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My thoughts exactly. But we can't rule out the possibility. Maybe 30lb McIntosh transformers don't buzz no matter how you abuse them? Another good point.

The sound that comes out the speaker is the product of the frequency distribution of the magnetic field generation (either low or RF frequency), the transfer function linking amp to speaker via EM fields, the transfer function of the conversion of EM field to electrical current in speaker, and...

Doodski, the 100Hz line is the one with the big space to the right of it, as the spacing always takes a big jump at powers of 10 in a log plot. So the smallest space is between 90 and 100, and the biggest space between 100 and 200. It wouldn't surprise me if 60Hz and its harmonics are not the...

Thanks. Posting before morning coffee is a bad idea!

Thanks. Could you refresh the page and try it again?

You can read my dissertation on the topic back at #144 if you're so inclined. Get a mug of coffee first!

Hmm. That shows a null at 60Hz.

I was thinking about this possibility too. It's a plausible hypothesis that could be tested. I don't want to overstate my level of certainty. I put out a hypothesis that I think best explains the observations. But I could be wrong! A hypothesis only value is it gives you something to test...

Buy one and try it. Better yet, send it to Amir for review.

Take a look at the McIntosh marketing info at #62. A 30lb transformer and six 27,000 uF, 100V caps. NOT a SMPS! That's an old fashioned brute force linear power supply.

Well, I hope not, because this is really unacceptable behavior. I trust McIntosh has competent engineers who wouldn't do this on purpose.

So no. Not a SMPS. And @Doodski , didn't you find a schematic of the power supply, a standard transformer and bridge rectifier?

Cool. That's empirical evidence for the idea that second order nonlinearities in the speaker can demodulate AM. I think something similar is happening here.

I vote yes.

You and me both. This is one of the most interesting and bizarre things I've seen in a long time.

Assuming @ClassG33 is in the US and not Europe, that does not support the idea it's 60Hz hum. However, this is one of the weirdest things I've heard of. It is not an ordinary occurrence, with ordinary answers! So we should keep open minds and not jump to conclusions. TLDR; Hypothesis: one or...

I agree, that's the sound coming from the speakers. But is it what the EM field is? It could also be a higher frequency AM modulated at 60Hz and harmonics. Speakers usually have multiple current loops through the crossovers, with large air core inductors that can turn AC EM fields into AC...

Did you use a standard power cord?

Let me be blunt. Something is very, very, seriously wrong with an amp that causes disconnected speakers to buzz. It is radiating a very high level of who knows what frequency. This is not a matter to take pallative actions on. This needs to be fixed. I agree with @mhardy6647 - disconnect...

I think @DVDdoug is right - this is just point to point over CAT6 wiring, not routable ethernet. Probably just an optical receiver, diff line driver, diff line receiver, coax and optical out. Maybe some clock recovery / retiming and error checking. No need for actual ethernet.