I've had preamps and amps that were sensitive to DC on the line before. I've tried many DC blockers and pretty much all of them hurt the dynamics. The one that I found to work best and not hurt my system dynamics is the Emotiva CMX2 AC Line Filter With DC Offset Eliminator. It is a great design and does what it needs to do, nothing more. I have one extra used one with the LED lights not working (a common reported problem) that I could let go for $75 plus shipping if you are interested. My new Atoll IN200 evo integrated does not hum at all in the same house and location.
Hegel hum?
Spent a week or two enjoying my new H400 and noticed a faint hum between the time I turn it on and before I play music. Also there when I pause after playing a while. Note that the hum is only apparent when I bring my ear a foot away from the amp. I’m quite pleased otherwise but am wondering if this is normal?