VFE Fuzz Duo

The VFE Fuzz Duo is a hybrid fuzz pedal that lets you switch between low-gain germanium and high-gain silicon transistors on the front end of a Fuzz Face circuit, or use a combination of both to create your own signature fuzz tone¹. Four knobs (Level, Fuzz, Bias, Treble) and a Ge/Si toggle sit on the outside, with two trimpots inside for feedback and LED brightness.

The pedal is currently listed as Out of Stock on the VFE Pedals site at a sale price of $129.00, down from a regular price of $179.00². A DIY build thread has described the Fuzz Duo as "soon to be discontinued"³.

The controls

Four external controls shape the fuzz, plus the Ge/Si toggle for voicing.

The Bias control deserves a note for anyone building or modding the pedal. In the Fuzz Duo it is placed in series with the 1k resistor, which means it changes the bias setting as well as adds a lot of extra volume¹. That is why the extremes of the knob cut output: the useful bias range sits between them.

The very first prototype worked differently from the production pedal. It had a 3-way rotary switch to toggle between germanium, silicon, and hybrid fuzz tones¹; the finished pedal uses the simpler two-way Ge/Si toggle with a combined option.

The internal trimpots

Inside the pedal there are two trimpots, and they do very different jobs².

• Main board trimpot (FDBK, 200k): affects the amount of feedback and voltage bias of the fuzz circuit. More feedback means less gain²¹.
• Lower trimpot: controls the brightness of the LED².

For builders, the manual also records measured transistor voltages for a working unit, which gives a reference point when biasing your own build: Q1 (Si) collector 1.35, base 81mV, emitter 6mV; Q2 (Ge) collector 168mV, base 84mV, emitter 7mV; Q3 (Si) collector 0.75, base 1.34, emitter 0.69; Q4 (Ge) collector 7.65, base 168mV, emitter 118mV¹.

Transistors and voicing

The Fuzz Duo runs two germanium and two silicon transistors. VFE's Peter often used BC108 for the silicon positions, listing hFE between 450 and 600 with a combined total between 1000 and 1200, the lower-gain one going in the Q1 position. For germanium he listed OC139 or OC140 with hFE between 70 and 130 and a combined total of 180 to 220, again with the lower-gain one first¹.

The madbean manual's author built his own version with NPN AC127 germanium transistors (hFE about 140 each) and SE4002 silicon transistors, and reported both worked out fine¹. A TO-5 style socket will fit the germanium positions if you want to socket them for swapping¹.

Power

The pedal accepts the industry standard 9 to 18 VDC, negative-tip power supply², with a current draw of about 11mA¹. The 9 to 18V range means it will run on a standard 9V supply but can also take higher voltage from a suitable source.

DIY builds and layouts

Two routes exist for building one yourself.

Madbean Pedals PCB: Madbean Pedals offers a PCB version, though it is not a VFE PCB but rather an approximation of one; the circuit is 100% original to VFE¹. Technical assistance for builds is available via the madbeanpedals forum¹.

The filter control on the original units works as a sweep: fully counterclockwise lets the full bass range through the input stage, turning clockwise to 12:00 cuts bass and tightens the low end, and from 12:00 to fully clockwise it cuts treble in the gain stage and smooths the top end³.

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