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AUDIO OUT AUDIO OUT L R By Jake Rothman The Penta-Fuzz ‘bender’ PCB (The Pre-Driver from last month) This new PCB can be used to build many different fuzz boxes. This month’s pedal offering includes a PCB that can accommodate five different fuzz box designs: a simple silicon diode circuit, a buffered output version, one with extra output gain, a generic Big Muff, and a negative-earth germanium output transistor fuzz pedal. Again, they draw on my Colorsound experience, and hopefully clear up the incorrect circuits online. I’ve even had one US company trying to sell me a schematic for a Colorsound circuit I designed! No more pot hassles And finally, the problem of fitting standard, low-cost 16mm potentiometers to a flat PCB has been solved after 20 years of head and pot scratching. It’s all thanks to our PCB designer Mike Grindle having an epiphany. Having been brought up on PCB tape-up and hand drilling, my mind was totally closed to the idea of drilling three 16.5mm holes in a small board. Grindle knew that modern PCB fabrication can deal with any sized hole, and this led to his simple solution, shown in Photo 1. He managed to fit the back of the pot into a hole routed in the PCB. If you use Tayda pots and they were supplied with dust covers, remove them before installation. Remember to cut off the anti-­rotation lug, as shown in Photo 2. Use old, strong side cutters (or grab it with chunky pliers and flex it until it snaps off). Don’t use your posh Swiss cutters! The Penta-Fuzz board The diagram of the available circuit blocks on the board is shown in Fig.1. This is the same as the basic fuzz pedal block diagram shown in Fig.3 of the November 2025 issue, but with an extra output stage after the volume control. The circuit diagram in Fig.2 shows all the component positions for the five designs. Of course, not all are required for each version, and there are value differences, but it’s useful for the experimenter to see the equivalent circuit of the whole PCB to allow one’s own circuits to be developed. There are three outputs on the PCB: normal, low-Z and ‘supa’. (Is it line level? Is it +4dBm? No, it’s supa!) The Silverback The simplest design is basically a Colorsound Silver Tonebender, but we can’t call it that – “Silverback” sounds suitably silly for a guitar pedal! This circuit is based on a single parallel back-to-back IN4148 diode clipper (diodes D4 and D5). This gives a smooth, soft square-wave fuzz. The AC coupling of the signal to the diodes provided by C9 reduces at low frequencies, which compensates for the increased output Fig.2: the full circuit diagram for the Penta Fuzz PCB. Note the three outputs available. You can configure this in many different ways! C2 470pF R3 470kΩ 1% R1 C1 33kΩ 100nF TR1 BC549 Input R4 15kΩ 1% C3 100nF CW VR1 100kΩ Log R7 8.2kΩ *560Ω Fuzz R2 100kΩ 1% R5 100Ω R6 1kΩ Photo 1: finally, a cheap solution for pot mounting! 62 Practical Electronics | February | 2026 1st gain stage 2nd gain stage Clipping stage High-pass and low-pass filters Tone control Master volume Drive or ‘Attack’ High-impedance Input Output stage Gain output (Supa) Low-impedance output Out 0V Fig.1: the Penta Fuzz block diagram. of the guitar at lower frequencies, giving more uniform clipping. The inherent harshness of square waves is moderated by the tone control, called a ‘tone stack’ in guitar parlance. This puts a dip in the midrange when set flat, called ‘scooping’. The sound is akin to that of a kazoo (obviously the instrument that all the best guitar shredders aim to imitate), which sounds smooth and integrates well with electronic sounds. So it is a safe fuzz box for beginners. The passive high-pass and low-pass filters are set to 1kHz and 500Hz, respectively. There is around 10dB attenuation here, giving a low output level, around 300mV peak-to-peak. This is sufficient to drive most guitar amplifiers, which have plenty of gain. The normal output of the board is used. 0V For the more electronically minded folk who prefer clockwise rotation to emphasise high frequencies, the high-pass and low-pass filters will have to be reversed. R17 will become C12 and C13 will become R18. The Bufftone The output impedance of the filter/volume circuit is high (25kΩ), and this can interact with long guitar leads that may have high capacitance (up to 20nF!). In this case, you can add a buffer stage using transistor TR4. R21 has to be linked out and R20 is increased in value, to 470kΩ. The result sounds slightly fizzier with a typical guitar lead than the Silverback and is also better at driving other effects units. The low-Z output is used. Supa trouper The stage around TR4 can also be configured as a common-emitter amplifier to give an extra boost of up to four times, to compensate for losses in the filter/volume circuit as well as the buffer stage. This is for those who want to overdrive their valve amps or need a higher output level (0.9V peak- Tone control On this board, it may appear to some that the tone control VR2 goes the wrong way, with the treble end being anti-clockwise and the bass end in the clockwise direction. This is because it was this way on the original Tonebender pedals, going from a ‘thin’ to a ‘full-bodied’ sound. Photo 2: cutting off the pot lug. to-peak, 318mV RMS, -7.7dBm, approaching line level status) for studio effects and power amplifiers. The circuit is basically the Colorsound Supa Tonebender; hence, the “supa” output is used. Wave Grinder I couldn’t think of a name worthy of surpassing Big Muff (the famous pedal first released around 1970), but the general circuit is simple enough. It was arguably a derivative of the Tonebender, but all fuzz designers copy each other anyway, so it is difficult to identify the true originators of these circuits. The transistors have been changed to PNP types (specifically, 2N5087s), plus an extra clipping stage and an output stage have been added. There are around 20 variations of the Big Muff, and they are well detailed on Kit Rae’s π page (www. bigmuffpage.com). The circuit board will accommodate all these circuits. The circuit I use on this board is based on the 1973 design and values shown in Fig.2. There’s no need to use PNP transistors; good old BC549s work perfectly. During testing, I left C5 off. This was so I could compare the +9V + R15 15kΩ *1.2kΩ C7 22µF Silver Tone Bender clipper stage D1 1N4148 D2 1N4148 R26 Jumper *3.3kΩ D6 *4.7V Omit C9, D5, D5 D4 for yellow Tone 1N4148 Bender D5 1N4148 Insert for ‘Big Muff’ only C9 100nF C5 470nF * values for the Yellow Tone Bender C10 470pF *1nF Normal output Optional output stage C6 470pF R9 470kΩ C4 100n *470nF R12 8.2kΩ *Link C8 100nF *470nF TR2 BC549 R8 100kΩ R11 100Ω R14 470kΩ *220kΩ TR3 BC549 *OC140 *D3 CG92 R13 100kΩ *Not used R16 100Ω *Link C11 100nF *1µF + R17 33kΩ *3.9kΩ R19 390kΩ CW C13 10nF *100nF VR2 100kΩ 20kΩ C12 4.7nF *33nF R18 33kΩ *3.9kΩ C14 100nF Tone R21 10kΩ Link TR4 BC549 R21 Link for low-impedance output C16 100nF Supa R23 100Ω VR3 100kΩ *22kΩ Log CW Volume R20 100kΩ (Supa) 470kΩ (Low-Z) R22 2.7kΩ R25 100kΩ C17 Low-impedance 10µF output + R10 10kΩ R24 33kΩ 0V Practical Electronics | February | 2026 63 difference between using two clipping networks rather than one. I preferred the more aggressive Big Muff sound with the extra network, especially with C5 selected as 470nF. A lot of Big Muffs have bigger coupling capacitors throughout, but I found that just increasing C5 made a difference, except with bass guitar, and then it becomes a Bass Fuzz. (The Colorsound Bass Fuzz is the Silver Tonebender circuit with all the coupling capacitors increased to 220nF). If you do not want to experiment, build the standard Big Muff/Wave Crimper circuit with the output gain stage. This is the best one, in my opinion. Germanium OC139 fuzz This germanium design is equally good but more expensive to make, offering a softer fuzz at low levels for jazzy sounds. A well-known trick among fuzz freaks is to use a flat battery. Fuzz pedals often sound better as the battery wears out; voltage starvation always increases non-linearity and clipping. In the Yellow Tonebender, I emulated this effect by clamping the 9V power rail with a 4.7V zener diode. The clipping stage (TR3) is a germanium common-emitter stage. It has to be run at twice the current (0.7mA) of the Silverback silicon stage because of the higher leakage current and lower impedance of the filter/volume stage. In the Yellow Tonebender, an NPN OC140 computer transistor selected for low leakage (<0.1mA) –12V R5 330Ω + C3 100µF 12V R3 180Ω TR3 OC140 C1 10µF TR1 OC71 2.75mA R6 33kΩ R1 10kΩ R2 330Ω E B C TR1,2,3,4 BC549 + C2 100µF 6V 80Ω used, but then a complete polarity flip is required where the other transistors are changed to PNPs, eg, BC559s, and all the diodes and electrolytic capacitors are reversed. I’ve found the old glass-cased (SO-2/SB3-2) germanium transistors, such as the OC series, to R8 Fig.4: the main PCB overlay (component placement) diagram for the Penta Fuzz pedal. R17 CW C 9 VR2 Tone CW TR2 –6V + Input TR2 OC72 allows for a high-value (220kΩ) bias resistor, R14. To get maximum gain, emitter resistor R16 is linked out. A germanium diode (D3) is also used for leakage cancellation and DC bias-shift clamping. If you can’t get a low-leakage NPN germanium transistor, a PNP can be D5 D4 C6 C R R R C D D R 8 1 4 9 10 11 12 C7 2 TR3 VR3 Volume C10 C 12 R C R R R R 16 11 13 18 14 15 + R4 1.8kΩ Photo 3: the assembled Wave Grinder board. The Phillips orange polyester capacitors are the modern replacement for the Mullard C280s. Not quite as good-looking, but at least the leads don’t fall off. + R 3 C 2 R 4 R 7 C 1 R 1 R C17 R 21 23 R 22 VR1 Drive C 5 TR4 TR1 C4 100µF+ 12V C 13 R 5 R 2 Input V+ R 6 C 3 CW C 14 R R R R 19 24 20 25 C 16 0V Fig.3: an interesting OC140 circuit from “Transformerless Circuits for Broadcast Receivers” by Macario and Broadberry, Wireless World, March 1960. 64 0V 0V Normal Low-impedance Supa output output output Practical Electronics | February | 2026 Photo 4: scraping clean dirty, oxidised OC139 leads. A long job. have lower leakage than the later European TO-1 metal-can type, such as the NKT214 and AC127. Proper hermetic (with a glass ring around each lead) TO-5 and TO-18 cases also seem to be good. The epoxy-filled base versions are not. Interestingly, the OC139/140 transistors are symmetrical in that the collector and emitter can be swapped with little change to the Hfe. This was revealed when the Peak transistor tester could not identify which was the collector and which was the emitter lead on some examples. The OC139 has half the Hfe of the OC140 (Hfe range 50 to 150) and is perfectly usable. [Editor’s note – early germanium transistors sometimes behave symmetrically due to constraints of the manufacturing processes of the time. Modern devices are deliberately asymmetrical, since optimising each region for its specific role yields far higher gain, lower noise and better overall performance.] Historical diversion The Mullard OC139/40 was one of the first European NPN transistors, introduced in 1959. An OC140, along with the OC72, made the first complementary-pair push-pull class-B audio amplifier published in the UK, shown in Fig.3. It delivered 150mW into an 80Ω loudspeaker. I will have to build one to see if it has a good fuzz sound! It is likely to have a very asymmetrical output waveform and might make a unique fuzzy practice amp. Output details By lowering the impedance of the tone stack and volume control, and increasing the output level from TR3, the circuit can drive a typical amplifier input directly. In other words, if using the tone section, a separate output buffer (TR4) is no longer required. The filter frequencies are widened slightly, to 400Hz and 1.2kHz. I used a 20kΩ W-law pot for the tone control. This law is specially designed for tone controls, having a softening of the slope at each end of the rotation, and often a centre detent. Assembly I’m a bit naughty; I often solder resistors from the component side of the board these days. This always ensures they lie flat on the board. When I use those foam-backed PCB holders, I usually find a few sitting up in the air when I’ve finished. I used to prevent this by bending the leads over. With plated-through holes there’s no need for bending, and doing it makes it much more difficult to remove components if that becomes necessary. Fig.4 is the overlay diagram that indicates which components go where, while Photo 3 shows the assembled board. Golden oldies When using old components such as germanium transistors and “tropical fish” C280 capacitors, it’s essential to scrape the oxide off the leads with a scalpel, as shown in Photo 4. Also, because the leads have lead (Pb) based tinning, 3% activated rosin flux 60/40 leaded solder should be used (for home construction). There was no RoHS back in the 1960s… My stock of OC139s and CG92 diodes is from 1963, and the leads are almost black with oxide. In the industry, an ultrasonic solder bath is used, which is so effective that the components can also be converted to RoHS lead-free status, assuming there is no lead inside. They then pass the external X-ray spectroscopy analysis that’s used to check for conformity when exporting to the EU. Mounting germanium devices These devices are heat sensitive, so solder them quickly, with long mounting leads. It’s another reason to avoid lead-free solder, which has to be hotter for longer to achieve satisfactory wetting. Photo 5 shows the mounting of the OC139. A small piece of double-sided tape on the board underneath stops it from flapping about on its long leads. Because clipping components D4, D5 and C9 are not used in this configuration, they provide a convenient space in which to bend the transistor over. Photo 6 shows the different components used Photo 6: the PCB built for the germanium transistor fuzz box. There are quite a few different components fitted, and the output stage parts are left off. Photo 5: mounting an OC139 germanium transistor for TR3. Practical Electronics | February | 2026 65 R8 Fig.5: the components used for the OC139 fuzz pedal option. R17 D3 CW VR2 Tone VR3 Volume CW E B C OC139/40 E B C TR1,2 BC549 TR2 C10 C6 C 8 D 6 R R R C C7 9 10 11 4 TR3 C R 12 26 + R R R 18 14 15 C 11 C 13 + R 3 C 2 R 4 R 7 VR1 Drive TR1 C 1 R 1 R 5 R 2 Input V+ R 6 C 3 CW 0V 0V Normal output NC NC Photo 7: the internal wiring of the Wave Grinder. Notice I’ve moved the battery clip to the other side so that the wires can go straight to that side of the jack PCB. compared to the standard board, while Fig.5 is the component overlay diagram. Boxing it up As in the previous pedals, I’ve used a Tayda 1590DD ‘Hammond clone’ box with virtually the same layout, apart from the battery clip, which I’ve swapped to the other side to get more lead length. This wiring is shown in Photo 7. The drilling is the same as before, except that the new potentiometer holes are smaller, at 7.5mm. The jack board is difficult to drill, so I have had a drilled fibreglass template made by the PCB company. It’s much easier to mark out the drilling positions using this. There is little leeway for error when dealing with PCB-mounted connectors and pots. For this reason, I’ve also made a pot template, which also acts as an under-board insulator if you forget to cut the component lead outs very short. These templates are shown in Photo 8. Place them in the desired position on your box, draw around the holes, centre punch, make a 3mm pilot hole and then drill to full size. Pfaffing about with a ruler is eliminated. Wiring The jack board is the same as last month, but is repeated in Fig.6 for completeness. Some early boards may be marked for positive earth with the LED square pad denoting the cathode (-Ve). Ignore that and follow this overlay diagram. The wiring diagram and switching are also the same (Fig.7) bar the three selectable outputs available on the board, and the Earth wire to the switch washer. I’ve standardised on a colour code for wiring pedals as follows: • Red: battery positive and DC connector output to board. Don’t use red for anything else! • Black: battery negative Earth, jacks to board Earth, switch washer Earth • Violet: guitar input signal from the jack socket to the switch • Grey: output signal going to the amplifier socket • Pink: output signal from the main board to the switch • Orange: input signal to the board from the switch • Green: Earth wire from the board to the switch • Brown: LED ground wire to the switch 66 Practical Electronics | February | 2026 DC input (centre negative) Guitar LED under board + – Amplifier + LED Gnd (spare) Gnd Violet Switch (S1) Black PCB Gnd Black Red Red To PP3 battery clip Grey Switch (S2) Brown PCB 9V Switch (S3) Fig.6: the jack board overlay diagram. also served to Earth the box. The new pot-mounting method doesn’t do this, because the pot bushes don’t go through Earthed holes on the board. Now the Earth point is an M12 washer on the stomp switch. This is connected by a black wire to the Earth tags on the switch, as shown in Photo 9 and Fig.7. Soldering the wire to a standard zinc-plated steel washer is difficult, so it may be better to use a crimp tag. I found some copper Photo 8: I can supply these templates to make the job of drilling the case easier. Earthy topics Since there is usually a multitude of Earth wires in any audio circuit, they can be differentiated from each other by using “earthy” colours. I use dual-colour green wire with various tracers. Occasionally I use blue, except where it is used for negative power rails (if present). Brown can be employed for signal Earths, but this may cause trouble if confused with the ludicrous EU colour for Live/Active in mains wiring. [Editor’s note – there are good reasons why brown was chosen, but if it weren’t for historical baggage, it’s likely we’d have a more sensible colour for Live wires, like red or orange.] I always use tinned 7/0.2 equipment wire for general hook-up jobs. It was once cheap, but it is not any more in Britain’s austere de-industrialised economy (or perhaps this just reflects the increased cost of copper). Because it doesn’t degrade with time, it’s worth going to radio rallies where the wares of – 9V Photo 9: a washer on the switch is used to Earth the case. Selected output + Black dead electronic engineers are sold off. No widow wants her house cluttered with dusty cable reels. The old pot-mounting system Red NC switch contact Centre pin Outer 2.1mm DC connector Input from jack board Red LED jack board 24 SWG link Pink Grey S2 Violet * Brown * Black 0V V+ 24 SWG link Input 0V Orange S2 Pre-driver Select output Input Supa Low Z Jack sleeve Ring S1 Tip Violet Jack stereo socket (switch contact not used) (power switched here) FX input from main board *24 SWG links Rear of 3PDT switch (Poles are centre pins in each switch section) Switch earth washer for box Output Tip NC 0V Jack sleeve Ground to switch (green) Brown V+ 5.6kΩ 0.25W Practical Electronics | February | 2026 Grey Pink 0V 0V Out To jack board ground (black) S3 Green Penta Fuzz Orange S1 Output from jack board S3 Green 0V Effect On Fig.7: the Penta Fuzz wiring diagram. 67 roofing washers in the local hardware shop, which were easy to solder, shown in Photo 12. Incidentally, the word Earth is capitalised in PE, partly to distinguish it from dirt, and partly for consistency with Live and Neutral. We capitalise these because want to make sure our descriptions of mains wiring are as clear as possible (so that there’s no ambiguity that we’re referring to specific mains wires). The finished unit is shown in Photo 10. Testing The current consumption for each version is: • Silverback: 2.6mA • Buffered Silverback: 4.0mA • OC139 germanium fuzz: 5.8mA • Wave Crimper: 2.9mA These are all very low, ensuring a long battery life. This allows cheap zinc-carbon batteries to be used. A common problem with testing guitar pedals is getting the two jack leads mixed up. With bypass mode enabled, the pedal works fine because the hard bypass switch conducts in both directions. It then doesn’t work when the effect is switched on, because the guitar is connected to the output. So if it only works in bypass mode, try swapping the leads. Electronic problems are usually revealed by checking the transistor collector voltages. The signal voltage also appears on the collectors, enabling oscilloscope tracing (or using an audio probe). Loss of signal is usually due to a missing component or link. The worst fault of all is the unsoldered PCB pad. With holes that are plated through or pads with hard bent-over leads, things can sometimes work fine for three months before failure of the contact due to oxidation occurs. We once sent a pedal to the USA w i t h t h i s u nknowingly self-­ inflicted fault. 5p of soldering work became $80 of postage, duty and hassle. Never again! Photo 10: the finished unit, one of many. All fuzzes sound different but also the same. Photo 12: copper washers are the easiest to solder. I can supply one to readers if needed. Photo 11: the miniaturised OC139 fuzz box. 68 Practical Electronics | February | 2026 Miniaturisation Mike Grindle has dispensed with batteries in his pedal designs, just going for the 2.1mm DC connector, avoiding the use of its unreliable battery switching contact. This, along with the use of rear-connected jack sockets with metal barrels for Earthing, allows the case size to be reduced to the absolute minimum. It does risk an absolute mess of cables if you’re using a lot of pedals, though, which is why axemen often preferred batteries. The choice is yours. I had a go at miniaturising the OC139 germanium fuzz into a 95 × 120 × 32mm Eddystone 29830/P diecast box, shown in Photos 11 & 13. It looks great, but is harder to build and service compared to the one in the large case. The jack board has to be mounted upside-down and the plastic jacks are touching the pots on the board below. The tags have to be cut off close to the board to stop them from shorting against the lid. Finally, foam has to be stuck to the unused output section of the board to clamp the battery when the lid’s screwed down. Another thing to look out for if powering a pedal with a plugpack is that almost all modern plugpacks are switch-mode designs. Many are fine for driving audio circuits, but some can inject high-frequency noise, especially in a circuit that’s dealing with low-level signals like from a guitar. Later on A reader asked me about making a phaser pedal, which sounds like a good idea, tying in with a column I’ll be doing on all-pass filters for audio circuits. Part one will be theoretical, but a practical project PE will follow. Photo 13: the miniature fuzz box internals. It is quite a squash. Parts List – Penta-Fuzz / “Big Muff” 1 double-sided main PCB coded AO-FEB26-1, 80 × 85mm 1 double-sided jack PCB coded AO-JAN26-2, 72.5 × 25mm 1 optional pedal insulation board/drilling template, coded AO-FEB26-2 1 optional jack board rear panel/drilling template, coded AO-FEB26-3 1 Tayda 1590DD diecast metal case, 190 × 121 × 37mm 1 Tayda 3PDT latching stomp switch (S1) 1 battery snap with 200mm-long flying leads [Rapid 18-0093] 1 9V PP3 style zinc-carbon battery 1 9V battery mounting clip [Rapid 18-3480] 1 2.1mm PCB-mount DC connector [Tayda A-4118] 2 6.35mm/¼-inch PCB-mount stereo switched jack sockets [Tayda A-5079] 1 M3 × 12mm countersunk machine screw, hex nut and washer 1 12.5mm diameter washer (must be solderable, eg, copper or bright steel) Various lengths and colours of medium-duty hookup wire A few small table ties and clips Semiconductors 4 BC549B/C NPN transistors (TR1-4) 4 1N4148 or similar small-signal diodes (D1, D2, D4, D5) 1 3mm low-current/high-brightness LED [orange Tayda A-264 recommended] Capacitors (all 63V ±20% unless noted) 1 22µF 16V radial or axial electrolytic (C7) 1 10µF 16V low-ESR radial or axial electrolytic (C17) 1 470nF polyester film (C5) 8 100nF polyester film (C1, C3, C4, C8, C9, C11, C14, C16) 1 4.7nF ±10% polyester film (C12) 1 10nF ±10% polyester film (C13) 3 470pF 50V ceramic (C2, C6, C10) Potentiometers (PCB-mount 16mm single-gang Alpha, 6.35mm/¼in shaft, M7 bush) 2 100kΩ log (VR1, VR3) [Tayda A-2427] 1 100kΩ linear (VR2) [Tayda A-5636] (Spare nuts are Tayda A-5037) Resistors (all ¼W ±5% carbon film or 1% metal film as noted) 2 470kΩ (R9, R14) 4 33kΩ (R1, R17, R18, R24) 1 2.7kΩ (R22) 1 470kΩ 1% (R3) 1 15kΩ (R15) 1 1kΩ (R6) 1 390kΩ (R19) 1 15kΩ ±1% (R4) 4 100Ω (R5, R11, R16, R23) 4 100kΩ (R8, R13, R20, R25) 2 10kΩ (R10, R21) 1 0Ω (R26) 1 100kΩ 1% (R2) 2 8.2kΩ (R7, R12) Substitutions/additions/deletions for Yellow Tonebender 1 OC139/40 germanium NPN small-signal transistor (replaces TR3) 1 CG92, OA91 or similar small-signal germanium diode (D3) 1 4.7V 400mW zener diode (D6) 1 1μF 16V tantalum (replaces C11, 100nF) 2 470nF ±20% polyester film capacitors (replace C4 & C8, both 100nF) 1 100nF ±10% polyester film capacitor (replaces C13, 10nF) 1 33nF ±10% polyester film capacitor (replaces C12, 4.7nF) 1 1nF 50V ceramic or polyester film capacitor (replaces C10, 470pF) 1 20kΩ W-law potentiometer (replaces VR2) [Tayda A-1959] 1 22kΩ log potentiometer (replaces VR3) [Tayda A-3558] delete C5 (470nF) Resistors (all ¼W ±5% carbon film) 1 220kΩ (replaces R14, 470kΩ) 2 3.9kΩ (replacing R17 & R18, 33kΩ) 1 3.3kΩ (replaces R26, 0Ω) 1 1.2kΩ (replaces R15, 15kΩ) 1 560Ω (replaces R7, 8.2kΩ) 1 0Ω (replaces R12, 8.2kΩ) delete R13 (100kΩ) Practical Electronics | February | 2026 69