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 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
| Value | Qty | SKU | Type | Notes |
|---|---|---|---|---|
Capacitors | ||||
| 100 pF | 1 | C-SM100 | Silver Mica Cap | |
| 1.5 nF | 1 | C-R82-1N5 | Film Cap | |
| 47 nF | 1 | C-MKT-D047-400 | Film Cap | |
| 100 nF | 1 | C-MKT-D1-400 | Film Cap | |
| 2.2 µF | 1 | C-BC-2D2-63 | Electrolytic | |
| 47 µF | 1 | C-BC-47-100 | Electrolytic | |
Potentiometers | ||||
| 100 kA | 1 | R-VAM100KA-SS | Harmonics control | |
| 50 kA | 1 | R-VAM50KA-SS | Balance control | |
Resistors | ||||
| 4.7 kΩ | 1 | R-I4D7K | Carbon Comp Resistor | |
| 51 kΩ | 1 | R-I51K | Carbon Comp Resistor | |
| 91 kΩ | 2 | R-I82K | Carbon Comp Resistor | 91 kΩ is an uncommon value. 82 kΩ is used instead. |
| 3.3 MΩ | 1 | R-J3D3M | Carbon Comp Resistor | 3.9 MΩ is an uncommon value. 3.3 MΩ is used instead. |
Semiconductors | ||||
| 2N3565 | 1 | P-Q2N3565-NOS | Silicon NPN transistor | |
| 2N404A | 1 | P-Q2N404A | Germanium NPN transistor | |
| 1N60 | 2 | P-Q1N60-KBK | Germanium diode | |
Other Items | ||||
| Silver 3PDT | 1 | P-H501-L | Footswitch | |
| Prewired red LED | 1 | P-LPW-FLAT-R | Indicator Light | |
| Brown 1590BB clone | 1 | P-H1590BBCE-BN | Enclosure | |
| 2x6 Turret Board | 1 | P-HTUR-STRIP-12 | Board | |
| Enclosed Switchcraft stereo jack | 1 | W-SC-112BX | Input Jack | |
| Enclosed Switchcraft mono jack | 1 | W-SC-111X | Output Jack | |
| Lumberg switched DC jack | 1 | P-JBLB-IN-S | Power Jack | |
| Rigid battery snap | 1 | P-BATC-SN-1S | Battery Snap | |
| Adhesive battery cushion | 1 | S-H165 | Battery Cushion | |
| White RCA-style knobs | 2 | P-K499-33-WHT | Knobs | |