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Old 08-15-2011
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AM/FM Radio Whine

I have a Dual MXDM66 AM/FM/CD/MP3 Player. It works great, however, when I turn the volume above a medium level, I get an electronic whine from the speakers. It occurs regardless of mode, and the boats motor is not running. Is there a filter or grounding technique I can use to eliminate the whine?

Last edited by L124C; 08-15-2011 at 04:15 PM.
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Old 08-16-2011
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Did you just install it, or is this a change to it working well previously?

Since this is independent of engine state, and controllable by the volume, I don't think that a filter will have any effect.

Just a guess, but is sounds like the internal amp is being asked to do more than it can (ie. 'clipping' the audio'). I see that it is 4 speakers x 50W peak, so that should be enough. Look to how your speakers are wired - you're using the harness wiring rather than the RCA's, right? The RCA's are preamp outputs.

Next I would look at the speakers themselves - they might be blown out. Try substituting from your home stereo.

Lastly, how good is the power you are delivering to the unit? You could bypass the boats harness and make a temporary connection to the battery with lamp cord (keep a fuse inline).

Good luck!
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Old 08-16-2011
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Check your ground wire too. I think everything should be wired to a grounding strip.
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Old 08-16-2011
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Is this a noise that is constant but gets louder and quieter with the volume (so a constant fraction of the music)?

Or does it onset suddenly when the volume reaches a certain point?

The former I would say is probably an interference noise source, while the latter is more likely an internal fault, or issue with the speaker wiring or speakers. Does it come from both speakers? If so it's really pointing to an internal fault.

Interference could be from the battery charger. Try turning it off. If that fixes it, you could try to fit a ferrite to the power leads before the radio.
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Old 08-17-2011
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I've had a similar hum picked up from 120V circuits in old speaker wiring in a house on dry land. Moving the speaker wires away from the power cables seemed to help.
Are you running an inverter to power your stereo? or cell phone/mobile recharger? RADAR? VHF? at the same time?
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Old 08-18-2011
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Turn on the stereo and turn it up until the whine is clear. Now go to the breaker panel and shut EVERYTHING ELSE OFF.

If the whine goes away, you turn circuits back on one at a time until you find out which one is making the whine, and work on fixing that. If you turn everything else off, and there are no gizmos plugged in outside of the breaker panel, and you're running on DC not on shore power with a converter, etc., then the noise is either coming from your neighbor, or the stereo has a problem internally.

Try again in a different location if you suspect the neighbors.

Once you find out the source of the noise, you can figure out how to best fix it. "Car" stereos aren't expensive these days, new ones with aux inputs for mp3 players and other music sources are common now too. If yours has an internal problem...could be time to replace it.
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Old 09-07-2011
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Did you recently install any LED lights? I bought an LED steaming light to replace the incandescent that was there on my mast, and it wiped out my AM/FM, my SSB, and my VHF radios.

A cheap disc ceramic capacitor (0.01 MFD, 50 VDC) connected across the LED terminals solved the problem. Cost: $1.59 at Radio Shack.
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