Some day I found a EKO Micky organ on a flea market. The orange enclosure was completly broken and large parts were missing. In a good condition it would have looked like in the picture above. Lucky me, the pcb`s were not broken and all the electronic parts and switches were still there. I deceided to take the pcb of the rhythm section and build it into a standalone drumbox.

First and most important to me was adding trigger inputs, so that I can play the sounds with an external step sequencer.

See picture below:

The 4 wires on the pcb are the 4 trigger inputs for the 4 sounds the circuit can generate.
Some parameters of the sound generation are tweakeable. On the pcb, there are already some trim potentiometers to tune the circuit. With this trimmers you already can alter the sound or the behavior of a filter, used to shape the sound. Often just replacing these trimmers with a correspondent potentiometer is enough. May a resitor has to be added to keep you inside the sweet spot. For the rest, it`s just experimenting. Find the resistors that are responsible for pitch or volume of a sound and then replace it with a potentiometer. I was satisfied, when I had found the following parameters tweakeable:

Kickdrum: pitch and decay

Snaredrum: volume and decay

Bongo: pitch and decay

Conga: pitch and decay

I then also added CV Control to these parameters. Therefore I used optocouplers. This works somehow, but is by far not perfect and could be much more elaborated.

You can see on the picture above:

some internal trimpots are replaced by potentiometers. On the right you see two Octocouplers used for CV-control.