Harmonic Percolator HP-1

The original Harmonic Percolator is a distortion pedal developed by Interfax Electronics in Milwaukee, Wisconsin during the 1970s. Rather than being based on an earlier design, it introduced a unique circuit using a silicon NPN transistor paired with a germanium PNP transistor, along with germanium diodes and a combination of Mylar, Silver Mica, Tantalum, and Ceramic capacitors. Its distinctive topology emphasizes even-order harmonics while suppressing odd-order harmonics, producing a character that ranges from enhanced sustain at lower settings to aggressive, articulate distortion capable of handling complex chords. The original design features two slider controls for input gain and balance, and has become one of the most distinctive and influential fuzz/distortion circuits ever produced. It is also closely associated with guitarist and producer Steve Albini, who used a Harmonic Percolator extensively as a key part of his signature guitar sound.