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Loud background noise: cables picking up RF?

I have a significant background noise problem in my system. At normal listening levels, I am getting static that is audible from 15 feet away, and also a whistling sound coming through the speakers from time to time. I suspect that it is possible that my system is picking up some RF from the air, or that it is coming up through the electrical system. FWIW, around 2 miles from my house and 500 feet up, there is a broadcast array: 5 full-power FM towers, 2 NTSC full-powers, and some lower-power FM stations. A potential issue?

If this is the case, should I be going to a shielded-type IC? I get the noise as soon as my preamp and amp are engaged, whether or not I have a source hooked up. Can I buy a cheap AV-style IC from Best Buy and and see if the cables are the problem, or are those low-end IC's they sell really shielded? Are the power cords also a likely culprit? FWIW, I have

Any other ideas? I recently had my entire system checked up by the manufacturers, so all of the equipment is in good working order, but I can't seem to remove that background noise. Both my preamp and CDP are tubed, not sure if that is bad or not.
dawgcatching
jea48
4,504 posts
 
I have a significant background noise problem in my system. At normal listening levels, I am getting static that is audible from 15 feet away, and also a whistling sound coming through the speakers from time to time.
I don't think I have read where transmissions from radio towers caused static.

Usually what is heard through the speakers is audible sounds. Sometimes the actual radio station can be heard. Sometimes the sound is garbled.

Can you be more specific what you hear.
dcstep
1,518 posts
 
You don't have to recognize the sounds for it to be RFI. A whistle, as described, can be an RFI issue. Usually it's just low level hash, but it can present as actual radio signals.

Of course, a whistle can be tube related also. I'd check all the tubes. Does the whistle come and go?

Dave
jea48
4,504 posts
 
You don't have to recognize the sounds for it to be RFI.
True. There are many forms of RFI. But with that said do you think if his problem is RFI, is it being caused from the communication towers?

An arcing from a loose electrical power connection can also create RFI. And in many cases it can be heard in the form of a static sound..

Of course, a whistle can be tube related also.
Also agree.

But, what about the static sound heard 15' away?

musicnoise
377 posts
 
When is the noise present? Always ? With or without a signal present ? For all sources ? etc. Does the volume of the noise change with a change in the position of the volume control? The first thing I would do is find out what the noise looks like and what frequencies are present - audible and inaudible. Scope the various points in the signal chain to see where it is present and to see what it looks like. If you don't have a scope - buy one - Kenwood sells fairly inexpensive scopes new and you can probably pick up an old tecktronix cheap. Its not like you'll never have another use for it. You are not hearing transmitted RF through your speakers - you cannot hear RF and your speakers cannot reproduce it - outside the frequency range for both. By seeing what it looks like and where it is you can do more than guess at it.
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shadorne
7,477 posts
 
Is everything plugged into the same electrical outlet? Also look at this - Jensen Transformer - it might be a ground loop and this will eliminate that. Of course it is best not to have anything at all in the signal path but you already have a major problem.
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