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Ultra-LD Mk.4 Power Amplifier Module, Pt.3 110W version plus power supply details • 2.4dB less power  • Same excellent performance figures   • Less expensive Ultra-LD Mk.4 Load Lines (One Pair Output Transistors, ±42V Supply) Ultra-LD Mk.4 Load Lines (Two Pairs Output Transistors, ±57V Supply) 10 10 ThermalTrak 50ms SOA 2 x ThermalTrak 50ms SOA (90% sharing) 8Ω Resistive Load 8Ω Resistive Load 8Ω Reactive Load, 75W (5.6+5.6j) 8Ω Reactive Load, 135W (5.6+5.6j) 8 8 4Ω Resistive Load 4Ω Resistive Load 4Ω Reactive Load, 200W (2.83+2.83j) Collector Current (Amps) Collector Current (Amps) 4Ω Reactive Load, 110W (2.83+2.83j) 6 4 2 0 0 6 4 2 20 40 60 80 Collector-Emitter Potential (Volts) 100 120 Fig.11: the blue, green and mauve plots show current/ voltage curves for resistive and reactive loads with 8-ohm & 4-ohm impedances driven with a sinewave at 75W and 110W respectively. Voltages are calculated for ±42V supply rails with an infinitely large capacitor bank. The red curve is the 50ms safe operating area for the NJL3281D & NJL1302D ThermalTrak output transistors. This shows that the transistors should not be damaged by driving such loads with an audio-frequency AC signal. 0 0 20 40 60 80 Collector-Emitter Potential (Volts) 100 120 Fig.12: the same load lines and safe operating area curves as for Fig.11 but this time for the higher ±57V supply rails and full power ratings of 135W into 8Ω and 200W into 4Ω. They are well within the safe operating area which has been moved up vertically to allow for the fact that the full-power version of the amplifier uses the output transistors in pairs. Note that we published a similar graph in the July 2011 issue however these plots are more accurate. Last month, we described how to build the new high-performance Ultra-LD Mk.4 amplifier module. Here are the details for the lower-power version, so you can save money while still obtaining the same ultra-low distortion and signal-to-noise ratio. We’ll also get into building the power supply plus testing and setting up both versions of the module. By Nicholas Vinen I F YOU’RE going to use the Ultra-LD Mk.4 to drive very sensitive speakers such as our Majestic (June & September 2014) or Senator (September & October 2015) designs, the full 135W into 8Ω is far more power than you’ll actually need for home listening. To save some time and money, you can 32  Silicon Chip build a lower power version which produces up to 75W into 8-ohm loads and 110W into 4-ohm loads, with a music power rating of around 85W into 8 ohms and 140W into 4 ohms. Its distortion and noise performance is very similar to the full-power module. For many people, the lower power version will have all the power and performance that they are ever likely to want. In fact, the power difference between the full and lower power versions of this amplifier is only 2.4dB; most people will never notice the difference! siliconchip.com.au +42V +42V 330Ω E2 E1 Q3a, Q3b: HN3A51F B1 C1 Q3b B 2.2k 12k 24V C2 Q3a 100Ω B1 1nF B1 Q2a C2 A 510Ω 135mV 68Ω 1000 µF 6.3V B2 C2 Q2b E2 68Ω 1 5 0pF 100V 100V 135mV 47µF 50V 15pF 50V C SC  20 1 5 E 2.2k K2 1nF 50V C E C Q4 BC846 E 2.2k B1 B2 C1 Q6 FZT696B 00 Ω 1W E1 C2 1 µF 50V (1000 µF) –42V NJL3281D, NJL1302D C B N/C 47k FUSE2 5A K A Q12 NJL1302D FZT796A, FZT696B MMBD1401A E2 C B C TP7 TP6 E B Q8 E1503 1 E B K1/A2 A1 µF HN3A51F, HN3C51F BAV99 BC846C B Q11 NJL3281D 0.1Ω 7-10 3 W mV K 110k 1 50 pF –41V 1 µF 50V C B 0.1Ω 7-10 3 W mV D2 MMBD1401A D1a,b BAV99 HN3C51F E1 E 12k B2 B C1 Q7 15030 47k (1000 µF) TP5 K1 A1 50V 47 µF 6.3V K2 A2 1 µF E 47Ω E2 Q1 a, Q1b: HN3A51F C B 4.7k VR2 100Ω OFFSET ADJUST C1 Q5 FZT796A 41.3V K E1 FUSE1 5A 25V λ LED1 47Ω E C 47 µF 4.7k A 68Ω 600mV 2.2k B2 220Ω 600mV 47 µF 6.3V X5R C ULTRA-LD MK. 4 11 0W AMPLIFIER MODULE CHANGES E B E CA K Fig.13: this diagram shows the circuit changes for the lower power version of the amplifier, compared to the full-power circuit shown in the August 2015 issue (pages 34 & 35). Differing component values and ratings are shown in red. The main changes are the removal of one pair of output transistors, changes in the feedback resistor value, lower current fuses, a reduced value current limiting resistor for Q4/Q6 and lower voltage ratings for many of the capacitors. The main cost saving with the lowerpower module is in the transformer, as a 160VA toroidal type is used instead of the 300VA type for the higher power version. You also save the cost of two power transistors per module, can use a smaller (and thus cheaper) heatsink and can also omit a few other passive components. Fig.11 shows resistive and reactive (ie, simulated speaker) load lines for 75W into 8Ω and 110W into 4Ω compared to the safe operating area (SOA) of one pair of ThermalTrak output transistors. As you can see, there is adequate margin of safety. The 50ms safe operating area was chosen based on a typical minimum operating fresiliconchip.com.au quency of 20Hz, although given that the limit is mainly at the peaks, this is sufficient even for lower frequency (inaudible) signals, should they be present in a recording. Compare this to Fig.12 which shows the same curves for the module using two pairs of output transistors at its full rated power of 135W into an 8-ohm load and 200W into a 4-ohm load. Circuit & PCB changes The changes to the circuit are shown in red on Fig.13. The most obvious change is the omission of one pair of output transistors and their associated emitter resistors. We chose to omit the outer pair in our prototype, mainly as this allows for the use of a smaller heatsink. The mains transformer changes from a 40V-0-40V 300VA type to 30V0-30V 160VA type, producing supply rails of nominally ±42V. These lower supply rails mean that many of the capacitors in the circuit can be lower voltage types which are a little easier to obtain and cheaper too. A few other component values in the amplifier module need to be changed. The two series 6.2kΩ resistors at Q3b’s collector drop to 4.7kΩ to keep its operating current the same. Importantly, the 150kΩ currentlimiting resistor for the VAS (Q4/Q6) must be reduced in value to 110kΩ, to October 2015  33 MJE15030 BD139 MJE15031 F1 M205 5A FAST BLOW FZT796A Q5 D2 472 222 110k 114 150pF 15pF 1nF Q4 2.2k 150pF 222 K A 2.2k 4.7k 472 LED1 1 µF 12k VR2 47µF 25V 330Ω 331 2x47Ω2x68Ω 68Ω Q2 Q3 2.2k AIR CORE (13.5T 1.25mm ECW) 68R Signal input D1 BAV99 100k 100k 104 104 68k 683 333 100k 511 CON1 102 104 1 1k 33k 104 47R 47R 1M 1 Q1 123 12k 47µF L1 100Ω 510Ω 47 µF 1000 µF 16V 6.3V NP 1nF1 µF 101 10R 105 10Ω 68R 222 12k 1 100k 222 123 2.2k 68R 123 4.7k L2 2.2 µH SILICON CHIP 100k Q16 ZD2 D5 Q14 ZD1Q15 D7 D6 104 100k CON4 A A LED4 CLIPPING 47k CON3 –42V F2 M205 5A FAST BLOW TP7 Q6 FZT696B K 47k +42V (2x27 Ω UNDER) 27Ω 27Ω 1W 1W K D4 A 0V 100nF 200V NP0 or PP POWER 331 121 1000 µF 50V LOW ESR (OPTIONAL) LED3 – SPK + 39 0Ω 1W 391 + HP K – D3 CON2 A OUTPUTS 1000 µF 50V LOW ESR (OPTIONAL) A 0.1Ω 3W (UNDER) 47 µF 50V Ultra-LD Mk.4 110W Amplifier Fig.14: use this diagram, along with the instructions in the article last month, to build the lower power version of the amplifier. The changed component values are shown in red. You may of course use capacitors with the original (higher) voltage ratings if desired. The only components left off the top side of the board are the outer pair of output transistors, Q10 and Q13. 101 47k K GREEN= FUSE OK TP4 473 LED2 TP6 1µF TP4 50V 27R 473 473 TP5 0.1Ω 3W (UNDER) NJL1302D TP2 100Ω VR1 120Ω 1k 330Ω 1µF 220Ω 50V (UNDER) (UNDER) 47 µF 6.3V 104 50V A 100Ω 101 TP5 1µF 47k Q9 TP1 TP3 Q12 Q8 473 Q7 27R NJL3281D 101 Q11 100Ω 1W K 01107151 RevB This view shows the fullyassembled 110W Ultra-LD Mk.4 module attached to its heatsink. Make sure that inductor L2 is orientated correctly (see Fig.9, on page 95 of the September issue). 34  Silicon Chip siliconchip.com.au 1µF 50V 220Ω 0R1 0.1Ω 3W 0.1Ω 3W 27R 0R1 221 27R Fig.15: the only changes to the components on the bottom side of the PCB for the lower power version are the omission of two of the 0.1Ω emitter resistors and the lower voltage rating on the 1µF capacitor. 27Ω 27Ω 1W 1W allow sufficient current for Q6 to pull the output low while still protecting it from excessive dissipation in a fault condition. We’ve also dropped the fuse ratings slightly, as the unit will draw less current from the power supply and a number of capacitors are rated at 50V (down from 63V/100V) or 100V (down from 200V). Construction Construction is the same as for the full-power module presented last month, except for the aforementioned changes. Use the overlay diagrams of Fig.14 and Fig.15 as a guide. As with the circuit, the changes are shown in red but note also that the two output transistors and their associated emitter resistors and bypass capacitors are all omitted entirely. Note that when the PCB is mounted on the smaller heatsink, it is not centred but is offset to the left. This has been done so that the transistor mounting screws fit between the fins of the heatsink. If you want to have the PCB mounted on the exact centre of the heatsink, the various screw holes will need to be blind-tapped from the front. The heatsink drilling diagram is shown in Fig.17. Power supply The complete power supply cirsiliconchip.com.au Six parts are fitted to the underside of the PCB for the 110W version – five SMD resistors and one SMD capacitor. Note that the two 0.1Ω resistors must be rated at 3W, while the 27Ω resistors must be rated at 1W. The 220Ω resistor at the top of the board (adjacent to the heatsink) is rated at 0.5W and is a thin-film type (see parts list on page 38 of the August 2015 issue). October 2015  35 ~ T1 CON1 TERM1 BR1 35A/600V + ~ 4700 µF 63V (50 V) 40V (3 0V) POWER S1 A 4700 µF 63V (50 V) 4700 µF 63V (50 V) 0V 3.3k 5W –57V (–42 V) A 40V (3 0V) 0V 4700 µF 63V (50 V) TERM3 15V N λ LED1 K TERM2 – 0V F1 5A (3A) +57V (+ 42V) A 4700 µF 63V (50 V) 4700 µF 63V (50 V) CON2 +57V (+ 42 V) λ LED2 K 0V 3.3k 5W –57V (–42 V) 0V CON4 15V CON5 30V AC 0V E T1: 2 3 0V TO 2x 40V/300VA, 2x 15V/7.5VA (T1: 2 3 0V TO 2x 3 0V/16 0VA, 2x 15V/7.5VA) CON6 D1 –D4 : 1N4004 K NOTE: VOLTAGES AND CURRENT/POWER RATINGS FOR LOWER-POWER VERSION SHOWN IN RED 0V A A K K A +20V K REG1 7815 IN +15V OUT GND 2200 µF 25V A CON3 100 µF 16V 0V 2200 µF 25V LEDS 1N4004 A IN –15V OUT REG2 7915 K A K 100 µF 16V GND 78 1 5 7 91 5 GND SC 2011 ULTRA-LD AMPLIFIER POWER SUPPLY GND IN GND IN OUT IN OUT Fig.16: the Ultra-LD Mk.4 power supply circuit is identical to that used for the Ultra-LD Mk.3. The changes necessary for the lower power version are shown in red. Power switch S1, fuse F1, transformer T1 and bridge rectifier BR1 are mounted on the chassis, while the rest of the parts are mounted on the power supply PCB. cuit diagram is shown in Fig.16. It is suitable for driving either one or two modules with normal program signal sources such as a CD player, FM/DAB tuner etc. The maximum continuous output power will be lower than specified when driving two modules from one transformer and power supply PCB but with normal program material this will still be more than adequate; the music power rating will only drop slightly when two modules share the same power supply. The power supply for the Ultra-LD Mk.4 is essentially identical to that used for the Mk.2 and Mk.3 versions. Various voltages differ for the lower power version and these are noted in CL (SCALE 50%) 33 28 A A A 42 75 A A 30 1 5 .25 5 25 5.25 150 36  Silicon Chip 75 Fig.17: this half-size diagram shows the heatsink drilling details. The holes can either be drilled and tapped (using a 2.5mm drill and M3 tap) or can be drilled to 3mm and the transistors mounted using machine screws, nuts & washers. square brackets in the following text. The supply is based on a toroidal mains transformer (T1) with two 40V [30V] windings and two 15V windings. The two 40V [30V] windings are connected together to give 80VAC [60VAC] centre-tapped and this arrangement drives bridge rectifier BR1. This in turn feeds six 4700µF 63V [50V] electrolytic capacitors (ie, 14,100µF on each side) to provide balanced ±57V [±42V] DC (nominal) rails to power the amplifier. Two LEDs are connected in series with 3.3kΩ 5W current-limiting resistors across these ±57V [±42V] supply rails. These serve two purposes: (1) they provide a handy indication that power is present on the supply rails (or when it is not present) and (2) they discharge the filter capacitors when the power is switched off (see warning panel). siliconchip.com.au (+42V) +57V + 0V 0 –57V - (–42V) CA V 5 1 TCT C 15V CAV 0 3 ~ 5 1 30VAC 15V 1 tuptu O OUTPUT 1 3.3k 5W A LED2 – + 4700 µF 63V (50V) + 4700 µF 63V (50V) + 4700 µF 63V (50V) A NI- 4004 4004 CON5 K A K A 4004 4004 K K 2200 µF 2200 µF 25V 25V REG2 7915 REG1 7815 TERM3 –IN D3–D6 TC TERM2 + 4700 µF 63V (50V) + 4700 µF 63V (50V) + 4700 µF 63V (50V) CT NI+ TERM1 +IN LED1 + CON2 OUTPUT 2 tuptu O–57V 0V +57V (+42V) (2–42V) - 220 µF 16V CON3 3.3k 5W + 220 µF 16V CON6 +20V –15V V 5 1- 00 +15V V 5 1 + 00 V 02+ 11190110 uS r e woP reifilpmA 2.k M DL-artlU Ultra-LD Mk.3 /4 Power Supply 0110 9 111 CON4 CON1 Fig.18: follow this parts layout diagram and the accompanying photo to assemble the power supply board. Note that the 4700μF capacitors must be rated at 63V if using a 40V-0-40V power transformer but you can use 50V-rated capacitors for a 30V-0-30V transformer. Note also that the low-voltage section at right can be cut off if it isn’t needed (eg, if you are building a power amplifier only and you intend using the revised speaker protection module to be described next month). The two 15V windings are also connected together to provide 30VAC centre-tapped. These drive bridge rectifier D1-D4 and two 2200µF 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. The +20V rail is also made available as an output, along with a 30VAC output. The +20V rail can be used to siliconchip.com.au power the “Universal Speaker Protector & Muting Module” described in the October 2011 issue, while the 30VAC output is connected to the “AC Sense” input of this module. This latter input is used to quickly disconnect the speaker when the power goes off, to avoid switch-off thumps. Updated speaker protector We intend to describe an updated QUICK CONNECT PC BOARD M4 FLAT WASHER M4 STAR WASHER M4 x 10mm SCREW & NUT Fig.19: if you can’t get the throughhole spade lugs or prefer to use the screw-mounting types, here’s how to attach them to the PCB. The power supply board has provision to use either type. October 2015  37 Parts List Changes For 110W Version Add these parts to the Ultra-LD parts list in August 2015 1 black anodised aluminium heatsink, 150 x 75 x 46mm (L x H x D) 2 5A M205 fast-blow fuses (F1, F2) Capacitors (add) 1 47µF 50V SMD (8mm) or through-hole electrolytic capacitor (eg, Digi-Key 4939427-1-ND) 1 47µF 25V SMD electrolytic, 6mm diameter (Digi-Key 493-94231-ND) 5 1µF 50V X7R (Digi-Key 12761068-1-ND) 2 1nF 50V NP0/C0G (Digi-Key 311-1122-1-ND) 2 150pF 100V NP0/C0G (Digi-Key 311-1839-1-ND) 1 15pF 50V NP0/C0G (Digi-Key 1276-1163-1-ND) Resistors (0.5W 1% Thin Film, 3216/1206) (add) 2 4.7kΩ or 4.75kΩ (Digi-Key RNCP1206FTD4K75CT-ND) Resistors (other) (add) 1 110kΩ 0.25W 1% 3216/1206 SMD Delete these parts from the Ultra-LD parts list in August 2015 1 black anodised aluminium heatsink, 200 x 75 x 45mm (L x H x D) version of the Universal Speaker Protector next month, specifically to suit the Ultra-LD Mk.4. Like the amplifier module, this will mainly use SMDs and adds a number of extra features such as indicator LEDs, simplified chassis wiring, NTC thermistors for easier temperature monitoring, the ability to drive a cooling fan if the amplifier reaches a certain temperature and more. Unlike the previous version, the updated speaker protector does not require a +20V rail; it can use the same transformer output for AC sensing and to power itself. In fact, it will even work from the same transformer windings that run the amplifier modules if your transformer lacks a 30VAC output. However, you can still use the October 2011 speaker protector with the UltraLD Mk.4 if you wish; this is currently 38  Silicon Chip 2 6.5A M205 fast-blow fuses (F1, F2) 2 TO-264 or TOP-3 silicone insulating washers Semiconductors (delete) 1 NJL3281D* NPN ThermalTrak transistor, TO264-5 1 NJL1302D* PNP ThermalTrak transistor, TO264-5 Capacitors (delete) 1 47µF 63V SMD (8mm) or throughhole electrolytic capacitor (eg, Digi-Key 493-6401-1-ND) 1 47µF 35V SMD electrolytic, 6mm diameter (Digi-Key 493-9433-1ND) 7 1µF 100V X7R (Digi-Key 1276-2747-1-ND) 2 1nF 100V NP0/C0G (Digi-Key 445-5759-1-ND) 2 150pF 200V NP0/C0G (Digi-Key 399-9174-1-ND) 1 15pF 100V NP0/C0G (Digi-Key 311-1838-1-ND) Resistors (0.5W 1% Thin Film, 3216/1206) (delete) 2 6.2kΩ or 6.49kΩ (Digi-Key RNCP1206FTD6K49CT-ND) Resistors (other) (delete) 1 150kΩ 0.25W 1% 3216/1206 SMD 2 0.1Ω 3W 1% Metal Film/Element (Digi-Key CRA2512-FZ-R100ELF) available as an Altronics kit (K5167). Power supply assembly Fig.18 shows the parts layout on the power supply PCB, which is coded 01109111. You can either purchase the PCB from the SILICON CHIP Online shop or you can buy a complete kit of the power supply from Altronics, Cat. K5168. Begin by fitting the two wire links using 0.71mm or 1mm-diameter tinned copper wire (1mm diameter is better but you may need to enlarge the holes slightly). If you bought the PCB from us, it will be double-sided so no wire links will be necessary. If you don’t need the low voltage regulated outputs, you can simply cut the PCB along the dotted line and discard the unwanted section. In this case, skip the instructions to install the components on that part of the board. It’s also possible to keep this part of the board and mount it separately, should your application require that. Assuming you do want the low voltage outputs, fit the four 1N4004 diodes (D1-D4), orientating them as shown. Then install the two 3-terminal regulators. You will need to bend their leads down by 90° so that they fit the PCB pads with the tab mounting hole lined up correctly. Attach each regulator to the board using an M3 x 6mm machine screw, shakeproof washer and nut, taking care not to get the two different types mixed up. Solder the leads after the screws have been tightened. The two LEDs can go in next. These sit flush against the PCB with the flat side of the lenses orientated as shown on the overlay. Follow these with the two 3.3kΩ 5W resistors. These should be stood off the board by about 2mm, to allow the air to circulate beneath them for cooling (use a cardboard spacer during soldering). The two 5-way screw-terminal connectors are made by dovetailing 2-way and 3-way blocks together. Be sure to fit these assemblies with the wire entry holes facing towards the adjacent edge of the PCB. The two 3-way terminal blocks for the ±57V (or ±42V) outputs can then go in. Alternatively, instead of fitting these blocks, you can solder the DC supply leads directly to the PCB pads if it will be mounted right next to the amplifier modules. The three Quick-Connect (spade) terminals are next. If you are using PCB-mount connectors, simply push the pins through and solder them in place. It will take a while to heat the connectors so that the solder will “take”. However, be careful not to overdo it, as the solder could “wick” through the hole and onto the spade section. If you are using 45° chassis spade lugs instead, screw them down tightly using M4 machine screws, nuts and washers – see Fig.19. If you can’t get single-ended chassis lugs, cut one side off double-sided lugs. Finally, fit the electrolytic capacitors, starting with the two 220µF units and finishing with the six large 4700µF units. Be sure to orientate them correctly and make sure that they all sit flush against the PCB. If you are building the lower power siliconchip.com.au The plug-in terminal block connectors on the power amplifier modules make installing and removing them much easier than before. Note that it’s important to use the thickest wire you can easily fit into the terminal blocks and to keep the wiring as short and as tight as possible. This is especially important if you opted not to fit the electrolytic supply bypass capacitors on the amplifier modules. Each set of three supply wires should be tightly coupled by twisting them together and/or covering the bundle with a length of heatshrink tubing (ideally both). Otherwise, the class-B currents flowing through the supply leads could couple into the amplifier module(s) and ruin the performance. Be careful when inserting the wires into the 3-way terminal block that you get the polarity right. Fig.20 shows the wiring polarity so be sure to match this. Initial testing We’ve come up with a revised procedure for powering up the amplifier the first time, to greatly reduce the chance of damage to any components if there are problems. This involves initially connecting 68Ω safety resistors in series with the supply connections before powering it up. The easiest way to do this is to insert one lead of a 68Ω 5W resistor into each of the two terminals at either end of the block and do the screws up tightly, then similarly screw the other ends into a 3-way mains terminal block. You can use insulated wire or a 0.1Ω 5W resistor for the ground connection – Fig.20. The advantage of doing it this way is that you can easily calculate the current flowing through the resistors by monitoring the voltage across them with a DMM. The lead are also unlikely to short together, as long as they are carefully arranged initially. The other side of the terminal block is wired to the DC outputs of the power siliconchip.com.au 473 47k CON3 68Ω 5W 5 6.5A LOW 0V +57V 100nF 200V NP0 or PP SPK + 39 0Ω 1W 391 + POWER -57V 0.1Ω 5W 68Ω 5W -57V 0V +57V OUTPUTS Cabling 1µF 100V A LED3 K 47k 473 version, you may have to crank out the 4700μF capacitor leads to suit the board (or stick with the 63V versions). In this case, it would also be a good idea to apply a little neutral-cure silicone sealant around the base of the capacitors so that they aren’t supported by the leads alone. Fig.20: this is the easiest way to wire up a newly-built amplifier module to the power supply and provide current limiting to minimise the chance of damage if there is a fault. The 68Ω resistors limit the current flow to 600800mA in the worst case. The 0.1Ω resistor is used simply for convenience; a short length of insulated wire could be used instead. Ideally, the voltage across both 68Ω resistors should be monitored initially. The expected current drain for a new module with the output stage bias set to minimum is less than 20mA, resulting in less than 1V across each safety resistor. supply. This will need to be built and wired up inside an earthed case. The simplest solution is to build the power supply into the case you intend to use for your final amplifier and then run an extra-long 3-way lead out of the case for testing purposes. Don’t skimp on this arrangement; make sure all the mains wiring is properly insulated and anchored for the tests. Once you have verified the module(s) are working you can then mount them in the case and complete the amplifier. Refer to the details on putting the power supply together later in this article (under the “Chassis Assembly” cross-heading). For the time being, we’ll assume that you already have a power supply (eg, if you built a previous version of the Ultra-LD amplifier). If so, take a look now at the “Danger: High Voltages” warning panel on this page. The power supply generates high AC and DC voltages and high DC voltages are also present on the amplifier module. Before you plug the power supply connector into CON3 on the amplifier board, switch on the now complete power supply and verify that the voltages at its output terminals are correct. The exact DC voltages will vary depending on your mains supply but you should get something like 54-57V for the full power version or 39-42V for the low-power version. Be especially careful to check for the correct polarity. Switch off and wait for the LEDs on the power supply board to go out before connecting the module. Then connect a DMM set to measure volts DANGER: HIGH VOLTAGES High DC and high AC voltages are present in this circuit. The power transformer has either an 80VAC or 60VAC output and the amplifier power supply rails are a total of 114V or 84V DC. DO NOT touch any part of the power supply or 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 alight, the power supply and amplifier boards are potentially dangerous. across each safety resistor using alligator clip leads. If you don’t have two DMMs, just monitor one resistor. If you don’t have alligator clip leads, you will have to hold the probes in place after switching power on. Now wind VR1 fully anti-clockwise and set VR2 to its halfway position using a small jeweller’s screwdriver. Ensure F1 and F2 have not been fitted, then switch the power on and check the on-board LEDs and the DMM readings. You should see LED1 (blue) on the amplifier PCB light up, along with LEDs2&3 (red). LED4 may flicker initially but should not stay on. Check for a reading of between 0.75V and 3V across each safety resistor and verify that the two readings are close in value. A typical reading will be just under October 2015  39 Using A Sewing Machine Bobbin To Wind The Air-Cored Inductor Overseas readers have had trouble locating a source for the plastic bobbin used to wind L2, the 2.2µH air-cored inductor which is part of the output filter. You can’t just use any old inductor here as it is must be perfectly linear to give good performance and only air-cored types can be relied on. The plastic bobbins supplied by Jaycar or Altronics have an inner diameter of 13mm, outer diameter of 20mm and width of 8mm. Unfortunately, we’ve had trouble finding other sources of bobbins with these same dimensions. Fortunately, it turns out that a common type of sewing machine bobbin has very similar dimensions and while these are normally made of steel (which would not be suitable), plastic types are now available. These appear to be made of some type of clear acrylic and they even have appropriately-sized holes in the right place for each end of the coil to emerge! These bobbins have an inner dia­ meter of 6mm, outer diameter of 20mm and width of 9mm. They are intended for use as cotton-feed spools in Singer, Janome and some Brother and Elna sewing machines – in fact, pretty much any domestic sewing machine. For convenience, we can also supply one or more of these bobbins along with 1V however as the output stage is under-biased initially, there can be a small amount of non-damaging oscillation present which will result in a higher initial current draw. Note that if you’ve fitted the 1000µF bypass capacitors, the reading will be much higher when they charge, starting at almost the full supply voltage and dropping to below 3V after a second or so. If the reading stays high, something is wrong, so switch off and check for faults such as short circuits, poor solder joints or incorrectly orientated or mixed up components. For example, if D3 and D4 were installed backwards, you will get virtually the fully supply voltage across the test resistors. Fitting the fuses Assuming it’s OK, switch off and wait for the LEDs to go out, which will probably take a couple of minutes. That done, fit F1 and F2, then switch 40  Silicon Chip PCBs for the Ultra-LD Mk4 – see our website for details. The accompanying photo shows a 2.2µH inductor wound using 1.25mm diameter enamelled copper wire on one of these sewing machine bobbins. The procedure is similar to that described in the article last month, except that we wound on four extra turns (ie, 17.5 turns total) to make up for the smaller inner diameter. Our LCR meter confirmed the resulting inductance is very close to the inductor used in our prototype, built on a Jaycar-sourced bobbin. If using the winding jig described last month, you will need to reduce the spindle diameter in order to fit the smaller bobbin. This may be as simple as unwinding some of the electrical tape wound around the bolt. We wound some electrical tape on a 6GA self-tapping screw until we reached a diameter of about 6mm, making it a snug fit through the centre of the bobbin. We were then able to wind the wire on with some difficulty (due to the increased curvature required by the smaller inner diameter). Try to pack the turns sideby-side. You should be able to wind on around six turns before having to start the second layer and you should reach 17.5 turns by the time the third layer is just about full. Note that while the wire back on and re-check everything. This time LED2 and LED3 should light green but nothing else should change. If it does, then the output stage is suspect, eg, there could be an isolation failure on one of the output transistor insulating washers. You can now check the output offset voltage by measuring between the top two pins (ie, the speaker output pins) of CON2. It should be less than 25mV and is usually about 10mV. Be careful not to short the two pins together! Now rotate VR1’s screw clockwise slowly while monitoring the voltage across a safety resistor. At first nothing should happen but eventually it will rise. This indicates that the VBE multiplier is working; stop turning VR1. Now rotate VR2 and check that the output offset voltage changes. You can trim it close to 0mV now, although you will need to make the final adjustment later. If you have a scope and signal generator, you can feed a low-level This view shows inductor L1 wound on a sewing machine bobbin. You will need to wind on 17.5 turns of 1.25mm enamelled copper wire (four more than for the Jaycar & Altronics bobbins) to get 2.2μH. specified will fit through the holes in the bobbin, it’s a tight fit and they may not appear large enough at first. But we got it through. Once you’ve finished winding, bend the wire over so it exits through a hole on the same side as the start. We applied two layers of clear heatshrink tubing to prevent the windings from moving. This inductor was used on our lower-power (110W) prototype, as you can see from the photo(s). signal into the amplifier (<250mV RMS) and check that the output signal looks clean. Note that with the safety resistors in-circuit, it won’t drive a load, nor will it handle high voltage swings or high-frequency signals. Quiescent current adjustment Switch off, wait for the LEDs to go off and remove the safety resistors. The 68Ω 5W resistors can now be soldered across a pair of blown fuses to make handy resistor fuse adaptors; see the accompanying panel. Fit these in place of F1 & F2 and wire up the power supply direct this time, as shown in the chassis wiring diagram of Fig.21. Given that the earlier tests were successful, it’s unlikely anything will go wrong at this stage but it’s still a good idea to have the safety resistors in place of the fuses initially. These limit the current through the output stage to about 840mA if there is a fault. siliconchip.com.au Adjusting The Quiescent Current Through The Power Amplifiers 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 for the full-power amplifier module or 4.75V for the lowerpower version – equivalent to a quiescent current of 70mA. The easiest way to connect the resistors is to “blow” the Note, however, that the 68Ω safety resistors will quickly burn out under such circumstances (since they would be dissipating close to 48W). Now use the following procedure to set the quiescent current and trim out the offset voltage: STEP 1: check that the safety resistors are installed and that their leads can’t short to any adjacent parts (note: do NOT connect the loudspeaker to the amplifier during this procedure). STEP 2: connect a DMM set to volts across one of the safety resistors (alligator clip leads are handy in this situation). STEP 3: turn trimpot VR1 fully anticlockwise. This can take as many as 25 turns but it will continue to turn even so. Many (but not all) multi-turn trimpots click when they are at the end-stop. If in doubt, check the resistance across it – it should be about 1kΩ. STEP 4: check that the power supply is off and that the filter capacitors are discharged (LEDs off!), then connect the ±57V [±42V] supply to the module. Check that the supply polarity is correct, otherwise the amplifier will be damaged when power is applied. STEP 5: apply power and check the voltage across the 68Ω resistor. It should be less than 1V (it may jump around a bit). If the reading is over 10V, switch off immediately and check for faults. STEP 6: using an insulated adjustment tool or a small flat-bladed screwdriver, slowly adjust trimpot VR1 clockwise. Be careful not to short any adjacent components. siliconchip.com.au 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. Be careful that their leads don’t touch anything while the module is powered up. STEP 7: after a few turns, the resistor voltage should stabilise and start to rise. Continue until it reads around 9.5V [4.75V]. It may drift a little but should be quite steady. STEP 8: switch off, wait for the capacitors to fully discharge (LEDs off) and replace the safety resistors with 6.5A [5A] fuses. STEP 9: connect a DMM set to volts between TP5 (near the upper-left corner of the board) and TP7 (near the centre). If you have fitted PC stakes, you can use alligator clip leads (make sure they can’t short to anything); otherwise you may need to get someone else to hold the probes in place while you perform the following steps. STEP 10: reapply power and check that the DMM reads close to 7mV. If necessary readjust trimpot VR1 to bring the voltage close to this figure. STEP 11: now check the voltage between TP4 and TP7. The reading should be similar. For the 200W module, do the same check with TP3/TP7 and TP6/ TP7. This verifies that all the output transistors are working and sharing the load current more or less equally. STEP 12: adjust VR2 until the voltage across the output pins is less than 0.5mV. This is easier to do if you screw a couple of bits of wire into the top two connections of the pluggable terminal block for CON2 and clip a DMM across it using alligator clip leads. Be extra careful not to short the output terminals together! Note that this is a trial-and-error process because you will probably find each time you remove the screwdriver from VR2, it will take several seconds for the output voltage to stabilise. You will need to make very small adjustments towards the end of the process. Recheck the quiescent current It’s a good idea to recheck the quiescent current by monitoring the voltage between TP5 & TP7 after the amplifier has been idling for an hour or so with the lid on. If the reading is more than 15mV, readjust VR1 anti-clockwise to bring it back within the 7-10mV range. The stability is such that it should stay below 15mV but it’s a good idea to check. That completes the adjustments. Note that if you wish to repeat the above procedure (ie, with the 68Ω resistors in place), you will first have to reset VR1 to minimum (ie, fully anti-clockwise). If you don’t do this, the amplifier may latch up when power is reapplied and burn out the safety resistors. Troubleshooting If there’s a fault in the module, a likely symptom is either excessive voltage across the safety resistors or the amplifier output voltage is pegged near one of the ±57V supply rails. If this happens, switch off and wait for the power supply capacitors to discharge. Then check that all the transistors are properly isolated from the heatsink. If this checks out, apply power to the amplifier without the fuses or safety October 2015  41 TO SPEAKER TERMINALS VIA SPEAKER PROTECTOR EARTH LUGS SECURED TO CHASSIS MALE IEC CONNECTOR WITH INTEGRAL FUSE 331 473 473 101 INSULATE WITH SILICONE 473 473 101 121 HEATSINK T1 CON3 –57V 0V 27R 622 27R 222 154 – SPK + 222 47R + HP – 391 68R 47R 68R 123 622 CON2 104 104 683 104 333 104 102 511 511 123 101 222 101 222 104 331 68R 2 3 0V PRIMARY LEADS +57V SILICON CHIP 104 105 10R CON4 A Ultra-LD Mk.4 200W Amplifier 0V CON1 Signal input 01107151 RevB 15 LEFT CHANNEL AMPLIFIER BOARD V 0V 1 0V 5V 4 0V 0V 40 V – RCA PLUG ~ CA V 5 1 TCT C 15V CAV 0 3 ~ 5 1 30VAC 15V 1 tuptu O 1 OUTPUT ±57V CON1 CON4 CON5 CON3 CON6 + 11190110 NI- + + TERM3 –IN TC TERM2 LEFT INPUT (RIGHT INPUT) + + + CT NI + TERM1 +IN 2 x 10k LOG POT (OPTIONAL) CON2 –57 V 0 +5 7 V 2 tuptu O OUTPUT 2 ±57V - POWER SUPPLY BOARD + + (RIGHT CHANNEL INPUT WIRING NOT SHOWN) +20V –15V V 5 1- 00 +15V V 5 1 + 00 V 02+ uS r e woP reifilpmA 2.k M DL-artlU 0110 9 111 + 00 –– +57V 0 –5 7 V ~ Ultra-LD Mk.3 Power Supply DIRECT WIRING IF POT IS NOT USED BR1 INSULATE ALL MAINS CONNECTIONS WITH HEATSHRINK SLEEVING S1 (TOP REAR) Fig.21: how to wire up the mains transformer, bridge rectifier, power supply board and amplifier module(s) to build a complete amplifier. The full-power version is shown here but the only differences for the lower power version are the power supply voltages and omission of one pair of output transistors. Most constructors will want to fit a volume control; use a 2x10kΩ log pot wired as shown or use our Ultra-LD Stereo Preamplifier, described in the November & December 2011 issues. Don’t forget to properly insulate all mains wiring and ensure the chassis is properly earthed as shown. resistors in place; ie, so that the output stage (Q7-Q13) is left un-powered. Now check the voltage between the bases of transistors Q7 & Q8, ie, between TP1 and TP2. This should be close to 2.2V. If this voltage is too high and you can’t reduce it with trimpot VR1, there could be a fault in the VBE multiplier (transistor Q9 and its associated components) or an open circuit between it and the diode leads of Q10-Q13. This could be due to an open-circuit track on the PCB or more likely, missed solder connections on the output transistor leads. If the voltage between the bases of transistors Q7 & Q8 is correct (ie, 2.2V), check the other voltages indicated on the circuit diagram. Note that the supply rails can vary by a few volts 42  Silicon Chip depending on your exact mains voltage, so some of the voltages can vary somewhat. In addition, check the base-emitter voltage of every transistor in the amplifier. In each case, you should get a reading of 0.5-0.7V if the transistor is working correctly. If not, then either the transistor is faulty or the wrong type has been used in that location. Making repairs If you need to remove a faulty though-hole component from a double-sided PCB, the best approach is to first cut the body of faulty component away from its leads. It’s then just a matter of grabbing them one at a time with pliers, heating the solder joint and pulling gently until the lead comes out. Once the leads have been removed, use a solder sucker or vacuum desoldering tool to clear the holes. Replacing SMD components is generally not too difficult. If you have a hot-air station, it’s simply a matter of heating the component until its solder joints melt and then lifting it off with a pair of metal tweezers. Note that doing this with a LED may damage its lens and it’s definitely not recommended with the fuseholders as you will melt or burn the plastic before the part budges! Having removed the part, it’s then just a matter of putting some flux paste on each pad and placing solder wick on top, then pressing down on the wick with the soldering iron and, once the solder has melted, sliding it off the pad. This will generally leave siliconchip.com.au INSULATED CRIMP EYLETS LOCKING NUT M4 x 10mm SCREW, NUTS AND STAR LOCKWASHER You MUST Use A Loudspeaker Protector BASE PLATE OF CASE NB: CLEAN PAINT AWAY FROM MOUNTING HOLE Fig.22: the chassis earth point is installed as shown here. Make sure it forms a very good electrical contact with the chassis (ie, scrape away any paint or coating under the eyelet lugs) and don’t use this screw for any other purpose. the pad clear of solder for fitting a new part. But don’t heat it for too long or you risk damaging the board. If you don’t have a hot-air rework station, you can still remove SMD parts but it’s a little more awkward. Basically, you need to heat the leads in a round-robin fashion until the part has heated up enough for all the solder to remain molten long enough for the part to be lifted off. It usually helps to add extra solder to each pin when doing this, bridging adjacent pins in the process so that you can heat multiple pins at once. We’ve successfully used this technique to remove resistors, capacitors, SOT-23, SOT-23-6 and SOT-223 package devices; ie, it works with just about any type of SMD on this board. Chassis assembly If you want to build a complete stereo Ultra-LD Mk.4 amplifier, the easiest approach is to build the UltraLD Mk.3 amplifier as described in the March-May 2012 issues and simply substitute the new amplifier modules. If desired, the revised speaker protector module that we will be presenting next month could also be used. Altronics have a complete kit for that project (K5165) as well as separate kits for the chassis (K5166), input selector (K5164), speaker protector (K5167), power supply (K5168) and preamplifier (K5169). Building it using these kits will be much easier than building from scratch, and give a professional appearance to the finished product. We strongly recommend that if you are going to build the Ultra-LD Mk.4 with a preamplifier and/or input switching, you use the design we desiliconchip.com.au A S STATED in the main body of the article, it’s essential to use a loudspeaker protector with the Ultra-LD Mk.4 amplifier module (and with any other high-power audio amplifier module for that matter). That’s because if a fault occurs in the amplifier (eg, if one of the transistors fails), this could apply one of the full 57V or 42V supply rails to the loudspeaker’s voice coil. As a result, the voice coil would quickly become red hot and burn out, irreparably damaging the speaker. This may also cause a fire! This new loudspeaker protector module to be described next month in scribed in the November & December 2011 issues, eg, from the Altronics kits mentioned immediately above. This is one of the few preamplifier designs around with the low distortion and noise needed to do justice to the UltraLD Mk.4 module. However, if you want to do it your own way, or just want to build a basic amplifier without the preamp, you can simply mount the modules in a suitable large steel case and wire them up as shown in Fig.21. The chassis layout is important to achieve the stated performance, so be sure to follow these instructions. In addition, safety is of the utmost importance, especially for mains wiring and chassis earthing. Basically, the amplifier module(s) and the power supply (along with the transformer) must be housed in an earthed metal case. This must be SILICON CHIP will prevent this from happening. Alternatively, you can use the Universal Speaker Protector & Muting Module described in the October 2011 issue (Altronics kit K5167) – see text. In either case, the device quickly disconnects the loudspeaker(s) in the event of a DC output fault. It also provides muting at switch-on and switch-off to prevent audible thumps and includes an input for an optional temperature sensor to disconnect the loudspeaker(s) if the output stage heatsink rises above a preset temperature. large enough to provide sufficient room between the transformer and the amplifier modules to avoid hum coupling. It’s also critical to use shielded cable for all the audio signal wiring, ie, between the input connectors and amplifier module(s). You will need a 2U or 3U extra-deep rack-mount metal case (or a similar enclosure) to fit a complete stereo amplifier. It will need to be quite strong to support the weight of the heatsinks and the transformer. Good ventilation is also important and ideally there should be vents immediately surrounding the heatsinks. The power transformer and IEC connector should be mounted towards the back (either in the lefthand or righthand rear corner), while the amplifier modules can be positioned on either side of the case, near the front. The power supply board can then fit October 2015  43 Parts List: Power Supply 1 PCB, code 01109111, 141 x 80mm 4 3-way PCB-mount terminal blocks, 5.08mm pitch (Altronics P2035A or equivalent) (CON1-4) 2 2-way PCB-mount terminal blocks, 5.08mm pitch (Altronics P2034A) (CON5-6) 3 PCB-mount or chassis-mount spade connectors (Altronics H2094) 3 M4 x 10mm screws, nuts, flat washers and shakeproof washers (if using chassismount spade connectors) 4 M3 x 9mm tapped Nylon spacers 10 M3 x 6mm machine screws 2 M3 shakeproof washers and nuts 1 150mm length of 0.7mm- diameter tinned copper wire Semiconductors 1 7815 1A 15V positive linear regulator (REG1) 1 7915 1A 15V negative linear regulator (REG2) 4 1N4004 1A diodes (D1-D4) 1 5mm green LED (LED1) 1 5mm yellow LED (LED2) Capacitors 6 4700µF 63V [50V*] electrolytic 2 2200µF 25V electrolytic 2 220µF 16V electrolytic Resistors 2 3.3kΩ 5W Parts For Complete Stereo Power Amplifier 2 Ultra-LD Mk.4 amplifier modules 1 Ultra-LD Mk.4 power supply module 1 speaker protection module (to be described next month) 1 vented metal case, 2U/3U rack-mount or similar size (eg, Altronics H5047) between the amplifier modules, with its ±57V [±42V] outputs near the supply connector(s) on the module(s). It’s also vital to include a loudspeaker protection module (not shown in Fig.21) – see panel on previous page. This module can be mounted towards the centre-rear of the chassis, while the RCA input connectors can 44  Silicon Chip 1 chassis-mount IEC mains input socket with fuseholder (use Altronics P8324 for recommended case) 1 M205 5A [3A*] fuse 1 mains-rated power switch (eg, Altronics S4243A) 1 300VA transformer with two 40VAC 300VA windings and two 15VAC 7.5VA windings for 200W Ultra-LD Mk.4 module OR 1 160VA transformer* with two 30VAC 169VA windings and two 15VAC 7.5VA windings for 110W Ultra-LD Mk.4 module 1 35A 400V chassis-mount bridge rectifier 1 white insulated chassis-mount RCA socket 1 red insulated chassis-mount RCA socket 2 red and 2 black chassis-mount speaker terminals (or two double speaker terminals) 1 10kΩ dual-gang log potentiometer with suitable knob (optional, for volume control) M3 and M4 screws, washers & nuts for mounting bridge rectifier, PCBs and heatsinks Mains flex (approximately 2m) Mains-rated heavy duty wire (approximately 2m) Shielded wire for input signals (approximately 2m) Speaker cable (about 0.5m) Heatshrink tubing Fully-insulated 6.3mm spade crimp connectors (about 20) Parts Availability The power supply PCB (code 0110911) can be purchased from the SILICON CHIP Online Shop or you can purchase a complete power supply kit from Altronics, Cat. K5168. * For 110W version be mounted in the opposite corner to the mains input. The volume control is optional but most constructors will want one, unless they are using an external preamplifier. No input switching is shown on Fig.21; the complete stereo amplifier described in the March-May 2012 issues has remote input switching with front panel buttons/indicator LEDs, as well as remote volume control. Checking the wiring Make sure that the chassis is securely earthed via the mains and be sure to insulate all exposed mains terminals with heatshrink sleeving, as shown in Fig.21. Fig.22 shows how the earth lugs are secured to the chassis using an M4 x 10mm screw, a lock-washer and two nuts. Make sure that the earth leads are securely crimped or soldered to these lugs before bolting them to the chassis. Once you’ve done this, use a multimeter to confirm the earth connection. You can do that by checking for continuity between the earth terminal of the IEC socket and the chassis. Testing the power supply 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. It’s now time to check that the power supply is functioning correctly but first a warning: the metal strap on the IEC mains socket that runs from the Active terminal to one end of the fuse has 230VAC on it. You should insulate this terminal using neutralcure silicone sealant or you can cover the IEC socket with a rubber boot, eg, Jaycar Cat. PM-4016. To check the power supply, first make sure that the supply wiring is disconnected from the amplifier. That done, apply power and check the various DC outputs. You should be able to measure close to ±57V [±42V] on CON1 & CON2, +20V on CON6, ±15V on CON3 and 30VAC on CON5. If you don’t get the correct voltages, switch off immediately and check for errors. Next month That’s it for now. If you need more information on building the completed amplifier modules into a chassis, refer to the Ultra-LD Mk.3 stereo amplifier construction details in the March and April 2012 issues. Next month, we’ll have the complete constructional article for our revised Speaker Protection Module. This has a number of new features and improvements compared to the previous version which was described in the SC October 2011 issue. siliconchip.com.au