Ground loop problem in aftermarket stereo install, 94 S4

[Duncan Wood]

Message: 5
From: Tim Sexton <5kcstq at codenet.net>
To: quattro at audifans.com
Date: Mon, 29 Apr 2002 09:28:49 -0600
Subject: Ground loop problem in aftermarket stereo install,  94 S4

Hello All,
    I have just installed an aftermarket stereo system in my 94 S4, and
have what I think is a ground loop.  However, being new the the car
stereo world, I am going to run it past some of you experts out there.
 The system consists of:  1.  Blaupunkt Munchen head unit  2.  Kenwood
KAC Q74 4 channel amp  3.  Blaupunkt CDC A08 changer  4.  Blaupunkt 5.25
components, front doors  5.  Pioneer TSA6999 6x9 rear fills.
    What occurs is,  with the engine off,  I can hear loud static and
electric motor noise when the head unit is in CD mode.  When I change
tracks on the CD, it sounds like you can hear the arm moving.  Also,
there is less static, but still audible, when the head unit is in tuner
or changer mode.
    For the amp, I pulled 12v directly from the battery, and pulled it's
ground from a tail light ground.  For the head unit, I pulled 12v from a
wire in the previous harness, and pulled ground from a ground point
under the dash.
    Does this sound like symptoms of a ground loop?  How does one
correct a ground loop?  What exactly causes a ground loop?

Short answer:Voltage difference between the grounds.
Make sure they're really good, esp. the amps, use a thick wire with acrimp
on the end & a serrated washer to attach to the chassis (or if you're really
keen the battery, in which case run it parallel with the live wire). Check
the screens ob the audio lines are connecetd properly & the plugs are making
good contact.If the hum's really stubborn you can add audio balancing
transformers at one end or both end of the audio cable, the cheap £5 are far
better than the audio response of a car amp.


In addition,  I had the exact same problem when I used the Munchen to
power the factory Bose junk via the pre-amp outs.
Thanks for any advice you can share.
Tim Sexton