Yes, there definitely are mods for all of the monotrons. The basics of modding them are all really similar, at least in terms of the gate/CV stuff (You've probably seen 2cv's gate+pitch+filter cv input mod, you can basically follow the same thing on the other monotrons AFAIK.)
The great thing about these is that Korg labeled a lot of the important points. However, there is some discrepancy between how pitch is labeled, at least comparing the O.G. Monotron to the Duo. On the O.G. and the Delay it is labeled as "Pitch", but on the DUO it is labeled "Vrib" and then there are actually points for the pitch of the second oscillator as well. On the Delay, there is a point for controlling the speed of the LFO. (I didn't notice a point for the delay time control, but you can probably just patch into pot for that parameter.)
My own experience modding these things is as follows: I was derping with my Monotron Duo and managed to permanently destroy the ribbon cable that connects the ribbon to the board. So i figured instead of throwing it out, I would just turn it into a voltage controlled module that I can control with my Eurorack. I basically just adapted 2cv's O.G. monotron mods, with a few differences:
1) as mentioned above, connect the pitch CV to Vrib (there is no point labeled Pitch on the Duo.) I followed 2cv's suggestion of using a 33k resistor plus 10k pot to trim the incoming CV, however the effect of the 10k pot is very minimal. This actually may be a good thing for making micro adjustments to the pitch, but I would be curious to play around with something bigger like 50k.
2) In the process of soldering, de-soldering, and generally derping around, I somehow pulled the copper off the Vrib point, and was left with nothing to solder to! (I was just having really bad luck with this particular monotron that day,) So I had to poke around looking for another point to inject the pitch CV. Luckily the middle pin on the OSC1 pitch control knob seems to do the trick just fine! So in my version I ended up going that route, but in your case, just stick with the Vrib point (or Pitch points on the other models.)
3) I find the gate on the Duo to be useless since it doesn't control the triggering of any envelopes, LFOs etc., it's merely a nuisance. And since I have a Eurorack modular system, I figure if I want to, I can always send the monotron through a VCA or something, and just treat the Duo as a sort of "Macro Oscillator" that works with my Eurorack. So I basically hardwired the gate to be permanently ON, so it behaves like a Eurorack Oscillator, always producing sound when it is powered. I did this by placing a jumper between two of the four pins where the ribbon cable once connected to the board. I just played around till I found the right two pins (there are only 4 to choose from, so it was easy to find.) The jumper basically tricks the monotron into thinking there is always a finger pressing down on the ribbon controller. Because I went this route, I didn't even have to worry about hooking up a gate input to the gate point on board. Of course it's up to you if you want to follow my method or 2cv's method, and it depends on the particular monotron as to whether gate is even important or not.
Following these methods, my DUO now seems to be working fine as a "MacroOscillator" that I control with my Eurorack (or Korg SQ-1).
I now have control over Osc1 Pitch, and Cutoff, with gate hardwired ON. In the future, I may add an additional CV input to control the pitch of OSC2.
Moral of my story is yes, there is plenty to do modding the other monotrons, and they really all follow the same basic model of modification, with some minor differences. And if you are unlucky and ever happen to wreck the ribbon controller, don't despair, just turn it into a ribbon-less synth with CV control.
Hope this helps!
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Topic: Monotron delay or duo mods? (Read 8319 times)