Slight hum in my amp. Is this normal?

It's a beautiful unit and extremely well made (big, beefy power cord). I don't need it so may try to return. Thanks for the heads-up!

atmasphere

But its still an AC waveform and so can travel through a transformer. But the output will still be asymmetrical.

Is it really DC in the true sense/meaning of the word? Does it build to a DC voltage and then fall to zero at each half of the waveform cycle? If so then I could see how it would pass though from the primary to the secondary winding of an isolation transformer.

Sorry for my ignorance. I am just trying to better understand what is going on.
I do know there are people that say that an isolation transformer will block DC offset on the AC mains from the secondary of the transformer. I personally do not have any personal experience whether it will or not.
I believe you when you say it will not. I also believe that to be the case from actual bench testing which you have done.

I know AC and DC can both travel in a circuit at the same time. And yes I know the DC can be blocked using a DC blocker allowing only the AC to pass though the circuit or another circuit.

I know a pulsating DC voltage source, such as a battery, can be transformed, for lack of a better word, but constant DC voltage cannot. (As long as the applied voltage is constant.) If a constant DC voltage could pass through a transformer then an output transformer on a tube power amp would pass DC to the speakers.
Jim

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Atmasphere 5-24-2017
DC on the line occurs when 1/2 of the AC line (for example, positive going portion of the AC waveform) is loaded while the other half is not.

Space heaters or hair dryers on half power do just exactly that. So one half of the AC line can have lower amplitude due to the loading as a result.

But its still an AC waveform and so can travel through a transformer. But the output will still be asymmetrical. The asymmetry can be filtered out by a DC blocker which is a simple circuit consisting of 2 or 4 diodes that are bypassed by some large capacity electrolytic caps.

Ralph, I share Jim’s puzzlement about that. If a waveform that is asymmetrical above and below zero volts is sent into a transformer, I would expect that what would emerge from the output winding of the transformer is a waveform that looks similar (assuming that the frequency components other than DC are within the transformer’s bandwidth), but that has been offset up or down such that the zero Hz (DC) component is eliminated.

Best regards,
-- Al

@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