Project 4 - Silicon Fuzz Face

What would Rock and Roll be with out Fuzz pedals? I mean, seriously, who doesn't love the sound of fuzz!! It should come as no surprise that I have decided to try and build one.

Originally, I wanted to build a simple one-knob fuzz and eventually graduate to building something a little more complex, but after finding the Silicon Fuzz Face schematic online, I couldn’t resist giving it a try. It's a fairly basic circuit that includes two transistors and only a few resistors and capacitors. Had I stuck to the schematic, I would have had this pedal completed in no time at all; but of course, I didn't take the easy road.

In my collection, I already have a few fuzz pedals, including my favorite, an MXR Jimi Hendrix Limited Edition 70th Anniversary Fuzz Face that I picked up last year. It's an incredible fuzz that is said to be a meticulously faithful reproduction of the 1969-70 Dallas Arbiter Fuzz Face that Jimi used on classic albums like Band of Gypsys. They only made 2300 of these, so I'm glad I grabbed one when I did.

The circuitry of the Hendrix Fuzz looks similar to what's on the Silicon Fuzz Face schematic, although I can't really make out what component values were used. The Hendrix also includes two variable resistors, which I assume are to control the biasing of each transistor.Event though there are a few differences between the two, they do actually sound quite similar. That being said, the Hendrix does have a nicer, warmer tone than the Silicon Fuzz Face.

While testing the Silicon Fuzz Face circuit on a breadboard, I tried using all the different NPN transistors I could find; including A, B and C versions of the BC107, BC108 and BC109 transistors. After spending several days swapping out all the transistors, I decided to go with a BC108A and a BC109C. In case you're wondering, the Hendrix Fuzz uses a BC108B and a BC1087C (which I assume is just a regular BC108C).

For the output capacitor, the schematic calls for 10nF. I did try several different capacitor values, both higher and lower, but found the 10nF actually sounded best. I also really liked the larger 0.12uF capacitor, since it gave the fuzz a slightly lower tone, but I ended up sticking with the original value.

Once I had completed the build and everything was working fine, I found myself still thinking about the 0.12uF capacitor. Since I already have the Hendrix Fuzz, did I really need another that sounds almost the same; or should I just go ahead and add-in the other capacitor?

After much consideration, I decided to add the 0.12uF capacitor and wire in a toggle switch so I could choose between the two capacitors.

Just so you know, the sound difference between the two capacitors is really quite subtle, especially when using a smaller amp - but there is a difference and it's a bit more noticeable when using the bridge pick-up on your guitar.

So that's it; build complete, right? Not so fast. A short time after adding the Silicon Fuzz Face to my pedal board, I noticed the LED would sometimes flicker or not light up at all. I opened the enclosure and, using my trusty multi-meter, attempted to diagnose the problem. Turns out the LED was faulty. So, I swapped it out.

I also decided to add some 1mm red foam to the enclosure lid to help prevent the components from touching the aluminium and possibly shorting out. Unfortunately, this reduced the space between the new large capacitor and enclosure lid, which prevented me from closing it.

This left only three options: remove the foam, build a new circuit that properly includes the second capacitor, or attempt to replace both capacitors, moving them to the top of the existing circuit board.

Since I wanted to keep the foam, and really didn't want to make an entirely new circuit, I went ahead and replaced the two output capacitors (you can see them in image 4 below).

I also needed to replace the switch, which would have been fine had I not melted one of the green output wires in the process.

Thankfully, after a couple days of frustration, I was eventually able to get everything back together. Now this Fuzz works as it should and sounds great.

Next, I’ll be stepping away from pedal building to experiment with chemical etching. It looks simple enough, I just hope I don't destroy my kitchen or dissolve any fingers while messing around with corrosive chemicals. I guess we'll find out soon enough. Thanks for reading.

Schematic for the Silicon Fuzz Face: