PT2399 hack

This began with me just wanting a quick and dirty echo for my billow. For recordings which are quite percussive I wanted some slapback.

Although I have a bunch of homegrown circuits using the PT2399, I also had a couple of reverb boards (bought 5 for 8 Euros) lying around for fast and dirty work. I remembered having seen someone document this hack. https://www.anexium.com/instruments/PT2399-Mods.html Oh, and I add a piezo pickup!

The linked doc from anexium is a good overview. However, it makes things more complicated than need be :) And is more dangerous than what I detail here. What follows is my take with a simplification and the addition of a piezo pickup.

A build:

I usually prepare the box first, keeping mind to allow space and then have a means for getting the correct measure of wire lengths.

Then I prepare the board….

The S and G inputs are highlighted as is the R27 resistor on the board pictured below:

1. Remove the SMD resistor R27
2. The 100K pot, will have it’s input pin (far right from above) soldered to the “S” input on the left in the above image. I do this by soldering wire throught the S hole.
3. The center pin of this pot is connected to a “G” (ground) hole Via a 1K resistor, on the left in the above image. I solder the resistor directly through the G spot (:)
4. If you want to have CV input to control this, just solder the resistor part of a vactrol in parallel to the legs of the pot.

Here a picture of the completed wiring.

On to the feedback:

5. The middle 100K pot will have it’s middle pin soldered to the middle pin of the pot on the board as seen at the bottom middle of the image below
6. This pot will also have it’s right (input) pin soldered to the + pin of the board output as seen at the left of the image below
7. As with delay time, you can add a cv input by soldering the resistor of a vactrol in parallel

Completed on the bottom.

Finally, I add a piezo as you can see in the following image.

And that’s about it. As one can see the number of steps and the danger of soldering near the SMD cap are not an issue. And it sounds the same.

This version has a bunch of springs and stuff attached as a noise maker machine.

You can also just use the guide from anexium :) However, it is not necessary to solder the feedback knob via the SMD capacior. My way has the same effect without being in a difficult to solder position.

I’ve also done a eurorack version of this with CV control. Have a look at https://poetaster.org/news/2026-04-06