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Next place to check is the phono connectors on the phono amp. They are renowned for developing faults. Sometimes interconnects have slightly varying pin sizes and weights of cable+connector can make a difference. Could be cold solder joint or wear and tear in the connectors.
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Did you move any of the positions (or relative positions) of the power cables (and phono cables?).
Try to avoid running power and phono cables alongside each other and if they need to cross each other try to do so at 90 degrees.
Airhead
danb
@freddo
Cross-posting from the CU forum to see if anyone (particularly the phonophiles here) can help.
I have a 50Hz-60Hz hum on one channel with only preamp and power amp connected. This problem has only manifested itself with new interconnects. The obvious conclusion is that the ICs are faulty, but I believe it is something more fundamental to the pre or power amp. Here's the results of my testing two sets of ICs, IC1 is a cheap set and IC2 are the new ones.
Possible conclusions:
Despite the lack of CE markings on either the pre or power amp, I believe that both units are double insulated (ie. no earth connection to the case) as there are only two pins on the mains cable socket. Therefore a ground-lift circuit will not help here.
Because PreTest 3 shows hum on the right speaker I can assume that the R channel on the Power amp is faulty and it is somehow picking up a current on the R channel from somewhere inside the power amp.
I seem to be able to also create hum on the L channel of the Power amp using either of the L or R preamp channels as sources, but only using IC2, not IC1. I don't have a decent explanation for this. Is it possible that the small amount of resistance in IC1s would isolate the signal sufficiently? Or that interconnects have a sound profile such that they might allow a given frequency to flow or be impeded? That would blow my mind.
Perplexingly I seem to be able to kill the Power amp R channel hum with IC1s but not IC2s from either L or R pre-amp source. What might explain this?
I'm going to get both the units serviced but I would really appreciate any thoughts as to what might be going on here as I don't feel qualified to make sense of the results.