Aliens,have infiltrated your stereo.Seriously though,check out some of the threads here on RFI.Lots of good suggestions to minimize or get rid of the problem.Good luck.BTW,are the aliens green or silver!!!!!
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Wow, I had the same thing happen to me this evening. Assumed it had something to the phono pre to pre amp cable I swapped out before my listening session. Sounded like one of the political guys from Fox News. It was very clear and a single broadcast. I read through the link Almarg posted above and will pursue a few of the ideas if I continue to have issue. What a small world.
Sounds like a good bet to me. Unshielded phono cables strike me as an invitation to this kind of problem, considering the low signal levels and high gain factors that are present.
I would suggest, though, that you verify that you don't hear the radio signals with the Linn preamp when nothing is connected to its phono inputs, and/or with shorting plugs connected to its phono inputs if you have them available.
The different results between the two preamps are likely due to the happenstance of the different characteristics of their input circuits -- one demodulates the rf signal and one does not.
Also, similar to the discussion in the other thread that I linked to, I suspect that you are really hearing am, not fm. I can't envision a means by which an audio system, apart from a tuner, can demodulate an fm signal.
I had to get rid of all my amalgam fillings for this very reason.
Congrats on tracking it down. The better cable suggestion should show a result.
The AM band is fairly long wavelengths, so I'm sure that changing 'antenna' orientation would help, but that should also be tried.
You could also try secondary shielding OVER the offending cables. Ground it at only 1 end.
Bad amalgam fillings you say? Would be cheaper to replace analog gear than pay $$ to my hi end dentist. I am researching wiring upgrade presently and that route sounds like it would improve the sound quality anyway.
The station is Fm and they do not broadcast a duplicate signal on Am to my knowledge.
What could I place over cables to shield them?
Do you have any gear with a switching powersupply?
Such power supplies operate NEAR Intermediate Frequencies of both FM (some) and more common AM radios. I have no basis for thinking this could actually happen.
As for shielding, a better cable would work better than either copper foil or mesh around wires. It would be a mess to boot.
Have you tried a power conditioner? This goes back to my first line in this post... It may be coming in over the power lines, though the phono pre seems 'the magic bullet' .
post if you find the final root cause / solution