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C28 Humming

It sounds like you have a classic volume control failure. I've had this happen to me. Another failure is that the 2 channels won't track together. different volume levels between channels. Plus the electrical on off function will fail. SaturationPt's suggestions are all good ones We live in a humid environment and contacts can oxidize. I exercise my controls from time to time. But I have had the volume controls replaced on 3 of my 4 C28s. Plus don't ever use a C28 to turn on power amps. Keep that current demand away from your volume control I have 3 SCR2 control devices that switch on all my power amps. I use power strips to turn on my C28s and leave the volume control in the on position.
Time to get the volume control replaced. Unfortunately the only replacements are after market items from China. No one else seems to supply them.
 
All good suggestions. All have been tried. Just a matter of where i take it/ship it. My biggest fear for this pre-amp is that the volume control problem is the culprit here. Tricky fix and no OEM parts for it.
 
If the original power-supply filter capacitors are still in the C28 — the large multi-section can capacitors — I would start there.

Try to get some help checking or replacing those old capacitors.

A failed filter capacitor can cause hum, and if one becomes very leaky or shorts, it can place a very heavy load on the power transformer and potentially damage it.
 
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