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Radio broadcast got caught by speaker cables

E

enflammer

New Member
Has anyone experience this? I've been hearing some kind of distortion on my system, especially during idle. Turns out it's an FM radio broadcast from a nearby station caught by speaker cables.

How do I solve this? Maybe wrap the cables with aluminum foils and ground the foils?

Inputs appreciated..
 
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Looping the cables through ferrite rings or something might work. Books on ham radio and CB should have sections on dealing with interference to stereo equipment. Public libraries should have copies of the ARRL Handbook.
 
How do you know it's the speakers cables? Do you hear it when the stereo is turned off? Speaker cables are in a low impedance circuit that is typically immune to injected noise. I suppose if the tower is shadowing your house the signal could be that strong. My suspicion is that the noise is induced in the circuits of your receiver.

I think ferrite rings are for suppressing radiated noise, so the cable doesn't transmit.
 
Someone in a town I used to live in ran a CB linear amp and it came out my speakers with nothing turned on. They did find him and shut him down. His neighbors didn't like when they couldn't watch Little House on the Prairie
 
I doubt it's the speaker cables, but ferrite rings on your interconnects might help. Phono input is a likely possibility, since that's a high-gain circuit. Sometimes an amp will do this even with no cables connected (listening with headphones).
 
It is exceptionally unlikely interference picked up by speaker cables is DIRECTLY converted to sound by the speakers - loudspeakers need far too much power for that.
BUT it may well be the speaker cables are acting as an antenna, and injecting interference into the audio system where it migrates to much more sensitive circuitry.

Ferrite rings or toroids on the cable should help, even 2 or three loops through the ring. Otherwise, attention to the earthing on the entire system or individual components may help.

Does this interference vanish if all sources are unplugged from the amplifier ?
 
It's possible for that signal to be injected and loop back through the amp via feedback circuitry, ending up amplified in the process (because there isn't a corresponding out of phase signal in the source that it would normally cancel against).

An expensive solution would be to switch to an amp with little or no negative feedback. As pointed out above, it's virtually impossible to inject enough signal this way for it to be audible in the speakers, once you eliminate the path back through the output stage.

John
 
P.S. Kimber Cable touts their braided cabling product as being immune to this...

I've seen a demonstration of that a long time ago, which was very compelling - until we wrecked the demo by asking them to repeat it using one of our amps, which had no feedback loop. Really stumped the salesman when there was no change when he applied noise to the "standard" zipcord speaker wires with that amp.

John
 
It reminds me of a story my father told me of a friend who lived near a radio broadcast station in the years before the broadcast power was regulated by the FCC. Everything in his house was broadcasting the station due to the gigawatts of the transmitter. His solution was to hook up an antenna and use the signal to light his house. Not sure if it's true or not, but does sound plausible.
 
You can try changing the length of your speaker cables. They may be resonant on that frequency and picking up the broadcast RF and letting it into the circuitry.

I use Type 31 clip-on ferrite cores on just about every cable in the house. Mostly on my own ham shack equipment. But also on the entertainment center to keep the wife happy. Sometimes the cable is small enough I can make a loop or two to clip onto. The more passes though the core, the better. I get mine from Newark electronics. They look similar to those plastic coated lumps on the video cable to your computer. Other equipment may come with those. The USB cable for my Maverick Audio Tubemagic D2 DAC has one on the cabling. They are not a sure fix. But may help. Even coiling up excess speaker cabling to create an RF choke may help.
 
If the interference is coming thru the speaker cables you try using shielded cable and ground the shield to the amp chassis and then ground the amp chassis to a earth ground.
 
Thank you everyone for the inputs

fly135 said:
How do you know it's the speakers cables? Do you hear it when the stereo is turned off? Speaker cables are in a low impedance circuit that is typically immune to injected noise. I suppose if the tower is shadowing your house the signal could be that strong. My suspicion is that the noise is induced in the circuits of your receiver.

I think ferrite rings are for suppressing radiated noise, so the cable doesn't transmit.
Click to expand...

RichPA said:
I doubt it's the speaker cables, but ferrite rings on your interconnects might help. Phono input is a likely possibility, since that's a high-gain circuit. Sometimes an amp will do this even with no cables connected (listening with headphones).
Click to expand...

I don't hear it when it's turned off. But the radio interference also stays on the same level wheter the volume is zero or max so I guess it doesn't interfere on the amplifier inputs.


sanford12 said:
Someone in a town I used to live in ran a CB linear amp and it came out my speakers with nothing turned on. They did find him and shut him down. His neighbors didn't like when they couldn't watch Little House on the Prairie
Click to expand...

LOL little house :D

steerpike2 said:
It is exceptionally unlikely interference picked up by speaker cables is DIRECTLY converted to sound by the speakers - loudspeakers need far too much power for that.
BUT it may well be the speaker cables are acting as an antenna, and injecting interference into the audio system where it migrates to much more sensitive circuitry.

Ferrite rings or toroids on the cable should help, even 2 or three loops through the ring. Otherwise, attention to the earthing on the entire system or individual components may help.

Does this interference vanish if all sources are unplugged from the amplifier ?
Click to expand...

Yes I suppose so, the speaker cables are acting as an antenna. The interference still persists after unplugging all the input sources.

I'll try the ferrite rings, my cable is 13mm in diameter, what size should I get?
 
enflammer said:
Thank you everyone for the inputs

Yes I suppose so, the speaker cables are acting as an antenna. The interference still persists after unplugging all the input sources.

I'll try the ferrite rings, my cable is 13mm in diameter, what size should I get?
Click to expand...

As your speaker cable is quite thick I would suggest you try to get the type of ferrite 'ring' that clamps over the cable, rather than actual 'rings'.

To explain
The cable should be in close contact with the ferrite of the ring or 'clamp'. With thinner cable and ring type ferrites, it is possible to wrap a few turns of speaker wire around the ring (i.e through the middle). In view of the thickness of the cable - the clamp type is best in this case, I do not know the availability of clamp type with 13mm cable hole.

EDIT:
Update - I just checked ferrite clamps with 13mm hole are widely available.
 
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Mouser is a good source for the clip-on ferrites also. The maker of those I use is Fair-rite. Their website may be less confusing to locate the model number. I use the type 31 mix. It could be that another choice may be better.
 
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