RFI from steel TV bracket?


Yesterday I installed a new TV on a steel wall-mounted extendable bracket between all my electronic components.
I now have a low hum/buzz from both speakers on all sources....even with the preamp on mute?
When I switch the preamp off.....the hum is still there.
The only way to remove the hum is to switch the amps off?
I tried grounding the steel bracket to the preamp and then the amps without success.
The previous TV was in the same location but sitting on the shelf.....not a steel wall bracket.
Any help would be dearly appreciated?
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My first thought is; it's not the rack but the TV. Try lifting the ground to the TV. Or possibly pluging the TV into a known different circuit that is on the opposite phase of the balance of your system. One other suggestion if you feel it is the rack, can you put the old TV(if you still have it) on the steel rack and determine if it is indeed the rack. And fiannly I assume you have tried unplugging the TV to see if the hum diminished?
I have been down this road and you just have to try every possibility to find the gremlin. Good luck.
Yes I unplugged the TV and also tried it in different GPOs.....even a power conditioner. I even disconnected the 'sound-out' of the TV from the preamp. Hum still there.
Interesting thing is that the hum is from the amps and not the preamp as when I listen to my headphones which are plugged into the 'tape-out' of the preamp......no hum?
Possibly, the interconnects to the amp aren't shielded and picking it up(?) or, if this TV is a Plasma, they do give more interference.
Last TV was plasma. No hum.
This TV is LCD......hum.
But it hums with the TV completely unplugged so I don't see how it can be the source?
Ground loop from your cable tv or sat box. Unhook the coax cable from the source tv direct/cable box or sat and turn everything else back on and take a listen. Tom
Yes I unplugged the TV and also tried it in different GPOs.....even a power conditioner. I even disconnected the 'sound-out' of the TV from the preamp. Hum still there.
11-13-11: Halcro


Want to rule in or rule out 100% the hum is being caused from the metal bracket? Take the TV down from the metal TV bracket, set the TV in the middle of the room, and then check for hum...
If I understand this you just installed the TV mount onthe wall. Is there any chance a screw cut into your Romex in the wall and is hitting a grownd wire? I would say try removing a screw at a time and check for the hum. It just odd that an LED Tv is doing this or that the metal mount is causing it.
I unhooked the cables from the cable TV......no change.
I then suspected the 2 metre long Cardas cable interconnects running on the shelf behind the TV and just under the steel brackets and plate.
The right-hand interconnect runs right across this 'field' before dropping down to connect with the speaker....whilst the left channel interconnect runs for only a foot before dropping down.
The left speaker only emits a light buzzing whilst the right speaker has the definite 'hum'.
So I wrapped both interconnects in aluminium foil and this reduced the level of the hum and buzz.

Not knowing much about electricity.......is it possible for the steel bracket combining with all the power outlets directly below it, to create an electro-magnetic field which the long runs of unshielded interconnects then acts as 'antennae' for the RFI/EMI?

If this is indeed the problem.......would going to fully balanced XLR interconnects, solve it?
What all do you have connected to the TV? Are you using a Pre-pro that you can connect everything to then just run HDMI from the Pre-Pro to the TV? If you are running analog IC's to the TV and they are picking up interference from the AC cable then maybe a shielded power cable would help. If possible try to have your analog IC's cross the AC cord at a 90 degree intersection, if they must cross. If they are coming out of the TV mount area and must be together, try sheilding them as much as you can.
Halcro, it really sounds like you may have created a primitive power transformer with your wiring setup. If that is the case, the metal frame is acting as the core and the speaker leads draped over it are the secondary.

Try re-routing the speaker leads.
Hi Ralph,
The interconnects were running under the steel bracket.......not draped over it.
The speaker leads are on the floor well away from the bracket (as they have always been).
I just re-routed the right channel interconnect to along the floor away from the steel bracket........but the hum is still there?
Again.......if I run in fully balanced configuration from preamp to amp......shouldn't this prevent any RFI/EMI interference?
Isn't that why all professional sound systems run in this way?
Sounds to me like you have more troubles than you thought.

So let's go back to the time you installed this bracket thing.

What *other* changes did you do?
What *other* changes did you do?
No other changes :^)
What happens if you unplug the interconnects from the inputs to the amps? Do they still buzz?

Right now I'm sticking to my original theory, only substitute 'interconnects' for 'speaker cables', and since the ICs are single-ended, this makes a lot more sense.
When I unplug the output from the pre-amp......the hum is still coming from the speaker.
But when I unplug the input to the amp (with the output still connected to the preamp)......the hum disappears :^)
If you're right.......any solutions other than removing the steel wall bracket?
Thanks
Henry
But when I unplug the input to the amp (with the output still connected to the preamp)......the hum disappears
I still think there is a possibility that the interconnects that go from the preamp to the amp my not be shielded enough for the new environment. Try a different pair (if you haven't already) between these two (amp and preamp) that may have better shielding, or a different design. Last resort (don't laugh), even some budget ones from Radio Shack, or even a big box store just temporarily to see if this can be the problem.
Hifihvn makes a good suggestion. You might be surprised how good some of Radio Shack's cables actually are.

Now. Since you are running single-ended cables, if there is a hum source (like the primitive transformer thing I mentioned), even if the cables are shielded you will still get a hum as single-ended cables have no 'Common mode rejection'. (IOW if you have balanced cables you may not have noticed a problem.)

So what I would do is temporarily reroute your cables so they are no-where near that bracket and for that matter, any power cords too. If you have to shut down everything but the amps, go ahead a do so for the purposes of this test. So hopefully you won't have to go to Radio Shack :)
Halcro, you may want to look at the Mogami 2534 or 2549 cable. It's what allot of studio's use because of their abillity to be quiet. Low capacitance and fairly cheap to what's out there.

http://www.markertek.com/Cables/Audio-Cables/RCA-to-RCA-Cables/TecNec-Cables-Connectors/MSC1-5RR.xhtml

http://www.mogamicable.com/category/bulk/microphone/quad/

http://www.mogamicable.com/category/bulk/microphone/quality_balanced/

Brad
I still think there is a possibility that the interconnects that go from the preamp to the amp my not be shielded enough for the new environment.
That was my initial thought which is why I wrapped them in aluminium foil which reduced the hum somewhat.
I hope we're all right as I've just ordered an XLR pair of Cardas Clear interconnects and George Cardas tells me they are the best shielded cables he knows of?
He guarantees my satisfaction.......which is a great attitude from a manufacturer.
I'll know in about 3-4 weeks when I receive them. Fingers crossed :^)
Thanks for all your help.
Cheers
Henry
Received the Cardas Clear XLR interconnects today and installed them between the Halcro DM10 pre and the DM58 monoblocks.
Absolutely no hum or buzz whatsoever.
The shielding in these cables is obviously so superior to the old Hexlink 5 interconnects and/or the balanced XLR method of connection combine to lower the noise floor from the speakers to nil :^)
Now I need time to see if I can 'hear' other benefits?
Sweet.
Sounds great.