Fuzz Face - Components

Components

The circuit uses eleven electronic components, plus a battery. Its sound is mostly dependent on the selection of transistors (type, hfe and leakage in case of germanium transistors), so it can vary a lot. The tolerances of the other components play a role, too. In addition, germanium transistors tend to be sensitive to temperature, so the sound produced using the box would change as the equipment heated up. According to Roger Mayer, his guitar tech, Hendrix would buy half a dozen Fuzz Faces and mark the one he liked best only to find out that he didn't like in a different environment.

The circuit uses the property of transistors known as "saturation". When used as an amplifier, a transistor's output level is directly related to the input level, but if the input level is high enough, the output reaches a maximum and goes no higher, regardless of the input level. The effect is to "cut off" the peaks of sound waves leaving a flat line instead of a rising curve. This introduces extra harmonics into the sound, producing the distortion or fuzz. The circuit of the basic Fuzz Face uses two transistors that both amplify the signal in sequence. The first transistor is biased close to the edge of saturation, so the amplified waveform is asymmetrical. The closer this is biased to saturation, the more "gargle" and fuzz effect you will get.

In extreme cases the smooth input wave is converted into a square wave which can sound harsh. This tends to occur using transistors with very high gain (output current divided by input current) where the first transistor's output is so high that the second one saturates quickly. Germanium transistors have low gain compared to most silicon transistors.

Early units used NKT275 germanium transistors. Later on BC183L, BC183KA, BC130C, BC108C and BC209C silicon transistors were used. The american made versions used BC109C transistors. Arbiter reissues used AC128s.

Modern Fuzz Face clones and modifications to the circuit use a variety of transistors, and given the subjectivity of guitar tone, there is no clearly preferred transistor.