Replacing Blaupunkt/Bose Head Unit...

[DICK MEYER <RSM@arlvax.arl.psu.edu>]

Maybe this has been covered before, but...

I just replaced the Audi/Bose Blaupunkt Delta unit in my V8 Quattro when
the on/off switch finally crapped out.  Even though Audi will do an
exchange for $85, I decided to go for something better.  

When I wired the line outputs of the new head unit to the inputs of the
Bose powered speaker units, I got a huge electronic "thud" each time
the pre-amp engaged, and a lot of alternator whine.  Upon further 
investigation, I found that the inputs of the speaker units were at a
potential of five volts (for some strange reason).  The problem was
solved by adding an isolation transformer between the line-outs of the
head unit, and the speaker line-inputs.  The isolation transformers are
readily available at any Radio Shack and are called ground loop isolators.

Any idea why Bose/Blaupunkt did this?

Dick Meyer
Applied Research Laboratory
Penn State University
State College, PA
rsm@arlvax.arl.psu.edu