On one leg or two legs?

Got you,
Hot- Neutral 120 V.
Hot- Ground 120 V.
Neutral- Ground 0 V.

With the amp. ON- Hot - Neutral 120 V.

BTW, thanks a lot for your patience.

The measurements are good......

The bad news is it does not help the hum problem.


From the pictures you supplied of the sub panel what I could see the electrician you hired did a good job. The only code violation I could see was the (4) 30 amp breakers he installed for branch circuit protection instead of 20 amp breakers..... Just guessing he did what you probably requested.
At any rate that would not be causing your hum problem.

You seem to have isolated your hum problem.... The problem exists between the power amps and the speakers.

Could your problem be RFI/EMI on the AC mains of your home's electrical system? Well if you live in an area that is warm at the present time you could shut off every breaker in the main panel except the 2 pole breaker that feeds the sub panel. Then check the amps for the hum.
LOL, take a flashlight with you....

If the hum is gone then start turning back on the breakers one at a time until you find the source of the problem.

Still hum? Then, jmho, I would think that would rule out RFI/EMI noise, interference, on the mains. That is, at least from a source within your home. That does not mean EMI/RFI noise is not coming in from outside your home on the utility power.

==========================
Maybe the problem is the power amps and the sensitivity of the speakers??

By chance do you have another pair of speakers you could try? Less efficient?

You might try a different pair of speaker cables. For a test just some cheapo Home Depot rip cord would do.

Sorry, I am out of ideas......

I did send an email to an EE who posts here on Agon. I asked him to read the thread and post a response if he has any ideas.

Jim

Well,
I already tried turning off all circuit breakers, no help.
Tomorrow I'll bring the amp to the living room to try with another pair of speakers and another outlet.
I have two other pairs of less efficient speakers, so I'll give it a try as well.
BTW, what's your take on the high chassis voltage, higher with the correct polarity?

Maril,

Wow, I just read through all of this, at Jea's suggestion. Let me make sure I understand what amp we are talking about. If I followed everything correctly, you are having the problem with your friend's pair of BAT VK-150SE's, not the VAC amps that are listed in your system profile. And you previously had (or still have) a BAT VK-75SE (similar to the 150SE but in stereo configuration), and it exhibited similar symptoms.

Do your VAC's have these symptoms as well?

I notice that the BAT amplifiers have a bandwidth spec of 200kHz, which is extremely wide, and approaches rf frequencies. I'm wondering if there may be rf interference coming from somewhere that is radiating directly into internal circuit point(s) within the amp, and somehow then intermodulating or being AM-detected somewhere in the amp circuitry, resulting in the sound you are hearing.

Can you tell if the sound is really 60Hz, together with its 120Hz and possibly 180Hz harmonics (corresponding to the power line frequency and its lower harmonics), or could it be some other frequency or frequencies, which would be suggestive of rfi pickup?

The computer that you mentioned is in the room would certainly be one such possible source. If you haven't already, try turning it off AND unplugging it -- as you probably realize some circuitry on the computer's motherboard, and parts of its switching power supply as well, are always powered up as long as the ac is connected. For that matter, unplug all other computers in the house, and if you have nearby neighbors, consider asking them to do the same.

Perhaps you could bring an AM portable radio into the room, or better yet if possible a portable that can receive the long-wave band (below 550kHz) and see if it picks up any interference. If it does, you could track down the source of the interference by walking around with the radio and seeing where it is loudest.

Also, just to be sure, did the XLR shorting plugs you put on the inputs have all three pins electrically connected together (such as by having pin 2 wired to pin 1 and pin 3 wired to pin 1)?

Regards,
-- Al

Almarg,
Yes, you're right, I'm talking about my friend's 150s.
I no longer have 75-SE, but am considering buying it again, that's the whole reason for this post.
VAC didn't have this symptoms, just some ground loop, that I corrected.
The hum is mostly coming from the tweeters, but can also be heard from mid and bass drivers.
Just a little bit of history: what started me on this wild goose chase, is a significant hum coming through the speakers with a phono input selected- I could see woofers moving.
In another lenghty troubleshooting session with Kevin of KAB, we narrowed it down to phonostage amplifying some AC interference. I could also hear phonostage picking-up a radio signal (actual radio broadcast).
All this information combined with BAT's bandwidth, gives your theory an extra credit.
I will experiment with computer and radio tonight.
Shorting plugs- I don't know how exactly they are wired, I'll look into it.
Thanks for your help. I hope you, Jea48 and others will hang with me for a while longer, until this gets resolved, or I commit suicide.