I just finished my fifth voice card and noticed some strange behavior this morning. After about a minute of on-time I experience random intermitttent noise fluctuations while the unit is sitting at idle. Additionally, I experience this pretty strange oscillator behavior while feeding midi notes in. I have updated the voicecard firmware and the problem persists.
Have you tried swapping this voicecard with another one to determine if the problem is with the voicecard itself or the signal path from the voicecard connector to the audio output?
Switching from port 6 to 4 to 2 produced the same behavior. Using one of my other voice cards on ports 6, 4 and 2 did not replicate the noise fluctuations or oscillator behavior.
Then go through the signal chain to find at which stage this is happening…
While running through the signal chain the problem disappeared with seemingly no action by me. Do any of these chips require burn-in time?
No burn-in time
Hmmmmm very interesting. The only likely cause I can think of is a possible short on the board when I cleaned it early this morning. I did give it a good 15 minutes or so with the hairdryer followed by an hour of air drying, but I suppose a small amount of water could have shorted any of the IC sockets.