You would think that a fuzz effect would be easily distinguishable from an overdrive or distortion—and some are—but others blur the line. Technically, there is a difference—distortions and overdrives usually use diodes and op-amps to achieve breakup, while fuzzes use transistors—but, sonically and feel-wise, there can be crossover.
Fuzz-pedal transistors can be of either the germanium or silicon variety. The first fuzz pedals used germanium transistors, and some players prefer these to later silicon transistors because they consider the latter harsher-sounding. Other players prefer the edgier silicon variety, with its extra gain. However, old germanium fuzzes were extremely inconsistent in tone, because the transistor values tended to vary greatly. Modern manufacturers such as Jim Dunlop, Electro-Harmonix, and Analog Man test each transistor to make certain the sound is more consistent.
Further, though some view fuzzes as a rather blunt and imprecise sonic “weapon,” some fuzz units are as dynamic as an overdrive pedal and clean up when the guitar volume is backed off and respond well to variations in pick attack. Others do not clean up, but rather distort in a different manner.
In basic terms, the two extremes of the fuzz spectrum are represented by the original Dallas Arbiter Fuzz Face on one end and the Electro-Harmonix Big Muff on the other. If you want to produce fat single notes with lots of sustain by running a fuzz through a clean amp, à la Robert Fripp, you are better served by a Big Muff-style fuzz. Why? Because, before it serves up a singing single note, a Fuzz Face-style unit needs the help of a slightly distorted amp or overdrive pedal placed between it and the amp, as well as a guitar with its own healthy sustain and modified picking techniques (aggressive picking helps). That said, there are also many fuzz units that fall between these two extremes.
Octave fuzz comes with its own set of proper playing techniques. The upper octaves come out best on the E and B strings above the 12th fret, and they’re enhanced by using the neck pickup and rolling off the Tone knob. Octave fuzz effects are designed for single-note lines, but some groups of notes can be played harmoniously. If you are into dissonance, they offer a whole other world filled with clashing intervals to explore.