hi,
included is very simple schematic. Better use precision opamp, like
common OP07, easy to find everywhere. You can supply the circuit from
MS20 power supply, but do not forget to add decoupling capacitors on
OP07 supply rails.
Opamp output should be connected to "VCO 1+2 CV IN" jack, below the
volume knob. It must be real plug, to disconnect internal keyboard when
using MIDI.
Let me know if that's OK with you or you need more info.
To connect MIDI2CV together with internal keyboard and be able to play
both at the same time, you need more complex circuit and I wouldn't
recommend it to do on breadboard. I will make such special MIDI2CV for
old Korgs in the future.
You can also set MIDImplant in V/oct mode and plug it to "FREQ" input,
which is tunable V/oct, but it may be difficult to tune the instrumnt
then properly.
The Source is very easy, plug the CV into CV in. Gate needs the same
transistor circuit as MS20, but MINICV can be used directly, if you set
it for reversed gate action via MIDI System Exclusive, as described in
MINICV manual chapter 5.4. I could not find gate part in Source
schematics, so I'm not 100% sure it will work that way, but the mod with
transistor circuit will always work with MIDImplant or MINICV.
Roman
