Korg MS20 Sample and hold - stability issue

[remork]

hi there!

i'm doing a lot of droney stuff with the MS-20 lately, and i noticed i get dramatic tuning drift over longer periods of time.

i tend to play a note and let go (so i can use both hands to twiddle knobs), cranking the initial gain so it can keep going.
the moment i let go of the note, the pitch starts to drop.

with notes on the keyboard held down i have no tuning issues whatsoever, from which i conclude i'm not looking at oscillator drift.

i plugged a patch cable into the Keyboard CV Out jack, and measured voltages. played the highest C = 8.23v.
one minute after letting go of the key, that had dropped to 7.98v.
5 minutes: 7.03v
12 minutes: 5.53v
20 minutes: 4v and so on.

as a test, i tried the S&H on the patchbay:
Keyboard CV Out > S&H In. S&H Out > VCO 1+2 CV In.
same note, pulled clock to gnd before letting go.
started out with 8.16v (due to multiple for measuring?)
one minute later: 7.96v
12 minutes: 6.18v

so, a slightly better performance, but still not stable enough to be useful for my purposes.


now, questions:

- do other users experience the same thing, aka normal behaviour?
- can anybody explain to me how the electronic construction (2 opamps and a fet) works? looking at the factory schematic, it seems to be the same for the patchbay S&H and the one in between the keyboard and the CV Out jack.
i don't mind opening her up for maintenance / measurement.
maybe a recap is in order anyway..