This is an improved clone of the Interfax Harmonic Percolator, an oddball overdrive/distortion pedal from the 1970s popularised by Steve Albini of Shellac. These pedals are built to the verified correct schematic and are a 100% accurate clone of the sought-after original, only with the addition of a switch to offer three different clipping options which greatly adds to the versatility of the effect.
The Fredric Effects Harmonic Percolator uses the correct vintage transitors (NOS 2N404 Germanium and 2N3565 Silicon) and 1N695 diodes - all the hard-to-find parts of the originals, but in a modern pedal-board friendly package, with DC power, LED indicator and normal rotary pots instead of sliders. So you can have the most accurate Harmonic Percolator clone possible without sacrificing usability.