Quote:I had system hum for years that I finally tracked down to some ICs close to the power outlets.
I just went through a similar experience. My understanding is that you can expect some transformer hum but it should not be audible unless your ear is very close to the speaker and at the driver level.
I just installed a Puritan PSM 156. That required that I adjust the power cable lengths. I also read the write up on the new DHC2 power cables. I have DHC1 cables that I terminated with Furutech plugs.
My intention was not only to adjust the power cable length to get rid of the excess so as to prevent any cables from touching each other but also to determine what lengths of shielded cables I would need.
I tightened all the plugs and made sure that the ground was well seated. Then as I went to turn off the UFO25 I contacted one of the VR tubes and the power cable to the amp and the amp momentarily shut down. WHAAA????
I was sure that I had the IEC well seated but checked it just in case only to discover that it was not seated all the way. Then I checked all the IECs only to find that the IEC on the Puritan was not fully seated. I was sure that it was.
After making sure that all cables were not touching each other and that all the plugs are fully seated I stood by the speaker, leaned over and heard nothing. To hear any hum at all I pretty much have to touch the grill with my ear. Before, to hear any hum I had to stand by the speaker lean over and be within a foot of the speaker, which I thought was normal.
So now I'm on a mission. Before I change any more components all the power cables are going to be changed to shielded cables and routed so none are in contact with any other cable.
Maybe some of this can be of help.