Fullscreen HTML5Med Res (??MB)HTML4

Ultra-LD Mk.3 135W/ch stereo amplifier Com p le t in g t h e w ir in g & m a k in g a d j us t m en t s Last month, we introduced our new Ultra-LD Mk.3 135W Stereo Amplifier and described the initial assembly details. In Pt.2 this month, we complete the assembly and describe the adjustment procedure for the power amplifier modules & the remote control. W E LEFT OFF last month with all the modules mounted in position, except for the two Ultra-LD Mk.3 power amplifier modules. We also described the transformer mounting. Once the transformer is in place, remove the adjacent side panel of the case by undoing the five self-tapping screws. Be careful during this procedure – the screws will initially be tight and one slip with the screwdriver is 60  Silicon Chip all it takes the leave an unsightly mark on the panel. Placing several layers of masking tape around the screw heads while you undo them is a worthwhile insurance policy here. The next step is to run the 230VAC wiring. This wiring must be installed in a professional manner with all connections securely crimped and insulated. Removing the side panel gives you good access to the chassis to install the mains wiring. This involves crimping a number of fully-insulated spade connectors onto various leads and it’s important to use a ratchet-driven crimping tool for this job (see panel last month). After crimping, you must also check that each connection is secure and that all wire strands are inside the connector – something that’s particularly important with mains wiring. siliconchip.com.au MAINS EARTH LEAD Obtaining A Shielded Power Transformer Last month, we indicated that the power transformer supplied with kits would come with an integral flux band. However, it transpires that Altronics will be supplying a stock transformer which doesn’t have this flux band, although this will still give quite good performance. For optimum signal-to-noise ratio, you can either fit this transformer with a copper strap or you can purchase a shielded transformer from either Harbuch Electronics or from Dyne Industries (see panel later in this article for details). Pt.2: By GREG SWAIN Begin by routing the blue and brown primary leads around the rear of the transformer and securing them with several cable ties (see photos & Fig.1 in Pt.1). The blue primary lead can then be trimmed to length (about 225mm), stripped of 5mm of insulation and terminated in a fully-insulated spade connector. If you want to be doubly-fussy here, it’s a good idea to cut a 17mm length of 5mm-diameter heatshrink and slip it over the blue lead before crimping on the connector. The heatshrink can then be slid over the rear section of the connector and shrunk down using a hot-air gun (but take it easy with the heat; gently does it). This connector can now by plugged into the Neutral terminal on the back of the IEC connector. That done, fit another cable tie to secure both primary leads close to the end of the heatshrink. Next, cut a 450mm length of brown 32/0.20mm mains-rated cable and terminate one end in another fullyinsulated spade connector (and again add the heatshrink). Plug this into the siliconchip.com.au Active terminal on the IEC connector, then feed both this lead and the brown transformer primary lead down a 360mm-length of 5mm-diameter heatshrink. That done, adjust the heatshrink so that it is about 20mm from the end of the fully-insulated spade connector and apply some gentle heat from a hot-air gun to shrink it down. Push the leads and the heatshrink down flat against the chassis as you do this, so that the leads sit side by side. This not only keeps the leads together but also double-insulates them where they run around the mains transformer and under the righthand power amplifier module, to keep everything nice and safe. The switch end of this cable should now be pushed through a rubber insulation boot (eg, Altronics H1472), after which the individual leads can be fitted with fully-insulated spade connectors. Once again, slip a 17mm length of 5mm heatshrink over each lead before crimping on the connector, then push the heatshrink into position over the end of the connector and shrink it down. That done, secure the mains wiring to the floor of the chassis using four 5mm P-clamps but leave the P-clamp nearest to the power switch out for the time being. Orientate the P-clamps that are fitted at this stage as shown in Fig.1 (and the photo on page 63) INSULATED CRIMP EYLET LOCKING NUT STAR LOCKWASHERS M4 x 10mm SCREW & NUT BASE PLATE OF CASE NB: CLEAN PAINT AWAY FROM MOUNTING HOLE Fig.6: the Earth lead from the IEC connector is secured to the case via an insulated crimp eyelet as shown here. The top nut serves as a lock-nut, so that the assembly cannot come loose. Make sure that the crimp eyelet makes good electrical contact with the case. and secure them using M4 x 10mm machine screws, flat washers and nuts. Important: as with the audio input cable, you must also install two M4 flat washers under the head of the screw that secures the P-clamp under the power amplifier module. This avoids the possibility of shorting the end of this screw to the underside of the amplifier. Finally, you can complete the mains wiring by installing the main green/ yellow Earth lead prepared earlier. This plugs into the Earth terminal of the IEC connector, while the other (eyelet) end is bolted to the main chassis earth point using an M4 x 10mm machine screw, two star washers and two nuts – see Fig.6 above. The second nut on top locks the assembly into position and ensures that the assembly cannot possibly come loose. Secondary wiring Now for the low-voltage secondary wiring. We’ll start with the two 40V AC windings which involves the four leads (orange, black, white & red on the prototype) closest to the primary leads. The first step is to tie the two adja- WARNING! HIGH VOLTAGE High AC and DC voltages are present in this circuit. In particular, mains voltages (230V AC) are present on the IEC socket and the primary side of the transformer (including the wiring to the power switch). In addition, the transformer secondary provides an 80V AC output (2 x 40V AC centre-tapped) and the amplifier power supply rails total 114V DC. Do not touch any part of the amplifier circuitry when power is applied otherwise you could get a severe electric shock. The two LEDs on the power supply board indicate when power is present. If they are lit, the power supply and amplifier boards are potentially dangerous. April 2012  61 Parts List: Ultra-LD Mk.3 Stereo Amplifier 1 custom pre-punched steel case with screened front & rear panels 1 32mm black aluminium knob with grub screw (Altronics H 6236) 1 300VA toroidal transformer with two 40VAC windings and two 15VAC 7.5A windings (brown primary lead must be 620mm long to reach the mains switch; blue primary lead must be 240mm long to reach IEC socket) 1 35A 400V chassis-mount bridge rectifier (Altronics Z 0091) 1 SPST 10A 250VAC rocker switch (Altronics S 3224) 1 chassis-mount male IEC socket with fuseholder (Altronics P 8324) 2 M205 3.15A 230VAC slow-blow fuses (one spare) (Altronics S 5657) 1 230VAC 3-pin IEC mains power lead 2 2-way loudspeaker terminal panels (Altronics P 2016) 2 6.3mm double-ended chassismount spade lugs (Altronics H 2261) 1 eyelet (ring) connector, 4mm inside diameter (Altronics H 2036A) 19 6.3mm female fully-insulated spade connectors (Altronics H 2001A) 1 piggyback crimp connector (Altronics H 2016A) 4 red right-angle RCA plugs (Altronics P 0169) 4 black right-angle RCA plugs (Altronics P 0170) cent centre leads together using a couple of cable ties. These leads are then trimmed to length (don’t cut them too short), after which you remove about 5mm of the spaghetti insulation from the ends. The enamel insulation must then be scraped away from the ends, after which they are lightly soldered together and terminated in a piggyback quick connector (Altronics Cat. H2016A) to form the centre tap. This centre-tap connector is now plugged into the CT terminal on the power supply PCB. The earth lead prepared earlier is then fitted between 62  Silicon Chip 13 Nylon P-clamps, 5mm diameter (Altronics H 4201) 1 Nylon P-clamp, 9.5mm diameter (Altronics H 4221) 4 self-adhesive flat cable clamps (Altronics H 4520) 2 self-adhesive cable tie mounts, 12.5mm (Altronics H 4107) 20 small Nylon cable ties 1 1-metre length of 5mm-diameter heatshrink tubing 1 rubber insulation boot to cover mains switch (Altronics H 1472) Heatsink compound for rectifier 1m red 32/0.20 extra heavy-duty hook-up wire (Altronics W 2283) 1m black 32/0.20 extra heavy-duty hook-up wire (Altronics W 2284) 250mm 32/0.20 heavy-duty blue hook-up wire (Altronics W 2275) 1m green 32/0.20 extra heavy-duty hook-up wire (Altronics W 2285) 1m figure-8 shielded audio cable (Altronics W 3022) 2m heavy-duty 102/0.12 or 41/0.20 speaker cable (Altronics W 1240) 500mm heavy-duty green/yellow mains-rated cable Modules Screws, nuts & spacers 2 Ultra-LD Mk.3 power amplifier modules (July-August 2011) 1 power supply module (September 2011) 1 loudspeaker protector module (October 2011) 1 stereo preamplifier module (November-December 2011) 1 3-way stereo input selector module plus switch board (November-December 2011) IDC headers & cables 2 10-pin IDC cable-mounting sockets (Altronics P 5310) 2 14-pin IDC cable-mounting sockets (Altronics P 5314) 1 550mm-length of 10-way IDC cable (Altronics W 2610) 1 650mm-length of 14-way IDC cable (Altronics W 2614) Wire & cable 1m brown 32/0.20 extra heavyduty mains-rated hook-up wire (Altronics W 2280) the remaining piggyback terminal and the relevant chassis quick connector. The outer 40V AC leads can now be trimmed, fitted with spade connectors and plugged into the AC terminals of the bridge rectifier. Use a couple of extra cable ties to bind these to the centre-tap leads. The two 15V AC secondary windings were similarly colour coded on the supplied prototype transfomer. As shown in Fig.1 last month, these leads are terminated in a 3-way screw terminal block on the power supply module, with the central black and white leads 50 M3 x 6mm pan-head machine screws 11 M3 x 10mm pan-head machine screws 4 M3 hex nuts 50 M3 flat washers 17 M4 x 10mm panhead screws 21 M4 nuts 1 M4 x 16mm screw (to secure bridge rectifier BR1) 16 M4 flat washers 10 M4 shakeproof washers (for bridge rectifier BR1 and chassis earth points) 14 M3 x 10mm tapped spacers (Altronics H 1216) 4 M3 x 25mm tapped spacers (Altronics H 1233) 3 M2 x 12mm machine screws, nuts and washers (to secure RCA sockets on input selector board to the rear panel) 6 6g x 12mm countersink selftapping screws (to secure IEC connector and loudspeaker terminal panels) again forming the centre tap. Begin by trimming these leads to length, then remove 5mm of insulation from the ends, scrape away the enamel and lightly solder them together before securing them in the screw-terminal block. The outer 15V AC leads can then be routed alongside the centre-tap leads, trimmed and secured to their relevant screw terminals. Cable ties can then be used to secure the four leads together. 12V windings & a nasty trap Our prototype transformer also siliconchip.com.au This inside view shows how the preamplifier and switch modules are mounted in position. Note that in the final version, an earth lead is also run from the base of the chassis to a spade connector on the front panel (see Fig.1 last month). came with two grey 12V tappings, which aren’t used here. If present, these leads can be shortened to 3035mm and covered in heatshrink. However, there’s a nasty trap here. Inside each length of grey spaghetti insulation are two enamel-covered leads. In each case, the ends of these two leads must be stripped of enamel and soldered together. If you don’t do that, the 15V windings will be open circuit. That’s because the 12V windings form part of the 15V windings, so failing to reconnect the wires inside each grey length of insulation renders the 15V windings inoperative. DO NOT under any circumstances connect the wires in one grey lead to the wires in the other grey lead. The best way to deal with these 12V leads is to cut them to unequal lengths, then join the two wires in each individual lead. These wires can then be insulated with some 1.5mm-diameter heatshrink, after which you can sleeve both leads together with some 5mmdiameter heatshrink (see photo below). Be gentle with the heat – the spaghetti insulation on the grey leads (and on adjacent leads) is easily damaged. You can now reattach the side to the chassis. Be careful when installing the self-tapping screw on the bottom edge at the rear – it must be well clear of the mains wiring. Mounting the amplifiers Before installing the two power amplifier modules, it’s first necessary to solder the two loudspeaker cables to their output pads on the underside of each PCB – see photo on page 65. As explained in the panel accompanying this photo, this is necessary to minimise distortion. The power amplifiers can now be mounted in the chassis. To do that, first turn the chassis upside down and check that the powder coating has been scraped away from around the Here’s how the 230V AC wiring is routed to the power switch on the front panel. This wiring is sleeved in 5mm-diameter heatshrink over most of its length and is secured to the floor of the chassis using Nylon P-clips. Note the rubber insulating boot (or cover) that’s pushed over the mains switch. siliconchip.com.au April 2012  63 Shielding The Toroidal Transfomer This view shows how the copper strap that’s used to shield the transformer is held in place using using a 90-120mm stainless-steel pipe clamp. T HE TOROIDAL transformer used in the Ultra-LD Mk.3 amplifier was initially unshielded. However, during testing, we found that the amount of hum and rectifier buzz from the windings was enough to cause some noise and hum in the output, albeit at a signal-to-noise (S/N) ratio of better than 100dB (which is still quite good). It was worse in the left channel which has its amplifier module closer to the transformer than the right channel. To fix this problem, we adopted a technique that was commonly employed in E-I transformers where it was common to wrap a copper strap in close proximity around the windings – see photo. The copper strap is referred to as a “flux band” and it effectively provides a shorted turn to all the leakage flux produced by the core of transformer. Above: it was quite common for Australian-made E-I transformers to be fitted with a copper strap to minimise the leakage flux. 64  Silicon Chip With E-I transformers (E & I refer to the shape of the stamped steel laminations), the copper strap is wrapped around the core and the outside of the windings and is soldered to produce a low resistance shorted turn. While we can fit a copper strap around the outside of a toroidal transformer, it is not possible to solder it, as to do so would damage the outside insulation. So to hold the copper strap tightly in place, we used a 90-120mm stainless steel pipe clamp with a worm-screw adjustment. These can be obtained from plumbing suppliers. The strap was cut from a sheet of 0.5mm-thick copper (obtained from a scrap metal dealer) to give a strap measuring 450 x 45mm. This is easily done if you have a guillotine but if you are careful you can do it with a pair of large tin-snips. The steps are as follows. Make sure that the copper sheet is as free from blemishes as possible. Any small dimples or ripples can be (gently) removed with a rubber mallet or soft-face hammer. Then polish the area to be cut off using Brasso or similar metal polish. Polish it on both sides to a bright shine. Hopefully, the sheet has one straight edge which can then be used for marking out the dimensions of the strap. So you need to scribe a line on the sheet on the copper, 45mm from the straight edge. Now there are several tricks to using tin-snips to make precision straight-line cuts. If at all possible, do a trial run on a piece of thin steel or aluminium sheet. By Leo Simpson When cutting with tin-snips, depending on whether they are left-hand or right-hand, you will find that one side of the cut material naturally curves up or down. You use this natural curvature to produce the copper strap – in our case we do want it curved. Proceed with your cut very slowly – don’t hurry it otherwise you are sure to get a crooked cut. Keep going until you have a strap more than 450mm long. Then scribe lines at right angles to produce squared-off ends of the strap. Again, cut these carefully and then nip of the corners. Do not try to straighten out the curve of the strap. If you have finger-marks on the copper surface, clean them off thoroughly. Now we want to bend the strap in a smooth circle so it will wrap smoothly around the outside of the transformer and produce an overlap of about 100mm. The important point about this is that you need a series of different circular formers, starting large and coming down to about 90mm diameter or so. We used a number of different sized paint tins and finished with a length of 90mm plastic storm-water pipe. The point about using different sized pain tins is that if you use too small a former to start with, you run the risk of putting kinks in the strap. Once you have finished with the smallest former, you will find that the resulting circular strap has a diameter of around 100 to 120mm and will be slightly springy. Good! That makes it a little easier to fit around the transformer. It can then be locked in place with the stainless steel pipe clamp referred to above. In our case, we fitted the copper strap to the transformer after it had been wired in place, which made it quite tricky. The copper strap improved the signal-to-noise ratio from just over -100dB to -111dB in the right channel and to -107dB in the left channel which is excellent. Some constructors may want to take the risk of not fitting the transformer with a copper strap initially. If they then decide that their finished amplifier is insufficiently quiet, they can still fit the strap. On the other hand, if you feel that you could not produce a neat and effective copper band, then you could purchase a shielded toroidal transformer from either of two suppliers: (1) Harbuch Electronics, phone (02) 9476 5854, www.harbuch.com.au (2) Dyne Industries, phone (03) 9720 7233, www.dyne.com.au siliconchip.com.au Solder The Loudspeaker Cable Connections For Low Distortion The loudspeaker cables are directly soldered to the underside of the power amplifier modules (left) and also to the loudspeaker protector module (right) to achieve the lowest possible distortion figures. As originally described in July 2011, the Ultra-LD Mk.3 Amplifier Module used a Molex Mini-fit Jr 4-pin socket as a loudspeaker connector (CON3). However, when we came to test the fully-assembled stereo amplifier, we found that the metal-to-metal contacts in these connectors were a significant cause of distortion. A similar effect was found with the spade connectors on the loudspeaker protection module. holes for the six screws that are used to secure the heatsinks. That done, secure each module to the chassis using three M3 x 10mm screws which go into the heatsinks, plus a lock washer under the head of each screw. The lock washers bite into the bare metal and ensure that the heatsinks are solidly earthed. Don’t over-tighten these screws – it’s all too easy to strip the threads inside the aluminium heatsinks if you do. Be sure to route the loudspeaker cables as shown in Fig.1 when installing the power amplifier modules. The cable for the right channel amplifier runs directly back under the PCB towards the rear of the chassis. By contrast, the loudspeaker cable from the left channel amplifier runs back under the board towards the front of the chassis. It then loops around and runs back under the right channel amplifier. Once the amplifier modules are in position, secure their spacers on the edges nearest the power supply to the chassis using M3 x 6mm screws. Temporarily loosen off the heatsink siliconchip.com.au The overall effect was sufficient to double the distortion readings of the complete amplifier. Accordingly, the final assembly eliminates the connectors on the power amplifier modules and the loudspeaker leads are directly soldered to the output terminals of the power amplifier modules instead. Similarly, the push-on (female) spade connectors have been eliminated from the loudspeaker cables that go to the screws to get everything to line up if necessary. The free ends of the loudspeaker cable can now be soldered to the loudspeaker protector module. If quick connect terminals have already been soldered on this board, then you can solder the loudpeaker cables directly to them. If not, you can temporarily remove the loudspeaker protector and drill holes in the PCB so that the loudspeaker cables can be directly soldered to the relevant copper pads. Don’t use bolt-on quick connectors on the loudspeaker protector board they will only cause distortion. Connecting the RCA cables The RCA audio cables can now be plugged into the preamplifier and to the power amplifier. Note that the RCA cable to the right-channel power amplifier is routed via a P-clamp that’s secured to one corner of the power supply module. A short piece of aerated foam wrapped around the cable will stop it from moving. You will have to remove the exist- loudspeaker protection module and all connections are directly soldered to the PCB (ie, the quick connect male spade terminals are eliminated). As far as the original Ultra-LD Mk.3 amplifier and loudspeaker protector modules are concerned, the original loudspeaker connection arrangement can be retained where extremely low distortion is not critical, eg, in a guitar amplifier. A small piece of red film is attached to the inside of the front panel, over the hole for the infrared receiver. ing M3 x 6mm mounting screw at this point and substitute an M3 x 10mm screw when the P-clamp is installed. The short RCA cable to the left-channel amplifier is secured to its adjacent audio input cable using a cable tie so that it cannot come loose and contact high voltage wiring. Do not plug the supply connectors into the power amplifier modules at April 2012  65 The rear panel of the amplifier carries the three pairs of RCA input sockets, the loudspeaker terminals and the IEC connector. Be sure to use self-tapping screws to secure the IEC connector, so that they are earthed to the chassis. this stage. That step comes later, after you have checked out the power supply voltages and the operation of the loudspeaker protector. Mounting the front panel Now for the final assembly. Snap the mains switch into its front-panel cut-out with its outside terminal to the top, then attach a small piece of red film to the inside of the panel over the hole for the infrared receiver. This can be cut into a strip and secured with short strips of duct tape at either end (see photo) or you can use silicone. The front panel can now be slid into position and secured along its bottom edge using the supplied countersink machine screws. The mains leads can then be connected to the switch and the earth lead connected between the lug on the rear of the front panel and the adjacent chassis earth point – see Fig.1 in Pt.1. Note: this earth connection is not present in the prototype. We decided to add it after we had the prototype metalwork made, to make it easier to securely earth the front panel rather than just rely on the machine screws that secure the panel to the chassis. Do not omit this earth connection. Once the switch wiring is complete, slide the rubber insulating boot over the switch and secure it in place by 66  Silicon Chip fitting a cable tie to the switch wires close to where they enter the boot. The remaining (fifth) P-clamp can then be used to secure the switch wiring to the chassis, before it disappears under the lefthand power amplifier module. Initial checks There are a few things to check before connecting the loudspeaker leads to the speaker protector or even plugging in a mains cord and switching on: CHECK 1: Check the 230V wiring to the IEC socket, mains transformer and mains switch. In particular, the female spade connectors should all be tightly crimped, the connectors must be fully insulated and there must be no wire strands outside these connectors. In addition, all spade connectors must be a tight fit onto their lugs, especially at the IEC socket, the mains switch and the bridge rectifier. Retension any connectors that slide on too easily. CHECK 2: Check that BR1’s positive and negative terminals connect to the correct terminals on the power supply board. CHECK 3: Check that all the electrolytic capacitors on the power supply board are installed with the correct polarity. These things have a nasty habit of exploding if they’re in the wrong way around. The same goes for other electrolytics across the supply rails on the other modules. In fact, it’s a good idea to wear safety glasses when switching on for the first time, in case you do have a capacitor in the wrong way around or you accidentally reverse the polarity to the power supply module. Exploding capacitors and eyeballs don’t mix too well! Better still, fit the lid to the case before initially applying power to the amplifier – see Step 5 below. CHECK 4: Use a multimeter to confirm that all the chassis panels are correctly earthed. Do that by checking for continuity between the earth terminal of the IEC socket and each of the panels in turn. Remove some of the powder coating from an inside surface of each panel to make this check, if necessary. Similarly, check that the heatsinks are earthed to the chassis and that all external screw heads are earthed. CHECK 5: Use a multimeter to confirm that the heatsink transistors (Q10-Q16) on each amplifier module are electrically isolated from the heatsink itself (see the article in the August 2011 issue). Test & adjustment The basic procedure here is to test the output rails from the power supply module before applying power to the remaining modules. siliconchip.com.au The quiescent current flowing in the output stage of each power amplifier is initially adjusted by installing 68W 5W resistors in place of the fuses. The voltage across one resistor is then monitored and trimpot VR1 adjusted for a reading of 9.5V – equivalent to a quiescent current of 140mA. The easiest way to connect the resistors is to “blow” the fuse wires in a couple of spare M205 fuses, then drill holes in the end caps and solder the resistors in place as shown. The original fuses can then be removed and the “modified” fuses clipped into place – see photo below. Here’s the step-by-step procedure: STEP 1: Disconnect the supply leads to the preamplifier and the loudspeaker protector (do this at the power supply module). STEP 2: Check that the DC supplies to the power amplifier modules are unplugged. STEP 3: Remove the fuses from the power amplifier modules. STEP 4: Slide out the fuse drawer at the bottom of the IEC connector, fit a 3A slow-blow fuse into the plastic lugs at the bottom of the drawer and slide the drawer back into position. STEP 5: Connect an IEC power cord to the amplifier and use a multimeter to confirm continuity between the earth pin of the plug and the chassis earth. That done, plug the cord into a mains socket and switch on. Warning: don’t go poking around the rear of the IEC socket and the front-panel switch when the device is plugged into the mains. Most of the terminals will be at 230V AC! Note also that high DC and AC voltages are present in siliconchip.com.au G r e a t V a l u e i n Te s t & M e a s u r e m e n t Adjusting The Quiescent Current Through The Power Amplifiers CAN bus analysis now also available in the oscilloscope entry level class 200 MHz 2[4] Channel Digital Oscilloscope HMO2022 [HMO2024]  2GSa/s Real Time, Low Noise Flash A/D Converter (Reference Class)  2MPts Memory, Memory Zoom up to 50,000:1  MSO (Mixed Signal Opt. HO3508) with 8 Logic Channels  Serial Bus Trigger and Hardware accelerated Decode incl. List View, I2C, SPI, UART/RS-232, CAN, LIN (optional)  Automatic Search for User defined Events  Pass/Fail Test based on Masks  Vertical Sensitivity 1mV/div., Offset Control ±0.2...±20V  12div. x-Axis Display Range, 20div. y-Axis Display Range (VirtualScreen)  Trigger Modes: Slope, Video, Pulsewidth, Logic, Delayed, Event Rohde & Schwarz (Australia) Pty Ltd Unit 2, 75 Epping Road, North Ryde NSW 2113 www.rohde-schwarz.com.au sales.australia<at>rohde-schwarz.com April 2012  67 Selecting The Mode & Programming The Remote As stated in the text, it’s necessary to program the universal remote control correctly. By default, the microcontroller’s RC5 code is set to TV but SAT1 or SAT2 can also be selected. Just press and hold button S1 on the Switch Board during power-up for SAT1 or button S2 for SAT2. Pressing S3 at power-up reverts to TV mode. Once you’ve chosen the mode or “device”, the correct code must be programmed into the remote. This involves selecting TV, SAT1 or SAT2 on the remote (to agree with the microcontroller set-up) and then programming in a three or 4-digit number for a Philips de- this circuit. In particular, the 40VAC transformer secondaries are connect­ed together to provide a total of 80VAC to the bridge rectifier, while the amplifier power supply rails total 114V DC. Do not touch any of this high-voltage circuitry (including the fuses on the power amplifiers) while power is applied – see warning panel. STEP 6: Use a multimeter to check the various DC outputs on the supply module. There should be close to ±57V on CON1 & CON2, ±15V on CON3 and +20V on CON6 (all with respect to 0V). In addition, you should be able to measure 30VAC on CON5. If you don’t get the correct voltages, switch off immediately and check for wiring and component errors. STEP 7: If the power supply checks out, switch off, wait until the LEDs on the supply board go out, then reconnect the AC and DC supplies to the loudspeaker protector module. Apply power and check that the relay turns on after about 5s. If it does, temporarily short the terminals on CON3 – the relay should immediately switch off. Similarly, the relay should immediately switch off if you disconnect one of the AC leads to CON2 (note: do not temporarily install a link between CON1 & CON2 for testing, as described in the October 2011 article, if the 30V AC leads are connected to CON2). Now check that that the relay switches off if you connect a 3V (eg, 2 x 1.5V cells in series) or 9V battery (either way around) between the LSPKIN+ terminal and the ground (-) terminal of CON1. Repeat this test for 68  Silicon Chip vice. That’s because most Philips devices (but not all) rely on the RC5 code standard. Most universal remote controls can be used, including the Altronics A1012 ($19.95). For this remote, use a code of 023 or 089 for TV mode, 242 for SAT1 or 035 for SAT2. In the case of other universal remotes, it’s just a matter of testing the various codes until you find one that works. There are usually no more than 15 codes (and usually a lot less) listed for each Philips device, so it shouldn’t take long to find the correct one. Note that some codes may only the RSPKIN+ terminal, then reverse the battery polarity and perform both tests again. STEP 8: Switch off, wait until the power supply LEDs to go out and reconnect the ±15V supply wiring from the preamplifier. Reapply power and check that the blue front-panel power LED lights. One of the blue switch LEDs should also light. Check that you can manually select the inputs by pressing the input switches. STEP 9: Set up and test the remote control functions for the preamp, as detailed in the December 2011 issue. That done, adjust trimpot VR2 as described, so that the muting function operates correctly. The Altronics A1012 universal remote shown above is ideal for use with this unit. Note that it must be programmed by choosing a mode (TV, SAT1 or SAT2) and entering in the corresponding code – see the above panel. STEP 10: Switch off again, wait for the supply LEDs to go out, then connect the ±57V DC supply for the right channel power amplifier. Check that the on-board fuses have been removed. STEP 11: Connect 68Ω 5W resistors across the fuse clips as described in the September 2011 article on the UltraLD Mk.3 amplifier module. That done, adjust the quiescent current through the output stage by following steps 1-11 in that article. STEP 12: Remove the safety resistors and install the fuses for that module. STEP 13: Repeat the last three steps for the left-channel power amplifier. The unit will work with most universal remotes including the Altronics A1012. partially work, eg, they might control the volume but not the input selection. In that case, try a different code. In addition, some remotes may only work in one mode (eg, TV but not SAT). Refer to the troubleshooting procedure in the September 2011 article if you strike problems. In particular, note that the DC offset voltage across each pair of speaker terminals should be less that ±50mV with power applied. Listening test That’s it – your new, high-performance Ultra-LD Mk.3 Stereo Amplifier is ready for action. Connect it to a CD and/or DVD player and a pair of loudspeakers, switch on and listen with your ear close to one of the loudspeakers but without any music playing. Even with the volume at full level, there should only be a barely perceptible “hiss” from the speaker (and that’s in a quiet room). Now turn the volume control back to a low level, select the appropriate input and play some music. You should be rewarded with clean, undistorted sound and the amplifier should have plenty of power when you wind the wick up. Finally, check that you can vary the volume and select inputs using the remote control. The yellow acknowledge (ACK) LED should flash each time a remote control button is pressed, while the yellow LED comes on when the sound is muted. That completes the assembly. Next month, we’ll publish the specifications and do a comparison between this new amplifier and the 20W Class-A Stereo Amplifier described from MaySC September 2007. siliconchip.com.au