[sdiy] Prophet 10 op-amp swaps?

[Oakley Sound]

 > The magic bullet was (similar to what Tony suggested) putting 100pF 
ceramic caps across pins 2 and 6 of both of them, which diminished the 
oscillation down to the idle noise level (i.e. practically zero).

Actually, I don't think that's a magic bullet at all. Any oscillation, 
even a small one, shows that you still have a problem. If the feedback 
cap doesn't stop the oscillation dead you have to move to plan B. I 
really think you need slower op-amps in there.

Part of the problem, I think, is the long length of tracking from the 
inverting pin of the op-amp around the PCB as well as a the non zero 
impedance to the non inverting pin of the op-amp. This is sometimes 
alleviated by the addition of an extra pole, created by the cap in the 
feedback loop, but if the oscillation is still there you have a problem. 
All that the extra cap is doing is filtering the oscillation rather than 
controlling the phase margin.

Tony

http://takla-makan.bandcamp.com/
http://www.oakleysound.com