Cheap and quite easy mod. First time I use A4’s CV for a synth ! (I used it once to sequence a guitar pedal expression input).
Gate (CVB) and Pitch (CVA) control.
I’ll give more details if someone is interested.
I’d like to solder cutoff next. @jaystink, some advices ?
Quick test, gives an idea.
Cutoff control is very easy. An alligator clip on the pot, done. 
With the CV Track, Envelope control of the filter, lfos…
Sounds very good!
Another test with Cutoff control. 100% Analog Four control.
(I updated the first test, so it’s the same above)
Is it possible to have Overbridge on the Monotron ?
Added Resonance control. That was tricky, but I found another simple solution :
Photocell + led + adhesive ! 
Another Monotron record, played 6 times at different speed in Octarack. Abusing resonance !
Bassline
2nd one is filthy!
these all sound great, nice companion to the A4
I have to say I really enjoyed A4 CV control possibilities ! The voltage tuning was necessary, and everything worked quite easily, after a few tests : yes, it works !
I have a 70$ XOX Heart to solder, and I believe the Monotron will be a little souvenir after…
Anyway I have to record a Rolling and Scratching cover with the Monotron, as its Ms 20 like filter sound similar as the MS 20 they were supposed to use. I already have the pattern for that, same tempo / note.
I need to find the right distortion (A4 overdrive is not enough), and I think the best candidate is Analog Drive ! Analog Heat is too gentle. 
