If you unplug everything else, do you get the hum on the ATI? Have you tried moving the ATI to another room and testing for hum?
ATI AT6007 amplifier hum
Long time reader and first time poster. I recently traded in my Pass Labs X600.8 amps to ATI AT6007 and AT528NC combo for my 9.1.4 setup. I have 3 dedicated 20A lines which I’ve used previously for the pass labs and now for the ATIs. I did not hear a hum from the pass labs but I’m now hearing a hum from the AT6007. I’m also using proper 20A power cables. There is no hum from the AT528NC. Please advise. Will I need a DC blocker or power conditioner?