I posted this on a forum in response to somebody with a Korg MS-20 and plans to add more modular stuff. I think it is a good quick primer. I’ll update this with more information when I get some time …
Be aware the MS-20 doesn’t play particularly nice with a lot of modular stuff, at least not without some coaxing.
The MS-20 uses S-triggers (closures) for gates, while the Eurorack world generally uses V-triggers (+5V). It is super easy to go from v-trig to s-trig using a simple adaptor, but going the other way requires a more costly conversion.
Also, the pitch CV output from the MS-20 is Hz/V (linear) while Eurorack is 1V/oct (exponential). This means that notes you play on the MS-20 will not translate to the same intervals on Eurorack. You can bring Eurorack V/oct into the MS-20’s modulation input and adjust the modulation amount and tuning – it will track quite well, but musically controlling Eurorack oscillators from the MS-20 again requires conversion.
There are modules that do all of these conversions quite well. But you need to know this stuff if you want to hook up your MS to anything else, including 0-coast.
Finally: the MS’s envelopes and LFO will work to modulate Eurorack stuff with no trouble.