Car Stereos: audio interference, power line noise, noise suppressor

Question
hi,  i asked you a question a week ago about my car speaker's humming.  ive got it down to the factory headunit that is causing it. if i put a noise suppressor onto the headunits 12v power should this fix it? thanx

Answer
Hi Danny,

Unfortunately, I doubt it's that simple.  Power line noise filters are designed to remove the AC "ripple" current that's a by-product of the alternator output.  However, as I recall, your noise problem is occurring even when the engine isn't running, which would eliminate AC ripple as the cause.  Installing a noise filter won't hurt anything (provided you get one with enough current capacity--10 amps should do it) but I doubt it will help in your situation.

If the head unit is the cause, then it's likely that there's a defect in the head unit's circuitry that's causing the problem.

I'm still curious about how you're getting the signal from the factory head unit to the amplifier.  Are you using high-level inputs, a line-out converter, or does the factory deck have RCA pre-outs?  If you're using a line-out converter, the problem might be in the converter itself, or a result of an installation error.  I recently worked on a noise problem with a line-out converter, that turned out to be caused by the installer mistaking an illumination wire for a speaker wire when he made the connections to the L.O.C.

Good luck!

Brian