Transformers humimg........again

I posting in this thread to save it for myself... Great info here so far. Thank you.

Did the original poster’s issue ever get solved? I’ve been fighting humming preamp transformers since I’ve moved into my current house and have posted here and other places. I’ve had 3 separate preamps and all hummed. I’ve tried a lot of things attempting to troubleshoot:

1. Only having my dedicated line breaker on with all of the others off (current preamp still hums, does not at a local electronics shop).
2. Replacing my current preamp’s power supply with another one that was cosmetically challenged but hummed less (hum has gotten worse over time, will check tightness of power supply mounts when I integrate the PS Audio Power Plant in to my system).
3. A Humbuster previously and an Emotiva CMX-2 now, neither eliminated the hum, the humbuster seemed to hurt dynamics and the CMX-2 seems to be doing better with the hum and persisting dynamics, plus the minor power filtering might be helping with my multiple dimmers RFI.
4. I’m getting a PS Audio Power Plant Premier on Friday to try out. Might try with the CMX-2 in front of the Power Plant.
5. I should have those measurements done on my panel where the mains come in also.  I need to find a good and experienced electrician that I can trust.  I had one but he retired.

The hum isn’t horrible but would sure like to get ride of it. My neighborhood’s substation is powered by very high voltage lines running to eastern WA and I suspect they are the culprit. Hopefully the Power Plant with maybe the CMX-2 in font of it fixes things...

What is your line voltage? It should not exceed 125V for more than a second. If its high that could explain the problem. The PS Audio should be able to correct that.

And what are the next steps if the following checks are not in spec?

1. Just a few things your electrician friend should check. Have him check the mains voltage at the main service electrical panel. Make sure the voltage is the normal voltage for your area.. Have him check hot L1 to hot L2.
2. Then check hot L1 to neutral, and then hot L2 to neutral. The two readings should be within a couple of volts of one another.
3. The combined voltage of L1 to neutral + L2 to neutral should equal the L1 to L2 voltage reading.
4. Next thing he needs to check is the Hz. It should be 60Hz possibly 59Hz.
5. Next have him check the voltage at the receptacle the audio equipment plugs into unload, nothing powered up, then check the voltage again with everything powered up. The voltage should not vary more than a couple volts.

Might PM some of the people on this thread directly if I don't hear anything.  Thanks everyone...

The most likely cause of a transformer mechanically humming, besides poor lamination, is DC on the AC line. That is, the + and - portions of the waveform are not equal and opposite.

DC can be injected from certain dimmer switches and switching power supplies (or fluorescents sometimes), among other things. 

If so, a balanced transformer will minimize this issue.

If not, it's a problem with the transformer's itself.

Best,

E