Slight hum in my amp. Is this normal?

@almarg , that's true, and if you look at my initial post I mentioned that DC on the line can also be interpreted as a 2nd harmonic. Its pretty clear that filtering using a transformer is an inefficient method; a DC blocker is a lot cheaper!

FWIW, most of the time the reason for DC on the line is an issue that is pretty closely associated with the local AC situation. For example, if there is a distribution transformer serving five houses, only one house might be running a space heater at half power, but all five houses would experience DC on the line.

Thanks, Ralph. To be clear, though, am I correct in believing that to the extent the asymmetry of the waveform corresponds to a 2nd harmonic component, neither a DC blocker nor a transformer would eliminate it?

Best regards,
-- Al

^^ Yes- and that is what we are dealing with when the power transformer in most audio equipment is involved. Its best to block the DC prior to a transformer- otherwise you have to use a very sophisticated power conditioner!

Is your system set up for pure stereo?  Or, are you connected to some video theatre stuff too?

If so....disconnect all the inputs from sources leaving only one source at a tine....cd, phono...etc.

I'm thinking you need to rule out groundloop.

oldshool1, 
I had the same problem to my Constellation Mono amp.  Amp checked and find nothing at the Constellation repairing center.  Checked with Shunyata Research, I used quite a lot electrical products from them, they said probably a DC on the main.  With a reasonable low cost for a try, I tailor-made 2 DC blockers (one for each channel), to which to ensure sufficient current serving the Mono amp.   No hum from amp anymore, and more importantly that would not affect the sonic performance.