Transformer Buzz

My 7125 emits a mechanical buzz, presumably from its power transformer, when my TV (Panasonic TC-P65VT50) is on. The buzz varies in level depending mainly on the brightness of the image at the moment, but it can be clearly audible at 15 feet if the soundtrack is fairly quiet at the time or off. The most interesting thing about this is that it occurs even if the TV is not connected to anything other than AC. I can disconnect all cables from the TV, run slides from a USB stick, turn on the amp, and the amp will buzz. (The Model 2200 I use as a subwoofer amp does the same, but it's behind a door, so its buzz is not really noticeable unless I open the door and listen for it.) Anyone have any ideas as to what might be causing this or how I can eliminate, or at least reduce, the buzz?

Thanks.

Are you sure that it is not from the Plasma TV itself? I have a 60" Pioneer Plasma that has an audible buzz from 15'. Same thing, if the screen is brighter, the buzz is more pronounced.

That's what I thought initially, but it's definitely from the amp. The TV does buzz a little on its own, but this is a separate issue.

Are the TV and amp on the same circuit? Do you have any sort of surge protection? If so, does it islotate each component from another?

Try running an extension cord from the wall plug of another circuit and see if the noise stops. It sounds kind of like the TV is putting noise on the circuit. Also, is there any lighting on that same circuit? Sometimes dimmers can be noisy.

I am with Sharkey on this. It definitely sounds like your tv is the culprit. Again....any surge protection or conditioning? Can you run the system with music or a movie for an audio only test? That is disconnect your tv from the system completely. First the power and then remove any interconnects like HDMI and cable.

Was the buzz happening while you had your equipment or did it just suddenly begin?

Is the buzz 60 Hz-which may indicate that you have a ground loop? Or is it a different frequency which indicates soemthing else?

There's basically two types of noise that could cause this: conductive and radiated. The first goes through the cables the second through the air. Can you move your amp? If you move it around without changing the cabling and the buzz changes volume then your problem is probably radiated noise. If it stays the same no matter where you move it, the noise is probably getting in through the wires. Maybe work with the 2200 as it's lighter and has fewer connections.

I would say it is a problem with the TV backfeeding a dirty signal to the pre-pro then affecting the 7125. Does the noise occur with the TV unplugged and disconnected fron the system?

Try swapping the HDMI port to an alternate input or change out the cable and see if that helps. It does sound like a ground loop hum in the video portion of the TV is affecting the sound. Make sure all of the components connected to the TV and the Amp share a good common ground. If there is a delta between the ground references then the hum will occur.

Yes, yes, and yes.


I did this on advice of Outlaw tech support, and it does reduce the effect significantly, although it does not eliminate it entirely. The tech's opinion was that the buzz is a consequence of voltage sag on the line, which is plausible, as the TV can draw widely varying, and sometimes very high, currents. I doubt it's noise feeding back through the AC line, as then I would expect it to find it's way through via other components, which doesn't seem to be happening.

Did this early on. The only circumstance in which the buzz occurs is when the TV is on, and the TV doesn't have to be connected to anything other than the power socket -- removal or addition of other connections makes no difference.


Started when the TV was installed.

If it were a ground loop the buzz would be coming from the speakers, which it isn't at all. It's mechanical buzz from the transformer. At this point I'm pretty much convinced that it's the transformer's response to fluctuating AC voltage.

Walks like a duck, smells like a duck looks like a duck, it's the TV Dude. Are you using the TVs speakers at all? If so, turn them off in the TV menu. What type of lighting does the TV use. It could be a bad inverter in the TV backfeeding into your AC circuit.

TV speakers are off. TV is a plasma. It's the TV in the sense that the TV is causing the voltage on the AC line to vary substantially. All the evidence points to that as the cause now. Makes complete sense. Probably would not have come up in the winter, when the grid and the house circuits are not so heavily loaded. Right now, I sometimes see the voltage to the A/V system drop as low as 111 volts, with the current up to as much as 6.7 amps, depending on what's on the screen. If it were noise on the line, I'd expect it to affect other components as well, and perhaps to manifest in the signal feeds, which doesn't happen.

Having said all this, can you call a troubleshooter..ie expert electrician who would be able to fix something in your lines and give the tv a dedicated line. I don't know if this will work. Because if you hear this noise in the quiet parts of the movie then there is a problem that will always bug you. Can you somehow TEST a different tv on your system. I know it is a huge job BUT maybe the tv has got to go. First get expert electrical advice.

I have an APC H-15 which maintains system voltage right at 124 vac where I have it set. You can get them online for $2-300. I actually got both of mine for less than $100 each a few years ago. They also provide great lightning protection. You can also get them with battery backup.

Fortunately there's a socket connected to another circuit nearby, so I'll just feed the amps from there. That effectively fixes the problem.

Yeah, I may go to something like that eventually. Thanks for the lead.

Maybe you can extend that line close to your system so you won't have to run an extension. Nice to keep the thing neat and tidy. The APC conditioner Xenonman suggested is worth the try.

Try checking the circuit at the breaker for any indications of overheating or loose connections. That will be easy to do. A loose connection on the circuit or its ground could be causing the problem. Turn the breaker off and check all of the receptacles fed by it for tight connections and good grounds. Pop the breaker out and replace it with the same style and amperage rating. The breakers are only like $6 at HD or Lowes and take 10 minutes to swap out.

Have you checked the internals of the 7125? It's possible the transformer is not bolted securely and that this is causing the buzzing. Or maybe something else is loose and vibrating under load?

It you open up the unit be careful of the caps. They may hold charge long after the unit has been unplugged.