An in depth look at the Fuzzy Wuzzy's circuit.
My original goal with the Fuzzy Wuzzy circuit was to recreate the classic sound of the 1969-70 Dallas Arbiter Fuzzface. The Fuzzface is a truly remarkable sounding fuzz but unfortunately has several shortcomings that make it difficult to use as a giging musician. A few of these are, the Fuzzface is very susceptible to RF interference, it can't be powered by a standard 'boss' style power adapter, they don't have a lot of output power (can't put them before other pedals), and last but most important, they will often quit working if they get too hot. One of the problems of the Fuzzface was that it used germanium transistors. This however is where the Fuzzface gets it's mojo. As you probably know, germanium transistors are unfortunately, very unreliable, often leaky, and vary in character with temperature changes. What makes (some of) them sound so nice however is that they have a much lower internal gain. The earliest FF's were made with AC128's. Here is a excerpt from 'The Technology of the Fuzz Face' by R.G. Keen.
"The fact is, the AC128 is not a super high quality transistor, and wasn't at the time. It is a moderate gain (90 typical) device with only modest frequency response. It was HIGHLY variable in gain. I have measured several hundred AC128's for gain, and they vary from a gain of 16 to probably 180. I say probably because the measured gains actually turn in numbers up to 500 or so, which are clearly leaky devices, not high gain devices. The semiconductor industry was new back then, and had not developed the technologies that let us make cheap, reliable, identical-as-peas-in-a-pod devices like we have become accustomed to.
The variation in gain is important because it is crucial to the tone of the FF. Reliable reports from people who actually bought and sold volumes of FF's in the "golden years" say that out of a case of fifty units, they all distorted all right, but only a few would sound really good, right out of the box. It was common for guitarists to make deals to presort a batch to get a good one. This practice continues today, with Eric Johnson's tech supporters tracking down and interviewing FF's to find the few "magic" ones. Fuzz Faces per se do not necessarily sound good without tweaking and transistor selection.
There is a definite sweet spot for musical sounding clipping at transistor gains of about 80-110. If you allow combinations of one high and one low gain device, the range widens out to 70 or so on the low end and perhaps 130 on the high end. "
The reason many silicon fuzz pedals sound so un-musical is because the transistor gain is typically much too high for the best sound in a fuzzface. Most silicon based Fuzz pedals use transistors that start around 250 and some are even higher. The Fuzzy Wuzzy uses two different silicon transistors, which are very reliable and also have a much lower internal gain that is almost identical to the sweet spot that Mr Keen talked about. Because of this (and a few other tricks) the Fuzzy Wuzzy sounds almost exactly like the original Fuzzface but is much more reliable and solves all of it's shortcomings.