2 Transistor English Fuzz
The "traditional" way to draw the schematic, with R shunt fb coming from the below.
A different way to draw the schematic, with R shunt fb coming from above.
First appearing in British Vox and Sola Sound products in 1965, this topology was a major step forward in fuzz's evolution towards distortion/overdrive. The previously dominating "No Bias" topology often suffered complaints of "no sustain" or "too percussive." This is due to its inherently non-linear operation. The 2 Transistor English Fuzz is not a non-linear amplifier. It is actually a very conventional linear amplifier, but can be easily overdriven into "fuzz" territory. When the volume is backed off, instead of becoming percussive like the No Bias fuzzes, the 2TEF cleans up and becomes more like a linear booster. It truly is a "proto-overdrive" as well as a classic fuzz.
A nice feature of this circuit, that is probably often overlooked, is that the output signal is in-phase with the input signal. (Single transistor distortion/fuzz circuits are inherently phase inverting.)
The above schematics are identical except in how they are drawn. The first schematic is typical of how the Fuzz Face components are usually laid out, with the shunt feedback resistor coming from below Q1.
The second schematic is drawn so as to explicitly point out how this complex 2 transistor circuit is actually made of combining the simple shunt feedback and simple series feedback amplifiers.
This is a very basic example of how a transistor can essentially replace a resistor in a circuit to improve it. In this case, the second base bias resistor for Q2 has been replaced by Q1, which serves to both provide a bias point for Q2 and our signal is coupled through here.
The 2 Transistor English Fuzz is my label for the controversial Fuzz Face topology. A more conventional term would be "shunt-series feedback voltage amplifier," or something along those lines.
The Fuzz Face is perhaps the most well know implementation of this topology, however two very similar effects predate the Fuzz Face, and the history of these units, and the mystery of the original designer, is a subject of much debate and fascination.
The controversial 3:
Vox Distortion Booster (1965)
Sola Sound Tone Bender ("Mk I.V" 1966)
Arbiter Fuzz Face (1966)
Split Collector Load
The controversial 3 have an unusual feature dubbed a "split collector load" by R.G. Keen. I'm not sure if I've ever seen that term used elsewhere. But the idea is similar to using a potentiometer as a collector load. The use of a pot is included in old transistor textbooks I have from the 1950s and 1960s, and can also be seen in the UMI Buzz Tone and Expander fuzz circuit, and in the instances of the 2TEF found in the Vox Super Beatles amplifiers.
The split collector load resistors reduce the available voltage output. I suspect this was intentional as a way of taming the square wave output, similar to how clipping diodes are used in many other designs. In fact, check out the Electro Harmonix Muff Fuzz for essentially this circuit with clipping diodes at the output. In addition to attenuating the output, the split load changes the symmetry of the clipping, which in turn will affect the final timbre of the effect.
Buzz Levine of Lark Street Music let me examine a Ken Fischer (Trainwreck amps) modded Crest Audio Fuzz Face. The most radical mod inside was the elimination of the split collector load. Ken moved the output to the Q2 collector terminal, and the collector resistor was changed to a more conventional value (I'll let the details remain a secret for now). The end result was less fuzz, more drive and boost.
The Fuzz Capacitor (ac feedback bypass capacitor)
On this last schematic I also threw in the fuzz capacitor that, if large enough, eliminates our ac negative feedback from both Q1 and Q2 while keeping the basic dc conditions the same. This maximizes the gain of the circuit and causes our desired square wave fuzz effect if the input signal is large enough. If we reduce our input signal, then we can clean up our sound because the circuit is still a linear amplifier. This circuit is not a guaranteed fuzz generator, but simply a very overdriven circuit with no ac negative feedback (when C ac bypass is fully connected).
To make this an actual Fuzz Face, we just need to replace the series feedback resistor with a potentiometer, and then connector our bypass capacitor to the wiper. This allows for variable ac feedback elimination.
A very instructive circuit is the Z. Vex Fuzz Factory which makes most of the resistors variable.
The Z. Vex Wooly Mammoth has a variable R shunt fb labelled PINCH.
The Fulltone '69 includes several features to fine tune the fuzz relatively politely (especially compared to the Z. Vex versions).
The Vox T.60 preamp, which is often cited as the precursor of the 2TEF topology. This preamp is set for clean, not fuzz, and it is instructive in how the circuit works. More on transistor designs (including this one) can be found in on the transistor amplifier page. The topology pops up in the Vox Super Beatle amplifiers as well.
Examples:
Vox T.60 (1963)
Vox Distortion Booster (1965)
Sola Sound Tone Bender Mk II (1966)
Arbiter Fuzz Face (1966)
Vox Super Beatle V1141 (1966/7?)
Colorsound Overdriver (1971)
Goya Panther Treble/Fuzz
Electro Harmonix Muff Fuzz / Little Muff Pi
Sam Ash Fuzz-Stainer
Z. Vex Fuzz Factory (simple shunt booster drives a 2TEF with nearly every resistor made variable)
Z. Vex Wooly Mammoth (PINCH is variable R shunt fb for a pseudo pulse width adjustment)
Boss FZ-3 Fuzz (1997)
