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Clean up the clicks & pops on your vinyl records with the Building the LP Doctor sure is a lot easier than under­standing how it works. All the parts are mounted on a single PC board and this is installed in a rack case to produce an attractive unit. Pt.2: By JOHN CLARKE The PC board for the LP Doctor is coded 01101011 and meas­ures 311 x 160mm. Begin construction by checking your board for any shorts between tracks or breaks in the copper traces. Check also that the holes sizes are correct. You will need 3mm holes for the board mounting screws, 1mm holes for the 1N4004 diodes and 1.5mm holes for the terminals of the two potentiometers (VR1 & VR2). Finally, check that the PC stake 76  Silicon Chip holes are the correct size for the stakes that you are using. In most cases, everything will be correct but it’s always a good idea to check before installing any of the parts. Fig.9 shows the parts layout for the PC board. You can now start the assembly by installing the links and resistors. The resistor values can be checked against the colour code table (Table 2) or you can check their values using a digital multimet­er. The best approach is to install and solder 10 or 12 resis­tors at a time. The excess lead lengths are then trimmed close to the board using sidecutters before moving on to the next batch. The PC stakes can go in next – there are 25 stakes in all and these are installed at the external wiring points (for the LEDs, power supply, earth, signal inputs and outputs, and switch S2). Once these are in, install inductors L1 and L2. These con­sist simply of short lengths of tinned copper wire which are threaded through 5mm-long RF ferrite beads. Now for the semiconductors. Make Below: this view shows the general layout of all the hardware. The rotary switch terminals are connected to PC stakes on the PC board using lengths of tinned copper wire. The LP Doctor can be used every time you listen to your LPs or it can be used to clean up the sound from LPs before transferring them to CD-ROM. sure that each IC goes in its designated position and that it is correctly orientated. The ICs all face in the same direction and pin 1 is always adjacent to a small dot or notch in one end of the plastic body of the device. Similarly, watch the orientation of the diodes and transis­tors when installing them. Take care also not to get the transis­tors mixed up – Q1 & Q3 are PNP BC558s, while Q2 & Q4 are NPN BC338s. Use the 1N4004 power diodes for D1-D5 and the smaller-bodied 1N4148s for D6-D10. The three 3-terminal regulators (REG1-REG3) all face in the same direction but note that these devices are all different so don’t get them mixed up. In particular, REG1 is an LM317 type, while REG2 is an LM337. The third regulator, REG3, is an LM29405. Install them with their metal tabs positioned as shown on Fig.9 The board assembly can now be completed by installing the capacitors, trimpots, potentiometers (VR1 & VR4) and the two crystals (X1 & X2). You will find that the ceramic and MKT ca­pacitors have their values marked in code – see Table 1. The capacitors and crystals can go in either way around but make sure that the electrolytic capacitors are installed with the correct polarity. The exceptions here are the bipolar (BP) or non-polarised (NP) electrolytic capacitors, which can be installed either way. There are quite a lot of these, so check the parts layout diagram carefully for their locations. Preparing the case As supplied, the case comes in pieces and it’s a good idea to drill the front and rear panels before putting it together. Use the front panel artwork (Fig.10), the signal input wiring diagram (Fig.11) and the mains wiring diagram (Fig.12) as a guide to positioning these holes. Starting with the front panel, you have to drill holes for mains switch S1, potentiometers VR1 & VR4, the three indicator LEDs and rotary switch S2. The square hole for the mains switch (S1) can be made by first drilling a series of small holes around the inside perimeter, then knocking out the centre piece and carefully filing it to shape. Don’t make this hole too big – the mains switch must be a tight fit so that it is properly secured by its retaining tabs. The rear panel requires holes for the safety fuseholder, the mains lead cordgrip grommet, the 4-way RCA socket and an adjacent earth lug. Take care with the hole for the cordgrip grommet. This hole is not round - instead, it must be carefully profiled to match the shape of the grommet, so that the grommet can not later be pulled out when the mains cord is fitted. Once all the holes have been drilled, assemble the case without the lid, using the machine screws supplied. The next bit is important: be sure to scrape away the paint at the countersunk screw points, so that each section of the case makes good metal-to-metal contact. This ensures that each section is properly earthed to mains earth (important for safety reasons) and also stops hum problems. Next, position the PC board on the base of the case on 10mm standoffs with the shafts of the potentiometers protruding through the front panel. You can now fit the knobs to the pot shafts and mark out the locations for the six standoff mounting holes. You should also mark out the mounting holes for the power transformer and the mains earth lug (4mm hole). This done, remove the PC board and drill all the marked holes in the base. Once the holes have been drilled, scrape away the paint or anodising from the area around the two earth lug mounting holes (ie, adjacent to the power transformer and 4-way RCA terminal block). This is necessary to FEBRUARY 2001  77 0V 9V 25V 470mF AC IN 0V/9V D1 D2 25V D3 D4 470mF REG1 0.1mF 10mF 22k 0.1mF 11k 150pF 22k 560pF 10k TP4 150pF + SWITCH S2 (REAR VIEW) 9 C A R L BP 39k 1mF 82k 10mF BP 150pF 82k 39k 1mF BP 10mF BP 82k 100k 150W 150W 78  Silicon Chip 22k 11k 22k .068mF 27W 0.1mF 0.1mF 22k 150W 100k 100k .0047mF 100pF 16k 200k 10mF BP 1k IC1 LM833 1 0.1mF 100k 100k 100k 82k BP 1 LEFT IN BP SIG GND 10mF RIGHT IN 1k L2 10mF 47mF 0.47mF 10mF LEFT OUT GND SIG SIG GND RIGHT OUT SIG TO CHASSIS EARTH L1 47mF 150W 9 BP 560pF 10mF 47mF + 8 L R IC9 LM833 560pF 100k 7 3 10mF 16k 10 C 150pF 1 390pF 100k 560pF 6 IC5 LM833 BP 10mF 10k .01mF 10mF 11 5 L 10k 100k 100k 2 PROCESS BYPASS 4 12 FILTER 1 BP 100k 47k H11F1 10mF 10k BP 150pF + 2 A R 10mF 11k 1 IC8 100k 1 IC4 BP 200k .01mF 22k 10mF + 3 8 L OUT 1 R 560pF 10mF BP 100k 330pF 0.1mF 10k 10k 10k 100k 10mF BP 10k 100k 150pF .068mF 10mF + TO SWITCH S2 PIN NO. 7 470mF 16V + VR1 10k 330pF H11F1 SOLDER TO POT BODY IC3 M65830P + 100k 100pF 1 + BP + LEVEL + BP 100pF 2MHz 1k 10k 2x 10mF X1 .001mF 10k 33mF 2.2k IC2 LM833 + 56k A LED1 1M 10mF 1 10mF + K IC6 LM393 1 + 10mF 1k 10k 33mF .015mF BP 56k 560pF 47k .015mF .0047mF 100pF 10k 10k 270W 10mF + 100k 47mF 10mF + 330pF Fig.10 (right): this is the front panel artwork, reproduced 50% actual size. .0068mF 10k 150pF .068mF BP 22k 100k 220W 27k 1M 1M .0068mF 270W 10k 1mF 10k SOLDER TO POT BODY 470mF 16V Fig.9: install the parts on the PC board as shown here. Make sure that all parts are correctly oriented and are mounted in their correct locations. 10k 10mF IC7 M65830P + VR7 250k 100pF 1 1 IC14 TL072 5.1k 27k .001mF 11k 10k TP3 100pF 2MHz .068mF 27W 10pF 4.7k D9 D8 + 4.7k 1M X2 BP 10mF 1N 4148 + VR4 50k 10pF BP 10mF 150pF 1N 4148 VR6 250k 47k 47k 10k 10k TP2 100k 1 IC10 TL072 BP 0.1mF 100k 220W SENSITIVITY 1mF 10k 220W Q4 10pF 10k VR3 250k LED3 A 1k 10pF 10k 10mF 5.1k + BP 1 10mF BC338 10mF IC11 TL072 Q3 BC558 Q2 + VR2 250k 10mF BC338 1N 4148 A K TP1 1N 4148 100k 10k + 220W LED2 BC558 D7 D6 + Q1 K 1 IC16 7555 1k 10k 10k 10mF + VR5 250k 100k 10k 1 IC13 7555 + 10k 1 IC12 LM393 VR8 250k 100k 1mF REG2 10mF 100k + 1 IC15 LM393 2.2k LM337 1 IC20 74HC165 22k 47k D10 22k 6.8k 560pF 1N 4148 + 100k 1mF 2.2k LM317 2200mF 100k REG3 2940-5 + 1k 4.7k 10mF 10mF BP + 100mF 100mF 0.1mF 1 + 10mF 10mF IC19 4022 + + IC18 4093 4.7k 10mF + .001mF + + IC17 4060 1 D5 1k + 10mF + 1 2200mF + 10mF Table 1: Capacitor Codes  Value IEC Code EIA Code  0.47µF   474   470n  0.1µF   104   100n  .068µF  683   68n  .015µF  153   15n  .01µF  103   10n  .0068µF  682   6n8  .0047µF  472   4n7  .001µF  102   1n0  560pF   561   560p  330pF   331   330p  150pF   151   150p  100pF   101   100p  10pF   10   10p ensure that the earth lugs make good contact with the bare metal of the case. Final assembly The various hardware items – including the power transform­er, switch S2 and the earth lugs – can now be installed in the case. Use the mounting kit supplied to secure the toroidal trans­former – the large rubber washer goes directly on top of the transformer, then the metal washer is positioned over the top of this and the assembly secured using the mounting bolt. Make sure that the mains earth lug is properly secured – it must be attached using an M3 screw, nut and Fig.11: here’s how to wire up the RCA sockets on the rear panel. These connections must be run using shielded cable. star washer. We also recommend that you fit a second lock “nut” to this assembly, so that it cannot possibly come loose later on. Once it’s fitted, use your multimeter to confirm a good contact between the earth lug and the various panels of the case. The earth lug adjacent to the input sockets is secured using one of the mounting screws that’s used to secured the 4-way RCA terminal panel. Begin the wiring by running shield­ed cable connections between the RCA sockets and the PC board (Fig.11). The adjacent earth lug is connected to a PC stake on the board using insulated hookup wire. An additional length of insulated hookup wire is then run from this point and soldered to the bodies of potentiom­ eters VR1 and VR4. You will need to scrape away the Table 2: Resistor Colour Codes  No.    4    2  27    4    2    5    2    2    9    2    4  26    1    2    4    3    8    2    4    4    2 Value 1MΩ 200kΩ 100kΩ 82kΩ 56kΩ 47kΩ 39kΩ 27kΩ 22kΩ 16kΩ 11kΩ 10kΩ 6.8kΩ 5.1kΩ 4.7kΩ 2.2kΩ 1kΩ 270Ω 220Ω 150Ω 27Ω 4-Band Code (1%) brown black green brown red black yellow brown brown black yellow brown grey red orange brown green blue orange brown yellow violet orange brown orange white orange brown red violet orange brown red red orange brown brown blue orange brown brown brown orange brown brown black orange brown blue grey red brown green brown red brown yellow violet red brown red red red brown brown black red brown red violet brown brown red red brown brown brown green brown brown red violet black brown 5-Band Code (1%) brown black black yellow brown red black black orange brown brown black black orange brown grey red black red brown green blue black red brown yellow violet black red brown orange white black red brown red violet black red brown red red black red brown brown blue black red brown brown brown black red brown brown black black red brown blue grey black brown brown green brown black brown brown yellow violet black brown brown red red black brown brown brown black black brown brown red violet black black brown red red black black brown brown green black black brown red violet black gold brown FEBRUARY 2001  79 INSULATE ALL EXPOSED MAINS CONNECTIONS! 250VAC MAINS CABLE F1 CORD GRIP GROMMET LO W PANEL MOUNT FUSE HOLDER SECURE LUG TO METAL CHASSIS WITH M3 SCREW, NUT & STAR WASHER Fig.12: follow this wiring diagram exactly to install the mains wiring. Be sure to use mains-rated cable for all mains wiring and make sure that the earth lug makes good contact with the chassis. All exposed mains terminations should be sleeved with heatshrink tubing and the wires should be laced together using cable ties – see text and photos. N BLU BR OW L E E GREEN/ Y T1 MT-2082 0V .001mF 250VAC D5 MAINS RATED S1 CLASS "X2" 250VAC CAPACITOR (REAR VIEW) passivating coating from the pot bodies so that the solder will “take”. If you don’t do this, you will get a “dry” joint for sure and the pot bodies will not be properly earthed to the signal input. And that could cause hum problems. The three LEDs are installed by pushing them through the holes in the front panel and then soldering their leads to the board-mounted PC stakes. Take care with the lead polarity – the anode lead is always the longer of the two and the cathode lead is adjacent to a flat on the plastic collar of the LED body. Switch S2 can be wired to the PC board using tinned copper wire. Make sure that the wires are positioned so that they don’t come in contact with one another. Mains wiring Fig.12 shows the mains wiring details. Exercise extreme caution when Table 3: Changing Delays For IC3 & IC7 With Linking On IC20 Delay 0.5ms 1.0ms 1.5ms 2.0ms 2.6ms 3.1ms 3.6ms 4.1ms 4.6ms 5.1ms Pin 12 GND GND GND GND GND GND GND GND GND GND 80  Silicon Chip Pin 13 GND GND GND GND GND GND GND GND GND GND Pin 14 GND GND GND GND GND GND GND GND + + Pin 3 GND GND GND GND + + + + GND GND Pin 4 GND GND + + GND GND + + GND GND Pin 5 GND + GND + GND + GND + GND + 9V 0V 9V D1 D2 D3 D4 470mF + 25V 470mF + 25V installing this wiring and be sure to follow Fig.12 exactly – your safety depends on it. First, strip back about 380mm from the outer sheath of the mains cord, so that the Active (brown) lead has sufficient length to reach both the fuse and the power switch (S1). This done, clamp the mains cord into position using the cordgrip grommet. Check that the grommet properly clamps the cord to the chassis; you must NOT be able to pull the cord back out. The Active (brown) lead goes to the centre terminal of the fuseholder and the excess lead then run between the outside terminal and the mains switch. Slip a 40mm length of heatshrink tubing over the two leads before soldering them to the fusehold­ er. Once the connections have been made, push the tubing over the body of the fuseholder (so that the terminals are covered) and shrink it down using a hot-air gun. The connections to the mains switch are made using fully-insulated female spade terminals. Make sure that the various leads are all securely crimped to these terminals before fitting them to the switch terminals (use the correct crimping tool for the job). The .001µF 250VAC capacitor is soldered (using minimum lead length) directly to the switch terminals, right at the switch body. It’s important to solder the leads right at the switch body, to leave sufficient room for the spade terminals to be pushed on. The earth (green/yellow) lead from the mains cord is sol­dered directly to the adjacent earth lug. This lead should be left long enough so that it will be the last connection to break if the mains cord is “reefed” out. Use four or five cable ties to lace the mains wiring to­gether, with one tie close to the mains switch and another close to the fuseholder. This will ensure that if a lead comes adrift, it will be secured to the other leads and the “live” end cannot make contact with the case. Finally, connect the transformer secondary leads to the relevant stakes on the PC board as shown in Fig.12. These leads should also be laced together using cable ties. Testing, testing At this stage, you should go over your work and carefully check the PC board assembly and chassis wiring. In particular check that all ICs and other semiconductors are correctly orien­tated and in their correct locations. You should also make cer­tain that the mains wiring is correct and that the chassis is properly earthed (use a multimeter to check for continuity bet­ween the chassis and the earth pin of the mains cord). Now install the fuse in the fuseholder, then set your multimeter to the DC volts range and connect its common lead to the metal tab of regulator REG3. Apply power and quickly check that there is +5V at pin 16 of IC17, +7.5V at pin 8 of IC1 and -7.5V at pin 4 of IC1. Note that the +7.5V supply rail will take a second or two to stabilise after power has been switched on. Also the voltage could be between 7.3V and 7.9V, depending on the particular regulator. If all is OK so far, you can check the supply rails to the other ICs. There should be +5V at pin 16 of IC17, IC19 Parts List 1 1U metal rack case (Altronics H 5035 or equivalent) 1 PC board, code 01101011, 311 x 160mm 1 9V 20VA toroidal transformer (Jaycar MT 2082 or equiv) (T1) 1 SPST mains rocker switch with neon (S1) 1 2P6W rotary switch (S2) 1 3AG panel-mount safety fuseholder (F1) 1 150mA 3AG slow blow fuse 1 cordgrip grommet for mains cable 1 7.5A mains cable and plug 4 rubber feet 1 dual 10kΩ linear 16mm pot (VR1) 1 dual 50kΩ linear 16mm pot (VR4) 6 250kΩ horizontal trimpots (VR2,VR3,VR5-VR8) 2 RF ferrite beads 5mm long (L1,L2) 2 16mm black anodised knobs 1 22mm black anodised knob 2 2MHz crystals (X1,X2) 1 7.5A mains power lead and plug 1 35mm length of 15mm diameter heatshrink tubing 1 4-way RCA socket strip 1 M4 x 10mm screw 1 M4 nut 1 M4 star washer 14 M3 x 6mm screws 2 M3 nuts 6 M3 shakeproof washers 6 M3 tapped spacers 10mm long 1 M4 crimp eyelet lug 1 M3 crimp eyelet lug 3 fully insulated 6.4mm female spade crimp lugs 1 4m length of 0.8mm tinned copper wire 1 400mm length of single shielded cable 1 300mm length of green hookup wire 6 100mm long cable ties 24 PC stakes Semiconductors 4 LM833 op amps (IC1,IC2,IC5,IC9) 2 M65830P or M65830BP (but NOT 65830AP (IC3,IC7) 2 H11F1 or H11F3 opto FETs (Quality Technologies QT or Isocom) (IC4,IC8) 3 LM393 comparators (IC6,IC12,IC15) 3 TL072, LF353 dual op amps (IC10,IC11,IC14) 2 7555 timers (IC13,IC16) 1 74HC165 8-bit shift register (IC20) 1 4022 divide by 8-counter (IC19) 1 4060 binary counter (IC17) 1 4093 quad dual NAND Schmitt trigger (IC18) 1 LM317T adjustable positive regulator (REG1) 1 LM337T adjustable negative regulator (REG2) 1 7805 5V regulator (REG3) 2 BC328 PNP transistor (Q1,Q3) 2 BC338 NPN transistor (Q2,Q4) 3 3mm red LEDs (LED1-LED3) 5 1N4004 1A diodes (D1-D5) 5 1N4148, 1N914 diodes (D6-D10) Capacitors 2 2200µF 16VW PC electrolytic 2 470µF 25VW PC electrolytic 2 470µF 16VW PC electrolytic 2 100µF 16VW PC electrolytic 2 47µF 25VW electrolytic 2 47µF bipolar electrolytic 2 33µF bipolar electrolytic 21 10µF 16VW electrolytic 15 10µF bipolar electrolytic 6 1µF bipolar electrolytic 1 0.47µF MKT polyester 9 0.1µF MKT polyester 4 .068µF MKT polyester 2 .015µF MKT polyester 2 .01µF MKT polyester 2 .0068µF MKT polyester 2 .0047µF MKT polyester 1 .001µF 250VAC X2 class polyester 3 .001µF MKT polyester 7 560pF ceramic 4 330pF ceramic 8 150pF ceramic 6 100pF ceramic 4 10pF ceramic Resistors (0.25W, 1%) 4 1MΩ 26 10kΩ 2 200kΩ 1 6.8kΩ 27 100kΩ 2 5.1kΩ 4 82kΩ 4 4.7kΩ 2 56kΩ 3 2.2kΩ 5 47kΩ 8 1kΩ 2 39kΩ 2 270Ω 2 27kΩ 4 220Ω 9 22kΩ 4 150Ω 2 16kΩ 2 27Ω 4 11kΩ FEBRUARY 2001  81 This is the view inside the completed unit. Keep the mains wiring tidy and make sure that the cord is properly secured. & IC20, pin 14 of IC18 and pins 1 & 24 of IC3 & IC7. Pin 8 of all the 8-pin ICs should be at +7.5V. Similarly, pin 4 of all the 8-pin ICs should be at -7.5V, except for IC13 & IC16. IC13 & IC16 should have +7.5V at pins 4 & 8 and -7.5V at pin 1. Assuming that all these voltages check out, you now have to adjust the voltage offsets using the onboard trimpots. The procedure is as follows: (1). Connect a multimeter to test point TP1 and adjust VR2 slowly until the voltage is below about ±60mV DC. This done, connect the meter to TP3 and adjust VR6 for a similar value. Note: this adjustment is a little tricky, as the voltage will jump suddenly from a positive value to a negative value, so proceed slowly here. (2) Monitor test point TP2 and adjust VR3 for 0mV, or as close to this as possible. (3) Monitor test point TP4 and adjust VR7 for a 0mV reading. (4) Set trimpot VR4 to mid-position and adjust trimpot VR5 so that the left blanking LED (LED2) is just past the threshold of turning off (ie, the LED should just remain off). Adjust VR8 so that LED3 also just remains off. 82  Silicon Chip You are now ready to give the LP Doctor a test run. To do this, connect a turntable to the inputs and connect the outputs to an auxiliary (line level) input on a stereo amplifier (use shielded leads fitted with RCA connectors for this job). Note that you must not connect to the LP Doctor’s outputs to the phono inputs on your amplifier. That’s because the LP Doctor has its own inbuilt RIAA phono preamplifier and you’ll really mess the sound up if you then feed the signal through another phono preamp stage. Now set the Sensitivity pot (VR4) fully anticlockwise, play an LP and adjust the Level pot (VR1) so that the clipping LED (LED1) just flashes on high level signals. You can then test the three positions for rotary switch S2 – ie, Bypass, Process and Process & Filter. In the Bypass mode, any clicks and pops on the LP will still be heard since no processing takes place. Switching to the Process mode should eliminate many of these clicks and pops, provided the sensitivity control is adjusted correctly. This control should be set so that the blanking LEDs light when there is a click or pop but not for normal program material. The third position (Process & Filter) should not only reduce clicks and pops but should reduce high frequency noise as well. Changing delay times Finally, some readers may want to experiment with different delay times for the delay chips (IC3 & IC7). This can be done by changing the connections to the D1-D6 inputs (ie, pins 12, 13, 14, 3, 4 & 5) of IC20. Table 3 shows the connections required for delays ranging from 0.5ms to 5.1ms in 0.5ms steps, which should be sufficient for experimenters. The PC board has been designed to make these changes easy. All you have to do is cut the thinned track sec­ t ions which connect each pin to the +5V or GND rail and solder a bridge to the alternative rail instead. Note that the pattern originally sets the delay to 1ms – ie, pin 5 high and the remaining pins low. Note also that the delay times for 7555 timers IC13 & IC16 must be greater than the set delay time for IC3 & IC7. This means that the .0068µF capacitor at pins 6 & 7 of IC13 & IC16 Silicon Chip Binders REAL VALUE AT $12.95 PLUS P&P These binders will protect your copies of S ILICON CHIP. They feature heavy-board covers & are made from a dis­ tinctive 2-tone green vinyl. They hold up to 14 issues & will look great on your bookshelf.   Hold up to 14 issues   80mm internal width  SILICON CHIP logo printed in gold-coloured lettering on spine & cover Price: $A12.95 plus $A5.50 p&p. Available only in Australia. Silicon Chip Publications PO Box 139 Collaroy Beach 2097 Or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. Use this handy form Enclosed is my cheque/money order for $________ or please debit my ❏ Bankcard  ❏  Visa   ❏ Mastercard Card No:_________________________ Card Expiry Date ____/____ Signature ________________________ Fig.13: this is the etching pattern for the PC board, reproduced 70% of full size. Name ___________________________ Address__________________________ should be changed when longer delays are programmed. The delay time for IC13 & IC16 is equal to 1.1RC, where R is the resistor value (1MΩ) and C is the capacitor value on pins 6 & 7. Use the next available capacitor value up from the SC calcu­lated value required. __________________ P/code_______ FEBRUARY 2001  83