Music Tech DIY • Re: MS10 - CV OUT = pitch decreases [SOLVED]

hello, I have a similar problem on ms20, suddenly the notes started to go down very quickly, plus the keyboard which deviates with the highest notes.
I started by changing all the power supply capacitors + the 2 regulators 7815, 7915. but the problem is still there.

I then thought about the C6, 220n capacitor, but no change with a new one.
I changed the CA3140 IC5 amp and the two 4558s (ic6 and ic13) no change.
I changed the diodes d12, d13, d14, nothing better.
transistors Q13, Q14, Q15, Q16, nothing better.
I changed C7, C18, C19, C20, C21 nothing better.
Trimmer & pot 2M are OK.

I don't have a k30A (gr) on hand.
So I tested with several different nFETs bf245, bf256, 2N5459, bs170, J201 nothing better.
I ordered k30a but not received yet.

In the meantime I finally managed to make it work by replacing the R5 10M resistor with a 1M and the C6 220n condo with a 6.8uF.
(see diagram below)
I have a little glide in the high notes but the duration of the notes is a little better. the bass goes down quite quickly, it seems to me.

the suspect remains the nfet transistor
Do you have any other idea where the problem could be coming from?

Thank you for your answers


http://pjmnc.free.fr/files/ms20/msKEY.PNG

Statistics: Posted by fg — Sat Jul 06, 2024 2:57 am

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