[urq] Re: Alternator noise to power AMP
Buchholz, Steven
Steven.Buchholz at kla-tencor.com
Mon Apr 4 21:03:49 EDT 2005
... I'm with Huw here. My car came with a funky Sony deck/amp set up
... now that I'm thinking about it, it may well have been the ground
noise issues that led to the PO setting up such an odd configuration. I
tried lots of the usual fixes ... I installed an isolation transformer
in the line level signals going from the deck to the amp ... which
*should* have fixed the issue, but did not ... in the end what I did was
to run a dedicated set of power and ground leads from the battery up to
the deck in the console, with the amp getting power and ground from the
same point. If you still have a problem you might need to make sure the
antenna is isolated from the vehicle ground as well. The noise is
without a doubt created by a "ground loop" where there are multiple
ground paths between two points, and the voltage induced in the ground
by the current creates a voltage "signal" which is then amplified by the
auxiliary amp.
Another approach that should work would be to locate the amp in very
close proximity to the deck. I have the amp nestled in that box in the
left rear seat armrest is, so that was not an option for me.
Steve B
San Jose, CA (USA)
>
> > After recently wiring in a power amp to the rear speakers for my '83
Ur
> > Quattro, there is a whine being picked up by the RCA inputs to the
amp. It
> > is not picked up by the stereo, front speakers, or if rears are
wired
> > directly to the stereo without an amp.
> >
> > How can I eliminate this or filter it? I am using high quality RCA
cables -
> > don't know if they are sheilded.
>
> Try rewiring your grounds so they are all attached to the same place.
> Also, "directional" RCA cables (shield only attached to ground at
> pre-amp end) can help. On my coupe I ran ground cables forward from
the
> amps to the shifter mounting bolts, and also grounded the head unit
> there. On my 90Q I ran a ground wire back from the head unit to a
> bumper mount bolt in the trunk where I grounded the amp. Neither car
> has any appreciable ignition/alternator noise, which is nice.
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