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Fuzz Face Notes By
Paul Marossy For a complete technical explanation on how the fuzz circuit works, by far and away the best one is The Technology of the Fuzz Face by RG Keen. There are other pages which give some more good information such as History of the Fuzz Face , or Small Bear Electronics' Fuzz Face Fanatic FAQ and Joe Gagan's FX page. There is some good information about the circuit and variants/mutants of the original Fuzz Face on these pages. The purpose of this page is to share my own thoughts and findings about the fuzz face circuit that I built. I built the
"Boutique Fuzz Face" found at www.generalguitargadgets.com which appears to be basically the
standard fuzz face circuit with Mike Fuller's modifications which
includes the addition of a contour pot. This circuit is also
known as the "Fulltone '69". It's a great sounding
circuit and is pretty versatile, it goes from a mild bluesy tone
to a wall of distortion, depending on what transistors you use
and how you set the controls. I used to ask: "What's the big deal about a Fuzz Face?" Well, after building one, I can see what all the fuss is about. The real secret to the sound of the Fuzz Face is a combination of many things, but I think the main reason why a Fuzz Face sounds like a Fuzz Face is because it utilizes voltage feedback biasing (VFB) and uses germanium (Ge) transistors. The fact that the Fuzz Face uses VFB gives it "touch sensitivity", meaning that if you play soft, distortion is at a minimum. When you really dig in and strum a big power chord, the distortion increases. In essence, it follows how you play - picking dynamics, changes in volume, etc. It's as expressive as you are! Part of what the fuss is all about. The germanium transistors originally used produce a softer sounding distortion (less harsh) than the silicon transistors that are in widespread use today and used in some of the later manufacture Fuzz Face and reissues. But, Ge transistors are reputedly not anywhere close to be being as consistent as the silicon transistors today and are affected more by changes in ambient temperature than silicon transistors are. So what does all this mean? Depending on the characteristics of the individual transistors, one Fuzz Face may sound awesome, and another one may sound rather like a dud. So, in order to get around this, when building a Fuzz Face circuit, some careful analysis of the transistors is required for the best possible tone - things like actual gain (Hfe), leakage current rates, etc. Many people have conducted extensive testing on this circuit and have found the best combination that comes close to reproducing the classic good Fuzz Face tone. There is a general consensus as to what sounds best, and I concur. I followed these recommendations with good results. I made a little a simple transistor tester for testing my transistors. I used the schematic from RG's Tech. of the Fuzz Face page to construct it. I wish I had built one of these sooner! They are such a simple circuit, a lot of beginners start off building one. I finally decided to build one after building twenty or so projects and wonder why I didn't build one sooner. It's just the sound I have been looking for many of the tunes that I play. There are three main trains of thought about the transistors used in a Fuzz Face: Germanium or die!, Silicon rocks!, or Hybridization is the Only Way. Naturally this is a very subjective matter, but I have done some testing of my own. This a good reason to use transistor sockets! When I first built my Fuzz Face, I used some metal can silicon 2N2905's. They didn't sound too bad to my ear, a little buzzier than the germanium transistors are. Next, I tried some metal can NOS germanium Raytheon T59247 audio transistors which I purchased from an individual on ebay. I thought that these sounded really good, smoother than silicon and very tube-like in sound. Interestingly, the germanium transistors had noticeably more gain than the silicon ones did, a rather unexpected result - of the twelve I had, the gains I measured ranged between 90 and about 250. The bias control can be used to adjust the maximum gain level to taste. I used a 200K pot which gives quite a range of adjustability. Then I tried the Ge/Si combination that some claim gives a great sound. That gives a little bit more "edge" but is not as "buzzy" as a pair of silicon transistors. Other than the amount of distortion produced, when playing chords, the differences between the different combinations of transistors are not so obviously apparent - there's too much going on to really be able to pick out things decisively. But the differences become much more apparent when playing single notes and double stops, when you can listen for things like the general quality of the tone, smoothness, buzziness and intermodulation distortion. One could incorporate a switch to get Ge only, Si only or a Ge/Si combination for a wide range of tones by switching the transistors in or out of the circuit. I may try this in the near future. In the end,
I decided upon a pair of carefully measured germanium
transistors, They just sounded the best to me. So, in conclusion,
when using germanium transistors for a Fuzz Face circuit,
measure, measure, measure! Out of the twelve that I purchased,
there was three ranges of gain that they fell in, and one was way
off of the scale, so to speak. No matter what transistors you use
in your Fuzz Face, if you are looking for the classic Fuzz Face
sound, they should be measured and placed in the circuit as
recommended by RG's Technology of the Fuzz face article mentioned
at the beginning of this page for best results. |