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eliminating Alternator whine

I bought one of those FM transmitters that plug into cig. lighter outlet in my car. Problem is alternator noise is coming thru the 12v adapter. Now I know they sell gnd loop isolators and filters at Radio shack-- but I would like to fix/filter the problem at the lighter or in the cable since I have several vehicles and don't want the expsense/hassle of installing gnd loopiso/filters on every one--since we want to use the FM transmitter/MP3 player in a portable fashion.

So, I'm looking for ideas on how I could best do this. Any ideas? or is there an in-line auto adapter that has a built-in filter/isolator? I looked for, but cannot find one.

Thanks,

Bo

Reply to
Bo
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You need a little series inductance and parallel capacitance. I've had great success at eliminating alternator whine by using the secondary of a 6V 1 amp transformer as the series inductance, and a plain old 1000uf 16 volt capacitor as the parallel capacitor. No more whine.

Reply to
Ancient_Hacker

Any idea how much inductance that transformer has?

I'd like to make this thing universal--portability wise... ie

12v car socket -<
Reply to
Bo

If the whine is being picked up by the antenna, and not coming through the power line, you cannot fix it at the radio. The simplest experiment you can do to reduce the noise through the power line is to clamp a split ferrite bead over both wires.

Reply to
John Popelish

IIRC they do.

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Reply to
Homer J Simpson

No idea. The inductance isnt critical, so I'd break open any small wall-wart power supply (give it a GOOD whack with a hammer). and use the transformer in there. If you're careful, you can use the case and wires too!. And if it was a DC supply, you can use the capacitor too!

Reply to
Ancient_Hacker

Could be distributor noise, try popping the top of the distributor and replacing the capatitor. Mick C

Reply to
Michael

Bo, do you hear the whine when the Tx is pluggged into the cig lighter but the audio lead NOT connected to the MP3 player?

Is the MP3 player battery powered or powered by the car?

Most FM Tx units I have seen are well regulated, even the cheap ones. you may have a ground loop problem with the audio lead if the MP3 player is also car powered.

Solution would be to run the MP3 player on batteries. Or connect the MP3 player to the SAME ground as the FM Tx.

Mark

Reply to
Mark

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