I have a Lepai LP-2020A+ audio amplifier and a König FM Pocket Radio. My problem is that the pocket radio works really well on its own, with the headphone plugged in, but when I connect the radio to the amplifier through a 2xPhono to jack cable, the radio signal disappears. I suspect this is because the radio uses the cord of the headphones as an antenna, but do you guys have any suggestions on why this is not working for the amp, and how to hack the setup such that the FM radio gets a strong signal, even when connected to the amp?
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1\$\begingroup\$ You need to use a sufficiently long cable between the radio and the amplifier and then figure out how radio detects headphones. What test equipment do you have available? \$\endgroup\$– AndrejaKoJul 1, 2012 at 14:20
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\$\begingroup\$ Your suspicions are likely correct, I would expect the phono shields to be grounded, which will conduct any induced radio signals to ground. Not sure how to fix - cutting the shield at the phono connectors would leave the audio signal floating. Can you say if the supplied headphones are 4pin or 3pin 3.5mm Jacks? \$\endgroup\$– shuckcJul 3, 2012 at 18:00
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Well at first you should never connect earphone output to the phono input of any amp. You will overload the amps preamp stage which at least would cause you distortion or worst blow the amp. I just looked at the amp its got a mp3 input: try that. The problem you got, is that it does use the earphones has a aerial so only thing I can think of is to strip some of the plastic of to expose the shielding plus it depends on the length of the wire, all a pain. I would go out and buy another radio.
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1\$\begingroup\$ He didn't actually say anything about using a phono input specifically, just phono plugs, which are near-universal, but another problem would be unwanted RIAA equalisation. \$\endgroup\$ Oct 10, 2012 at 4:36