MP-3 Noise

Posted by jumpsturdy (A) on March 23, 2015 at 15:34:17

Recently, I have experienced two separate noise issues with my MP-3. Both occurred with the volume off but amps (M60s) on. The first was with the Trim controls generating a moderate amount of static/noise when turned back and forth, sounding like an old volume pot that has been unused for a while. By itself the noise is not particularly problematic as it only happened when the trim control was turned. I raise the issue as it may have some relationship to the second noise problem I am having.
The second issue is more of a concern. After the preamp had been on for about two hours I began to hear a noise that rapidly increased in volume through the speakers despite the volume on the pre being off. It became alarmingly loud and I had to shut off the MP-3. I removed the top and restarted it. As it warmed up the noise began again and upon inspection seemed to be related to one of the 12AU7s. Moving the tube in the socket seemed to affect the noise and it stopped for a while. Next day it was back even though I had changed both 12AU7s and cleaned the tube sockets. Only now it was coming from (being affected by) the other 12AU7 socket/tube than the previous day. Further tube swaps only showed that despite additional tube changes (3 tubes tried in each socket) that the noise would intermittently appear and that jiggling the tubes in one or the other socket seemed to temporarily silence the noise. The problem could not be localized to either a specific tube or socket and it has continued to occur sporadically and when it does, it sounds like a smoke alarm has gone off. Today, I was in the workshop after having turned the system on and all of a sudden I heard the noise from two floors away... really loud.
I have inspected the solder connections on both tube sockets and they look perfect so I am at a loss as to what may be causing the issue. Thoughts and suggestions are welcomed. Thanks.

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Topic - MP-3 Noise - jumpsturdy 15:34:17 03/23/15 (4)

First you need to sort out if its a tube - Ralph 14:30:13 03/24/15 (1)

RE: First you need to sort out if its a tube - jumpsturdy 15:40:05 03/24/15 (0)

RE: MP-3 Noise - Lew 18:03:36 03/23/15 (1)

RE: MP-3 Noise - jumpsturdy 08:32:36 03/24/15 (0)

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