Ground loop problem in aftermarket stereo install, 94 S4

[John Lagnese]

Ground loop isolators. Its just a capacitor. The only time I needed one was with
a portable CD player. It had a pre-amp input on the radio. The isolator hooked
up in line. It had RCA jacks on both ends.
John

Duncan Wood wrote:

> 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