I finished building my C2A a couple of weeks ago, and everything tested within spec. After a day of listening, I installed the TwoQuiet upgrade.
The problem I'm having is, when I turn the fine attenuator knob from one position to the next, about 75% of the time the sound immediately collapses to mono. Sometimes I can just jiggle the knob slightly to restore stereo, and other times I can go one more position and then come back to the previous position to get stereo back. In other words, starting from position 1 (stereo), I turn to position 2 and get mono. Turn to position 3 (also mono), then back to 2, which is now stereo.
Every position on the fine adjustment experiences this problem. It doesn't matter which position you start from or what direction you turn the knob. Again, it happens about 80% of the time and it doesn't matter which direction you're turning the knob. I can always get stereo back one way or another, but it's quite annoying to have to play with the knob almost every time I turn it.
The coarse adjustment attenuator is rock solid, and it's position has no effect on the behavior of the fine adjustment with respect to the symptoms.
Since the trouble isn't happening consistently, I tend to think the attenuator itself is faulty rather than the wiring or solder joints. I have no idea what would cause the stereo signal to revert to mono upon changing the position. I've inspected the solder joints and they all look good.
As the manual recommended, I turned the knob repeatedly through it's range, both slowly and very quickly, in hopes of cleaning the contacts a bit. I didn't use any DeOxit. Should I try it?
Any suggestions as to what might cause this type of problem?
edit: I should mention that the fine attenuation works as expected. The volume goes up and down in predictable steps as I turn the knob. It's just that the signal becomes mono when I select a new position 80% of the time.
