Low level buzzing coming from tweeters.

Buy an receptacle tester at the hardware store.
This is about $10...
This has 3 lights, that tells you if the ground is good, and if the power is wired correctly.

Yes there could be something wrong with the utility.
This type problem is analyzed with test equipment, that detects noise or harmonics in the incoming power. (Fluke power analyzer)
A specialist will have this type equipment available to test with.
But you can not usually rely on the utility to detect or fix a problem.

I’ve tried both of these. I don’t have cable TV. I’ve long had only the pre-amp with a three-prong plug.

I believe the issue may be deeper in the electrical. I had an electrician out who does installs for a high-end audio shop and he couldn’t find anything.

Could the power company’s electric feed be the source? The other night I was not getting the hum/buzz for the first time in a long while. This confounds me even more . . . 

1. The first thing I think of is a ground loop between cable TV and house ground.
Disconnect cable TV from the entire house, and re-test.
(the CATV ground should be entirely isolated from the house ground)
If noise goes away when CATV is disconnected:
In order to cure this, use a cable TV isolation transformer which is designed to stop audio buzz by isolating the cable ground from the house ground.
This type isolation transformer can be purchased ready made -or - you can make one by connecting 2X 75 ohm to 300 ohm antenna transformers, you connect the 300 ohm ends wire to wire. Then you connect your 75 ohm cable (in/out) to the coax ends of the transformers.
This will make an effective isolation transformer for about $10...You can make these out of Radio Shack antenna transformers.

2. Second thing that comes to mind is an ordinary ground loop.
Allow the preamp to use a 3 prong grounded plug. Then lift all other grounds (at the mains power plug) using adapters.
These power plug adapters (2 to 3 prong) are available at the hardware store.
You need 1 adapter for every piece of equipment that has a 3 prong plug.
Including: Lift TV, Lift sub woofer amp, etc...until all the grounds are lifted at the power plug, except 1.
This type of loop occurs when there are repeat grounds (more than 1 ground). The equipment is already grounded together using the audio cables...and the video cable.
Then, you ground everything to the mains power (3 prong plugs) and this makes the loop.
By lifting some or all of the grounds...you can stop this loop.

@cleeds 
I feel somewhat relieved to hear this, as I have had confidence in my electrician who has done some extensive work for me, including upgrading my electric service, installing a new panel with a built-in transfer switch for my generator along with the outdoor plug for it and ground, as well as the separate ground for the audio system.

As I am not knowledgeable in these matters, I must rely on others for their expertise. The electrician is tentatively scheduled for Monday afternoon.

atmasphere

... you are far better off if the ground is tied to the water mains as is traditional. Stakes in the ground tend to be variable, and if the ground connection is indeed on the water mains, the stake in the ground should not be used at all unless all your water connections involve plastic pipes

I'm surprised to see Ralph state this. IMO, you are best served by complying with NEC and local codes. That usually requires stakes in the ground bonded to the ground in the service panel.

The water main should be iron, as it is an older house (1957). I’ve got the same pole type, but separate, ground for my large portable generator. Another discussion with my electrician. We’ve touched base and he will be coming over to check things out.

FWIW, you are far better off if the ground is tied to the water mains as is traditional. Stakes in the ground tend to be variable, and if the ground connection is indeed on the water mains, the stake in the ground should not be used at all unless all your water connections involve plastic pipes.

@atmasphere 
Yes, it is a pole, about 15-20’, driven into the ground with ground wires fused to it.

@ozzy 
Yes, the dual 30 amp breaker is near the top of the right side of the box and the 20 amp breaker is also on the right side near the bottom. There are five “blanks” and two more breakers between them.

I’m trying to contact the electrician who installed the panel and the outside ground.

I appreciate all the input!

No, if the system is all on one side of the breaker box with one on top of each other then that is causing the hum. The breakers are staggered.
https://images.search.yahoo.com/search/images?p=breaker+box+inside+pictures&fr=yfp-t&imgurl=...
https://i.pinimg.com/originals/b1/04/95/b10495877e448c7626e2b9046f295001.jpg

ozzy

The amps are on a dedicated 30 amp breaker, the rest of the system on a dedicated 20 amp. There is an outdoor imbedded ground for, I believe, the entire system.

Is this a stake that someone put outside somewhere to make a ground?

The system, including the amps, are on the same (right) side of the electrical panel. Should I assume that means they are on the same side of the AC power?

The amps are on a dedicated 30 amp breaker, the rest of the system on a dedicated 20 amp. There is an outdoor imbedded ground for, I believe, the entire system.

This excessive hum arose well after the dedicated lines, panel, and ground were installed. It probably began within the past year, maybe during the summer. I wasn’t paying much attention as I was in constant shoulder pain, then surgery, so I can’t really identify exactly when I first heard it or anything that might have occurred which could have precipitated it. 

Usually the AC power comes from two halves of the incoming 240V from outside the house. If the amps are on one half and the rest of the system on the other, sometimes you can get hum if the amplifier's grounding isn't really worked out all that well.

So the extension cord may be going to an outlet on the same side of the AC power as the preamp's power is.

If OTOH the preamp and amp share the same outlet than something else is at play.

At a friend’s suggestion, I ran a long extension cord from each amp separately to an outlet at the other end of the house. There was now a barely audible hum that could not be heard about 2 1/2 feet from the tweeters. My listening position is 12 feet from the speakers and the buzz, which I now better describe as a loud hum, was loud enough to be annoying . . . and aggravating.

This makes more sense to me as I presumed the odds of both amps having the same exact problem to be unlikely.

Next stop . . . an electrician.

@atmasphere Thanks for the confirmation.

@analogluvr  At your suggestion, I changed the input tubes. No luck. I also have a Lutron 4-zone dimmer, but no change with the lights on or off.

Very frustrating, as you can imagine.

Gotta be the amps?

Yes.

 I have a pair of atmosphere m60s and had that problem and it turned out to be an input tube.  I also have a LuTron dimmer in my room and whenever the lights are on I get a little buzz as well.

Switched the amps between the tweeters & woofers. Buzz was originally from the tweeters. The buzz now came from the woofers, tweeters silent.. Gotta be the amps?

@atmasphere 

Thanks for the tip. Saves me from a futile testing regimen.

I’m planning on trying a solid state amp this weekend to rule out possible electrical problem.

@ncarv

If a tube is doing this, it won’t be one of the output tubes. They can make cracking and popping sounds but a low level buzz is unlikely.

I’ve been thinking about the tubes and whether they could be the culprit. There’s about 2200 hours on the power tubes (WingC 6550’s). It will be a chore to test them (12 per amp). I have a B&K 747. Then there’s the small tubes (driver and input, 3 each amp).
Sooo . . . I’m looking at 30 tubes. I guess I’ve got to get myself cranked up to do that.

In the meantime, I’m going to test with a solid state amp (the horror!) just to confirm it is the amps. I’m still a little puzzled over why both speakers have the same issue (the buzz). What are the odds?

The amps are old VTL Deluxe 500's and, though the caps were replaced, there is some transformer hum. I'm wondering if it has just gotten worse over time and is transmitting to the speakers.

Probably not. But depending on how the tubes are lit, if any of the tubes have developed leakage (as measured on a tube tester) that could easily be causing your problem.

atmosphere - I appreciate the suggestion. My tech guy, extremely knowledgeable and competent, but who no longer lives nearby, suggested the "no input" test. He knows the amps, having extensively worked on them, suggested trying without inputs. He said there should not be any buzz with the inputs removed. The amps are old VTL Deluxe 500's and, though the caps were replaced, there is some transformer hum. I'm wondering if it has just gotten worse over time and is transmitting to the speakers.

ebm - The amps do not have balanced inputs, only single ended. In any case, I'm using all Transparent Reference cables, so I don't think that should be an issue.

I'm going to hook up one of my Anthem solid state amps and see if that makes a difference.

Thanks to both.

Read the thread buzz is gone using balanced Purist cables!!

@ncarv  Short the inputs to the amps- if not shorted and no input, a buzz might be normal.

Nice to know you solved it, ebm.

Mine is a different problem, probably my amps. Even disconnected interconnects, unplugged everything except amps, turned off all circuit breakers, except those dedicated to amps . . . still buzzing.

Got balanced cables as i now have a balanced preamp Purist made my single ended cables balanced buzzing is now gone.I will now used balanced always and use Purist always.Thanks!!!!

Nothing here. Same set-up. Can’t say when it began. (I was recovering from shoulder surgery, not paying close attention, and couldn’t do anything even if I was more aware.)

I hope I’m not hijacking ebm’s thread. I thought if this is a common problem, we could both benefit. If I am (hijacking), I’ll be happy to bug off. (and sorry)

Any recent changes to cabling?  How about home electrical (e.g., new switches?) Could (unshielded?) speaker cable be picking up some airborne interference?  

Wow! I’ve got the same problem. The mute does reduce the volume of the buzz. I did disconnect the preamp, but still a buzz. My monoblocks are each driving only the tweeters. Possibly both amps with the same issue, but this makes me think it might be an electrical problem? I tried unplugging every piece of gear and plugging the amps into different sockets . . . no luck. Any help would be greatly appreciated!

Turn off amp. Disconnect the pre. Short the input to amp. Turn on amp. This is to see if it is coming from inside the amp or if it is being picked up from ourside the amp.