hi so I just did some more tests. im using AS3340 and CEM3340 each do the same with me. i popped it on middle C and im getting a drift under 1hz which is nothing. (and findings seem to compliment the notes to hz response quite similarly up and down the range)
im quite surprised by your findings which makes me think maybe its something else with your setup. what power supply are you using? even in none modified mode these should not be fluctuating as much as your readings are saying… unmodified you cant notice the pitch drift with your ears… my findings below sort of match that.
I did the mod to 4 oscillators and all had a similar response to the mod 20M is more than adequate. (sweet s[pot could be anywhere between 18 and 25M for absolutely zero drift but 20M is more than adequate).
So I just did a bit more checking im running around the C at around 260hz. my findings are
no modification… drift of under 1hz (not noticeable)
modification of R13 of just the 200k a drift of 3hz (too big)
with the 20m mod it now has a drift of 0.5hz near enough (not noticeable)
in the Lower register Lower C 130hz this finding is less (hence why my readings dont match yours) and higher registers its a tiny bit more but this matches up to the note response and all in all throughout the whole audible range im not noticing anything.
so yeah it might be worth someone else giving it a go! if they want more pulse width from the square out but not at a loss of pitch drift.
my only suggestion is mess with the 20M value if the note is pitching up increase resistance, if note is drifting down decrease resistance… or find a 5m trimpot or something ha.
Im very pleased with this mod personally and has vastly reduced the component count on the design of mk2…
I dont know about you but an unspoken rule in DIY synth fun is a magic ratio…
that ratio being KNOBS:COMPONENT COUNT
too many knobs to components the knobs do less fun things… but ooh lots of knobs to twist!
too many components to knobs! arse ache to build and go big…aaah not enough knobs to twist haha