eliminating Alternator whine

[Bo]

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

 

[Ancient_Hacker]

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

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.

 

[Bo]

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.

Any idea how much inductance that transformer has?

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

12v car socket -< <plug-- LC filter -- socket< <---plug: any portable
audio device

You'd think some mfr would make something like this...

Thanks,

Bo

 

[John Popelish]

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

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.

 

[Homer J Simpson]

12v car socket -< <plug-- LC filter -- socket< <---plug: any portable
audio device

You'd think some mfr would make something like this...

IIRC they do.

http://search.ebay.com/search/search.dll?from=R40&satitle=alternator+filter

 

[Ancient_Hacker]

Any idea how much inductance that transformer has?

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

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!

 

[Michael]

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.

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

 

[Mark]

Any idea how much inductance that transformer has?

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

12v car socket -< <plug-- LC filter -- socket< <---plug: any portable
audio device

You'd think some mfr would make something like this...

Thanks,

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