[sdiy] Arp Avatar ADSR problem

[Karl Ekdahl]

Hi Tony

> Hi Karl, I don't know if you got this
> fixed yet by substitution.

It has not so thanks for your help!
 
> After studying the ADSR cct description in the service
> manual you might want to check the peak-detector, Q15, this
> is supposed to supply a 'feedback' 10 V (max) and reset the
> Attack latch, Q17 and Q18. I have a 2800 on the bench now if
> you want me to scope around.

Yeah so i think what's happening on my side is that (for one reason or another) when the attack-period is short, the peak-detector fires and resets Q17 / Q18 which somehow goes into oscillation. I can see this osicllation both at the junction of CR14 / CR15 and C9 / R55, but hell knows why or where it comes from. 

Making the attack slower supresses the oscillations amplitude until it disappears and the decay-period actually starts working at that point.

Karl


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