The Phobos Germanium Fuzz is a clone of the Colorsound / Sola Sound Tone Bender Mk III. While the first version was essentially the same topology as a Fuzz Face, and the second version added a gain stage in front, this third version from 1967-1968 was a completely different circuit, using a Darlington-pair transistor configuration to drive a third transistor, followed by a tone control which the earlier versions were missing.
While the Mk. III Tone Bender was itself a variation of the Baldwin-Burns Buzzaround, it had a few variants of its own, both official and unofficial. The Vox Tone Bender was a licensed variant with a few parts substitutions. The Park Fuzz Sound by Park Amplification (Jim Marshall’s side-brand) was a contemporary clone. The Elka Dizzytone and the Prescription Electronics Yard Box were two others. Aside from the Buzzaround, all of the rest of these variations can be build on this PCB.
A note about the name: the original Colorsound / Sola Sound unit was not called the “Mark III”, but the Vox-licensed version was. As a result, this circuit is commonly called both the “Mark III” and the “three-knob” Tone Bender. This project will refer to it as the Mk III to differentiate it from the Mk II, which is available as another project called the Deimos.
The Phobos project has a voltage inverter which allows you to power the effect with a standard center-negative adapter while maintaining the positive-ground operation of the original. The PCB also includes biasing trim pots so you can dial in a perfect bias without having to swap out resistors.