Vintage Minimoog VCOs fall in pitch as VCA decays

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1

I have a vintage 1974 Minimoog (with oscillator board 3 installed) that has an issue when the decay is on. The notes will gradually fall in pitch when the decay is turned on; when the decay is short, the notes gradually fall maybe a half step and as you turn the decay up the notes fall gradually lower and lower.

Any ideas? Am I missing something obvious?

2

Yes, your keyboards sampled voltage is slowly leaking away.
The pitch is falling away all the time… you just don’t hear it all when you set the decay short.
You have a fault. Could be a few things… faulty component or dirty (conductive) circuit board etc… take it to a tech.

Cheers,
Tom

3

Yep. Follow Tom’s wise advice, take it to a tech.

I suggest Chris Hewitt. He does excellent work. You can contact him through his web site ThisOldSynth.com.

4

Thanks guys! I am a tech, just haven’t worked on a Mini before. Emailed Chris and he gave me some tips. Y’all rock!

5

Fixed it! It was one of the FETs - replaced it and the Mini is good as new.