It's not a difficult mod, but not everything does exactly what you'd think it might. I added inputs for 'Pitch', 'Gate', Filter Cut Off and LFO rate plus an output for the Oscillator. I also converted the annoying stereo aux in and headphones out into regular mono so they connect easily to other modules or other mono outboard gear. The final thing was to change the power supply from battery to 5V Eurorack.
'Pitch' and 'Gate' have inverted commas for good reason. Although there's a solder pad on the pcb marked 'Pitch', it doesn't really allow the oscillator pitch to be controlled by 1V/Oct CV, as one might expect. There's probably some elaborate way of making this happen, but that's clearly beyond my ken. However, I did find it responded to the volts coming out of my home made Velleman LED sequencer. I can't really say I know what it's doing, but it does something and that's enough to warrant giving it its own jack socket.
'Gate', on the other hand, does more than it promises. Sending CV to this, from the MiniBrute keyboard or the Verbos Voltage MultiStage, gives a response from the oscillator pitch and its gate. It doesn't really track in any meaningful musical sense, but using a sequencer or arpeggiator means simple melodic patterns can be created.
The shortcomings of the oscillator control is no big deal. For me the big story here is the behaviour of the filter and the delay when a signal is fed through them. This module is an instant extreme dub machine.
Here's quick recording from it's first try out. This is just a TR-626 drum pattern being filtered and delayed. All the oscillations you can hear in this are being generated by the delay circuit.
Although the inputs for Cut-Off, Pitch and Gate don't behave in regular ways, they do all seem to affect the filter and its tracking, and how much the delay is allowed to go into self oscillation.
Here's a little clip with the Monotron's own oscillator being sequenced by the Verbos MultiStage.
As you can see from this, the ribbon controller remains an important part of how this module achieves its sound. I have to say that the 'Eurotron' has become my new favourite delay, trumping the expensive Strymon boxes and my 'vintage' Boss and Yamahas.
So, all in all, a mod well worth doing. If you've been putting off doing this yourself, delay no longer!