I’m always looking for the cheapest way to build pedals. I found these boards on OSH Park.com. Besides being a service for prototyping boards it’s also an open source repository of projects uploaded by the community. A board uploaded to OSH Park marked public can be ordered by anyone. The search function is not so great but it is searchable. I spent a day searching OSH Park for stompbox projects and found more than a few things that look worth building.
The OSH Park standard service is $5 per square inch with the requirement that you order three boards, and shipping is free. This usually cheaper than ordering boards from vendors but there is no support. One of the projects I found was a this Fuzz Factory. It looked well laid out and the cost was $7.75 for 3 boards, about $2.50 per board, which was pretty reasonable.
With no build Docs you’re on your own. The Fuzz Factory is not a complex pedal and the schematic is readily available. Some OSH Park projects will link to documentation and other do not. This is a good way to level up your skills!
The Fuzz Factory is not a hard pedal to clone. The toughest part is wiring the pots. Getting a board where the pots mount directly to the board is a great help. Here three of the five pots mount to the board and two require off board wiring which makes a pretty easy build.
The Fuzz Factory has only a handful of parts. I soldered everything except the pots and the two germanium transistors. You’ll want to test a few transistors if you’re using germanium to get some that sound best. That said really everything even silicon can sound good in this circuit.
For the enclosure I used a black powder coat 1590B from Tayda. For the logo and labels I milled the box using a desktop mill. The powder coat is removed to reveal the design. I created the design in Sketch on the computer exported some SVG files and loaded these into the mill.
I decided to try out a relay switching system. This uses a soft touch momentary SPST switch and some circuitry. I used boards from DIYGuitarPedals.com. Their system uses some discreet logic and a relay to handle switching and the status LED.
The PCB is designed to fit a 1590B or larger enclosure. It requires a few parts which are mostly easily available. The relay is available through Mouser. Erik over at DIYGuitarPedals was generous enough to send me two boards and the relays, thanks again Erik! Check out their web site and their YouTube channel.
The system uses a relay which is an electromechanical switch in a little box. The switch in this case is the RY9W-K. It’s a DPDT but rather than being engaged by a button or lever it’s engaging by an electrical voltage applied to a control pin.
In the picture below you can see the relay has 8 pins. The 6 pins on the left are the switching connections, each row is one switch, the center is the common connection that bridge to the outer connections depending on the state of the switch. Hey those six pins on the left are just like the pins on a regular DPDT switch-. The two pins on the right are the control and ground.
The board, relay, SPST switch, and other parts make up a single assembly that replace the 3PDT switches typically used for guitar pedals. You can see it neatly fits the lower bout of the 1590B enclosure.
Here is what the whole system looks like assembled. This is complete and could be dropped into any pedal replacing the standard blue 3PDT.
How does it work?
Unlike many relay systems that rely on a micro controllers this circuit uses only discreet logic. There are pros and cons to each. Using a micro controller requires some extra circuitry since the Micro Controller runs on 5v. They can be proprietary since someone has to write the software that runs the system. Using a Micro controller you can fit all the logic into an 8 pin DIP and add new features or up date the existing code. Using discreet logic your system can run on 9v, might have fewer parts, and won’t suffer from software bugs.
This system relies on the 4011 quad NAND gate to handle the switching logic. Check out this video for a more in-depth explanation of the switching logic.
Assembling the NAND Bypass board is pretty easy. Easier than making the Fuzz Factory board. It’s got very few parts and there is plenty of room to work. If you wanted to give this type of switching a try this would be a good place to start.
Building and wiring the Fuzz Face
The board mounts the three 10k pots and will accept 9mm or 16mm pots. If you are trying to fit this into a 1590B box in portrait orientation you’ll need to use 9mm pots! The two 5k pots are mounted off board. You could also build this in portrait with all 16mm pots.
I mounted the pots in the enclosure then soldered them to the board to make sure they were perpendicular to the enclosure.
I had some ribbon cable salvaged from an old computer. I used this to wire the off board 5k pots. The board marks the pins 1 and 3. Pin 1 also has a square pad. I used 16mm pots with pins that stick out perpendicular to the shaft. I cut a couple pieces strip board to interface the wires and the pots. This made for some nice clean wiring.
The bottom of the PCB is pretty close the corners of the enclosure. I’ll have to be careful it doesn’t short out there! This was a test fit. I needed to mark the positioning for the power, input and output jacks, then disassemble everything and drill these.
Once I got everything drilled I added some wires and reassembled everything. I realized I needed to move the two pots in the second row inboard a millimeter or two. You can see I had to file the holes a little.
I also installed the switching board. I stuck a little piece of wood to the side of the switch to brace it against the back of the enclosure. There was no way to brace the switch when tightening the nut.
You may have noticed the two germanium transistors are missing. Since these are notoriously inconsistent I decided I wanted to audition a few before selecting which would be used for this project. I have a bag of 40 I’ll test and measure these to find suitable pairs.
I have this TC1 Multi-function Tester. This cost about $17 on eBay. Well worth the money. It tests resistors, capacitors, diodes, transistors, and more. It will tell you all of the most useful information. It will also differentiate NPN, PNP, JFET, and MOSFET devices, and tell which pin is the base, collector, emitter, gate, source, or drain. Super handy.
Germanium transistors have a high degree of variation. Their hfe and leakage is very inconsistent across devices with the same part number. There is a lot of debate about what hfe values work best for different circuits. Some people like to judge by the numbers others like to use their ears. I’m going to go with a hybrid approach use the numbers to get in the ballpark and then audition by ear.
I measured all of the Germanium transistors in the parts bin, marked each with a number and made a spreadsheet of all the values I measured with the TC1.
This is a Fuzz Factory I built using a board from AionFX, it has a few extra knobs. I used sockets for the transistors. I figure I can plug some transistors into this to hear how they sound before soldering them into the new Fuzz Factories.
Here I wired up everything in the box. The NAND Bypass board is well laid out and labeled making wiring easy. Input and output jacks go to the input “In Jack” and “Out Jack” and the input and output from the PCB go to the “To PCB Input” and “To PCB Output”. It’s paint by numbers really!
At this point I gave it a test. I the LED worked, and bypass was working. So we’re goo to go. The last step is finding and installing some Ge transistors.
Tested some transistors in the green fuzz factory and decided on 1 and 9 from the spreadsheet. They had numbers that seemed to be the right range and sounded good.
Taco Fry Fuzz #1
The first us out of the way time to audition a couple more transistors and make the second box.
Tested a few more transistors and decided on #60 for Q2 70 hfe, and #21 for Q3 190 hfe. These sound good and we’re very close to the values for the first pedal. Which should make these sound very close.
What does it sound like?
The Fuzz factory is a highly variable fuzz. The sounds range from standard distortion to fuzz into high gain. It’s possible to dial in gated fuzz and zipper sounds. Not all of it useful in many cases. It’s all fun and inspiring.