Alternator noise to power AMP

Ben Swann benswann at
Tue Apr 5 14:17:12 EDT 2005

Well I took a brief look at my wiring on the amp side.  The cables do have a shield ground - it is attached to the amp ground point.  Is this bass akwards.  I don't recall if I grounded sheild at the stereo or if the cable had a sheild ground wire.  So from what i understand so far, it is best to have the radio/pre-amp side of the RCA cable sheilds grounded and not the amp side - correct?

Hope I don't have to re-run these cables.

  ----- Original Message ----- 
  From: Thomas Hall 
  To: quattro at 
  Cc: benswann at 
  Sent: Tuesday, April 05, 2005 8:47 AM
  Subject: Re: Alternator noise to power AMP

  The RCA circuit of some amplifiers also create a "gound loop" which will also cause this noise.  If beefing up the power wiring fails to remedy the issue, then a RCA ground loop isolator should assist in knocking out the noise.  It is simply a noise filter that inserts in the RCA line between the radio and the amplifier.  This is commonly found at Radio Shack and i have even seen them in Wallmart for a little over $10.00.  Also make sure you are using high quality RCA cables to minimize resistance and to better shield against signal loss and against noise. While capacitors are quite effective they are also very dangerous when charged, I would try the suggested methods before resorting to a large capacitor.  IMHO a capacitor is a kludge against inadequate power to the amplifier in 90% of cases.  I would be happy to assist in helping you isolate this offline if you need it, I have been installing higher end systems since the 80's with over 300 installs under my belt.


    > > 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.
    > > 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...

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