Re: Grounding radio/popping

[Preston Brown <pbrown@econ.yale.edu>]

On Tue, 2 Apr 1996, Al Powell wrote:

> Preston - I don't know what to make out of this speaker mess.  
> To clarify: You don't have the Bose system, right?  And I do.....
> 
> Can you re-cast your diagram in this (net-proof) layout?

OK, let's try again to solve this popping noise problem when the radio is
turned on or radio channels changed.  I apologize for my crappy ASCII art
for the last two diagrams.  Your suggestion makes sense. 

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.  Nothing is Bose, as 
far as I can tell.  They must have introduced the Bose stuff a few years 
later.  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-.

The NEW head unit is an Aiwa.  It has quite a bit more power than the old
stock one (17x4 Watts), but only 6 speaker leads.  There are only 2
negative leads, with 4 positive ones -- the negative ones are shared by
front and rear.

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? 

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.  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.

Radio LR+ -> PWRMTCH LR+ input
Radio RR+ -> PWRMTCH RR+ input
PWRMTCH LR+ output -> Speaker LR+
Speaker LR- -> Grounded to head unit
PWRMTCH RR+ output -> Speaker RR+
Speaker RR- -> Grounded to 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.

---
 -Preston Brown
  preston.brown@yale.edu