Build - Pedal Project: Harmonic Percolator - Albini Version

This version of the Harmonic Percolator circuit is a clone of a build modified to Steve Albini’s preferences. If you’d prefer to build the stock Interfax version, you should instead use our Harmonic Percolator - Stock Version pedal guide

Harmonic Percolator - Stock Version

The HP-1 Harmonic Percolator was a unique fuzz pedal made in very small quantities in the 1970s by Interfax, a Wisconsin-based company. The Harmonic Percolator is a particularly unique-sounding fuzz circuit, and it is most well known for its use by engineer and guitarist Steve Albini of Big Black and Shellac fame. Though it’s largely known to be a cutting, aggressive fuzz, it is capable of a range of sounds including warm, subtle coloration at low settings. There were multiple versions of the HP-1 made, though the most well-known version uses an NPN silicon 2N3565 and a PNP germanium 2N404A.

The “Harmonics” control functions as an input attenuator, controlling how much signal makes it into the circuit (all the way down to silence). Turning this control up increases harmonics by creating harder clipping as the input level is raised. The “Balance” control is simply an output attenuator that functions as a volume control for the effect. This “Albini” variant of the HP-1 circuit copies the values used in an HP-1 circuit modified to Steve Albini’s preferences, and tends to provide a smoother, less compressed sound than the stock variant.

Figure 1: Turret board layout of the Harmonic Percolator, Albini variant.

Figure 1: Turret board layout of the Harmonic Percolator, Albini variant.

Figure 2: Schematic of the Harmonic Percolator, Albini variant

Figure 2: Schematic of the Harmonic Percolator, Albini variant

See Figure 3 in our Guitar Pedal Footswitch and Jack Wiring article for the recommended footswitch and I/O wiring.

Parts List

100 pF1C-SM100Silver Mica Cap
1.5 nF1C-R82-1N5Film Cap
47 nF1C-MKT-D047-400Film Cap
100 nF1C-MKT-D1-400Film Cap
2.2 µF1C-BC-2D2-63Electrolytic
47 µF1C-BC-47-100Electrolytic
100 kA1R-VAM100KA-SSHarmonics control
50 kA1R-VAM50KA-SSBalance control
4.7 kΩ1R-I4D7KCarbon Comp Resistor
51 kΩ1R-I51KCarbon Comp Resistor
91 kΩ2R-I82KCarbon Comp Resistor91 kΩ is an uncommon value. 82 kΩ is used instead.
3.3 MΩ1R-J3D3MCarbon Comp Resistor3.9 MΩ is an uncommon value. 3.3 MΩ is used instead.
2N35651P-Q2N3565-NOSSilicon NPN transistor
2N404A1P-Q2N404AGermanium NPN transistor
1N602P-Q1N60-KBKGermanium diode
Other Items
Silver 3PDT1P-H501-LFootswitch
Prewired red LED1P-LPW-FLAT-RIndicator Light
Brown 1590BB clone1P-H1590BBCE-BNEnclosure
2x6 Turret Board1P-HTUR-STRIP-12Board
Enclosed Switchcraft stereo jack1W-SC-112BXInput Jack
Enclosed Switchcraft mono jack1W-SC-111XOutput Jack
Lumberg switched DC jack1P-JBLB-IN-SPower Jack
Rigid battery snap1P-BATC-SN-1SBattery Snap
Adhesive battery cushion1S-H165Battery Cushion
White RCA-style knobs2P-K499-33-WHTKnobs

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