Harmonic Energizer


Here is a clone of the Systech Harmonic Energizer. This is a parametric EQ. It’s like a single-band equalizer with a control to set the width of the frequency band that it affects. It also has a control to sweep the frequency similar to a wah pedal.

The Harmonic Energizer has been described as the “secret weapon” of Frank Zappa. Read more about it here.

I followed a schematic I found online. There were a couple and all were mostly the same. None of these seemed to work, or at least not work well. Q1 was not biased correctly. With some help from the friendly people over at DYStompboxes.com I was able to fix this.

Here is the schematic I made that follows along with what I found online:

Harmonic Energizer V1 – with problems!

I’m not sure if the schematics are correctly copied from an original device or if mistakes were made reverse engineering. With some help over at the DIYStompboxes.com forum I came up with this schematic which works pretty well!

Harmonic Energizer v2 – Fixed

The changes are:

  • R1 connects to VREF instead of ground. This biases Q1 correctly.
  • C9 seems to be backwards. This works either way but isn’t correct in the first schematic.

For this project, I created a PCB in Eagle and had some prototypes manufactured at PCBWay.com. It was only $5 for 10 boards which were reasonable and left me with plenty of PCBs to prototype with.

Luckily the fix was easy to implement on the PCBs I had manufactured. I just had to reroute R1 to some point where the bias voltage is available. In the image above, R1 runs vertically to the left side of R15.

I milled this Pink powder-coated enclosure. The color made sense for this project. I heard Frank Zappa was a fan of the original Systech pedal, so I named this one ”Zap Frequency” which seems to describe the effect to some extent also.

Would I recommend building this pedal? If you like the ”cocked wah” sound this would be a good way to get that sound. This circuit might be good inside a wah pedal. It might also be good for a ”lead tone” boost. On the last point for myself it sounds best before a fuzz or distortion rather than after. If you don’t like that ”cocked wah” sound this might do much for you.


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