norwegian port Narvik, and to the Swedish harbour at Luea on the Gulf of Bothnia. It became the communication lifeline for all people to the far north of both countries. Even today, this single-track line carries 67% of all Norwegian freight rail traffic. With snow-bound mountainous terrain and the need to transport coal for steam locomotives over long distances, the line presented real problems in operation. Thus, the numerous high rivers (for possible hydroelectric power generation) turned the engineers' minds towards electrification. Noting the BLS Railway's success, the Norwegians and Swedes chose to electrify the whole Lappland Line, from Lulea on the Gulf of Bothnia in Sweden to Narvik in Norway, where the Atlantic Ocean confronts the Arctic Ocean. Though geographically mostly in Sweden, this line had always been a joint effort by both countries, a shining example of peaceful cooperation. AC 15Hz system It was decided to electrify the line using a 15kV 15Hz system initially, derived from low-speed water-turbine driven alternators installed specifically for traction power. Traction was provided by series AC motors operating on convenient medium voltages between 200 and 1000 volts, provided by the highpower secondary winding of an onboard transformer. The · transformer's 15kV primary was fed by the insulated pantograph atop the locomotive, with the circuit return path being via the running wheels and rails. As with later German systems, .auxiliaries and electric lamps on the train were run from separate low-power secondary windings. Such lamps operate best on very low voltage, so that high current filaments may be used. The large thermal inertia of the heavy filament minimises the annoying, very visible flicker caused by the lowfrequency supply. An alternative was to supply lighting from low voltage batteries charged by an onboard AC/DC motor-generator set. Rod-drive locomotives lig.1: the Swedish Dm3 class triple-unit rod-drive electric locomotive is one of the most powerful electric locos in Europe. These locos operate from a 15kV 16.6Hz supply, are rated at 7.2MW and have 24 driving wheels. (Photo Sfl. 84 SILICON CHIP The locomotives used today on the Luea to Narvik line are the roddrive type illustrated last month. The Dm class are rated at 4.8MW (6434HP) and 20 of these locos were built between 1953 and 1971. The Dm3 class, of which 19 were built between 1960 and 1970, are tric train schedules to the point where hourly express trains run right across the country from Stockholm to Goteborg and also to Malmo, a journey of 619 kilometres. Early passenger electric locomotives were of the rod-drive type, such as the standard electric 1-3-1 (ie, one leading axle, three driven axles, one trailing bogie) which have quite high power efficiency. But because of their basic "singlechassis and single-axle leading bogie" design, they too are limited in speed. Bogie locomotives Fig.2: these 81-tonne capacity iron-ore wagons are used in regular 5280-tonne trains hauled by the Dm3 class locos on the Lulea to Narvik line. (Photo sn. The ASEA company of Sweden, which had been in the forefront since the beginning of electrification in Sweden and Norway, ultimately produced bogie-type electric locomotives. These were capable of higher speeds because of the shorter fixed wheelbase of the bogies compared to the long wheelbase of a rod-drive locos. Synchronous frequency changers Fig.3: a mobile rotary frequency converter used by the Swedish Railways. It converts a 6kV 50Hz input to provide a 15kV 16.6Hz 10MVA output. The 198-tonne converter wagon is at left while the equipment wagon is at right. (Photo sn. rated at 7.2MW (9652HP). These rod-drive locos are limited in speed to 75km/h but are capable of considerable tractive effort. The tripleunit Dm3 class, illustrated in Fig.l, haul 5280 tonne trains on a regular basis, although the line gradients are limited to 1 in 100 (ie, 1 % ). Centralised traffic control is used over the whole 660km length. The eight wheel wagons used (Fig.2) carry 81 tonnes of iron ore. These high efficiency trains use only 24.6 watt-hours per kilometre for each tonne of train weight, a truly remarkable performance. Being so impressed with the performance of their far northern electric railway, the Swedish Government Railways, SJ, began electrifying their complete railway system. In 1926 the StockholmGoteborg line electrification was completed, dramatically reducing the original 1862 steam-hauled running time of 14 hours. Today, passenger demand has increased in response to the fast elec- Not wishing to install special low frequency power stations all over the country (as originally provided in the far north to generate the 15Hz traction supply), the SJ used the normal 3-phase 50Hz national supply to drive synchronous motoralternator frequency conversion sets. These consist of a 3-phase 50Hz 6kV synchronous motor direct coupled to a single phase 15kV 16.6Hz alternator. The motor has three times as many poles as the alternator, so giving the frequency ratio of 3:1. Such motor-alternator units were installed at trackside substations, between two and five units per substation. The units range from 3.lMVA to 5.BMVA to lOMVA each. Substations are at varying intervals depending on traffic density. Eventually the same "50Hz motor 16.6Hz alternator" substation scheme replaced the original 15Hz Porjus power station in the Arctic. As SJ extended the electrification of the main lines, maintenance of motor-alternator sets and replacement of faulty units in rare ]ULY 1988 85 track) than does a similarly powered locomotive of the "Bo-Bo" design. Bo-Bo electric locomotives Fig.4: the Swedish electric BoBo locomotives operate in very cold conditions. Wet snow on the high-voltage (15kV) insulators is a constant problem for the engineers. (Photo sn. Fig.5: a diesel-powered snowplow at work on the Swedish Railways. (Photo emergencies prompted the idea of mobile motor-alternator sets. Accordingly a number of units were constructed, each consisting of a 12-wheel wagon carrying one 10MVA motor-alternator unit. This wagon, complete with motor-alternator and DC exciter generator, weighs 198 tonnes. Direct coupled to this wagon is an 8-wheel equfpment wagon containing a single phase transformer, high voltage switchgear and control equipment. An example of one of 86 SILICON CHIP sn. these 10MVA mobile frequency converters is shown in Fig.3. The first bogie electric locomotives were of the Co-Co wheel arrangement, meaning three driving axles in each of the two bogies. Thus each locomotive was propelled by six traction motors. Designers today realize that this basic Co-Co design, (popular though it eventually became worldwide), is heavier, more expensive and involves more friction between wheel-flanges and rail (on curved A Bo-Bo electric locomotive uses two traction motors and two driven. axles in each of two bogies. The original problem with trying to make four pairs of driving wheels produce as much tractive effort as that produced by six pairs of driving wheels boiled down to the wheel-slip limitations of steel wheels on steel rails. How that problem was solved is a story we will leave to a later episode in this series. In the mid 1950s, ASEA produced the Swedish class Rb2 Bo-Bo type, 8-wheel electric locomotive, propelled by four 825kW single phase AC series traction motors, running on the 16.6Hz supply. Rated at an armature speed of 96 to 1320 revolutions per minute and geared to a driving axle, each motor was 1.154 metres in diameter and weighed four tonnes. The total locomotive power was 3.3MW (4424HP). A similar locomotive was the Ra class of 2.64MW (3540HP), designed for express passenger service with a top speed of 150 km/hour. Ten of this class were built between 1955 and 1961. As such, they proved to be excellent for express train haulage but were too high-geared for freight service. Later SJ locomotives built by ASEA have been designed to be powerful enough for freight work but fast enough for express passenger trains. As Figs.4 and 5 show, railways and their electrical equipment in such cold countries must withstand snow, blizzards, rain and ice. At night-time it can be so cold that the track points freeze solid and refuse to move when power is applied. To prevent this, many track points have heaters installed to maintain a reliable working temperature. Altogether, throughout the SJ railway system, a total of 25MW of heating power is used to keep some 5000 track points operational. SJ system electrical figures are impressive: total electricity con- Long mountain tunnels Fig.6: a train-carrying ship en-route in the Baltic Sea between Malmo in Sweden and continental Europe. These ships have five rail tracks for passenger and freight trains and can carry up to 700 metres of train length. (Photo sn. sumption for the whole SJ system amounts to 1,530,000 MW-hours for the year, used by the 754 electric locomotives and 186 rail car sets, running over the 7063km of electrified mainlines. A total of 58 frequency converting trackside substations are in use and the system has 47 remotelycontrolled frequency converting substations. High efficiency rod-drive locos the Swedish hydro-electric power station. Very large iron ore trains ran from the mines in Sweden, westwards up and over the coastal Kongsbakkind mountain range at Riksgransen on an elevation of 550 metres above sea level, before dropping to sea level in a distance of 39 kilometres. Today, centralised track control (CTC} of signals and points allow maximum usage of this long, high, snowy mountain railway. An interesting figure is the SJ railway average W.h (watt-hours} of energy used for every kilometre travelled and every tonne carried. For the whole system the average used is 32.5 watt-hours of energy per tonne per kilometre. Compare that with the Arctic iron-ore carrying section of the railway, with the huge 72MW (9650HP} rod-drive locomotives, which use only 24.7 watt-hours of energy per tonne per kilometre. Norway electrifies Being close to the Swedish nation culturally, geographically and technically, the people of Norway also commenced electrification of their railways quite early this century. Completing electrification of the Norwegian section of the Lappland line in the Arctic between 1919 and 1923, they originally used the same 15kV 15Hz supply from Fig.7: through rain and hail and snow and ice - a Swedish electric Bo-Bo class locomotive in near blizzard conditions. (Photo sn. The Norwegian Government followed the electrification of their Lappland section with a program to electrify all main lines. This work commenced in a westerly direction from Oslo, with electrification of all main lines completed by 1970 except for the northernmost section to Bodo inside the Arctic Circle. Some very high track exists on the western line from Oslo to Bergen, and some of the tunnels reach heights of 1282 metres, comparable to the height of the Swiss Lotschberg tunnel. Other electrified tunnels, though lower in elevation, total 10.72km, close to the length of famous Swiss tunnels. Let us pause to make a comparison of AC versus DC traction, under the conditions existing between 1900 and 1930: • AC can be transformed from high voltages down to lower voltages, while DC cannot. • AC single phase high voltage low frequency supply for the overhead contact wire can be taken either straight from low frequency power station alternators or derived via transformers from still higher voltage transmission lines. • The use of high voltages on the overhead contact wire means lower current (for the same power} and thus lower voltage drop problems. • Trackside substations for high voltage AC are simple and comparatively inexpensive, consisting only of switching, protection and possibly transformers. Furthermore, these need little maintenance, occupy only small space and require no buildings or operating staff. • The engineers can select the system voltage, for optimum design of the traction motors. These points contrast with DC overhead supply railway systems (at that time} as follows: • As DC cannot be transformed, the full overhead supply voltage is used for the motors. This can be awkward as around 750 to 1500 volts appears to be optimum for motor operation. Sometimes, as in the NSW-SRA 46 class 1500V DC locomotives, pairs of traction motors are per]UL Y 1988 87 Fig.8: track maintainance on the Swedish Railways is highly mechanised to cope with the heavy workload imposed by a harsh climate. (Photo Sfl. ' Fig.9: despite electrical heating, tr-ack points require frequent maintainence in the snowy conditions. Over 5000 track points are heated to keep the system operational in cold weather. (Photo Sfl. manently wired in series and controlled as one motor. By this means, the critical voltage across one motor commutator is kept down to half the overhead line voltage, though armature slot insulation for the full voltage must be provided. • As all large power stations are AC, trackside substations for DC electric railways are required to convert the AC to DC. Though comparatively easy in 1988 using large banks of silicon rectifiers, in the 1900-1930 period the only AC-DC conversion means available were 88 SILICON CHIP rotary converters, motor converters or motor generators, each requiring costly buildings and operating and/or maintenance staff. Rotary-converters, though the most efficient of these three, require a low frequency supply, either 25Hz or 16.6Hz. Therefore, in the 1910-1930 period, the choice of either AC or DC traction demanded the provision of special low frequency alternators at the power station. (Thus Sydney and Newcastle Railway power stations generated more 25Hz power than 50Hz power). • Feasible DC traction systems are limited to 1500 or 3000 volts, resulting in higher currents in the overhead contact wire (for the same power) than high voltage systems. For example, a Swiss 6. 7MW (9000HP) loco on a 15kV system takes 450 amps running and 900 amps starting current, compared to a NSW-SRA triple-header 46-class of comparable power taking 4500 amps running and 9000 amps starting in the mountains. Therefore, DC systems require trackside substations at frequent intervals to avoid excessive voltage drop in the overhead wire. • Because of the rotary machinery used in 1910-1930, trackside substations for DC railways were expensive. Furthermore, in order to limit the voltage between brush sets around a commutator, some 1.5kV and 3kV rotary converters used the device of running pairs of rotary converters in series within the substation. So two 1.5kV machines could run in series to generate 3kV. In Argyle Substation (on the south end of Sydney Harbour bridge), two 750 volt rotary converters were used, running in series to generate 1.5kV for the electric trains. Naturally both machines had to be insulated for the full DC contact wire voltage. (These have now been replaced by large banks of silicon diodes). Two series rotary converters are more expensive and less efficient that one machine of equivalent total power. • Apart from the "pairs-ofmotors" technique mentioned above, the motor designer had to prepare the motors for the full overhead contact wire voltage. Next month we'll look at high voltage single phase railway systems in Central Europe. Acknowledgements Thanks to ASEA/Brown Boveri, SBB (Swiss. Federal Railway), BLS {Bern-Lots c h be r g-Simplon Railway), SJ (Swedish Railways), FS (Italian State Railway), and GE (General Electric Company, USA and Aust.) for data, photos and permission to publish. ~ THE ELECTRONICS MAGAZINE FOR THE ENTHUSIAST WE INVITE BECOME A You To SUPPORTER We believe that electronics is a fascinating pursuit, and the most useful hobby that anyone can have, particularly for a young person in school. Anyone with a good grounding in electronics is better prepared to meet the challenge of today's and tomorrow's technology. Because we believed that many more people should come to know about and enjoy electronics, we decided to start a new magazine expressly for electronics enthusiasts, whether they be nervous beginners or seasoned veterans. We called it SILICON CHIP, a name which focuses on the very basis of today's electronics technology. We started SILICON CHIP as an independent magazine completely free from the influence of any existing publishing company, because we wanted to establish the . highest possible standards for accuracy and attention to detail. Our team is very small: founders Leo Simpson and Greg Swain, plus full time staff members John Clarke and Bob Flynn. SILICON CHIP has now been on sale for nine months and has been very well received. Even at this early stage, you, the readers, have clearly indicated that SILICON CHIP is the most entertaining and best produced electronics magazine in Australia. Considering the hard work in getting started, it has been a very gratifying response. But we want to make SILICON CHIP even better. To do this, we need the resources to employ more people; we need the services of technical illustrators, writers, designers and other creative people. This is the only way that we can be sure of attaining the highest possible editorial standard. We know this is what you want. Your letters tell us. But we can only do this with your en.: thusiastic support. Already, many hundreds of readers have taken out subscriptions to give SILICON CHIP a solid start but we would like to have thousands more. If you haven't already done so, please give us your vote by becoming a subscriber. By doing so, you will be ensuring the future of an entertaining, informative and independent SILICON CHIP magazine. Regular Features Constructional Projects For * The Enthusiast Review * HiFi Electronics Course * Digital Circuit Notebook * Vintage Radio * Junk Mail The Serviceman's Log * Amateur Radio, by Garry * Cratt, VK2YBX The Way I See It, by Neville * Willams * Book Reviews Most magazines sell their subscriber list to mail order companies, to earn extra income. We will not do this. We will lose some money by adopting this policy but we believe that your privacy is paramount. BECOME A SUPPORTER BY FILLING OUT THE POSTAGE FREE SUBSCRIPTION COUPON OVERLEAF ► JULY1988 89 FREEPOST SUBSCRIPTION COUPON BACK ISSUES To: Freepost 25, Silicon Chip Publications, PO Box 139, Collaroy Beach, NSW 2097, Australia. NO POSTAGE STAMP REQUIRED IN AUSTRALIA NAME (Mr/Mrs/Ms) ........... ................ ........................................................ . STREET ...................................................................................................... . SUBURB/TOWN ............................. ............................. POSTCODE ............ . Subscription cost: 1 year (12 issues) 2 years (24 issues) Within Australia D $42 D $84 Overseas surface mail D $62 D $124 Overseas air mail D $120 D $240 Enclosed is my cheque or money order for$ ........... or please debit my □ Bankcard □ Visa Card Card No ........................ .............................................................................. . Signature ..................................................Card expiry date ...... ./ ......./ ...... . Subscription to commence in ....................................... ........................... •••• GIFT 1 to: NAME (Mr/Mrs/Ms). ....................................... .......................................... .. Issue Highlights STREET ............ .. ......... ......... ....... .... ........................................................... . March 1988: Remote Switch for Car Alarms; Telephone Line Grabber; Low Cost Function Generator; Endless-Loop Tape Player. SUBURB/TOWN ...... .... ....... ......................................... POSTCODE ............. Subscription cost: 1 year (12 issues) 2 years (24 issues) Within Australia D $42 D $84 Overseas surface mail D $62 □ $124 Overseas air mail D $120 D $240 Enclosed is my cheque or money order for$ ........... or please debit my □ Bankcard □ Visa Card Card No ....................................................................................... ............... . April 1988: Walkaround Throttle for Model Railroads; pH Meter for Swimming Pools; Slave Flash Trigger; Mobile Antennas for the VHF and UHF Bands. Signature ................................................. .Card expiry date ...... ./ ...... ./ ...... . Subscription to commence in ....................................................................... May 1988: Optical Tachometer tor Aeromodellers; High Energy Ignition for Cars; Ultrasonic Car Burglar Alarm; Restoring Vintage Radio Receivers. GIFT 2 to: NAME (Mr/Mrs/Ms)......................................... ...... ........................... ......... . June 1988: Stereo Control Preamplifier; Breakerless Ignition For Cars; Automatic Light Controller; Mega-Fast Nicad Battery Charger. STREET ..... ........................................ ......................................................... . SUBURB/TOWN ....... ........................ .......... ................. POSTCODE .... ......... Subscription cost: 1 year (12 issues) 2 years (24 issues) Within Australia D $42 D $84 Overseas surface mail D $62 D $124 Overseas air mail D $120 D $240 Enclosed is my cheque or money order for$ ........... or please debit my 0 Bankcard D Visa Card Price: $5.00 each (incl. p&p). Fill out the coupon on page 92 (or photostat copy or letter) and send it to: Silicon Chip Publications, PO Box 139, Collaroy Beach, NSW 2097. a Card No ........ ........................................ .... ................ ........ ........ .. ................ . LIMITED NUMBERS OF BACK ISSUES ARE AVAILABLE SO DON'T DELAY Signature ................... ............................... Card expiry date ...... ./ ....... /...... . Subscription to commence in ... .................................................................. . Note: photocopy this coupon if you don't wish to cut the magazine, or include the relevant details in a letter. 90 SILICON CHIP W at ---------1 IPRODUCT SHOWCASE I Keep a record of your phone calls When you receive your phone bill, have you ever wondered whether you did make all those calls? Tandy's CPA-1000 computerized phone accountant may help solve that problem. The CPA-1000 is plugged across your phone line, via a parallel socket, and is powered with a 9V DC plugpack. From then on, whenever you make or receive a call, the GPA-1000 records the details. It records the number dialled, time, whether or not you were transferred and the time you hang up. It even records the time the phone was off the hook and how many incoming calls were not answered. All these details are Fuel cut-off solenoid the ignition, the fuel solenoid will be automatically energised next time the car is started. Fig.3 fixes that problem. Fig.3 works as follows. If the ignition is turned on and S1 is open, diode Dt will conduct to energise the buzzer and also charge the 2200µF capacitor. The buzzer current will pass through the solenoid but will not be enough to energise it. When S1 is closed, the solenoid will be energised and the buzzer will stop. When the ignition is turned off, the 2200µF capacitor discharges and briefly sounds the buzzer. This acts as a reminder to turn off the fuel solenoid. l!til available on the printout, which is produced at 11.59 each night. Backup batteries (4 AA cells) keep the unit operational if the power fails. The unit also has internal protection circuitry to guard against voltage surges on the mains or phone lines. For anyone wanting to keep a record of their telephone calls the CPA-1000 is an easy machine to operate. It is available from all Tandy stores at $299.95. Large breadboard for computer peripherals These large breadboards are getting to be a bit of a worry aren't they? Maybe in the future they'll be so large we'll have to set up bigger workbenches. In the meantime, we were impressed with this one which comes with four base sockets (64 pins long) and six accompanying bus sockets. These allow you to breadboard one very large prototype circuit or several smaller circuits. It also has male and female RS-232 (DB-25) connectors which can be connected across to the base sockets via bridging wires. As well, there are four binding post terminals and a removea ble vertical plate on which can be mounted a variety of pots and switches. This plate can be mounted adjacent to the RS-232 connector panel or at one end of the breadboard. Designated the IIB-46, the breadboard is priced at $92.48 and is available from David Reid Electronics, 127 York Street, Sydney, NSW 2000. Phone (02) 267 1385. The original and best nibbling tool ctd from page 14 Although the fuel cut-off solenoid can be installed in the engine compartment, it should ideally be hidden from view underneath the vehicle. How many chassis have been cut out with these tools in the past? They save money on more expensive notching tools and dies which only sheetmetal shops can afford and strengthen your wrists at the same time. The original nibbling tool was made by Adel Tool Co, Chicago, US but most nibbling tools sold in Australia in recent years would have come from Taiwan, because of the cheaper currency. Now in an interesting twist, the currency of south east Asian countries has risen against the Australian dollar while the US dollar has now fallen. So the JULY 1988 91 Did you miss these issues? original Adel nibbling tool is again available. It is suitable for steel up to 18 gauge or 1.2mm thick (you need strong wrists for much of that) or aluminium up to 1.5mm. It can also be used for notching printed circuit boards and plastic panels. Priced at $29.95, the Adel nibbling tool is available from all Jaycar stores. They also have the replacement punches available - handy if you have an old original model. Sanyo Video 8 camcorder from DSE Issue Highlights November 1987: Car Stereo in Your Home; 1GHz Frequency Meter; Capacitance Adapter for DMMs. December 1987: 1 00W Power Amplifier Module; Passive lnfrared Sensor for Burglar Alarms; Universal Speed Control and Lamp Dimmer; 24V to 12V DC Converter February 1988: 200 Watt Stereo Power Amplifier; Deluxe Car Burglar Alarm; End of File Indicator for Modems; Simple Door Minder; Low Ohms Adapter for Multimeters. March 1988: Remote Switch for Car Alarms; Telephone Line Grabber; Low Cost Function Generator; Endless-Loop Tape Player. April 1988: Walkaround Throttle for Model Railroads; pH Meter for Swimming Pools; Slave Flash Trigger; Mobile Antennas for the VHF and UHF Bands. May 1988: Optical Tachometer for Aeromodellers; High Energy Ignition for Cars; Ultrasonic Car Burglar Alarm; Restoring Vintage Radio Receivers. June 1988: Stereo Control Preamplifier; Breakerless Ignition For Cars; Automatic Light Controller; Mega-Fast Nicad Battery Charger. Price: $5 .00 each (incl. p&p). Fill out the coupon below (or a photostat copy or letter) and send it to: Dick Smith Electronics have entered the consumer video field and are now stocking the Sanyo Video 8 recorder which is a very compact example of the art weighing in at just 1.27kg. It has auto focus, backlight compensation, 6x zoom and can work in ambient light down to as low as 9 lux. Another video item in the DSE video range is the Sanyo Digital Picture VHS recorder which can display up to nine video frames on the screen simultaneously and provide a number of other high-tech effects. Price of the Sanyo camcorder is $2499 while the VHS digital recorder is $1499 . They're available at all DSE stores. SILICON CHIP, PO Box 139, Collaroy Beach, NSW 2097. Ultra-miniature relays Please send me a back issue for D November 1987 D December 1987 -El de:i,1:1aF~1 rnaa (Sold Out) D February 1 988 D March 1 988 D April 1 988 D May 1 988 D June 1 988 Enclosed is my cheque or money order for $ .. ...... or please debit my D Bankcard D Visa Card Name ... ..... ... ... .. .... ............. .. .. ....... ...... .......................... ...... ...... ... . Address ................. ... .. .. .......... .............................. .................. ..... . Suburb/town .. ..... ..... ........ ... ........... .... ........ ... ... Postcode ......... ...... . Card No ........... ..... .... ...... ..... ..... ... ... .... ... ...... .... ..... .... ............... .. .. . Signature ... ..... ... ... ....... .... ................ Card expiry date ...... ./ ...... ./ ...... . ~-----------------------~ 92 SILICON CHIP Three new series of miniature relays by Potter & Brumfield are now available from Tecnico Electronics. Series T81 have gold clad SPDT contacts designed to handle 1 amp .at 24V DC or 0.5 amps at 120VAC, with resistive loads. Standard or sensitive coils are available over the range from 1.5 to 24V DC. Series T82N have DPDT contacts and will fit in a 16-pin DIP socket. Contact rating is up to 2 amps (voltage unspecified). Series T84 are intended for telecommunications use. They can withstand 1000V RMS between open contacts and have standard or sensitive coils available in standard DC voltages from 3 to 48V. For further information, contact Tecnico Electronics, 11 Waltham Street, Artarmon, NSW 2064. Phone (02) 439 2200. Mouse for IBM PCs or PC-compatibles Many programs these days call for a mouse to move the cursor, select commands from a menu and so on. This unit is intended for use with IBM PCs or compatibles and is plugged into the RS-232 port. It has the usual heavy silicone ball to roll Mailbag continued from page 3 recommends or requires the states' 25 supply authorities to carry out routine inspection of the consumer's neutral and earth connections. (2). There is no basis at this time for the development of a policy requiring routine inspections of the neutraU earth connections associated with the MEN system. It is further pointed out that domestic electrical installations are frequently extended or altered in order to accommodate additional electrical equipment. It is not uncommon for the neutraUearth connection to be effectively checked in such situations where the overhead service, meter or main earthing systems are affected. (3). The 'nuisance shock' factor was known when the MEN system was first introduced into common use. The nuisance shocks reported to this Department are both low in shock around on a hard bench surface and three pressbutton switches. It is well made and supplied complete with a test floppy disc. hazard and incidence. Notwithstanding this experience, the changing environment has seen that the requirements for equipment associated with the earthing system have been modified in a number of ways since the adoption of the MEN system. These include the use of an earth electrode, the duplication and improved design of connectors used at the attachment of the aerial service to the dwelling, and the deprecation of aluminium as a conductor for consumers' wiring. I trust this information will further clarify this matter. N. C. Watson Secretary NSW Department of Energy. Unfortunately, you still miss the point. The thrust of our November article was that old MEN installations are becoming hazardous with the passage of time. They do not have the benefit of the third electrode introduced since 1976. They are priced at $124.95 from David Reid Electronics, 127 York Street, Sydney 2000. Phone (02) 267 1385. SERMOTECH COMPUTER SERVICES SERVICING MODERN TECHNOLOGY TELEPHONE (02) 689 3327. SHOP 1,114 MACQUARIE STREET, PARRAMATTA 2150. HARDWARE COMPUTER MONITORS Composite TTL Dual Scan Hi Res White EGA 14" Multi Scan VIDEO CARDS CGA Here Mono/Gr Mon/Col Auto EGA Auto PGA 640x480 FLOPPY DRIVES Teak 360K Teak 1.2MB DRIVE CAi:IDS 360k/1.2MB Card for XT Multi I/O STAR PRINTERS NX1000 NX 1000 Col ND 15 NR 15 STAR RIBBONS NX 1000 NX 1000 Col NB 15 $ 199 199 255 289 828 1080 $ 99 123 173 317 396 $ 180 216 $ 79 55 130 $ 489 586 936 1080 $ 13.50 26.50 24.50 HARD DRIVES Seagate 20MB Miniscribe 20MB 85m/s 40MB 60m/s 44MB 28m/s MOTHERBOARDS XT 10MHZ AT12MHZ 386 20MHZ NETWORKING 0-Link Card Netbios Soft CABLES IBM Printer Serial 25x25 Serial 9x25 Mac Plus Adpt Any Cable Made Up CONNECTORS OB9PorS DB15PorS D825 P or S IDC 26 S JOYSTICKS IBM Commodore Deluxe PERIPHERAL & $ 468 569 778 1288 $ 195 684 2520 $ 499 195 $ 24 24 24 14 $ 1.60 1.95 1.99 2.99 SUPPLIERS COMPUTER SYSTEMS $ ASI XT (10MHZ) - 640k - 2x360k Drives - Multi 1/0 Port Monochrome Monitor Above System with 20MB HO Clk/Cal - ASI XT (10MHZ) - 640k Multi 1/0 Port RGB Colour Monitor Clk/Cal - 2x360k Drives - RS232 1699 2299 RS232 2138 ASI AT (6/8/12MHZ) - 640k Ram - 2x1 .2MB/360k Drives - Serial/ Par Port-Juko Auto switch Mono/Col Card-Dual Scan Hi Res White Monitor Above System with 20MB HO 2399 2999 ASI Computers are being used by Newcastie University (140) , Brokers, Channel 9, Museum Of Arts & Sciences, and many other discerning groups. MODEMS Avtek Avtek Avtek Avtek $ 195 350 429 429 Mini Modem with Phone Megamodem 12 Megamodem PC-IN-MODEM Megamodem 123E BRAND DISKETTES $ 16.00 39.00 S Y," DS DD (10) 3Y," OS OD (10) $ 29.00 25.00 BANKCARD & MASTERCARD WELCOME • MAILORDER • ALL PRICES SUBJECT TO CHANGE WITHOUT NOTICE WRITE OR PHONE FOR PRICE LIST JULY 1988 93 ASK SIUCON CHIP Got a technical problem? Can't understand a piece of jargon or some electronic principle? Drop us a line and we'll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097. Wants info on old oscilloscope Like J. Sweet in your January 1988 edition, I was lucky enough to obtain a piece of valve equipment from a friend who knew it was going to the tip. It is a Solartron 3-1/2 inch dual channel oscilloscope, Solarscope model CD1014-2. I have been unable to obtain any documentation regarding its circuit operation and diagrams. Replacing several of the 6DJ8 (ECC88) valves and capacitors restored operation of the vertical channels but unfortunately similar success was not achieved in the timebase. Feeding a sawtooth wave into the horizontal amplifier shows that the stages beyond the timebase generator are all functioning correctly. Are you aware of anyone who knows something about these old oscilloscopes? With the facilities that a CRO, even of this vintage, offers for the home constructor, I am How to kill an amplifier I built your 100W amplifier module as described in the December 1987 issue and made the unforgiveable mistake of wiring the power supply back to front (ie, positive rail to negative input and vice versa). Two 1000 resistors immediately fizzled (though they still seem OK) but after realising my mistake I cannot measure any voltage across the 5600 resistors. I assume I've blown the output transistors or would I have blown the lot? Is there any easy way to check transistors or should I just buy a new set? (M.R., Wynyard, Tas). • We sympathise with you over your mistake with the amplifier module. Still, perhaps all is not 94 SILICON CHIP keen to get the instrument back into working order. (Paul Killeen, 40 Aldershot Drive, Keilor Downs, Vic. 3038}. • We have published your name and address, as requested, in the hope that readers may be able to help you. Loves the 100 watt amplifier module I hav~ just recently completed your excellent 100 watt module and was quite surprised at the result. As I have only very limited electronic knowledge and experience, I found it very pleasing to construct. Your circuit design and PCB layout were so clearly detailed that construction was a simple task. To my astonishment (this being my first big project}, the amplifier worked first time. I have used the amplifier as a guitar unit and have connected it with a guitar preamp, also built from a kit. The clean sound of the lost. We have not had experience with this sort of ·problem and it is just possible, because you had the 5600 limiting resistors in place (you did, didn't you?), that no major damage has been done. Maybe that's a fond hope but don't despair, you might get away with just having to replace the small signal transistors. It is possible to check out all the transistors using your multimeter switched to a low ohms range (or a diode range if you have it). The idea is to check whether each junction functions as a diode. Accordingly, the base-emitter junction should show conduction in one direction and none in the other; so should the collector base junction. If there is a low resistance between collector and emitter, the transistor has "pun- amplifier is really remarkable compared to another guitar amplifier I have of the same power rating. Just to satisfy my curiosity, there are a few points I hope you can help me with. All voltage tests were within 10% of the values specified on the circuit. The only difference was at the output where I measured 3.8 millivolts. Have I used the wrong measurement points, read the meter wrongly, or is it acceptable? Also, would repositioning of the 6.BµH choke have any effect on the voltage? Because of the larger diameter of the choke supplied in the kit, I couldn't position it as shown in your photo. I had to stand it on edge. If the output voltage is incorrect, would it have any affect on the output performance? When compared with the other amplifier I have, it is not quite as loud. Is there anything I can do about this? (D.W., Capalaba, Qld). • Congratulations, your amplifier ched through". These checks can usually be made without removing the transistors from circuit. The checks are not foolproof but are a good start. Another guide to see if major damage has been done is to apply power (with 5600 limiting resistors in place) and measure the voltage at the output of the amplifier. If the voltage is close to zero and there is no smoke it would suggest that the amplifier is functioning more or less as as it should. Check all the voltages on the circuit. If you can't adjust the quiescent current up from zero there is a strong chance that Q7, the Vbe multiplier, is short circuit. You can confirm this by measuring the voltage between its collector and emitter. If it is zero, Q7 is dead. is operating as it should. The 3.8mV DC voltage you've measured at the output is within (ie, less than) the figure of ± 30mV we specified in the article. Nor is the orientation of the output choke critical so you have nothing to worry about as far as the amplifier's performance is concerned. It is possible that your guitar preamp was intended to drive a power amplifier with more sensitivity, which could explain why your new guitar amplifier does not sound quite as loud as your old one. This can be fixed by increasing the gain of the 100W module. To do this, reduce the lkO resistor connected to the base of Q3 to 5600. This will almost double the module's sensitivity. Don't reduce the resistor any more though otherwise amplifier stability might be a problem. Wants polycone loudspeaker system I'd like to see a speaker project using the cheaper polycone speakers which seem to be readily available. Those from Europe are getting a bit expensive now. Also a few photography projects please. I intend building the Studio 200 stereo power amplifier in the near future. Is there any errata on it? Keep up the good work. (P.G., Orient Point, NSW). • We have checked out a number of polypropylene speakers since we started and have found them generally disappointing and certainly not good enough to make a good speaker system. At the moment we have a good woofer and quite a good midrange and tweeter in the workshop. The only problem is that the woofer is 6dB more efficient than the midrange and tweeter. That's a pretty insurmountable problem. When we do come up with the right combination, we will publish the results. Your request for photographic projects is noted. Design info for dedicated ZBOA I wish to build a dedicated microcomputer system based on the Z80A but I can't find the necessary information on it and the Z80 PIO, SIO, CTC, DMA and DART. I won't be using all these chips but I would like information on them all. If you have the data could you send me copies of it or could you tell me where to find it? I also need to know how to program EPROMs. I would also like a course that helped teach the required information to gain an amateur radio licence. (A.R., St George, Qld). • Obtaining all the data you will need for your Z80A project will not be easy - we are certainly not in a position to supply it. The Australian distributors for Zilog are the George Brown Group and they would certainly be able to supply comprehensive data on the Z80 and Amcron power amplifier - ctd from page 17 and 40; never mind the 10 condition. We did confirm enough of the amplifier's specs though to be able to state that this amplifier is a real performer. Its typical harmonic distortion, at just before the onset of clipping, is just .002 % . And the signal to noise ratio was + 104dB Aweighted with respect to 300 watts into 80. These are very respectable figures for any amplifier. What we can't say is how well it performs under gruelling " on road" conditions. But based on our examination of the construction, its low voltage bridge-connected amplifiers and our limited benchtesting, it must be one of the most conservatively rated amplifiers around. Amcron must be confident in its reliablity as they give an unlimited transferable 5-year warranty on all performance specs; and that even covers freight costs. Recommended retail price is $2802. At that price, it must be just about unbeatable for value too. In short, it's a winner. For further information, contact Bose Australia Inc, 11 Muriel Avenue, Rydalmere NSW 2116. Phone (02) 684 1255. (R.F.& L.S). ~ related products. Their phone number in Sydney is (02) 519 5855. However, just having the data might not be enough info for the project you are considering. We suggest that you also consider buying a number of texts on the subject, such as the Z80 Microcomputer Handbook or Z80 Microcomputer Design Projects. Both these texts are available from Jaycar at $24.95 and $25.95 respectively. These texts will also tell you something of EPROMs. You can also obtain a handy chart on the Z80 containing the full instruction set, ASCII, hex and decimal conversions, interrupts, , disassembly table etc from Jaycar for $12.50. Obtaining info on becoming an amateur radio operator is easier. Contact the Wireless Institute of Australia, PO Box 300, Caulfield South, Vic. 3162. Notes & Errata Remote Switch for Car Alarms, March 1988: the inductor marked 12 in the receiver should have an F29 slug, not F16 as specified. PRODUCT SAFETY RECALL DICK SMITH PTY. LTD. ■ L■ CTRONICS NOTICE TO CUSTOMERS BEAT TRIGGERED STROBE KITS Cat No. K-3153 sold In component form for customer construction have been sold in all states and may, If proper safety procedures are ignored, constitute a serious risk when constructed, as the power switch supplied with some kits is incompatible with the wiring diagram. Customers are asked to return this product, whether or not assembled, as a matter of urgency to the nearest Dick Smith Electronics store for Immediate attention to the problem. We apologise for any inconvenience caused. Further enquiries may be made by contacting Rex Callaghan, Technical Service Division (02) 888 3200 or your nearest Dick Smith store. JULY 1988 95 CENl Cash in your sutplus gear. Advertise it here in Silicon Chip. Advertising rates for this page: Classified ads - $7.00 for up to 15 words plus 40 cents for each additional word; Display ads (casual rate) - $20 per column centimetre (max. 10cm). Closing date: five weeks prior to month of sale. If you use a PO Box number, you must include your permanent address and phone number for our files. We cannot accept ads submitted without this information. To run your own classified ad. put one word on each of the lines below and send this form with your payment to: Silicon Chip Classifieds. PO Box 139, Collaroy Beach. NSW 2097. PLEASE PRINT EACH WORD SEPARATELY, IN BLOCK LETTERS 2 3 4 5 6 7 8 9 10 11 12 13 14 15 ($7.00) 16 ($7.40) 17 ($7.80) 18 ($8.20) 19 ($8.60) 20 ($9.00) Name .......... .......... ... ... .... ... ....... ... ... ... ...... ..... .... ..... .. .. ....... ....... .... ... ............... .. ... . Address ..... ............. ..... ......... .......... ...... ..... ..... ..... ..... ... ............. ........ ..... ........... .. .. Suburb/Town ............ .......... ...... ......................... .. ..... .. ...... Postcode .............. .. Enclosed is my cheque or money order for$ ...... ....... .. .... ..... ....... .... .. or please debit my Bankcard D Visa Card D Card No ....... ...................... .... ... ........... ...... ..... ..... ... ....... ..... .......... ... ..... .. ....... .... ... Signature .. ... .......... ........... .. .. ..... .... .... ... . FOR SALE NEARLY 1500 PRINTER buffer kits now sold. Prices start at $39 for a 256K short form kit. All items advertised are in stock. Dealer enquiries welcome. Bulk discounts. Schools, Govt. Depts. orders accepted. Oh yes!! IBM compatible. Australian designed and manufactured. Ideal project' for user groups and students. For a free catalog send a 37c stamp to: Don McKenzie, 29 Ellesmere Crescent, Tullamarine 3043. KIT FIX SERVICE - Having trouble getting your EA/ETI/SC kit to work? Phone (03) 7 49 3480 for estimate or send kit to K. Hunter, 5 Yatama Crescent, Werribee 3030 . OATLEY ELECTRONICS - here we list some more of our kits. Ultrasonic Burglar Alarm (SILICON CHIP, May 1988): this unit features a quality crystal locked ultrasonic movement detector. Can be used as a detector only or as a self-standing alarm. Has provision for bonnet and boot wiring. 96 SILICON CHIP Advertisers Index Our advertisers are vital to the success of SILICON CHIP. Please give them your support. Altronics ............... .... ..... 52-55 Arista Electronics ..... .. .... .. .... 21 Avtek .. ... ... ........................ IBC Bose ........ .. .... ......... .. ......... 39 David Reid ..... ............. ........ 1 5 Dick Smith Electronics ........ 8,9, 68,69,95 Geoff Wood Electronics .... .... 77 Jaycar Electronics .......... 22-29 J.V. Tuners ......................... 38 Kenwood Australia ............ OBC Oatley Electronics .......... 37,96 RCS Radio .... ...................... 21 Rod Irving Electronics ..... ...... 81 Scan Audio .. .. ............... .... .. 83 Sermotech .. .. ...................... 93 Tandy Electronics .... ........... IFC PC Boards Printed circuit boards tor SILICON CHIP projects are made by: Optional flashing light and back up battery operation. Easily connected to our UHF Remote Key. You don't even need the relay supplied with the UHF kit, however you can use it for the blinker flashing or perhaps for switching a high power siren from the ultrasonic alarm. Prices are as follows: PCB plus onboard parts $25 .90; optional light flasher/back up battery circuit $7 .50; pair of transducers $13.50; transducer mounting kit $2.50; piezo screamer $16.00; 1.2Ah gel battery $24.90; relay kit $3.80. Add $2.50 p&p ($4.00 p&p tor battery). Shock Detecting Car Alarm (ETI, March 1988): has low level vibration detector to detect gentle knocks. Flashes the car's blinkers and sounds the horn twice. Has high level detector that activates the full alarm period . Provision tor activation from existing door switches or additional bonnet/boot switches. Has provision tor external detectors. Can be wired into an existing alarm in order to add vibration detection, blinker flashing and/or pulsed horn sounding. Two heavy duty relays for blinker/horn provided. An incredibly versatile unit! PCB and • RCS Radio Pty Ltd, 651 Forest Rd, Bexley, NSW 2207. Phone (02) 587 3491. • Jemal Products, 5 Forge St, Welshpool, WA 6106. Phone (09) 350 5555. • Marday Services, 2139 Great North Rd, Avondale, Auckland, NZ. Phone 88 5730. components kit at only $32.95 plus $3.00 p&p. The Untouchable Bike Alarm (ETI, May 1988): this small and totally selfcontained alarm is simply firmly attached to the object you wish to protect. Use it tor your bicycle, motorbike, boat trailer etc. Triggered by vibration. Single barrel key operation. Negligible battery consumption means that the battery can last for up to its full shelf life. Can drive piezospeakers, piezo buzzers, relays, speakers and piezo screamers. Doubles up as simple vibration detector. PCB and components kit at only $14.95; piezo buzzer $2.70; piezo screamer $16.00. P&p $2.50. For address and ordering procedure see our advert on page 37. MODEMS Don>t buy imported unsupported The Avtek advantage • Australian designed Australian manufactured Australian supported MEGAMODEMS 12/123 The Avtek Megamodems provide Australia's best value communications products, with a range of fully automatic, autodialling modems. Megamodems are suitable for data transfer from personal computers, terminals, mainframes and mini host computers and for all videotex services such as Viatel. The use of the latest technology has enabled us to make the Megamodem more compact and reliable than any other modem. Price is very competitive and reflects efficiencies incorporated in the design. The Megamodems are locally designed and built. Service, support and specialist R&D for the Megamodem range is all based in Australia. Available either as a standalone RS232 model or as a plug in 1/2 card for IBM PCs and compatibles. The Megamodem range of modems are Telecom authorised. Specifications Data Rates MAIL ORDER WELCOME Fully Hayes AT Smartmodem Compatible: The Megamodems are industry standard ''HAYESSMARTMODEM "compatible which means they can take advantage of all the communications facilities of packages such as Crosstalk, Open Access, Symphony and Multicom. All communications parameters such as baud rate, parity and number of stop bits are set up automatically by the software and the Megamodem. Using appropriate software data can be sent and received while the Megamodem is unattended. l■ -c~ VISA Automatic Dial, Answer, and Disconnect: The Megamodems will automatically answer an incoming call and connect the computer to the line.When originating a call it will then dial out the required number and auto-connect to the computer at the other end. It will then "hang-up" at the end of a communications session. Both pulse and tone dialling are supported. The modem Is compatible with new Telecom exchanges and modern PABXs and can handle high speed tone dialling, CCITTV21, Bell 103, CCITT V22 Bell 212. (123 model only CCITT V23) 300/300, 1200/1200 (123 model only 1200/75, 75/ 1200) Data Standards BUY DIRECT FROM THE MANUFACTURER Model 12 & PC12 $375nctax Model 123 & PC123 $449nctax r~--L~!_;·~·-=CJ =-~vTrl( I ~J ~, PO Box 651 Lane Cove 2066 Telephone (02) 888 5533 Facsimile (02) 887 2839