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Ultra-LD Mk.2 200W Power Amplifier All the assembly details plus building a power supply Last month, we introduced our new Ultra-LD Mk.2 200W Amplifier module and described the circuit. This month, we give the assembly details and describe a suitable power supply. T HIS NEW 200W audio amplifier module gives superlative performance – better than any of our previous class-AB amplifiers. That’s been made possible by the use of On Semiconductor’s new ThermalTrak power transistors, a circuit based largely on our high-performance Class-A Amplifier (published in 2007) and a new doublesided PC board with plated-through holes. As mentioned last month, the double-sided PC board is critical to the performance of this amplifier module. 58  Silicon Chip It not only simplifies the supply wiring but has also been designed to largely cancel the magnetic fields produced by the asymmetric currents drawn by each half of the class-B output stage. In addition, the double-sided board eliminates the need for wire links, the exception being a couple of 0W resistors. The assembly is really quite straightforward although there’s a fair bit of work involved to do the job properly. When building a high-power amplifier module like this, it’s important to take your time, do a neat job and check your work carefully at each assembly stage. After all, blowing up expensive output transistors can be a real pain. Transistor quality We’ll begin the assembly details shortly but first a word about the transistors used in this module. To ensure published performance, the NJL3281D & NJL1302D power transistors must be On Semiconductor branded parts, while the 2SA970 lownoise devices must be from Toshiba. siliconchip.com.au Pt.2: By JOHN CLARKE & GREG SWAIN Be wary of counterfeit parts (although it’s probably too early for counterfeit versions of the power output devices). We recommend that all other transistors used in this project be from reputable manufacturers, such as Philips (NXP Semiconductors), On Semiconductor and ST Microelectronics. This applies particularly to the MJE15030 & MJE15031 output driver transistors. PC board changes Fig.9 shows the parts layout on the siliconchip.com.au double-sided PC board. This board is coded 01108081 and measures 135 x 115mm. The orange tracks and pads show the copper on the top of the board, while the blue-grey tracks are on the underside of the board. The first thing to note is that the PC pattern differs slightly from that used for the prototype module. That’s because we subsequently decided to increase the number of vias used to link the top and bottom supply rail tracks. Up to 4.5A peak can flow through each output transistor when the module is operated into a 4W load, so it’s important to ensure sufficient current-carrying capability. However, the main reason for increasing the number of vias was to make sure that a fault in the output stage would not cause the vias to fuse, instead of the 5A fuses blowing. If that happened, the board would be difficult to repair, as the solder mask goes right up to the edges of the vias. As a result, we’ve increased the number of parallel vias in the high-current paths, generally grouping them together in patterns of five or more (so that they look like the face of a dice). Note that, unlike the outer vias, the middle via of each group of five has a solder pad on both sides of the board. This allows a tinned copper wire “feed-through” to be fitted to each of these middle vias and soldered in place. These tinned copper wire feedthroughs ensure that the vias can not possibly fuse in the event of an output stage fault. They also ensure very low resistance between the top and bottom track sections. We’ve also added extra vias to connect the low-current signal tracks on both sides of the PC board, in the interests of redundancy. This is a “belts ‘n braces” measure but is still good practice. Finally a 390W 1W resistor was added to the board to provide the headphone output. As part of this change, CON3 was changed from a 2-way terminal block to a 3-way terminal block to give the “Phones Out” terminal (note: these changes are not shown on the photos). A few minor changes were also made to improve component fit. Board assembly Fig.9 shows the assembly details. Begin by installing the tinned copper WARNING! High AC & DC voltages are present on the power supply and power amplifier modules when power is applied. In particular, make sure you don’t get across the two 40V AC input terminals on the power supply. The 40V AC transformer windings that connect to these terminals are wired in series, so there’s 80V AC between them. Similarly, note that there is 110V DC between the +55V and -55V supply rails, both on the power supply module and the amplifier module. Do not touch any of this AC or DC supply wiring (including the fuseholders) when the amplifier is operating, otherwise you could get a very nasty shock which could even prove fatal. wire feed-throughs to the middle pad of each group of five vias. It’s simply a matter of pushing the wire through each via and soldering it on one side. When you do this, the solder should run up inside the via and onto the solder pad on the other side of the board. If not, solder it on the other side of the board as well, then cut the wire off short on both sides of the board. Note that it isn’t really necessary to fit feed-throughs to the vias immediately below the fuseholders, since the fuseholder pins themselves act as feed-throughs. However, they can be installed if you wish. Don’t forget the via that sits under the two 0.1W resistors at top left. Once the feed-throughs are in, install the two 1N4148 diodes (D1 & D2), followed by the resistors (but not the 5W types) and the capacitors. The resistor colour codes are shown in Table 1 but we strongly advise that you also check each value using a multimeter before it is installed. Mount them so that they all face in the same direction, to facilitate checking later on. Make sure that the diodes and electrolytic capacitors are all installed with the correct polarity. If you make a mistake, it’s not as easy to remove a component from a double-sided board with plated-through holes as it is from a single-sided board. It can be done, although you usually have to sacrifice the part – see the panel headed “Removing Parts From The PC Board” for details on removing components. We suggest that you leave the two September 2008  59 MJE15030 MJE15031 BF470 L1 6.8  1W 10  1W 100pF 100V 12k 6.8 H 390  1W BF469 Q9 6.2k NJL1302D 18080110 FUSE 2 (5A) reifilpmA 2.KM DL-artlU 0.1  5W 100 100nF Q7 2.2k 1000 F 63V Q5,Q6: BC556 2.2k Q5 Q6 100nF 100nF 6.8k 1W 100 100 100 47 F 35V 47 F 47 0.1  5W 0.1  5W FUSE 1 (5A) 6.2k 100nF Q15 NJL1302D Q11 Q10 1000 F 63V Q14 0.1  5W NJL3281D 100 Q13 NJL3281D 2.2k Q12 2 x 2SA970 100 510 12k 1M 47 F NP 820pF 220 F 10 0 D1 4148 4148 D2 Q8 BC639 0 Q3 Q4 CON2 2 x BC546 470 F 63V 100nF 22k 150nF 400V Q1 Q2 68 100 68 100 CON3 SPEAKER + SPEAKER – PHONES OUT CON1 SIG COM +55V 0V –55V Fig.9: follow this parts layout diagram and the instructions in the text to build the UltraLD Mk.2 Amplifier module. Note that you should install a tinned copper wire feed-through wherever there’s a via with a solder pad, typically in the middle of each group of five vias. 1000mF electrolytic capacitors off the board for the time being, as this makes it easier to secure transistors Q10 & Q11 to the heatsink later on. Even with the capacitors in place, you still have good screwdriver access to these transistors. However, there’s a risk that one of these capacitors could be damaged if the screwdriver slips while doing up the mounting screws. Note that the 100pF capacitor on the collector of transistor Q9 should be rated at 100V. Alternatively, use a 3kV type, such as the Altronics R-2882. Now install the four 0.1W 5W resistors. These have their leads bent down through 90° some 5mm from their bodies and should be mounted about 1.5mm above the surface of the PC board, to allow the air to circulate beneath them for cooling. The easiest way to do this is to use a strip of cardboard about 20mm wide and 1.5mm thick as a spacer. You simply push the resistor all the way down onto the cardboard, solder the leads, then pull the cardboard back out. Mount the 5W resistors with their values all facing up and reading in the same direction. Again, this makes it easier to check them later on. The fuse clips are next on the list. Note the each fuse clip has a little lug on one end which stops the fuse from moving lengthways. If you install the clips the wrong way around, those lugs will stop you from fitting the fuses. It’s a good idea to use sticky tape to hold the fuse clips in place while you solder their leads. This same trick is also useful when it comes to mounting some of the other parts, such as the screw terminal blocks. Small signal transistors The leads of the TO-92 transistors should be cranked to fit their mounting holes in PC board using a pair of needle-nose pliers. Here’s how it’s done. 60  Silicon Chip The small-signal (TO-92-package) transistors (2SA970s, BC546s, BC556s & BC639) can now go in. As supplied, these transistors usually have their leads in a straight line, although the centre lead may sometimes be cranked out. These leads should be splayed siliconchip.com.au This prototype module differs slightly from the version shown in Fig.9. Take care to ensure that all transistors go in their correct locations and are correctly orientated. It’s a good idea to slightly splay the bottom fins of the heatsinks fitted to Q7 & Q9, to increase the clearance to the solder pads of the adjacent 6.2kW & 2.2kW resistors. outwards and cranked to fit nicely into their allocated holes. The way to do this is as follows: first, grip the three leads adjacent to the transistor body using a pair of needlenose pliers and bend the centre lead back and up by about 70° (if it hasn’t already been cranked). That done, grip each of the two outer leads in turn and bend them outwards and up by about 70°. Finally, grip each lead in turn at the end of the pliers and bend it downwards again – see photos. Install each transistor after dressing its leads. If the leads are dressed correctly, the transistors will each sit siliconchip.com.au about 4mm proud of the PC board. Note that transistor pairs Q1 & Q2, Q3 & Q4 and Q5 & Q6 are installed with their flat sides facing each other. Make sure that you don’t install these transistors in the wrong positions. Inadvertently swapping 2SA­ 970s for BC556s will cause problems (even though they are both PNP types) because their pin-outs are different. Similarly, swapping BC546 NPN transistors for BC556 or 2SA970 PNP types could cause serious damage when the amplifier is powered up. You have been warned! The TO-126-package transistors, Q7 & Q9, are fitted to U-shaped flag heatsinks before they are soldered to the PC board. The best approach is to first loosely attach one transistor to the inside face of its heatsink using an M3 x 10mm screw, nut and two flat washers – see Fig.10. The assembly is then be fitted in position and pushed all the way down until the heatsink contacts the PC board. That done, the transistor’s leads are soldered and the heatsink mounting screw tightened. As with the fuse clips, you can use some sticky tape to hold the assembly in place while the leads are soldered. It’s best to lightly September 2008  61 6021 TYPE TO-220 HEATSINK BF469/470 TRANSISTOR SILICONE INSULATING WASHER M3 x 10mm SCREW M3 NUT FLAT WASHER FLAT WASHER PC BOARD Fig.10: follow this diagram to attach the BF469 and BF470 transistors to their respective heatsinks. The silicone insulating washer is optional but it’s not a bad idea to isolate the heatsinks from the transistor collectors to prevent accidents when testing. solder one lead first and then make any adjustments that may be necessary before soldering the other two leads. Repeat this procedure for the other transistor. Be sure to use a BF470 (PNP) transistor for Q7 and a BF469 (NPN) for Q9. Don’t get them mixed up, otherwise the smoke will get out when you apply power! It’s important to centre these heatsinks so that their fins cannot contact the solder pads of the adjacent 6.2kW and 2.2kW resistors (splay the bottom fins of each heatsink slightly if necessary). If you’re fussy, you can fit TO-126 silicone insulating washers to isolate the collectors of the transistors from the heatsinks (we did this to avoid accidents with test probes while testing the prototype). However, provided you centre the heatsinks correctly, it’s not really necessary. Table 2: Capacitor Codes Winding the choke Value 150nF 100nF 820pF 100pF The next step is to wind the 6.8mH inductor. This is done by closewinding about 1.5m of 1mm-diameter enamelled copper wire onto a plastic bobbin (Altronics L-5305 or Jaycar LF1062). This bobbin can have an inside diameter of either 10mm or 11.8mm (OD = 20mm or 21mm). It order to do a neat job, it’s necessary to make a small winding jig to hold the bobbin. This jig not only prevents the bobbin from being damaged but also makes the job much easier. The accompanying panel (“Making A Winding Jig For The 6.8mH Inductor”) shows how the winding jig is made. Once you have the jig, begin the winding by feeding about 40mm of the wire through one of the bobbin slots and the exit hole in the jig (loosen the handle if necessary to do this). Bend this end back through 180° to secure it, then tighten the handle and wind on 25.5 turns as evenly and tightly as possible. Finish by bending the remaining wire length through 90° so that it exits down through the opposite slot. The windings are now secured using a couple of layers of insulation tape and the bobbin removed from the jig. That done, cut off the excess leads at each end, leaving about 10mm protruding. Finally, complete the inductor by fitting some 20mm-diameter (9mm wide) heatshrink tubing over the windings. Be careful when shrinking it down with a hot-air gun though – too much mF Code 0.15mF 0.1mF .001mF NA IEC Code 150n 100n 820p 100p EIA Code 154 104 821 101 heat will damage the bobbin. You can now test fit the finished inductor on the PC board, bending its leads as necessary to get the bobbin to sit down flush on the board. It’s then just a matter of stripping the enamel from the wire ends and tinning them before soldering the inductor in place. Heatsink transistor mounting As shown in the photos, the driver and output transistors (Q10-Q15) are all mounted on a large finned heatsink measuring 200 x 75 x 48mm (L x H x D); eg, Jaycar HH-8546. You’ve got two choices when it comes to mounting these transistors: (1) drill 3mm holes right through the back of the heatsink and attach the transistors using M3 screws, nuts and washers; or (2) drill and tap mounting holes and attach the transistors using M3 screws and washers. Drilling the holes right through the heatsink is the easiest option but note that you will have to offset the module horizontally by 10mm towards one end so that the holes go between the heatsink fins. Alternatively, if you elect to tap the heatsink, the module can be centred horizontally. This method also makes it easier to install Table 1: Resistor Colour Codes o o o o o o o o o o o o o o o o o 62  Silicon Chip No. 1 1 2 1 2 3 1 1 8 2 1 1 1 1 4 2 Value 1MW 22kW 12kW 6.8kW 1W 5% 6.2kW 2.2kW 510W 390W 100W 68W 47W 6.8W 1W 5% 10W 10W 1W 5% 0.1W 0W 4-Band Code (1%) brown black green brown red red orange brown brown red orange brown blue grey red gold blue red red brown red red red brown green brown brown brown orange white brown brown brown black brown brown blue grey black brown yellow violet black brown blue grey gold gold brown black black brown brown black black gold not applicable black 5-Band Code (1%) brown black black yellow brown red red black red brown brown red black red brown not applicable blue red black brown brown red red black brown brown green brown black black brown orange white black black brown brown black black black brown blue grey black gold brown yellow violet black gold brown not applicable brown black black gold brown not applicable not applicable black siliconchip.com.au Making A Winding Jig For The 6.8mH m Inductor ➊ ➋ ➍ ➌ These photos show how the winding jig is used to make the 6.8mH inductor. First, the bobbin is slipped over the collar on the bolt (1), then an end cheek is attached and the wire threaded through the exit slot (2). The handle is then attached and the coil tightly wound onto the bobbin using 25.5 turns of 1mmdiameter enamelled copper wire (3). The finished coil (4) is secured using a couple of layers of insulation tape and a band of heatshrink tubing. The winding jig consists of an M5 x 70mm bolt, two M5 nuts, an M5 flat washer, a piece of scrap PC board material (40 x 50mm approx.) and a scrap piece of timber (140 x 45 x 20mm approx.) for the handle. In use, the flat washer goes against the head of the bolt, after which a collar is fitted over the bolt to take the bobbin. This collar should have a width that’s slightly less than the the mounting screws. The heatsink drilling details are shown in Fig.11. You should also refer to the accompanying panel for information on drilling and tapping aluminium, since there are some special techniques to be followed if the job is to be a success. We’ll assume here that you’ve tapped the heatsink, ie, by drilling and tapping the white holes marked “A” on Fig.11. siliconchip.com.au width (height) of the bobbin and can be wound on using insulation tape. Wind on sufficient tape so that the bobbin fits snugly over this collar without being too tight. Next, drill a 5mm hole through the centre of the scrap PC board material, followed by a 1.5mm exit hole about 8mm away that will align with one of the slots in the bobbin. The bobbin can be slipped over the collar, after which Begin the heatsink assembly by attaching the two driver transistors, Q10 & Q11. Fig.12 (A) shows the mounting details for these devices. Note that they must each be electrically insulated from the heatsink using a TO-220 silicone insulating washer and insulating bush. However, because Q10 & Q11 are quite close together, it’s necessary to trim about 1mm off the adjacent sides of each insulating washer so that they don’t overlap. the scrap PC board “end cheek” is slipped over the bolt (ie, the bobbin is sandwiched into position between the washer and the scrap PC board). Align the bobbin so that one of its slots lines up with the exit hole in the end cheek, then install the first nut and secure it tightly. The handle can then be fitted by drilling a 5mm hole through one end, then slipping it over the bolt and installing the second nut. Use an MJE15030 for Q10 and an MJE15031 for Q11 – don’t get them mixed up. Both devices are secured using an M3 x 6mm screw and flat washer. Do the screws all the way up but don’t tighten them yet. Next, fit a 10mm spacer to each of the four corner mounting positions on the PC board. When they’re on, sit the board assembly on a flat surface and then lower the heatsink assembly into position so that Q10 & Q11’s leads go September 2008  63 Drilling & Tapping The Aluminium Heatsink CL 60 55 B A B A B B 41 25 20 30 25 11 B 55 50 A B A 75 A A 30 5.5 5.5 200 HOLES A: DRILL 2.5mm DIAMETER, TAP FOR M3 SCREW 100 HOLES B: DRILL 3.5mm DIAMETER (SCALE 1/2) Fig.11: this half-size diagram shows the drilling details for the heatsink. For tapped holes, mark out and drill the white holes marked “A” to a depth of 7mm (2.5mm drill, M3 tap). Alternatively, if you intend drilling right through the heatsink, drill the blue holes marked “B” (3.5mm drill). F IG.11 ABOVE SHOWS the heatsink drilling details. The white holes are drilled if you intend tapping the holes, while the blue holes are drilled if you want to drill right through the heatsink (ie, between the fins). If you intend drilling right through the heatsink, simply mark out the blue hole locations using a sharp pencil, then accurately drill the holes using a drill press. Use a pilot drill to begin with – the holes have to go between the fins so it’s vital to accurately position them. Be sure to use a suitable lubricant when drilling the holes. Kerosene is the recommended lubricant for aluminium but we found that light machine oil (eg, Singer) also works well for jobs like this. Don’t try drilling the holes in one go. When drilling aluminium, it’s important to regularly remove the bit from the hole and clear away the metal swarf. If you don’t do this, the aluminium has a habit of migrating onto the drill bit and ruining it. Don’t even think of using a hand-drill for this job by the way. There’s no way you’ll get the holes perfectly perpendicular to the mounting face. Once the holes have been drilled, deburr them using an oversize drill to remove any metal swarf from the mounting surface. This is vital to prevent punch-through of the insulating washers. Finally, the heatsink should be thoroughly scrubbed cleaned using water and detergent and allowed to dry. Drilling & tapping Alternatively, if you want to centre the module horizontally on the heatsink, you will have to drill and tap holes to accept M3 screws in the locations shown (ie, the white holes). This method is more time-consuming than drilling right through but it does make it easier to mount the transistors when it’s done. To do the job, you will need a 2.5mm drill, an M3 intermediate (or starting) tap and an M3 finishing tap. If you are unable to obtain a finishing tap, you can make one by grinding most of the tapered end off an intermediate tap. The first step is to mark out and drill the mounting holes to a depth of exactly 7mm using a 2.5mm drill. As before, be sure to regularly clear the hole and the drill bit of any metal swarf and keep the drill bit well-lubricated. Once the holes have been drilled, tap each one in turn, starting with the M3 intermediate tap and then finishing with the M3 finishing tap. The trick here is to take it nice and slowly. Keep the lubricant up and regularly wind the tap out to clear the metal swarf from the hole. You will know when you’re coming to the end of the hole by the increased resistance to turning the tap handle. Do not at any stage apply undue force to the tap. It’s easy to break a tap in half and if the break occurs at or below the heatsink’s face, you can scratch both the tap and the heatsink (and about $25). As before deburr the holes using an oversize drill and scrub the heatsink clean using water and detergent. Make sure that the mounting surface is perfectly smooth before moving installing the heatsink transistors. 64  Silicon Chip through their mounting holes. The four output devices (Q12Q15) can now be fitted. As shown in Fig.12 (B), these devices must also be insulated from the heatsink by using silicone insulating washers. Start by fitting Q12. The procedure here is to push its leads into their PC mounting holes, then lean the device back, feed through the mounting screw, hang the insulating washer off the end of the screw and finally loosely screw the assembly to the heatsink. The remaining three devices are installed the same way, taking care to fit the correct transistor type at each location. Once they’re in, push the board down so that all four spacers are in contact with the benchtop – this automatically adjusts the transistor lead lengths and ensures that the bottom of the board sits exactly 10mm above the bottom edge of the heatsink. Now adjust the PC board assembly horizontally so that each side is 32.5mm in from its adjacent heatsink end, then do up the transistor mounting screws while keeping the insulating washers correctly aligned. The next step is to lightly solder the outside leads of Q12 & Q15 to their pads on the top of the board. The assembly is then turned upside down and the remaining heatsink transistor leads soldered. Before soldering the leads though, it’s important to prop the front edge of the board up so that the board sits at right-angles to the heatsink. If you don’t do this, it will sag under its own weight and will remain in this condition after the leads have been soldered. Complete the soldering, then turn the board right way up again and tighten down the transistor mounting screws. They should be tight to ensure good thermal coupling between the devices and the heatsink. Checking device isolation Now check that each device is indeed electrically isolated from the heatsink. That’s done by switching your multimeter to a high ohms range and checking for shorts between the heatsink mounting surface and the collectors of the heatsink transistors (note: the collector of each device is connected to its metal face or tab). In practice, it’s simply a matter of checking between the fuse-clips closest to the heatsink and the heatsink itself. That’s because the device colsiliconchip.com.au lectors in each half of the output stage are connected together and run to their respective fuseholder. In each case, you should get an open-circuit reading. If you do find a short, undo each transistor mounting screw in turn until the short disappears. It’s then simply a matter of locating the cause of the problem and remounting the offending transistor. Be sure to replace the insulating washer if it has been damaged in any way (eg, punched through). MAIN PLATE OF HEATSINK SILICONE INSULATING WASHER SILICONE INSULATING WASHER INSULATING BUSH FLAT WASHER 6mm LONG M3 SCREW 10mm LONG M3 SCREW M3 TAPPED HOLE Completing the assembly The assembly can now be completed by installing the two 1000mF 63V cap­ acitors and the three screw terminal blocks (CON1-CON3). Take care when installing the latter – the access holes must face outwards. You should also remove the two support spacers from the edge of the board adjacent to the heatsink. In fact, it’s quite important that the rear edge of the board be supported only by the heatsink transistor leads. Basically, this avoids the risk of eventually cracking the PC tracks and pads around the heatsink transistors due to thermal expansion and contraction of their leads as they heat up and cool down. In short, the rear spacers are installed only while you install the heatsink transistors and must then be removed. They play no part in securing the module. Instead, this edge of the module is secured by bolting the heatsink itself to the chassis. This can be done by tapping M3 or M4 holes into the main plate on the underside of the heatsink or by using right-angle brackets. The front of the board can be secured using the two M3 x 10mm spacers fitted earlier. That completes the assembly of the power amplifier module. The next step is to build the power supply module. Power supply As noted last month, this new design dispenses with the regulated power supply used for the original Ultra-LD amplifier module. Instead, the Mk.2 module is powered using unregulated ±55V rails only. Fig.13 shows the circuit details of the power supply. It’s based on a centre-tapped (toroidal) mains transformer (T1) with two 40V windings and two 15V windings. As shown, the two 40V windings are connected together to give 80VAC siliconchip.com.au (HEATSINK FINS) NJL3281D OR NJL1302D TRANSISTOR (TO-264) MJE15030 OR MJE15031 TRANSISTOR (TO-220) AMPLIFIER PC BOARD M3 TAPPED HOLE A AMPLIFIER PC BOARD B Fig.12: this diagram shows the mounting details for the TO-220 driver transistors (A) and the four output transistors (B). After mounting these transistors, use your multimeter to confirm that they are properly isolated from the heatsink – see text. centre-tapped and this arrangement drives bridge rectifier BR1. This in turn feeds six 4700mF 63V electrolytic capacitors (ie, 14,100mF on each side) to provide balanced ±55V DC supply rails to power the amplifier. In addition, two LEDs are connected in series with 3.3kW 5W current-limiting resistors across the ±55V supply rails. These serve two purposes: (1) they provide a handy indication that power is present on the supply rails; and (2) they (slowly) discharge the filter capacitors when the power is switched off (see warning panel). The two 15V windings are also connected together (to provide 30VAC centre-tapped) and these drive bridge rectifier D1-D4 and two 2200mF filter capacitors to derive unregulated rails of about ±20V. These rails are then fed to 3-terminal regulators REG1 & REG2 to derive regulated ±15V supply rails to power a preamplifier module. In addition, the +20V rail is also made available as an output, along with a 30VAC output. The +20V rail can be used to power the “Universal Speaker Protector & Muting Module” (SILICON CHIP, July 2007), while the 30VAC output is connected to the “AC Sense” input of this module (it’s used to quickly disconnect the speaker when the power goes off, to avoid switch-off thumps). By the way, if you’re looking for a preamplifier to use with the Ultra-LD Mk.2 amplifier, the preamplifier module described in August 2007 SILICON CHIP (and used in the Class-A Stereo Amplifier) is ideal. Note, however, that 3-terminal regulators REG1 & REG2 on that preamplifier board must be replaced by wire links if powering it from the power supply described here. These links are connected between what were the IN and OUT pads for each regulator on the preamplifier board. Power supply assembly Fig.15 shows the parts layout for the power supply board. This board is coded 01109081 and carries all the parts following the transformer except for 35A bridge rectifier BR1 which must be mounted on a metal chassis to ensure adequate heatsinking. Begin by installing diodes D1-D4, the two LEDs and 3-terminal regulators REG1 & REG2. Make sure these parts are all orientated correctly and don’t get REG1 & REG2 mixed up. Both regulators are mounted with their metal tabs flat against the PC board. To install them, first bend their centre leads down through 90° about 5mm from their bodies, then bend their outer leads down through 90° about 7mm from the bodies. The regulators can then be fitted to the PC board and secured using M3 x 6mm screws, flat September 2008  65 BR1 35A/600V + ~ T1 CON1 TERMINAL 1 ~ 4700 F 63V  LED1 4700 F 63V 4700 F 63V K 3.3k 5W 40V POWER S1 0V F1: 5A A – TERMINAL 2 0V A 40V 0V 4700 F 63V TERMINAL 3  LED2 4700 F 63V 4700 F 63V K 3.3k 5W 15V N +55V A 0V –55V CON3 15V CON5 30V AC 0V E T1: 240V TO 2x 40V/300VA, 2x 15V/7.5VA CON4 D1–D4: 1N4004 K +20V 0V K A A K K REG1 7815 +15V OUT IN GND 2200 F 25V A A CON2 100 F 16V 0V 2200 F 25V LEDS 1N4004 A IN –15V OUT REG2 7915 K A K 100 F 16V GND 7815 7915 GND SC 2008 ULTRA-LD AMPLIFIER MK2 POWER SUPPLY GND IN GND IN IN OUT OUT Fig.13: the power supply is based on a toroidal transformer (T1) with two 40V windings and two 15V windings. The two 40V windings are connected in series and drive bridge rectifier BR1 and six 4700mF filter capacitors to produce the ±55V rails. Similarly, the 15V windings drive a bridge rectifier based on diodes D1-D4. This feeds 3-terminal regulators REG1 & REG2 to produce ±15V rails for a preamplifier. The +20V rail, derived from the output of D1-D4, is used to power the loudspeaker protector. washers and nuts. Tighten the screws firmly before soldering the device leads. Note that there’s enough room on the PC board to fit mini-heatsinks to the regulators. This will depend on the current drawn by the preamplifier you elect to use but should not be necessary in most cases. The three Quick-Connect male spade terminals (TERMINAL1-TERMINAL3) are next on the list. These are used to terminate the connections from bridge rectifier BR1 and the centre-tap of the 40V transformer windings. They are each secured in place using an M4 x 10mm screw, nut, flat washer and star washer – see Fig.14. The trick here is to use a Phillipshead screwdriver to hold the M4 screw 66  Silicon Chip stationary while you do up the nut with a ratchet-driven socket. Once all the Quick-Connect terminals have been tightly secured to the PC board, you can then install the remaining parts. These include the two 3.3kW 5W resistors, the electrolytic capacitors and the screw terminal blocks. Note that the two 5W resistors should be stood off the board by 1-2mm, to allow the air to circulate beneath them for cooling (use a cardboard spacer). Be sure to install the electrolytic capacitors with the correct orientation. These things have a nasty habit of exploding if they’re installed the wrong way around so double-check them. Be sure also to dovetail connectors CON3 & CON5 together (to form a 5-way connector) before installing QUICK CONNECT PC BOARD M4 STAR WASHER M4 FLAT WASHER M4 x 10mm SCREW & NUT Fig.14: here’s how the single-ended male Quick Connects are secured to the Power Supply module PC board. them on the PC board. If you solder one connector to the board first, you may not be able to dovetail them. The same goes for connectors CON4 & CON2. Putting it in a case The completed amplifier module and its power supply should be housed siliconchip.com.au Fig.15: install the parts on the power supply board as shown here, taking care to ensure that all the electrolytic capacitors are mounted with the correct polarity. Be sure also to use the correct regulator at each location. The two LEDs indicate when power is applied and remain lit until the 4700mF capacitors discharge after switch-off. We modified the power supply PC board after this prototype was produced, so that heatsinks could be fitted to the two 3-terminal regulators if necessary. This will depend on the current drawn by the preamplifier. siliconchip.com.au September 2008  67 HEATSINK EARTH LUGS SECURED TO CHASSIS MALE IEC CONNECTOR WITH 5A INTEGRAL FUSE 18080110 reifilpmA 2.KM DL-artlU T1 240V PRIMARY LEADS 0V Q1 Q2 CON2 0V -57V SHIELD 0V 1 5V AMPLIFIER BOARD Ultra-LD Mk.2 Amplifier power CON2 CON4 INSULATE ALL MAINS CONNECTIONS WITH HEATSHRINK SLEEVING 40 V – BR1 ~ + CON5 01109081 4 0V ~ POWER SUPPLY BOARD AUDIO INPUT LED2 CON1 SECURE EARTH LUGS TO CHASSIS USING M4 x 10MM SCREW, LOCKWASHER & TWO NUTS - SEE FIG.17 0V TO SPEAKER TERMINALS VIA LS PROTECTOR COM +57V V 0V CON3 SIG 15 LED1 S1 (TOP REAR) Fig.16: here’s how to wire the completed power amplifier and power supply boards into a metal case. The mains wiring at right would be typical of most installations but ensure that all exposed terminals are fully insulated. in an earthed metal case but we’ll leave the details of this up to you. However, don’t get involved in mains wiring unless you are experienced and know exactly what you are doing. Fig.16 shows the suggested wiring layout (but without a speaker protector or preamplifier). Make sure that the chassis is securely earthed via the mains and be sure to insulate all exposed mains terminals. Note that you will have to use a piggyback female spade connector (eg, Altronics H-2016A) to terminate the commoned 40V & 0V connections from the toroidal transformer. This connector plugs into the 0V terminal (TERMINAL 2) on the power supply module. The female spade connector fitted to the green earth lead is then plugged into the back of this connector. The other end of this earth lead is crimped to an earth lug. Similarly, 68  Silicon Chip the mains earth lead (green/yellow) is crimped to a second earth lug and the two earth lugs are securely bolted to the chassis. Once the assembly is complete, check your wiring very carefully. In particular, make sure that BR1’s positive and negative terminals connect to the correct terminals on the power supply board. You should also use a multimeter to confirm that the chassis is correctly earthed. Do that by checking for continuity between the earth terminal of the IEC socket and the chassis. Testing the power supply It’s now time to check that the power supply is functioning correctly but first a warning: avoid contact with the ±55V rails, both on the power supply module and on the amplifier module. There’s 110V between them and getting across the two rails simultaneously could have serious consequences. The same goes for the transformer secondary windings – make sure that you don’t get across either of the two 40VAC windings or the 80VAC that’s applied to bridge rectifier BR1. You must also allow the 4700mF filter capacitors on the power supply module to discharge down to a couple of volts before attempting to work on this module. Don’t just rely on the LED indicators – use your multimeter to confirm that the supply rails have indeed dropped to a low value before touching it. Similarly, make sure these capacitors have discharged before connecting the power supply to the amplifier module or disconnecting it (otherwise you could damage the amplifier). To check the power supply, first siliconchip.com.au Power Supply Parts List PC Board Module The 68W 5W test resistors are soldered to the fuse-clip pads on the underside of the PC board. make sure that the supply wiring is disconnected from the amplifier. That done, apply power to the power supply board and check the various DC outputs. You should be able to measure close to ±55V on CON1, +20V on CON4, ±15V on CON2 and 30VAC on CON5. If you don’t get the correct voltages, switch off immediately and check for wiring and component errors. Testing the power amplifier Assuming you do get the correct voltages, switch the power supply off and follow this step-by-step procedure to check the power amplifier module: STEP 1: remove the fuses from the amplifier module and install two 68W 5W resistors in their place. The best way to do this is to tack solder the resistors across the fuseholder pads on the underside of the PC board. They should be mounted about 5mm away from the edge of the board, to prevent heat damage during testing – see photo. The 68W resistors are there to limit the current through the output stage to about 800mA if there is a fault in the amplifier that turns the output transistors hard on. This protects the output transistors from damage but note that the 68W resistors will quickly burn out under such circumstances (since they will be dissipating over 40W). STEP 2: use your multimeter to again check that the heatsink transistors are all isolated from the heatsink. If one of these is shorted, its corresponding siliconchip.com.au 68W 5W resistor will again quickly burn out if power is applied. STEP 3: check that the power supply is off and that the filter capacitors are discharged, then connect the +55V, 0V and -55V supply leads to the amplifier at CON2. Make sure these are connected correctly, otherwise the amplifier will be damaged when power is applied. STEP 4: apply power and check the supply voltages at the fuseholders (ie, at the ends furthest away from the heatsink). You should get +55V at FUSE1 (with respect to the 0V rail) and -55V at CON2. STEP 5: check the voltage across each 68W 5W resistor. This should be in the range from 9-14V (depending on the supply rails and the exact value of the 68W test resistors). Switch off immediately and go to the troubleshooting procedure if you get a value that’s much higher than 14V. STEP 6: check the voltage at the loudspeaker terminals. You should get a reading of ±30mV or less. STEP 7: check the voltage across each of the 0.1W 5W emitter resistors in the output stage. This voltage should be between 7-10mV. This equates to a current of 70-100mA through each output transistor which means that the total output stage quiescent current is in the range of 140-200mA. Be careful not to short a resistor lead to the adjacent +55V and -55V tracks on the top of the board when making these voltage checks. 1 PC board, code 01109081, 126 x 96mm 3 3-way PC-mount terminal blocks, 5mm pitch (Altronics P2035A or equivalent) (CON1-CON3) 2 2-way PC-mount terminal blocks, 5mm pitch (Altronics P2034A or equivalent) (CON4-CON5) 3 chassis-mount single-ended Quick Connect (spade) terminals (TERM1-TERM3) (Jaycar PT-4910 or equivalent) 3 M4 x 10 screws 3 M4 a 10mm nuts 3 M4 flat washers 3 M4 shakeproof washers 4 M3 x 9mm tapped Nylon spacers 6 M3 x 6mm screws 6 M3 nuts 2 M3 shakeproof washers Semiconductors 4 1N4004 diodes (D1-D4) 1 7815 15V regulator (REG1) 1 7915 -15V regulator (REG2) 2 3mm red LEDs (LED1,LED2) Capacitors 6 4700mF 63V electrolytic 2 2200mF 25V electrolytic 2 100mF 16V electrolytic Resistors 2 3.3kW 5W Additional Parts 1 300VA transformer with 2 x 40VAC 300VA windings and 2 x 15VAC 7.5VA windings 1 35A 400V bridge rectifier (BR1) 1 chassis-mount IEC male socket with fuseholder (eg, Jaycar PP-4004, Altronics P-8324) 1 DPST mains switch (S1) 1 M205 5A fuse Miscellaneous Earth crimp lugs, female Quick Connectors, 240VAC cable, machine screws & nuts, etc. If the voltage across the 0.1W 5W emitter resistors exceeds 10mV, increase the 47W resistor between the supply rail and Q7’s emitter to 56W, or even to 68W if necessary to bring September 2008  69 Removing Parts From The PC Board If you need to remove components such as resistors or transistors from this doublesided board, the easiest way to do it is to first remove as much solder as you can from each pad using a solder sucker. Next, you clip away the body of the component using small sidecutters, then grab each lead with needle-nose pliers on the top of the board while you heat up its copper pad underneath. The lead can the voltage back into the 7-10mV range. This resistor is located on the far lefthand side of the PC board, immediately below a 100nF capacitor. Do not reduce Q7’s emitter resistor to less than 47W. STEP 8: check the voltages marked on the circuit diagram (Fig.1) last month. These should all be close to the indicated values. STEP 9: if everything is correct, switch off and allow the power supply filter capacitors to discharge to a low level (around 2V or less). When they reach this level, disconnect the power supply, remove the 68W 5W resistors from then be pulled out from the top. You then use solder-wick (or desoldering braid) to remove the residual solder in the plated through holes but be careful not to overheat the PC pads, as they may detach themselves from the board. Often, it will be necessary to drill out the holes to clear the solder, so that you can install the new component’s leads. the amplifier module and install the 5A fuses. STEP 10: connect an audio signal source and a loudspeaker (preferably via a loudspeaker protector module), then re-apply power and test the amplifier module with music. Troubleshooting If the voltage across the 68W test resistors is much greater than 14V (eg, close to the supply rail), switch off immediately (note: the resistors may burn out before you do this). The first thing to check is that the heatsink transistors are all correctly isolated from the heatsink. If this checks out, apply power to the amplifier without the fuses or test resistors in place – ie, so that the output stage (Q10-Q15) is left unpowered. Now check the voltage between the bases of transistors Q10 & Q11. This should be close to 2.2V. If it’s much higher than 2.2V, this indicates that the DQ12-DQ15 diode string is open circuit. This could be due to an opencircuit track on the PC board or more likely, a missed solder connection on one of the output transistor leads (ie, the “A” & “K” diode leads). If the voltage across the diode string is correct, check the base-emitter voltage of each transistor in the amplifier. In each case, you should get a reading of 0.6-0.7V if the transistor is working correctly. Check that the correct transistor has been used at each location. Finally, be sure to use this module with a loudspeaker protector, as a fault in the output stage can quickly burn out an expensive loudspeaker system (and maybe even start a fire due to a red-hot voice-coil). The recommended unit is the “Universal Speaker Protector & Muting Module” SC (see SILICON CHIP, July 2007). Radio, Television & Hobbies: the COMPLETE archive on DVD YES! NA R MO E THA URY ENT QUARTER C NICS O OF ELECTR ! Y R O T IS H This remarkable collection of PDFs covers every issue of R & H, as it was known from the beginning (April 1939 – price sixpence!) right through to the final edition of R, TV & H in March 1965, before it disappeared forever with the change of name to EA. For the first time ever, complete and in one handy DVD, every article and every issue is covered. If you’re an old timer (or even young timer!) into vintage radio, it doesn’t get much more vintage than this. If you’re a student of history, this archive gives an extraordinary insight into the amazing breakthroughs made in radio and electronics technology following the war years. And speaking of the war years, R & H had some of the best propaganda imaginable! Even if you’re just an electronics dabbler, there’s something here to interest you. • Every issue individually archived, by month and year • Complete with index for each year • A must-have for everyone interested in electronics Please note: this archive is in PDF format on DVD for PC. Your computer will need a DVD-ROM or DVD-recorder (not a CD!) and Acrobat Reader 6 or above (free download) to enable you to view this archive. This DVD is NOT playable through a standard A/V-type DVD player. Exclusive to SILICON CHIP ONLY 62 $ 00 +$10.00 P&P HERE’S HOW TO ORDER YOUR COPY: BY PHONE:* (02) 9939 3295 9-4 Mon-Fri BY FAX:# (02) 9939 2648 24 Hours 7 Days <at> BY EMAIL:# silchip<at>siliconchip.com.au 24 Hours 7 Days BY MAIL:# PO Box 139, Collaroy NSW 2097 * Please have your credit card handy! # Don’t forget to include your name, address, phone no and credit card details. 70  Silicon Chip BY INTERNET:^ siliconchip.com.au 24 Hours 7 Days ^ You will be prompted for required information siliconchip.com.au STIC FANTAIDEA GIFT UDENTS FOR SFT ALL O S! AGE THEAMATEUR SCIENTIST An incredible CD with over 1000 classic projects from the pages of Scientific American, covering every field of science... THE LATEST VERSION 4 – WITH EVEN MORE FEATURES! Arguably THE most IMPORTANT collection of scientific projects ever put together! This is version 4, Super Science Fair Edition from the pages of Scientific American. As well as specific project material, the CDs contain hints and tips by experienced amateur scientists, details on building science apparatus, a large database of chemicals and so much more. ONLY 62 $ 00 PLUS $10 Pack and Post within Australia NZ P&P: $AU12.00, Elsewhere: $AU18.00 “A must for every science student, science teacher, science lab . . . or simply for those with an enquiring mind . . .” Just a tiny selection of the incredible range of projects: ! Build a seismograph to study earthquakes ! Make soap bubbles that last for months ! Monitor the health of local streams ! Preserve biological specimens ! Build a carbon dioxide laser ! Grow bacteria cultures safely at home ! Build a ripple tank to study wave phenomena ! Discover how plants grow in low gravity ! Do strange experiments with sound ! Use a hot wire to study the crystal structure of steel ! Extract and purify DNA in your kitchen !Create a laser hologram ! Study variable stars like a pro ! Investigate vortexes in water ! Cultivate slime moulds ! Study the flight efficiency of soaring birds ! How to make an Electret ! Construct fluid lenses ! Raise butterflies as experimental animals ! Study the physics of spinning tops ! Build an apparatus for studying chaotic systems ! Detect metals in air, liquids, or solids ! Photograph an ant's brain and nervous system ! Use magnets to make fluids into solids ! Measure the metabolism of an insect . . . ! and many, many more (a thousand more, in fact!) See the V2 review in SILICON CHIP, October 2004. . . or read on line at siliconchip.com.au This is the ALL-NEW Version 4 . . . it’s even BETTER! HERE’S HOW TO ORDER YOUR COPY: BY PHONE:* (02) 9939 3295 9-5 Mon-Fri BY FAX:# <at> (02) 9939 2648 24 Hours 7 Days BY EMAIL:# silicon<at>siliconchip.com.au 24 Hours 7 Days BY MAIL:# BY PAYPAL:# PO Box 139, Collaroy NSW 2097 silicon<at>siliconchip.com.au 24 Hours 7 Days * Please have your credit card handy! # Don’t forget to include your name, address, phone no and credit card details. BY INTERNET:^ siliconchip.com.au 24 Hours 7 Days ^ You will be prompted for required information There’s also a handy order form inside this issue. Exclusive in SILICON Australia to: CHIP siliconchip.com.au siliconchip.com.au September 2008  71