The Harmonic Percolator is a distortion pedal that was created by Ed Giese of Interfax Electronics in Milwaukee, Wisconsin in the 1970’s. It used a silicon NPN transistor and a germanium PNP transistor in a design that passes even order harmonics while suppressing odd order harmonics. These even order harmonics are more pleasing to the ear than odd order harmonics. At low settings the Harmonic Percolator will give added sustain without ‘coloring’ the sound. Higher settings will give a mean distortion that performs well with multiple notes. Legendary guitar-abuser Steve Albini (Big Black, Rapeman, Shellac) uses a Harmonic Percolator for some of those Guitar noises he gives birth to…
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Interfax HP-1
Wow I was amazed to come across this article.
I do remember interfax electronics, they had a shop near my parents house on the North side of Milwaukee Wisconsin and I think my Dad even had a radio repaired there! The building still stands there and looks like its now a charity donation resale shop. I remember a big stink in the area at the local music stores as almost right after interfax closed the pedal was cloned and sold by another effects pedal company in Milwaukee named ACEffects. I can’t remember what they called it.
It brought back memories so I googled the place who made the clones and I was shocked they were still running. I emailed them and they wrote back they have boards and parts for percolators still in stock! Makes me feel old now remembering this!