2. cables
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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
4,764 posts
 
Describing the sound: I get a whistling sound when my CDP is engaged and I am on that input (probably some sort of DC leaking there)

From this statement it sounds like you think the whistling sound is caused by the CDP. or possibly the ics used to connect the CDP to the preamp.

By chance do you have a DVD player you could substitute in place of the CDP and connect to your preamp?

That should tell if the whistling noise is being caused by the CDP.

and a general hum when I turn the amp and preamp on together (not present when the amp only is activated).
09-14-08: Dawgcatching

You lumped this statement in with the whistling statement in the same sentence.
If the CDP is not connected to the Line inputs of the preamp is the hum still present?
================================

I am also getting a static background noise when I have my preamp hooked up (a Herron) but the preamp was just back at the factory and checked out fine. Perhaps it has something to do with the preamp tubes picking up something out of the air, although my backup preamp (EE Minimax, also tubed) isn't picking it up, and is much quieter.
09-14-08: Dawgcatching
Are you using the same tubes in Herron that was in the preamp when it was checked by the factory?

Static can be caused by something as simple as dirty or corroded tube pins. The static can also be caused by poor contact pressure between a tube pin/s and the socket/s of the tube socket. Tube socket/s can loose their tension memory, the ability to maintain a good pressure contact against a tubes pin/s.

Like tube pins, tube sockets can also become dirty and corroded.

And then there is the tube itself..... Did you try substituting other tubes in the preamp?

The static is pretty constant: the whistling noise and hum comes and goes, although I usually hear the Whistling around 15 minutes into listening. It tends to diminish over time, but can still be heard at high volumes.
09-14-08: Dawgcatching

Have to ask again, does all of these problems only exist if using the CDP and the ics used to connect the the CDP to the preamp?

If the CDP and ics are totally disconnected from the preamp, even to the point of unplugging the CDP from the power wall outlet, with only the preamp and the power amp on.... Does any of the problems you have described still exist? If so, please explain which ones?
jea48
4,764 posts
 
09-14-08: Dawgcatching
Is there any way I can check for a ground loop w/o buying equipment? If it comes to that, so be it, but is there any way I can test it? I tried grounding my preamp, with no change.


You might try temporarily lifting all the safety equipment grounds.....

Here is some good reading material

http://www.jensen-transformers.com/an/an004.pdf

http://www.smartdev.com/pdf/ac_power.pdf

http://www.soundstage.com/weaver01.htm

http://www.audaud.com/audaud/JUL01/EQUIP/equip3JUL01.html
musicnoise
377 posts
 
Jea48: After looking through my own copy of ARRL's Radio Frequency Interference: How to Find it and Fix it, (sec. 2-8, 22-11, and 3-18) and looking at the schematic of a couple power amps I tend to agree that it is possible to inject RFI via speaker leads. What was troubling me was the mode of getting it through the amplifier. It appears that this is possible via the feedback path all the way to just past the differential stage. Having been a Ham all my life I cannot say that I ever had any complaints from my neighbors or family when I was transmitting but it certainly appears that it is possible to feed the RF back through the amp in this manner. I would think however, that the active components would end up detecting the modulating signal and you would end up with voice at the speakers, at least in the Ham setup (unless of course transmitting CW).
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