My "Fuzz Farm" multi-mode fuzz pedal has the distinction of being a modified clone of a modified clone. The basic circuit is from the venerable Dallas Arbiter Fuzz Face design, but this version is based upon the more elaborate Fulltone '69 pedal. This pedal, now out of production, was a Fuzz Face that was modified with two additional controls--Bias and Contour--to alow greater control over the character of the fuzz distortion. The Fulltone '69's therefore had four control knobs vs. the Fuzz Face's customary pair.
Naturally, those weren't quite enough tonal options for me! I further modified the Fulltone design by changing the pedal's internal trimpot for setting the transistor bias voltage to an external control pot. And why should this be necessary, you ask? Isn't the transistor bias something that just needs to be set once when the pedal is first built? Or at most, whenever the transistors are replaced?
Generally yes, but this is no ordinary fuzz pedal. That's because the other major departure from the Fulltone design is two pairs of switchable transistors--one pair of the "traditional" germanium type (Ge), and the second of the more pervasive silicon variety (Si). Each of the pedal's two transistor slots, a.k.a. "Q1" and "Q2", can be switched between the Ge or Si transistor types via a toggle switch, for a different fuzz tonal character. The germaniums give a somewhat softer and warmer fuzz tone, where the silicons offer higher gain and a bit harder sounding edge. Because the two types have different characteristics, the ability to change the transistor bias voltage is critical to getting the best tone when switching back and forth between types. So having that external control pot for the bias voltage is a big plus--beats the heck out of having to go inside the pedal and twiddle a trimpot every time you switch trannies!!
One other rather unusual feature of this pedal bears mention--it's a "positive ground" pedal, as opposed to the negative ground wiring scheme used in the vast majority of modern effects. This has to do with the "PNP" germanium transistors used in the original Fuzz Face pedals and several other early fuzzes. The "NPN" types of transistors used pervasively today were apparently much more difficult to manufacture for germanium trannies, so this reversed ground wiring scheme was employed so that the PNP type could be used. The pedal will still work with a standard center-negative 9V AC adapter, but it cannot be "daisy-chained" together with negative ground effects. Doing so will cause the pedals not to work, and may burn out the AC adapter. So get yourself a dedicated "wall wart" for the pedal or run it on 9V batteries, and you'll be fine.
The pedal was built using a PCB and assembly directions from General Guitar Gadgets. I sourced the rest of the components and hardware myself, including a matched pair of AC128 germanium transistors (now sold out) from Jack Orman at Muzique.com.
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