I started using SpinCAD again for the first time in years and stumbled across a common problem.
Sometimes when you have a delay with a feedback loop, the sound will disappear suddenly or gradually. This happens with either the simulator or the actual chip. I haven't put it on a scope to see what is happening but I believe this is due to DC offset building up and then the output gets slammed into one of the rails and can't recover.
A simple way to avoid this is to put a 1-pole high pass filter into the feedback loop. That blocks DC and prevents the problem and only costs two instructions. Four if you don't optimize the inter-block connection.
