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AUDIO OUT AUDIO OUT L R By Jake Rothman The Transmanium fuzz box, part 2 – assembly Last month, I described the circuit design and PCB for this new fuzz box, based on germanium transistors. Now it’s time to put it all together, giving the result shown in Photo 1. Being a foot pedal for musicians, the criteria are different from a normal desktop electronic enclosure. It has to be tough, because it’s on the floor and the effect is switched in/out by a brutal boot on what’s literally called a stomp switch. A metal enclosure is needed; plastic will only last a few weeks in use. It is also necessary for screening, with it being a high-gain, high-­impedance unit. The case is Earthed through the pot bushes via the PCB. If the case is painted, it will be necessary to de-burr the hole edges to bare metal so that the pot bodies make electric contact. If even the switch body isn’t Earthed, clicks will result. Photo 1: the finished fuzz box. 30 Boxing clever Most pedal manufacturers have to invest a considerable amount into enclosure tooling. The Colorsound presses cost well over £5k. Luckily, they survived the Hemel Hempstead Buncefield oil explosion in 2005, which destroyed the factory. For small-scale production, ready-made die-cast enclosures are the best because they are easy to drill. Companies like Hammond Manufacturing and Tayda make excellent cases in many colours and offer a small-quantity drilling service. The drilling diagram can be downloaded from https://pemag. au/link/ac8p. Ready-drilled boxes will be made available, which will be used as a format for further designs as well. Readers can have the Tayda drilling file on request. Because the sides of diecast boxes are sloped with curved edges (to enable release from the mould), it is difficult to give accurate measurements from the edge. The way around this is to measure from the Photo 2: rubber hole plugs on the base prevent slipping. Cabinet feet make it too tall. The knobs have to be top-mounted so that you can see the settings, and easily make adjustments which makes the pot shafts vulnerable. As a result, Solid metal shafts are preferred. If plastic shafts are unavoidable, a 6mm diameter is the minimum. The knobs have to be spaced away from the switch area by a least 40mm to avoid damage. This necessitates a relatively long, large box for the electronics contained within. It is tradition and good practice to have the sockets on the back to keep the leads out of the way of the performer. Photo 3 shows the layout of the mounted components. Rubber hole plugs have been fitted as ‘feet’ to stop the unit from moving about on the floor, visible in Photo 2. Most guitarists stick their pedals to a pedalboard with Velcro, so these can be left off if desired. It saves a lot of drilling. Practical Electronics | December | 2025 Photo 6: The battery should be securely fitted in a clip. Use a Nylock nut so it doesn’t back off. It’s not good enough to just use a lump of foam like some pedals. Screen in cable shorts earth LED connections under board Output amplifier +– Photo 5: The back of the box with the jacks. The plastic plate hides the wonky hole for the barrel socket. centre lines of the box, as Tayda specifies for their drilling. Jack board The 2° ±1° sloped sides also mean it is difficult to mount the jack sockets on the main board without stressing the pins. This problem is avoided by using a separate jack board, shown in Photo 4. Fig.1 is the overlay diagram for this board. Of course, the sockets can be hard-wired without this board if that’s how you want to roll. This makes assembly more difficult, but future parts replacement easier. I have found PCB-mounted 6.3mm jacks to be very reliable. The 5.5mm outer diameter, 2.1mm + Input instrument – Input Output Earth Earth – Positive earth pedal Output Input GND LED V Bat Bat (–) (+) Fig.1: the jack PCB overlay. inner diameter power barrel jacks are not so good. On this unit, the sockets follow normal circuit signal flow convention with the input on the left and the output on the right when looking at the front panel. This is how Colorsound do it, but I’ve since found most guitar pedals do it the other way around, because the guitarist’s lead comes out on the right (at least, if they’re a right-hander playing a right-handed guitar). Having the pedal’s input on the right avoids crossing the leads over. I will make a ‘normal’ board option later; it could be done simply by turning the board over, but this means the components can’t be seen, an aesthetic no-no Negative earth pedal Fig.2: when a positive Earth pedal is powered by the same supply as a negative Earth unit, it is shorted out. in guitar pedal circles. Also, the power socket hole would have to be repositioned after flipping it over. The socket end is shown in Photo 5. Note how the power socket sticks out from the board slightly (Photo 4). This necessitates the use of washers on the inside of the audio jacks. Positive Earth Because the circuit uses a positive Earth, the power socket is centre-pin positive, which goes against the guitar pedal convention. It is necessary for this pedal to have its own power supply to prevent shorting with negative-­ Earth pedals anyway, so I don’t think that is a problem. This shorting is illustrated in Fig.2. Photo 4: the jack PCB. Remember to put the jack washers on before you mount it in the box. Photo 3: the PCBs and switch are separate in the box due to the different heights required. Practical Electronics | December | 2025 31 Photo 8: a thin copper foil shim can be wrapped around the 6mm shaft to fit 6.35mm (¼-inch) knobs. This is achieved by the long Earth sleeve of a mono jack plug shorting together the sleeve and Photo 7: these Alpha 24mm pots from Rapid had ring contacts of a stereo jack socket (or using a insufficient bushing length to reach the case so they are secure to the board. Always solder after socket with a built-in switch actuated by the tightening to prevent stress on the joints. plug shaft). The current consumption is The Earth connection of the 3.7mA, so an ordinary zinc-carbon battery is connected to the centre PP3-type battery lasts a long time. terminal/ring of the jack. Thus, The battery needs to be held se- it is the Earth connection that is curely by a clip (Rapid) as shown switched, not VCC. in Photo 6. Use the best battery It is best to perform the switchconnector (‘snap’ to guitarists) you ing on the input jack to minimise can find. The ones that are mould- the loud crack that occurs when ed are less likely to fail than the the lead is inserted. crimped plastic-film ones. Although guitarists don’t seem to care about loud bangs, I think the Power switch? amplifier should be muted when Another strange convention plugging in to protect one’s hearwith guitar pedals is that no power ing. Lastly, don’t forget to pull the switch is provided. Power switch- lead out when you are finished, or ing is achieved by using a jack you may end up with a flat battery. socket as a switch, switching on the unit when a jack plug is inserted. Pot problems An unforeseen problem with the diecast case was its thickness compared to the pressed steel Colorsound cases, which meant the bushings on most pots were not long enough to mount to the PCB (see Photo 7). The solution, for now, is to fix the board with mounting holes using countersunk head M3 screws. An expensive solution is to order Omeg or Bourns pots with the longer bushings. The final solution will be milled holes in the PCB to accommodate normal cheap 16mm pots with standard pins. My PCB designer, Mike Grindle, is working on it now. Photo 11: wiring the switch links. Shafted Another pot irritant is shaft size. Most low-cost pots with round shafts have a 6mm diameter, while most knobs are for ¼-inch or 6.35mm diameter: a typical engineering imperial/metric mixup. This difference causes an ugly eccentricity as the knob is rotated. One way around this is to add a thin copper strip shim around the shaft (as in Photo 8), or better still, buy some brass adaptor tubes from the synthesiser shop Thonk or Tayda, as shown in Photo 9. 32 Practical Electronics | December | 2025 Knobs I don’t like push-on knobs because they often fall off. They are also generally designed to fit splined shafts that are prone to snapping because the split weakens the structure. They are great for manufacturing though, where time is money. The home constructor can use quality grub-screw fixing types, although there is a subtle art to mounting them. Having fitted thousands in my time, I make it look easy, but it is not. The key is to turn all the shafts hard one way and then put the knobs on. Lift the knobs by 0.5mm and line up the marker line/pointer and tighten the screw a little bit, almost at the same time. Turn the knob fully the other way to make sure it’s symmetrical and not scraping. If it’s all okay, fully tighten the screw. Occasionally, grub screws are lost, rendering the knob useless. No need to worry, they are now Photo 10: the LED is mounted using a solderless connector under the jack board. A bit of Evostik (rubber-based glue) will help keep it in place. Photo 9: ready-made pot shaft adaptors are an even better solution. available from Tayda for 3p each following a lot of pestering. If the screw is obscure, such as a 4BA type, I’ve found model suppliers have them, but they are expensive. For pedals, I like to use traditional pointer (aka ‘chicken head’) knobs as shown or ‘Marshall-style’ silver-cap types with marker lines. These are available from Tayda and Action Hardware. Bypass switching The fuzz box uses a ‘hard’ bypass that enables the guitarist to carry on playing if there is a failure, such as a flat battery. The circuit is shown in Fig.3 overleaf. The input of the fuzz box is grounded to prevent hum pickup when bypassed. This helps prevent a click when the effect is switched back in. LED wiring A switch section is also used for the LED. A 5.6kΩ current-­ limiting resistor (marked CLR) gives sufficient brightness with high-­ efficiency LEDs, such as the Tayda or Kingbright types shown. I always prefer orange LEDs myself; blue ones give me ‘mental health issues’! I tried to mount the LED directly underneath the PCB, but the con- voluted bending caused too much stress and cracked the LED’s case. It’s a tricky PCB design problem because the LED needs to go where the power socket pads are located. For now, until Grindle’s spatial brain finds a solution, a solderless LED holder (Rapid or Tayda) is used, stuck down with double-­ sided tape, as shown in Photo 10. Remaining wiring The next job is to put the links on the switch (see Photo 11) using 24 SWG (0.56mm diameter) tinned copper wire or resistor lead off-cuts. The interconnecting wires between the switch and the two boards are shown in Photos 12 & Photo 12: the completed wiring. Practical Electronics | December | 2025 33 cables are screened, all the wires can be cable-tied together without feedback occurring. The switch wiring is the most difficult part of the construction, so great care is needed (see Photo 13). Don’t overheat the tags or move the wire while soldering. The plastic can melt, losing the internal connection, rendering the second most expensive part useless. Photo 13: the switch wiring is a difficult job. The cable screens go to the earth link on the lower right hand corner and are not connected at the other end. 13. I always use 7/0.2 stranded wire for this sort of work. Solid-­ core wire snaps off with vibration unless very well clamped. The completed wiring loom is shown in Photo 12. There are two screw-mounted cable clamps. One is for the battery clip wires, with a bit of silicone rubber sleeve for grip, with the other for the main loom. Clicks can be reduced by using a screened wire for the input cables, since ordinary wire becomes microphonic in high impedance situations, generating a voltage when it moves, such as when the switch is pressed. Because the sensitive input Testing At least a simple thing like this can be fully tested, unlike modern software-based equipment. After all, there are only three knobs! The most common problem is hum and instability from poor Earthing. There is a provision for the stabilising capacitor (C9) and tuning capacitor (C10) on the new boards being supplied, if required. Be aware that with this style of construction, it is possible for shorts to occur from the underside of the PCB to the metal case. The clearance is only around 1.2mm, provided by the pot mounting nuts, so make sure all the component leads are cut very short. This is easy using flush side-cutters on boards with plated through-holes Using it Fuzz boxes are most commonly used with an electric guitar or Photo 14: the fuzz box being used with a bass synth. In this case, an open-source kit for an improved TB-303 from Adafruit, the x0xb0x (pronounced “zocks-box”). It’s well worth building one: https://www.ladyada.net/make/x0xb0x/ 34 Practical Electronics | December | 2025 + bass. However, these days they are also used to add a bit of dynamic grunge to what may be sterile synth bass lines. Using a fuzz box with the Roland TB-303 Bassline synthesiser, shown in Photo 14, is now a techno staple, with the fuzz adding a harmonic boost to the TB-303’s accent, giving a wonderful ‘bark’ to the sound. A bit of fuzz on distant filtered vocals can also work wonders to give a ‘military comms’ sound, such as the one in Kate Bush’s nuclear holocaust song Breathing, coldly calculating of size of a nuclear explosion. Distortion effects still work better in analog rather than digital, since the harmonics generated cause aliasing products that fold down into the audio. A very high sampling rate is thus needed to perform similar effects digitally, which consumes valuable processing power that most studio engineers would rather apply to other plug-ins. Besides, this fuzz box is very portable! PE 9V Red – Parts List – Transmanium fuzz box extras 1 assembled main PCB, 85×80mm (AO-NOV25-01) – details in last month’s article 1 jack PCB, 72.5×26mm (AO-DEC25-01) 1 Hammond 1590 DD or Tayda A-5141 case [Rapid 30-4687] 3 pointer knobs, Tayda “Marshall” type A-1838 or Action Hardware KPM-1674 [Rapid 32-0175] 3 80 × 3mm cable ties [Rapid 04-0630] 1 CPC CBBR7741 screw-mount cable tie 1 cable tie mounting clip/eyelet [Rapid 04-0600] 1 PP3 battery snap/holder [Rapid 18-0093] 1 Comf BH980 battery mounting spring clip [Rapid 18-3480] 1 solderless LED socket with leads [Rapid 55-0167] 1 Kingbright L-7104SEC diffused orange 3mm high-efficiency LED [Rapid 72-8972 Tayda A-264] 1 TruConnect 2.1mm inner diameter, 5.5mm outer diameter DC barrel power socket [Rapid 20-0970, Tayda A-4118] 2 stereo 6.3mm PCB-mount jack sockets [Tayda A-5079] 1 1m length of 7/0.2 equipment wire 1 200mm length of 3-5mm screened cable 3 pot shaft adaptors [Tayda A-7023] 3 Vishay ACCTR511-3002 ⅜-inch pot nuts [Mouser 594-511-3002] 1 hex nut for Alpha potentiometers [Tayda A-5037] 6 12.5mm rubber hole plugs [RS 605-661] 5 M3 × 12mm countersunk head machine screws and nuts Pot grub screws (if needed) [Tayda A-7804 (M3), Tayda A-7805 (M4)] All parts available individually from the AOShop. Black Centre pin Outer Pink FX output NC switch contact 2.1mm DC connector Violet S2 White Input Blue S1 Input Orange White Jack sleave Ring –V Input S2 Fuzz Output 0V Jack stereo socket (switch contact not used) (power switched here) 0V screen 0V screen To jack board ground (green) Ground to switch (black) Rear of 3PDT switch (Poles are centre pins in each switch section) Pink Output 0V 0V Tip FX input S3 Black 24 SWG link Orange S1 Brown LED 24 SWG link Output Tip NC Brown 0V Jack sleave S3 Black –V 5.6kΩ 0.25W 0V Effect On Fig.3: all the connections in the fuzz box that are made off the circuit board. If you’re unsure while wiring it, check this! FIND ALL YOUR ELECTRONIC COMPONENTS IN ONE PLACE BASIC MICRO E L E CT R O N I C S C O M P O N E N T S U P P L I E R w w w . basicmicro . co . u k High-quality, genuine parts Practical Electronics | December | 2025 35