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Harmonic Percolator

Harmonic Percolator - Exact physical and electrical duplicate!

The Harmonic Percolator is a distortion pedal that was made in Milwaukee, Wisconsin in the 1970's. It used a silicon and a germanium 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. The Harmonic Percolator also responds well with multiple notes.

The left slider is the input gain or distortion control and the right one is the output control. The input is on the left and the output is to the right when looking down on it. This is opposite pedals of today but in its time this made sense. Left to Right - the same way you read.

This is THE original circuit, not someone's interpretation of it. I have seen incorrect diagrams of this circuit on the internet and they are still posted as of 2020. This is understandable since I have found FIVE different original versions of this circuit and that does create confusion. I make the version I think sounds the best. I hope you agree. All of my experience in the last 30 years shows that every original Harmonic Percolator used a complimentary Darlington circuit. (Sziklai pair) Interfax never used two NPN silicon transistors.

This EXACT duplicate of the original 1970's pedal employs the same obsolete type number Germanium transistor and same number Silicon transistor. This silicon transistor was potted with a metal ring using jeweler's dopping wax to discourage people from reading the number on it. That was a lot of work to do each transistor that way. It is a Fairchild 2N3565. The Germanium transistor had black paint on the number.

The Germanium transistor is not a common Chinese copy. They are genuine Texas Instrument 2N404A with original box dated 6-2-66. Also used are the exact same type number 1N695 obsolete Germanium diodes. (They are NOT the common 1N34 or 1N60) These are from BKC Semiconductor in Boston. The same type capacitors also are used. Mylar-Silver Mica, Tantalum, and Ceramic. The slider controls are the same as in the original. These New Old Stock parts have the original packing slip dated February 19, 1968!

Counterfeit parts are everywhere, you would not believe how bad it is. I once was sold some 1N695 Germanium diodes from a 'reputable supplier'. What I received was a bunch of generic Silicon diodes painted silver with the number I wanted stenciled on. Are you that desperate for money to go through all that work? Did they think it was too hard to measure the difference between silicon and germanium diodes? Unbelievable. The paint didn't even last very long. It started to flake and wear off shortly after my 'purchase'. Another great fraud were 5 watt ceramic wirewound resistors broken open to reveal a 3 watt carbon inside. I now go to great lengths to procure genuine parts and it is very time consuming.

Various 2N404A's are available. Currently using the Texas Instrument part.

2N404A Texas Instrument

2N404A Solid State Inc.

2N404A Generic House Number 'Pulls'

2N404A NTE

Three original pedals were dismantled to help create this duplicate. One Percolator was totally dismantled, all its parts removed and measured. (Thanks John D. and Jay T. for trusting your pedals to me!).

Legendary guitar-abuser Steve Albini (Big Black, Rapeman) uses a Harmonic Percolator for some of those Guitar noises he gives birth to! This is known to be the same circuit version he uses! At low settings the Harmonic Percolator will give you added sustain without 'coloring' your sound. Higher settings will give a mean distortion that performs well with multiple notes. These duplicates are in the exact same case and finished with a super tough powder coating in the original tan and brown style. This is a faithful duplication of the effects pedals created by Ed Giese in Milwaukee Wisconsin during the 1970's. The term Harmonic Percolator has finally been trademarked. I am happy to be able to provide a genuine product and also to protect the name from incorrect circuit representations!



  • Same type number obsolete transistors and original number Germanium diodes. (Not easy to get 1N34A or 1N60!)
  • Same type capacitors. (Mylar, Silver Mica, Tantalum, Ceramic Disk)
  • Classic brown and tan powder coated case...exact same physical style!
  • Same type and value slider controls
  • Better battery holder and rubber feet
  • True bypass switching
  • An exact piece of classic effects.

This is the seldom seen original info sheet for the original Harmonic Percolator. Which version is anybody's guess.

Click on this link for an advertisement from the old INTERFAX company!

Chuck Collins
P.O.Box 33
Big Bend WI 53149