Re: Grounding radio/popping

["Al Powell" <APOWELL@agcom.tamu.edu>]

> OK, let's try again to solve this popping noise problem when the radio is
> turned on or radio channels changed. 
> 
> First, let me thoroughly explain the radio system.  The stock radio for 
> the 86 5000CST is a Blaupunkt, which outputs amplified signal to the 
> front, line out to the rear.  In the trunk is an Audi 
> "booster"/amplifier for the rear door/deck speakers.  

OK - this conforms to the factory diagram for my 200 - it shows a separate 
factory amp for the rear speakers.

> The Blaupunkt head unit had 8 speaker leads, 4 for the front, 4 
> for the rear, i.e. LF+, LF-, RF+, RF-, LR+, LR-, RR+, RR-.

That much is conventional....gee, a surprise!!!!!!
 
> The NEW head unit is an Aiwa. [snip]  There are only 2
> negative leads, with 4 positive ones -- the negative ones are shared by
> front and rear.

So you have:
One - Left side negative lead, and:
One - Right side negative lead.
 
> In order to supply line-out to the rear "booster", the Crutchfield "Power
> Matching Adapter" is used (Item 166PWRMTCH, for those interested).  The
> description that comes with the installation sheet is as follows:  "The
> 166PWRMTCH is an interface that allows a receiver with a floating ground
> speaker output to be installed in a vehicle that is equipped with a
> factory amplifier or common ground speaker wires (less than 8 wires) that
> are connected to the chassis of the vehicle."  I guess that this is what
> fits the bill, right? 

It does sound correct for this installation, as you need to reduce 
amplified feed to line level.  If I remember correctly, the PWRMTCH 
gathers all speaker grounds into one black wire at its output.
 
> The diagram suggests attaching all the NEGATIVE leads from the speaker
> harness to the chassis of the radio, as a "signal ground".  It also
> suggests to tape off the negative speaker leads from the radio, as they
> will not be used.  

The second part of your comment is as per the verbal instructions I received 
from Crutchfield when working with this adapter.  I don't recall on 
the first part.

> However, I had to use them for the front speaker
> circuits, so I didn't do this...The diagram also shows how to use the
> adapter for both front and rear.  However, I only need it for the rear,
> Crutchfield said to only wire it into the rear.  Here is how I wired it: 
> 
> Radio Ground wire -> black ground wire for the old radio
> 
> Speaker wires:
> 
> Radio LF+ -> Speaker LF+
> Radio L- -> Speaker LF-
> Radio RF+ -> Speaker RF+
> Radio R- -> Speaker RF-
> 
> PWRMTCH LF+ input, RF+ input have been taped off.

Everything good so far!
 
> Radio LR+ -> PWRMTCH LR+ input
> Radio RR+ -> PWRMTCH RR+ input
> PWRMTCH LR+ output -> Speaker LR+
> PWRMTCH RR+ output -> Speaker RR+

Looks good so far - nothing to argue with.

> Speaker RR- -> Grounded to head unit
> Speaker LR- -> Grounded to head unit

These two leads seem to me likely to be the source of the problem.  I 
don't think they should be grounded to the head unit.
 
> Now:  Seeing as I DON'T have the type of radio as they describe, maybe I 
> shouldn't ground the speaker negative leads to the radio at all, but 
> instead solder them in with the the radio R- and L- leads in the fron 
> speaker circuits?!  This is how I would have worked things if there was 
> no stinking amplifier...like I said, worked fine in the Honda.

Since the radio is already grounded to the PWRMTCH adapter thru its 
black ground wire, I would try connecting the negative speaker leads 
directly to the negative speaker leads on the radio as you sugest.  
If this doesn't work, I would also try connecting them to the 
negative speaker wire inputs into the PWRMTCH  adapter.  It should 
not cause any damage to connect those speaker negative wires 
together.

BUT - The more I think about it, I would try connecting them to the 
adapter first, THEN try connecting them to the speaker negative wires 
coming from the radio.  Connecting them to the radio wires may result 
in the fader working improperly.

Try it and post again, Mr. Preston!!


Al Powell                           Voice:  409/845-2807
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