Sytek preamp with intermittent distortion issues. Momentarily sounds like a dirty pot, thin papery light fuzz with a fading quality, then signal back again. Seems to occur on all channels. Infrequent enough that you might not hear it for several hours, and it might not show up at all on the bench. PSU output looks solid on a meter. So, I multed a 100Hz tone into all 4 channels, and recorded 25 minutes of the outputs.
Channels 3 and 4 both, at differing times, dropped about 3 dB in gain over the course of several minutes. I then raised the gain again to rematch the channels. 1-2 held (mostly) consistent output levels, while 3 and 4 always show a rapid level modulation, 4 the most, about 0.1 dB variation. Channel 4 also had the obvious distortion notch, which slowly disappeared as the gain dropped, then back again when raised to re-match. I note a few spots where 1-2 both modulated a bit, together.
Ideas?
Channels 3 and 4 both, at differing times, dropped about 3 dB in gain over the course of several minutes. I then raised the gain again to rematch the channels. 1-2 held (mostly) consistent output levels, while 3 and 4 always show a rapid level modulation, 4 the most, about 0.1 dB variation. Channel 4 also had the obvious distortion notch, which slowly disappeared as the gain dropped, then back again when raised to re-match. I note a few spots where 1-2 both modulated a bit, together.
Ideas?