The Vaderin Pedals HP-X Harmonic Percolator is a Harmonic Percolator-style fuzz pedal from builder Vaderin Pedals, covered by Delicious Audio in September 20211. The Harmonic Percolator itself is a distinctive, rare and sought-after mid 70s fuzz pedal, originally made by Interfax as an unwieldy-looking fuzz box with two slider controls23. The HP-X takes after that original unit, modernized for today's differing climates4.
What sets the HP-X apart from most Percolator-inspired pedals is its transistors: it runs silicon throughout, including a silicon transistor in the PNP position where the classic circuit used germanium14.
Silicon transistors in a Percolator circuit
The original Interfax Harmonic Percolator HP-1 featured a 2N404 germanium transistor and a 2N3565 silicon transistor5. The HP-X replaces the germanium device in the PNP position with a silicon transistor, and both of the silicon transistors that make up the circuit are measured and carefully selected so the circuit biases right every time1. The pedal also features a specially selected combination of silver mica, poly film and ceramic capacitors1.
Because of the silicon design, Pedal of the Day's reviewer noted that the HP-X is going to sound the same every time you click it on, regardless of temperature or playing conditions4. That consistency is one of the practical differences between silicon and germanium-based builds.
"There are no compromises in sound here. In fact, we like this version the best!"
Controls
The HP-X offers the traditional two controls of the original plus a three-way clipping switch1.
| Control | What it does |
|---|---|
| Input level (left knob) | Turn left for less and right for more; turning right increases compression, distortion and overall gating, from even-order overdrive to gated fuzz harmonics1 |
| Harmonics | Distortion control, as on the original layout4 |
| Balance | Volume control4 |
| Clipping options switch | Three-way switch; left position is asymmetrical germanium diode clipping1 |
Fuzz or distortion?
Both, depending on where you set it. Delicious Audio describes the HP-X as providing a super solid distortion/fuzz tone for any application, with tones ranging from overdrive to distortion to fuzz, and says the pedal always sounds aggressive, punchy and has plenty of output, with a clear and present but warm sound1. Pedal of the Day filed it as a harmonic percolator fuzz/distortion pedal4.
The Harmonic Percolator family
The HP-X is one of several modern takes on the Interfax design. The original HP-1 has been described as a weird fuzzy distortion creation that creates an extremely unique sound6. Other versions covered elsewhere on this site include the Fredric Effects Silicon Harmonic Percolator, a fuzz pedal based on that mid 70s original2, and the BSRI Audio Hydrazine Harmonic Percolator Fuzz, a modern interpretation of the Interfax circuit with updates to give players a wider range of tones, covering crunch, dirt, boost, fuzziness and breakup7. For more in this territory, see Fuzz Pedals and Distortion Pedals.
What reviewers said
Pedal of the Day's 2021 review was enthusiastic: "We love this thing"4. Delicious Audio, which covered the pedal at its introduction and added it to its roundup of Harmonic Percolator-inspired fuzz pedals, reported that the builder prefers this silicon version to a germanium build1.
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Questions
What is a Harmonic Percolator fuzz?
The Harmonic Percolator is a fuzz pedal originally made by Interfax in the mid 1970s, a distinctive, rare and sought-after fuzz box with two slider controls. The original circuit used a 2N404 germanium transistor and a 2N3565 silicon transistor. Its odd, fuzzy distortion character has made it a favorite of players and builders, and a number of modern pedals take the circuit as their starting point.
Does the Vaderin HP-X use germanium or silicon transistors?
The HP-X uses two silicon transistors, including a silicon transistor in the PNP position where the original Harmonic Percolator used germanium. Both transistors are measured and carefully selected so the circuit biases right every time, and the builder reports no compromises in sound compared with the germanium version.
What does the input level control do on the HP-X?
The left knob is the input level: turn left for less and right for more. Turning it right increases compression, distortion and overall gating, taking the pedal from even-order overdrive up to gated fuzz harmonics.
Is the HP-X more of a fuzz or a distortion?
It covers both. Delicious Audio describes it as providing a super solid distortion/fuzz tone for any application, and the input level control sweeps from overdrive through distortion to gated fuzz, with a three-way clipping switch adding further tonal options.
Sources (7)
- Vaderin Pedals HP-X Harmonic Percolator-style Fuzz, Delicious Audio, 2021-09-14
- Fredric Effects Silicon Harmonic Perc, Premier Guitar, 2025-07-25
- Zander Circuitry Cafetiere review: A brilliantly tweakable take on the InterFax Harmonic Percolator, Guitar.com, 2022-06-14
- Vaderin Pedals HP-X Harmonic Percolator, Pedal of the Day, 2021-10-21
- Guitar Pedal X, Guitar Pedal X, 2024-05-13
- Paperboy Pedals Harmonic Percolator Clone, Pedal of the Day, 2024-02-08
- BSRI Audio + PEDALXCHANGE.com Hydrazine Harmonic Percolator Fuzz, Pedal of the Day, 2026-04-25
