Recorded through grounded sound card for 12+ hours. No spikes.You might just ground the input to the sound card to see if it's supply or sound card.
If I understand the difference between circuit post#15 (which spikes) and circuit post#20 (which does not spike), the former references the capacitor to the negative rail and the latter does not. Wouldn't this make the negative rail of the supply suspect?Doesn't make any sense, because it looks like your sound card is already AC coupled. Unless the DC voltage is to high for the sound card.
If the sound card ground and negative rail are commoned, any spikes on the negative rail shouldn't get recorded.Wouldn't this make the negative rail of the supply suspect?
In that case, I am at a loss.If the sound card ground and negative rail are commoned, any spikes on the negative rail shouldn't get recorded.