Fullscreen HTML5Med Res (??MB)HTML4

16-Channel Mixing Desk, Pt.3 In this third article on our new 16-Channel Mixing Desk, we present details of construction. All told, there are 2 3 circuit boards to be assembled: 16 preamplifier boards, 2 effects boards, 4 equaliser/VU boards and one board for the power supply. By JOHN CLARKE & LEO SIMPSON This mixer is a very big unit to assemble and so it is wise to proceed slowly and carefully. Don't barge in and start assembling all 16 preamplifier boards at once. If you do it that way, you are likely to duplicate your mistakes 16 times. To avoid that sort of debacle, we suggest you first assemble and test one of each of the boards. That way, you will presumably make mistakes only once. Furthermore, we suggest that every board is assembled and tested before it is mounted on the mixer panel. This will avoid the frustration of removing any defect board for repair. If you have a power supply which can deliver ± 15V, you can test the preamplifier and effects boards. To test the 5-band equaliser/VU boards you will need an additional power supply which can deliver + 5V. If you don't have power supplies with this capability, you will need to assemble the mixer power supply before any board testing can be done. The LEDs on the equaliser/VU meter hoards are aligned by mounting them on a jig and then gluing a 105 x 3mm strip of aluminium to them. The LED leads are then soldered to Molex pins on the PC hoard. 72 SILICON CHIP Therefore, our suggested assembly procedure is this: assemble one of each of the boards, including the power supply board. You can then complete the power supply and use it to test each of the three signal boards so far assembled. That done, learn by your mistakes and proceed to assemble and test the remaining 19 boards. Ideally, to do the testing you will need a digital multimeter. An audio oscillator is essential for verifying the boost and cut of the equaliser controls and the response of the VU meters. Now let's assume that you have the required power supply and so can go straight to assembling the signal boards. Assembling a preamplifier board The first step in assembling any board is to carefully inspect it for defects. Are all the holes correctly drilled? Are there any shorts between tracks or any breaks? If there are any defects, they should be corrected before proceeding further. This done, insert the PC pins at each end of the board. These are essential for making connections to the boards. Check the component overlay diagram of Fig.6 to see the number of PC pins required. There are 13 PC pins at the selector switch (S1) end of the board, including two for LED 21. At the other end of the board, there are 11 PC pins. Next, install the small polarised components: the three diodes (Dl, D2 & D3) and the two transistors (Ql & Q2). By installing these polarised components at this early stage, into an uncluttered board, it is easier to see that they are correctly inserted. Using the same thinking, bung in the electrolytic INPUT ATTENUATOR VR1 TREBLE VR4 10kHz VR18 BALANCED LINE OUTPUT (TO CH1 OUTPUT SOCKET) MIO VR3 J.5kHz VR17 1kHz VR16 PAN VAS 240Hz VR15 EFFECTS VAT 60Hz VR14 FOLDBACK VAS 0 ~ ~ 2 3 .,"' TO CH2 HEADPHONE OUTPUT a ~ CH1 BUS TO INPUT 2, S2 • al cl i= CH2 BUS TO INPUT 2, S2 EFFECTS BUS TO INPUT 2, S2 FADER VR6 0 0 Fig.6 at left shows the parts layout for a preamplifier PCB while Fig.7 (above) is the parts layout for an equaliser/VU board. APRIL 1990 73 TABLE 1: CAPACITOR CODES Value D D D D D D D D D D D D D D D D D D D D D D D 22pF 33pF 39pF 100pF 150pF 220pF 330pF 560pF .0012µF .0015µF .0027µF .0047µF .0058µF .01µF .012µF .015µF .018µF .022µF .047µF .082µF 0 .1µF 0 .18µF 0.22µF Alt Value IEC Code EIA Code (10%) 1.2nF 1.5nF 2.7nF 4.7nF 5.6nF 10nF 12nF 15nF 18nF 22nF 47nF 82nF 100nf 180nF 220nF 22p 33p 39p 100p 150p 220p 330p 560p 1n2 1n5 2n7 4n7 5n6 10n 12n 15n 18n 22n 47n 82n 100n 180n 220n 22K 33K 39K 101K 151K 221K 331K 561K 122K 152K 272K 472K 562K 103K 123K 153K 183K 223K 473K 823K 104K 184K 224K capacitors now. There are 8 in all. Make sure they go in the right way .a round. Next come the links and resistors. The links are easy. Cut them to length out of tinned copper wire and solder them in. Resistors are next. Use your digital multimeter to check each value before it is installed. Remember that the 1 % resistors will have 5 colour bands and the last (tolerance} band is brown. The capacitors are next to be installed. These can be labelled in a variety of ways, so we have listed the IEC and EIA codes for all the non-electrolytic capacitors in the mixer. So before installing each capacitor, check its coding against Table 1. The trimpot and the 5 ICs are next. Note that all five ICs are oriented in the same direction; ie, the dimple faces up to the end where the two 33µF capacitors are. The overload LED (LED 21} is soldered to two PC stakes at the end of the board. Its leads should be bent at rightangles close to the LED 74 SILICON CHIP body and soldered to PC stakes so that the LED stands 19.5mm above the PCB. By the way, our prototype preamp boards had the overload LED fitted to flying leads, as you can see from the photo published last month. Subsequently, we modified the boards so that flying leads weren't necessary. Potentiometers Before installing the 7 pots, their shafts should be cut to a length of 10mm. File any burrs off the shafts so that the knobs will go on easily, when they are finally fitted. The locating tabs on each pot should be bent as in the photo so they do not foul when the board is ultimately installed onto the mixer control panel. Solder in each of the pots and then clip off their lugs which protrude from the copper side of the board. This will prevent the leads from shorting to the pot bodies on the adjacent board (when they' re mounted on the mixer panel}. Finally, check your work careful- ly against the component diagram of Fig.6 and the circuit diagram of Fig.2 , published last month. You should then proceed to the section on testing or to the next board to be assembled. Assembling an equaliser/VU board Again, check the board carefully for missed holes and any etching defects before installing any components. Note that this board has one end cut at an angle to ensure clearance from the chassis when it is in place. The component overlay diagram for this board is shown in Fig.7. From here on in, follow the same general order of assembly that we suggested for the preamplifier board above. That means PC pins first, then diodes (D4, D5 , D6 and D7}, transistors (Q3, Q4} and electrolytic capacitors. Check that each of these components is in the right way around before proceeding further. Next, install the links and resistors, capacitors and ICs. Note that IC9, IClO, ICll and IC12 are oriented differently from the rest of the ICs on this board. All five pot shafts should be cut to 10mm length and cleaned up with a file before they are soldered into the board. Clip off the pot terminals where they protrude from the copper side of the board. Installing the LEDs One job that does need to be done carefully is installation of the 20 LEDs. They all need to be precisely in line otherwise they will not look good when they are installed in the mixer panel. There is no easy way to ensure this so we suggest you make a jig as shown in Fig.8. The jig consists of a wood block with a couple of strips of aluminium screwed to it, together with layer of electrical insulation tape, sticky side up (or you could use double sided tape}. The idea is to line up the 20 LEDs in the jig and then glue a 3mm wide strip of aluminium 105mm long to one side with epoxy adhesive. That way, all the LEDs are held precisely in line before being installed on the board. Note particularly that the LEDs must all be laid down precisely in WOOD BLOCK ALUMINIUM STRIP 102mm \ / ~ e -~~------~~~~~~~~___.____.____.___ ALUMINIUM STRIP 3mm WI OE GLUED TO LEDS INSULATION TAPE CLAMPED UNDER ALUMINIUM STRIP (STICKY SIDE UP) I \ WOOD BLOCK t LED LEADS Fig.8: this simple jig can be used to precisely align the LEDs on the equaliser/VU boards. The LEDs are all be laid down with the same orientation (anodes to the right) and then glued to an aluminium strip. the same way, with the anode and cathode leads as shown in the lower diagram of Fig.8. After the epoxy adhesive has set, the leads of each LED should be bent at right angles close to the body. The next step is to solder the 40-way Molex strip into the board. That done, clip off the top section of the Molex strip so that you have 40 individual Molex clips on the board. The strip of LEDs is soldered to the clips. When finished, each LED should appear as shown in Fig.9. Assembling an effects board Having read the article to this point, you can see the general procedure for assembling the two ef- LED / ![ , BENO CLO SE TO LED MOLE X PIN c ! =:=:=:=:::::P::;:C :/ B::::::=:> Fig.9: when the adhesive has set, the LED leads are bent at right angles and soldered to Molex clips on the PC board. fects boards. Only three ICs need to be installed and they are all oriented in the same direction. Follow the component overlay diagram of Fig.10. Power supply board To wire up this board, follow the This is the jig we used to align the LEDs. They are held in position by the sticky surface of the insulation tape. Note that the longer anode leads are to the right. component overlay diagram of Fig.11. Whack in the PC pins first, then the tinned copper wire links and diodes. Electrolytic capacitors are next, followed by the 3-terminal regulators. Make absolutely sure that you install the capacitors the right way around otherwise they are likely to seriously overheat and perhaps even spew out their insides when power is applied. Each of the regulators is attached to a small heatsink, which is retained by a screw and nut to the printed circuit board. Completing the power supply When the boards are ready for testing, you will need to assemble the power supply into the chassis. One of the first steps in this process is to add an 8VAC winding to the toroidal transformer. This will need to be done with at least the first batch of transformers supplied by Jaycar Electronics. Adding a winding to a conventional power transformer is a major task but with a toroidal transformer, as specified for the mixer, it is fairly straightforward. All that has to be done is to wind on 70 turns of 0.5mm tinned copper wire. To do this, you will need about 10 metres of wire. The idea is to thread the wire through the centre of the toroid and make sure that each turn is tight and not likely to rattle around. The 70 turns should be as evenly spaced as possible around the toroid, to After the aluminium strip has been glued in position, the LED assembly can be clamped using a second block of wood until the glue dries. APRIL 1990 75 MORE DEALS TO MAKE THE High performance AT/386Hard Disk/Floppy Disk Controllers Universal Wirewrap Card CAT IF'054 This universal wirewrap card is ideal for engineers and other technical people developing hardware add-ons for IBM PC/XT/AT/386 or compatibles The card provides a complete built-in data bus, address bus and VO !me buffer circuit. It incorporates a universal address decoding chip (0-3FF, step 8 or 16) and a D25 female connector. Buffering of the inputs and outputs makes damage to the PC's bus from faults on the card impossible. The wire-wrap area is 4000 holes which are plated through for easy prototyping work The card is built to a very high standard and can withstand heavy use. NORMALLY $129 ONLY $99, SAVE $36 Features: • Capable of addressing hard disks with up to 16 heads and 2408 cylinders. 1 or 2 dnves are supported. • Will run at up to 16MHz on a suitable high speed machme, delivering a massive 200% improvement in throughput from this feature alone! • The DCAHF is available with a built-in floppy disk controller, supporting up to 2 drives which may be any mix of 360K or 1.2MB 5¼" or 720K or 1.44MB 31,,z" drives. ONLY $9.75 each Parallel Centronic Printer Cables CAT. LACPP3 3 metre cable CAT. LACPP5 5 metre cable CAT. LACPPl0 10 metre cable Standard nrinter cables with DB25 pin plug to 36 ,>in Centronics plug . Suits all popular parallel printers and computers printer ports. CAT LACPP3, only $15.00 CAT LACPP5, only $18.00 CAT LACPP10, only $25.00 Serial Printer Cables- 3 Metres WAS $95 NOW $59, SAVE $36 ONLY $225 SAVE $24 CAT. LAAPS2 PS2 to AT keyboard connector adaptor. Enables AT style keyboards to be used on PS/2 computers CAT. LAGC25M, CAT, LAGC25F ONLY$9.75 Modem cable 25 pin plug to 25 pin socket. All pmsare wired stra ight through Hardware Control CAT.LACSP25 graphics card adaptor. 9 pin to 15 pin adaptor enables multisync monitors to plug into the 15 pin analog output of VGA graphics cards. ONLY $9.75 each AMERE$9.75 CAT. LACM9 Modem ca ble 9 pin socket CAT. LANULL Null Modem Adaptor Modem Cables - 2 Metres CAT LACM9 CAT LACM25 'Type 0 Compute t End 25 Pm Female Mu<iAm Comput.P.1 •mci2S pUl •md 25 Pll l fl nci 9 pm :-·1-m1a!H nml+-i 1 femalH I $9.75 each 2 3 19 20 568 ?t1nte1 ?nntei End 9 ?in En<l 25 ?m Female Male 3 _ __ • Suits all parallel printers • Crossover switch • 36 pin centronics connectors ONLY$39.95 RS-232 Break-OutBox ...,,,,,,¼~.~~..., CAT LAAB Used totestand _ _ _ re-wire RS-232 interfaces ONLY $29.95 Serial Printer Cables- 3 Metres xon/x off Hardware Control CATLACSPX25 CATLACSPX9 Type2 Typel Comµute1 End 25 P::1 P11mei End 25 Pin M a!P. 3 Modem end 2r} pm r.m l~ . 2 Compute! End 9 P1:-. Pi U.tl:!I End 2S ?:.:1 Fem;:i!e 16 20 2_ 3_ 68 .. 20 20 68 8 ___ _ _ _ ,; 20 2,0 CAT CATBP This compact case 1s the same as used m the famous Sibcon Chip Pro1ect AT It has plenty of room for a full XT, AT or 386 system, and has drive bays for 2 x 5.25" and 2 x 3.5" d rives . Front nower switch, reset, tur bo and disk dnve light and keyswitch . And bemg a "mmi-tower'' rt takes up very bttle space Normal price 1s $299. but for this month orJy Reduced to $199 while stocks last! '/ . li nes LO g ive AT Cases, going for a Song! Mini Tower Case with200WAT Power Supply 5.6.8 Use 7 (or 8) wire cable find 1n g CAT.ACDS22 1,6,8 _ _ _ 19 _ __ 7 20 4 . Serial Quick Tester LEDs monitor the insui nt feed back ONLY$29.95 Use 4 wire cable ? CAT.LAOT Type4 Computet End 25 Pm M all'l 568 Type 6 Compute1 CATLACSP9 Type3 CAT. LAAVGA VGA $9.75 each • Suits all parallel printers • 2 computers to one prmter or one computer to 2 printers • 36 pin centronics connector For connection between serial devices. All pins straig ht through CAT.DCAHF to 25 µ,n plug . The aµproria te pi ns are connected (TXD to Tl<D, RX Lo RX ctc ) ,, 9 pin socket . to 25 pin plugThe .-~ ~·' appropriate . pins connect internally to . allow for matching of senal equipment usmga mixture of 9 pin and 25 pin connectors (eg. a 9 pin serial connector on a serial mouse to a 25 pin serial port on a PC). Serial Printer Cables ONLY $175 SAVE $50 Gr0c1L fo r faull plug to 25 pin socket. EXTRA SPECIAL!!! DISK BOX WITH 100 DISKETTES CAT.DCAH Modem Accessories Data Switches CATACDS21 CAT. LA9F25M CAT DCAH (HDD) or CAT DCA HJ-' (H OD & F'DD) Speed up the disk performance of your AT or 386 machine by a factor of around 2:1 with these fast cachmg disk controllers. 1:1 sector interleaving, using the latest Western Digital 1006 chip set greatly increases performance with most drives . Adaptors CAT. LA9M25F 9 pin ONLY $15. 75 each SAVE$100 USE:: 9 (OR 10) lNl RE CABLES ONLY $19.90 $15. 75each CALL US NOW FOR OUR GREAT CATALOGUE WITH ALL OUR PRODUCTS LISTED! OPPOSITION HATE OUR GUTS! BABY AT CASE + POWER SUPPLY CATCAATBP MULTISYNC MONITOR + VGA Save 40% on 2 Serial/1 parallel Port Card CAT !OPS2 Need more ports on your PC? T his compact half slot card comes complete wit h 2 serial and 1 parallel pow er and all the connectors, plus a 9 pi n to 25 pin DB adaptrn cable for the serial port. CARD CAT A CMM & CAT. VC0B00 This compact PC/AT case features a flip-top lid and facilities for expansion for up to 8 slot mother boards. The i nternal drive mounting tray will accept up to 3 half height 5¼ hard or floppy drives. LEDs and switches for Reset/Turbo/Power are provided . A keylock and key are also provided. Dimensions are: 360mm(W) x 165mm(H) x400mm(D) Normally $85 Limited stock: ONLY$45, SAVE$25! ! The cards provide complete register level compatibility with the IBM Video Graphics Array standard (VGA), w hile being backwards compatible with EGA. CGA 0 nd Hercules Graphics/MDA monochrome standards. The VC1024 is fitted with an additional 256K of display memory for up to 1024 x 768 pixel resolution. Prices the competition can't match!! 12MHz 0-wait state Normally $1,298 11half-size" AT Only $995, SAVE $303 motherboard Great Deal with TheTurboXT Motherboard CAT MB1600 Includes a heavy duty 200W AT Power Supply. Limited Stock Save $246 on 12MHz ONLY $175, SAVE $74 0-wait-state Baby-Size" AT Motherboard 11 Monitor Madness!!! 14" EGA MONITOR + EGA CARD CATACMEGA & CAT.VCEGA The ACMEGA is a full EGA colour monitor, providing both text and graphics display with all EGA and EGA compatible graphics cards. It features a 0.31mm dot pitch tube with anti-reflective coating . A tilt and swivel stand is provided This high perfonnance AT motherboard features ultra-fast performance and a full 8 slot expansion bus. It is switchable to 6, 8, 10 and 12MHz and can accept 256K , 512K, 640K or 1MB of memory on t he motherboard. The range of speeds allows slower memory to be used when available. The design uses the powerful CHIPS & TECHNOLOGY chip set (12 5MHz version) for very high performance and reliability. It outperforms other 12MHz designs by a wide margi n. Normally $848, now only $675. SAVE $173 Normal price $595. But while current stocks last: only $349 Magic Combo" 11 Mono/Colour Graphics Card + High-Resolution Monochrome Monitor CAT VCCOMBO/CAT ACMA This is the video card and monitor to suit all occasions I The Magic Combo Card dnves both your old CGA colour monitor and this blil~ant new monochrome monitor to the two most popular standards. 1. Colour Graphics Adaptor (CGA) standard. When usmg the TTL monochrome monitor, grey tones are used to simulate colours. 2. Monochrome Display adaptor with Hercules graphics (720 x 348 pixels) w hen dnving it as a TTL monochrome monitor. Now you don't need to put up with gritty CGA graphics for your text - switch to high quality 720 x 348 pixel MDA/hercules. Nor do you have to m iss out on all the games software because you can't run CGA graphics. You get the best of both worlds with the Magic Combo. Normally$328, nowonly$275. SAVE $53 per oimance motherboard has a full 6 expansion slots (5x16 bit, 1x8 bit) and a full 1MB of sons memory for maximum performance - 13.7 on Nortons SI rating ! 8 or 12MHz operation is keyboard selectable. The small size of t he board makes it ideal for replacement in both XTs and slower ATs. The mounting holes match those of both XT and AT machines Normally $495 plus $295 for 1MB of RAM. Sale Price $495 complete, SAVE $295!! The MB1600 is an IBM PC/XT compatible motherboard . It measures only 8½'' x 9" T he board runs at 10 M Hz or 4.77MHz, providing complete compatibility with the IBM standard . Eight 62 pin edge con nectors are also mounted to the board. The VO channel is bussed across the eight expansion slots. The heart of the M B1600 is an 8088-3 microprocessor. The system board supports both ROM/EPROM and R/W memory. It has space for 32K x 1 and SK x 1 of ROM or EPROM . A full 640K of high speed RAM can be fitted on the motherboard . NORMALLY $149 ONLY $99, SAVE $50 with V20 chip $109 Only while stocks last!! ................................. ipg~ I! ~~:: ;:~: : : ■ ~ ---••••-••-•-••• Fax (02) 906 5222 We accept Bankcard, Mastercard & VISA Mail orders our specialty. Freight on smaller items is now $9.00 + $2.50 P&P • All prices include sales tax • All products carry a 14 day money back guarantee (software and hard d isks excepted) • All products carry a full 3 month warranty • All cards come with full documentation • Ring for quantity discounts and tax free prices Owing to technical advances products we supply may in some cases vary from those pictured. In all cases they are guaranteed to pe rform to an equal or higher standard . ................................. "' . ~+---....lEFFEfJ:u;ETURN (TO 1-8 SOCKET) EFFECTS RETURN VR9 EFFECTS SEND OUTPUT (TO 1-8 SOCKET) PAN VR1O FOLDBACK LINE OUTPUT (TO 1-8 SOCKET) EFFECTS SEND VR11 FOLDBACK VR12 TO 1-8 FO ov ---./ TO 1 8 EFFECTS 8 TO CH2 EQUALISER CH2/CH4 +15V -15V EFFECTS POWER BUS TO CH1 EQUALISER PCB --•-CH3 I I I CH4 9-16 EFFECTS BUS ~ 9-16 FOLDBACK BUS 2CH/4CH SWITCH 1 TO 9-16 EFFECTS PCB Fig.10: parts layout for the two effects boards. Don't forget the link on the PC board that runs beneath the bottom two pots (VR11 & VR12). The ICs are all oriented in the same direction. assure a neat job. When you have finished winding on the turns, they should be well secured by winding electrical insulation tape over them. The two ends of the finished winding should then be stripped of enamel and tinned with your soldering iron. Fit a length of plastic sleeving over each winding end and secure it to the toroid with another few turns of insulation tape. Installing the transformer Before installing the transformer or any hardware in the chassis, it is a good idea to fit some solid rubber feet to the underside, to avoid scratching your workbench or table. The transformer is mounted directly on78 SILICON CHIP to the chassis using the hardware supplied with it. This consists of a long bolt which runs up through the centre of the toroid, to retain it with a large washer plate. A large rubber washer is fitted to either side of the transformer, to mount it compliantly yet firmly. Having mounted the transformer, fit the mains cord and associated wiring, according to the layout shown in Fig.11. Follow the diagram carefully to avoid mistakes. The mains cord must be secured with a cordgrip grommet so that it is firmly anchored. Leave 15cm or so free so that the three wires (Brown - Active, Blue - Neutral and Green/Yellow - Earth) can be stripped and terminated. The Active and Neutral wires are terminated to the power switch (S3). On the other side of the switch, the Active wire goes to one side of the fuseholder. The transformer primary is then terminated to the fuseholder and to the Neutral side of the power switch. The earth wire is connected to the chassis via an earth lug which is secured with a screw, nut and star washer. It is preferable to fit shrinkable sleeving over the fuseholder and power switch wiring, to make it safe from accidental contact. When the mains section of the wiring is complete, it is necessary to identify the start and finish of each of the two 15V secondary windings. Join the green and blue secondary wires and then make sure that none of the secondary wires are touching the chassis; then switch on the mains power. Set your multimeter to measure 30V AC and check the voltage between the red and brown secondary windings. It should be 30VAC or thereabouts. If it is zero, disconnect the green and blue wires, join the red to the green and measure the voltage between the blue and brown. This effectively reverses the phase of one of the windings. Disconnect the mains plug from the mains and continue with assembly of the power supply. The power supply board should be mounted on the chassis with four 6mm spacers, screws, nuts and lockwashers. That done, connect the transformer to the power supply PCB. Checking the power supply Now switch on power and check the output supply rails for + 15V, - 15V and + 5V. With these correct, you are ready to check the signal boards. To test each signal board, you will need an audio signal oscillator and a digital multimeter. If you have access to an oscilloscope and perhaps an AC millivoltmeter, so much the better. In our experience, any problems found on the PCBs are most likely to be incorrectly placed or incorrectly oriented components or shorts between PC tracks. It is seldom that !Cs are found to be faulty, unless Fig.11: parts layout & wiring diagram for the power supply. The completed power supply can be used to test the other boards before installing them in the chassis. 0 HEATSINK TO BAR DISPLAY BUS HEATSINK NEUTRAL (BLUE) POWER TRANSFORMER COROGRIP GROMMET \ AINS © EARTH LUG APRIL 1990 79 PARTS LIST FOR 16-CHANNEL MIXER Input Channel Boards (16 required} 1 PCB, code SC01102903 1 3mm red LED and bezel (LED 21) 25 PC stakes Semiconductors 3 LM833 dual op amps (IC1, IC2, IC3) 1 CA3140 op amp (IC4) 1 7555 CMOS timer (IC5) 1 BC338 NPN transistor (01) 1 BC328 PNP transistor (02) 3 1 N914, 1 N4148 diodes (D1, D2, D3) Capacitors 1 330µF 16VW PC electrolytic 2 1 OOµF 16VW PC electrolytic 2 33µF 1 OVW PC electrolytic 2 6.8µF 16VW PC electrolytic 1 3.3µF 16VW axial electrolytic 1 2.2µF 16VW axial electrolytic 2 1µF 1 6VW PC electrolytic 6 0 .1µF monolithic ceramic 1 .01 5µF metallised polyester 1 .012µF metallised polyester 1 .01 µF metallised polyester 1 .0027 metallised polyester 1 .001 5 metallised polyester 1 330pF ceramic 1 220pF ceramic 3 1 50pF ceramic 1 1OOpF ceramic 1 39pF ceramic Resistors (¼W, 1 470k0 2 220k0 1 4 7k0 3 33k0 4 15k0 2 12k0 10 1 OkO 1 10k0 1 % 2 6.8k0 2 2k0 1 % 5%) 1 1.8k0 1% 1 1 .5k0 1 1 .2k0 1 % 2 1k0 3 1 kO 1 % 1 6800 1 5600 1 % 1 4700 1 % 1 1500 1 1000 the supply rails have been inadvertently reversed. Testing a preamplifier board Before applying any power, you will need to wire in the main slider (VR6) and connect a link between the two PC pins marked "X" on the diagram of Fig.6. In this condition, 80 SILICON CHIP 1 910 1 % 1 680 2 330 1 130 1 % 2 4. 70 Potentiometers 3 1 OOkO linear PCB mount pots 3 1 OkO log PCB mount pots 1 1 OkO linear PCB mount pot 1 1 OkO log slider pot 1 1Ok miniature horizontal trimpot Chassis hardware 1 XLR 3-pin chassis mount female socket 1 3-pole 3 position rotary switch (S1) 1 4-pole 2 position miniature toggle switch (S2) 1 6. 5mm insulated panel mount stereo socket 7 small knobs to suit pots: 1 green, 1 blue, 3 grey, 1 red, 1 white Effects Boards (2 required} 1 PCB, SC01102901 3 6.5mm insulated mono panel sockets 4 knobs to suit pots: 1 red, 1 green, 1 white, 1 yellow 20 PC stakes Semiconductors 3 LM833 dual op amps (IC6, IC?, IC8) Capacitors 2 1 OOµF 16VW PC electrolytic 2 4 7 µF 1 6VW PC electrolytic 2 4. 7µF 16VW PC electrolytic 1 2 .2µF 16VW PC electrolytic 5 1µF 1 6VW PC electrolytic 2 0.1 µF monolithic ceramic 3 220pF ceramic 4 1 50pF ceramic 2 39pF ceramic ICla will be set in the microphone balanced mode and will have a gain of 10 [by virtue of the 10kn resistor between its pins 1 and 2). Apply power to the circuit and check the voltages. You should find + 15V present at pin 8 of ICl, IC2 and IC3, at pin 7 of IC4, and pins 4 & 8 of IC5. You should find - 15V Resistors ( ¼ W, 5%) 3 6.8k0 2 1 OOkO 3 47k0 3 2.2k0 2 39k0 6 1kO 1 22k0 2 330 4 15k0 Potentiometers 3 1 OkO log PCB mount pots 1 1 OkO linear PCB mount pot Equaliser & Meter Boards (4 required} 1 PCB, code SC01102902 1 XLR 3-pin male plug 1 stereo 6. 5mm panel socket 5 grey knobs to suit pots 1 40-way Molex strip 22 PC stakes Semiconductors 3 LM833 dual op amps (IC9, IC10, IC11) 4 TL071 op amps (IC13, IC16, IC18, IC19) 1 CA3140 op amp (IC17) 1 TL07 4 quad op amp (IC12) 2 LM3915 logarithmic LED drivers (IC14, IC15) 1 7555 CMOS timer (IC20) 1 4066 CMOS quad gate (IC21) 1 BC338 NPN transistor (03) 1 BC328 PNP transistor (04) 4 1 N4148, 1 N914 signal diodes (D4, D5, D6, D7) 20 red rectangular LEDs (LED 1 to LED 20) Capacitors 2 1OOµF 16VW PC electrolytic 2 4 7 µF 1 6VW PC electrolytic 9 1OµF 1 6VW PC electrolytic 2 4 .7 µF 16VW PC electrolytic 4 1µF 1 6VW PC electrolytic 1 0.22µF metallised polyester 1 0.18µF metallised polyester 2 0 .1µF monolithic ceramic 1 .082µF metallised polyester 1 .04 7µF metallised polyester 1 .022µF metallised polyester present at pin 4 of ICl, IC2 and IC3. OV should be at pin 4 of IC4 and pin 1 of IC5. In addition, the voltage at pins 1 and 7 of ICl, IC2 and IC3 should be very close to OV, say within ± 20mV. If you find any deviation from these voltages, you should switch off and check your work carefully 1 .018µF metallised polyester 1 .01 µF metallised polyester 1 .0056µF metallised polyester 1 .004 7 µF metallised polyester 1 .0012µF metallised polyester 1 560pF ceramic 1 220pF ceramic 1 1 50pF ceramic 2 33pF ceramic 1 22pF ceramic Resistors (1.4W, 5%) 8 1OOkO 3 2.2k0 1 75k0 2 2k0 1% 1 68k0 4 1 kO 1 62k0 1 % 3 1kO 1 % 2 47k0 5 9100 1 36k0 1% 1 9100 1% 1 30k0 1 % 1 6800 1 22k0 2 6800 1% 9 10k0 1 680 1 6.8k0 4 330 2 4 .7k0 1 4.70 2 3.9k0 Potentiometers 5 1 OOkO linear PCB pots 2 1 OOkO miniature vertical trimpots 1 1Ok{} log slider pot 1 1 OkO miniature vertical trimpot Power Supply 1 PCB, code SC01102904 1 30V centre tapped 80V A toroidal mains transformer with 8V 1 A winding 1 illuminated DPDT 240VAC rocker switch (S3) 1 3AG panel fuse holder 1 250mA slow blow 3AG fuse 1 mains cord and plug 1 cord grip grommet 3 T0-220 heatsinks (Jaycar Cat. HH-8508) 1 solder lug 1 screw, nut and star washer to suit above 4 6mm standoffs 4 screws and nuts to suit above 3 screws and nuts for regulators 14 PC stakes Semiconductors 8 1 N4004 1 A diodes (D8 to D15) 1 7805 5V 3-terminal regulator 1 7815 15V 3-terminal regulator 1 7915 -15V 3-terminal regulator Capacitors 4 2500µF 25VW axial electrolytic 2 2500µF 16VW axial electrolytic 3 1 OµF 16VW PC electrolytic 3 1µF 25VW PC electrolytic Additional Chassis Hardware 2 insulated 6.5mm stereo panel sockets 5 large rubber feet Wire 2 metres tinned copper wire 10 metres 0.8mm enamelled copper 1 metre grey 24 x 0.2mm hookup wire 5.5 metres black 24 x 0.2mm hookup wire 6 metres red 24 x 0.2mm hookup wire 9 metres green 24 x 0.2mm hookup wire 6 metres blue 24 x 0.2mm hookup wire 3.5 metres yellow 24 x 0.2mm hookup wire 0.5 metres 19 x 0.193mm figure-8 polarised wire 1 O metres single core shielded wire 7 metres twin shielded wire Miscellaneous Thermal grease for heatsinks, cable ties, heatshrink tubing for mains switch and fuse holder. Made here in Austrara? Polystryrene Capacitors - 1 0pF to 1mF Voltage Range 63VDCW to 10,000 VDCW Tolerance - 0.25% to 10% Allied Capacitors A ustra/ia manufactures capacitors to the specification of the customers using high quality, imported polystyrene and aluminium foil with a tolerance of 1 micron. Our capacitors are manufactured to the system of Total Quality Control. We can provide Just In Time delivery if required, together with a Certificate of Conformance if requested. Specific values between 10pF and 1uF are no more expensive than standard value components. You can now design circuits to use a single capacitor rather than a number in parallel or series to achieve a desired value . Personalised labelling is available at no extra cost. Your component code or name can be built into the capacitor. Minill'!um runs of only 25 allow you to specify a particular value for a prototype run. Delivery lead time for short runs is 3 to 4 working days, and for longer runs is less than 2 weeks. We are also able to produce capacitor styles for applications such as dual mount, end filled and mini style capacitors. Call us now on: before proceeding further. Now apply a signal of about lOOmV at lkHz to the input; ie, PCpin 1 (ground) and pin 2 (signal active). Use the circuit diagram (Fig.2) and the overlay diagram (Fig.6) to aid in checking the signal flow through the circuit. With lOOmV RMS applied to the input, the lkHz signal at pin 1 of ICla should be close to 1 volt RMS. At pin 7 of IClb, the signal should be 2 volts RMS with the attenuator, VRl, set fully anticlockwise. Now reduce the lkHz input signal to lOmV RMS and wind the attentuator VRl fully clockwise, to give maximum gain. The signal at pin 7 (02) 938 4690 ALLIED CAPACITORS AUSTRALIA PO Box 740 Brookvale, NSW 2100 APRIL 1990 81 of signal on the foldback and effects bus outputs and the operation of the relevant controls, VR5 and VR7. Operation of the bass control can be tested by applying a signal at around 40Hz and then checking for boost and cut and the extremes of rotation of VR2. To test the midrange control, VR3, apply a signal of around 700Hz while the treble control, VR4, can be checked at lOkHz. Testing the effects PCB The pots on the two effects boards are angled slightly so that the bottom edge of the board clears the chassis. should now be close 10 volts RMS. Now wind VR 1 fully anticlockwise and increase the input signal back to 100mV RMS, which should give 2 volts RMS at pin 7 of IC1 and also at pin 1 of IC2a, provided the three equaliser controls, VRZ, VR3 and VR4, are all at mid setting. The same voltage output should also appear at pin 1 of IC3a and at the headphone output (via the 680 resistor). All these test results should also be obtained if you apply the input signal to PC pin 3, to check the noninverting input of IC1a. Adjusting the peak detector The peak detector is adjusted by varying the TRIM 1 trimpot associated with IC3. With an input signal of 100mV applied, you should be able to get the peak detector LED to light by winding up the input attenuator VR1 or the main attenuator VR6, depending on the setting of the TRIM 1 trimpot. Our suggestion for setting the peak detector is to adjust the attenuators (VR1 and VR6) until the signal level at pin 7 of ICZ is 8.5 volts RMS. You then adjust TRIM 1 until the LED just lights. Alternatively, if you have access to an oscilloscope, you can adjust the attenuators until the signal at pin 7 of ICZ is just on the verge of clipping. You then adjust TRIM 1 until the LED just lights. Check for the presence of signal on the Channel1/Channel2 buses and operate the Pan control VR8 to vary the signal between the two buses. Also check for the presence ·'-·••11;. ;r.~~~~:.1;: 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. 82 SILICON CHIP Connect the supply rails to the board, apply power and check the voltages. You should find + 15V present at pin 8 of IC6, IC7 and IC8. You should find - 15V present at pin 4 of IC6, IC7 and IC8. In addition, the voltage at pins 1 and 7 of these three ICs should be very close to 0V, say within ± Z0mV. If you find any deviation from these voltages, you should switch off and check your work carefully before proceeding further. Apply a 100mV RMS signal at 1kHz to the effects return input and measure the signal at pin 7 of IC6 which should also be lO0mV RMS, as expected from a unity gain stage. Rotate the effects return control VR9 fully clockwise and measure the signal at pin 1. It should be 400mV RMS. Check for the presence of signal on the Channel 1 and Channel 2 bus pins and see that the pan control, VR10, varies the signal on these buses. Now feed a 50mV RMS signal to the effects bus pin. The signal at pin 1 of IC7a should be 886mV RMS. Wind up the master Effects Send control, VR 11, and a signal of 6.9 volts RMS should be present at pin 7 of IC7. Similarly, apply a 50mV RMS signal to the foldback bus PC pin. The signal at pin 1 of IC8 should again be 886mV. Wind up the master foldback control, VR12, and a signal of 6.9 volts RMS should be present at pin 7 of IC8. Next month we will complete the discription of the mixer by presenting the test procedure for the equaliser/VU meter boards and then the wiring and assembly procedure for the mixer panel and chassis. ~