The Fuzz Face series: 2-Alchemy Fuzz

The process that lead to my first (semi-)successful silicon Fuzz Face was a long, difficult and at times frustrating one, but working through several ideas about fuzzes and electronics in general and talking about this with my colleagues (Thei's blogspot) gave me a huge boost and a structural idea about why certain components work better than other. However, I came from almost nowhere and there's still a long way to go :)

The Alchemy Fuzz in glorious baby-blue finish :)

When I started building the Alchemy Fuzz I first decided on using Siemens MKT caps for input (.22uF) and output (.01uF) and a tantalum 22uF for on the fuzz pot. Also, I thought it was a good idea to make up the collector resistor for Q2 as a 4k7 resistor plus a 10k trimpot, because I figured I would never need less than half of the resistance that's in the original schematic. After testing, I found out that a 10k trimpot would've been plenty and that having a precision trimpot is not necessarily making things easy to work with. The 33k collector resistor for Q1 was made up of a 22k and a 11k metal oxide resistor in series.

When I got this up and running, it was time to try out different combinations of transistors, constantly trying to keep Vce for Q2 at around 4.5Volts. By now, a couple of months later, I find that this keeping to 4.5Volts very strictly doesn't necessarily give the best results, but I only found that out when I started listening instead of looking at the DMM. :-) Here, the precision trimpot doesn't help gain that knowledge, because the differences only start to be obvious after several turns of the set screw.

It's funny to see my notes from the original design transistor testing, because I was changing so many variables that they hardly make any sense now, but I did find out what kind of transistors I did and did not like. These are the notes I made for the original design:

• 2n2222a + 2n2222a: low gain, fizzy (by now, I know I just don't like the 2n2222a, their high frequency response is very fizzy and brittle)
• BC337-16 + BC107B: plasticky (I don't like the BC337-16 either, they sound flat and compressed)
• 2n2222a + BC337-16: "metal", very little low end
• BC107B + BC107B: "typical" silicon fuzz face sound.
• 2n2222a + BC107B: nice combo, nice "open" sounding low end, a little fizz on the top. A bit hissy though. This is the only one which has the Q2 collector resistor value jotted down: 10k4 (which seems a bit high)
• 2n2222a + BC107A: sounds a lot like the BC107B variety, a little bit less gain.

In the end I went with the 2n2222a + BC107B setup. But.. then I tried to compare it to my Arbiter/Crest Fuzz Face and I was in for a surprise..

At home, with a small amp and no real Fuzz Face to compare it to, it sounded cool, nice low end, cool grainy high end, but in the studio, on my MusicMan 115 Sixty-Five, compared to the Arbiter/Crest Fuzz Face, it sounded... completely different. The high end turned out to be much more muffled than I imagined, the low end sounded out of control, and the fuzz knob and volume control both influence the tone in a massive way. Dialling down the Volume acts as a high pass filter, but dialling down the Fuzz knob gives you less high end..

So I showed my board to my colleague and the first thing he said was: get rid of the tantalum cap, it probably adds the wrong kind of distortion. Also, he said the MKT caps are probably detrimental to the high end response. Reading up on this further I also came to the conclusion that I wouldn't want any MKT caps in any signal-bearing part of the schematic, except maybe in a tone stack where you are specifically looking for this low-pass sort of behaviour.

Last version: Ero capacitor, 2N1711 and BC107 transistors, styro 10.000pF

So, back to the drawing board: I got rid of the Siemens MKT input cap and changed it for a vintage Ero .22uF capacitor. I'm told it's a metallized capacitor, so it probably made little difference.. Better luck next time. To get rid of some of the fizziness I added a 47pF styroflex capacitor between de collector of Q1 and the collector of Q2, as described in the Axis Face schematic. Actually this schematic calls for a 100pF cap, but I found that to cut too much high end. In fact I tried a couple of different capacitors:

• 8.2pF ceramic: no noticeable difference, I guess the cut off freq is too high
• 47pF styro: a little bit of grit is still there, but the high end fizz is gone
• 100pF styro: the grit is gone too
• 220pF styro: noticeable less high end

I also got rid of the MKT output capacitor and put in a 0.01uF styroflex capacitor instead. The 22uF tantalum capacitor was disengaged as well and replaced with a 22uF audio grade electrolytic cap. At the same time I got rid of the 2N2222A in Q1 and obtained a low gain TFK 2N1711 transistor. It's got a Hfe of between 20-60. With such a low gain Q1 I probably could have done without the RF/HF blocker cap, but hey, it's there now. The Bias trimmer is all turned all the way down (0 Ohm), but the 4k7 resistor in series with it keeps Vce for Q2 at a supposedly okay 4.36V. 

L-R: Bias trimmer, BC107, 47pF styroflex anti RF, 2N1711, Ero .22uF

The result, as you might imagine, was completely different from the first version.. However, it doesn't sound like the original Crest Fuzz Face. By now I'm starting to think the BC107B in Q2 might not be the best option after all. And with the Bias trimmer all the way down, there's no way to try anything else. Yet, as a proof of concept it was a complete success and it helped me so much in understanding fuzz electronics. And it does look nice in its baby blue box. Next up I'll be looking at some varieties that, even though they still don't sound like an original, are very useable and they even got a place on my pedalboard :)

Alchemy Fuzz schematic