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Receiving radio stn through PC speakers

By soulsmiths ·
I have been using a pair of external ZoltriXound speakers attached to my Toshiba laptop for the last 4 years. Recently I moved to a different area of the city & am now faintly picking up what sounds like a radio channel, when I turn them on. Toshibaadvises it is not the sound card. I have tried wiring to a separate room & changing the speaker wires & unplugging the remote phone attached to the same power source to no avail.
I am not sure if it is the quality of the speakers, if there is a shortwave or satellite dish nearby that may be affecting the reception.
To date no one has heard of this problem & a search on your database doesn't bring this specific topic up, although it does talk about interference. (I tried the suggestions in that article.)
Any advice is appreciated.

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I'm surprised

by epepke In reply to Receiving radio stn throu ...

that nobody has ever heard of this problem. It's a common one with any audio equipment that's near a transmitter. It could be anything from oxide on switches or plugs (which can act as a detector) to poor grounding and ground loops. I'd first make sure that the ground where you live is really a ground. When I was a kid, my parents lived in a house with a floating ground for a while. (I eventually detected that it was floating.) You can get one of those three-way testers that plug into thewall to see, but these aren't very sensitive.

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by soulsmiths In reply to I'm surprised

Thanks for your response. You're the 1st person to even offer a logical answer from all the people I've asked. But if it is grounding, why would this not effect my stereo which is in the same house but on another floor? If the tester shows poor grounding, does this become a house problem or something I can resolve that deals with the speakers only?
I use the CDROM primarily to play music so one option is to get some remote speakers attached to my stereo but I wonder, now, if I would have the same problem.

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It isn't that easy

by epepke In reply to WHY ONLY PC SPEAKERS

Grounding problems are not simple and aren't amenable to simple answers. There are dozens of things that can go wrong. Radio and audio magazines used to devote entire series of columns to grounding problems.

Modern audio equipment is usually isolated from the signal ground, and low-voltage components are shielded. The wire to your speaker, however, is a relatively low voltage signal. It's signal ground is connected to the computer's signal ground. If that isn't a true ground, there's the possibility that the entire signal ground of your system could be acting like an antenna.

Then there are ground loops, where if a system is grounded at two points, the loop itself can act as an antenna. This usually only results in 60 Hz. hum, but if you have a strong enough radio signal, that can get in, too, especially if it's low frequency. The bottom of the AM band is 540 KHz, which is not so high.

There are all sorts of things to try, but many of them fall into the "don't try thisat home, kids" realm. One that doesn't is this: you might be able to solve the problem with an isolation transformer between your speakers and the computer. That way, if your computer signal ground is floating and picking up signals, the signal may not get into the speakers, and all you have to worry about is the speaker cord itself as a possible antenna.

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Not easy cont'd

by epepke In reply to WHY ONLY PC SPEAKERS

Unplug the speakers, turn the volume all the way up, and see if you hear the radio station. Try shorting the pins on the plug coming out of the speakers (the input, do NOT short the output from the computer). If the noise goes away, an isolation transformer might help. The trouble is that it might not help, either. There might be a problem with a differential inside the computer. You might try, with the sound off, hooking up a cheap crystal earphone to the computer output. (Crystal phonesare more sensitive than dynamic.) If you can hear the radio station in this, then you're sunk.

Another thing to try is to clean the contacts on the plug. A thin layer of oxide can act as a rectifier, which is all you need to pick up AM radio. Of course, this won't help if the rectification is happening somewhere else, say on the input stage of the speakers.

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