Alternator noise to power AMP

Huw Powell audi at
Mon Apr 4 19:44:26 EDT 2005

> 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.

> Also, what kind of capaciter would be good to eliminate powere clipping?

Although I know people seem to love their 1 F etc. caps in the trunk, a 
good heavy power/ground cable ought to be enough - your battery is one 
heck of a charge storage device...

Huw Powell

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