[s-cars] stereo upgrade

Sun Mar 4 15:46:26 EST 2007

Aaron,

What you have is an ignition noise filter (choke) that goes inline with 
the positive supply. Most aftermarket head units have one of these built 
in and an additional one will not make much difference. You should not 
assume that the RCA shields are grounded as the head unit could have 
internal isolation.

One easy way to determine if the noise is coming from the head unit or 
amps is to hook up and external battery powered device such as an MP3 
player to the RCAs. If you still have noise, the issue is with the amps or 
cabling to the amps. Another good test is to disconnect the amplifers one 
at a time to see if the noise is origininating from one of them.

The brown wire appears to be the line-level shield ground from the 
schematic, but IIRC that was the one that was giving me problems. I will 
forward you thisn schematic.

 	-Kurt

On Sun, 4 Mar 2007, Aaron Ryba wrote:

> Well, I already tried having a dedicated ground for the stereo and also 
> tried it with the ground loop isolator as well and still the noise 
> persisted.
Again, I am not using the RCA preamp outputs due to the voltage 
requirement of my line-level converter. My head unit only has one ground 
for the whole wiring so I assume this means that the RCAs (if I were to 
use them) are tied to the chassis ground by default. But a moot point for 
me? The line-level converter does have an input/output ground connection 
with different settings for RCA-out and "Wired" (line)-out. I guess it 
wouldn't hurt to try grounding this output connection.

I just looked at what I thought was my ground loop isolator and it is in 
fact a "In-Line Noise Filter" specifically made to connect to a 12v 
connection between the source and the device. Is this not the same thing 
as a ground loop isolator? The innards look just like a coil wire and a 
capacitor. Again, I had to get a "wired" style one since I can't use my 
RCA preamp outs on the head unit.

This just seems a bit weird since it looked like I had repaired my hacked 
wiring back to stock and my head unit is wired through the factory 
connections.  I checked the repaired factory line-level shields and they 
are all properly grounded. Did the stock head units independently ground 
the "RCA" leads to the chassis (other than the line-level shields)? There 
is a brown wire at the back of the stock head unit which doesn't seem to 
be listed anywhere in the wiring diagram. The connection looks like it 
just grounds the chassis of the stereo?? Or is it possibly part of the 
antenna? I just left it disconnected.

Thanks for your advice.

Aaron

----- Original Message ----
From: Kurt Deschler <desch at alum.wpi.edu>
To: Aaron Ryba <aaronryba at yahoo.com>
Cc: s-car-list <s-car-list at audifans.com>; calvinlc at earthlink.net
Sent: Sunday, March 4, 2007 7:22:07 AM
Subject: Re: stereo upgrade

Aaron,
In my case, I think that the ground loop was between the ground points at 
the head unit and the groud point at the harness or amps. Eliminating the 
ground point at the head unit alone cured my problem. I was thinking that 
you would at least need to do this, then possibly add a ground loop 
isolator as well if the RCAs on the head unit were tied directly to the 
chassis ground. You are not going to hurt anything if temporarily remove 
the ground from the RCA to test.

      -Kurt

On Sat, 3 Mar 2007, Aaron Ryba wrote:

> 
> I have the popping but not the ground problem.  Did the ground problem come
> when you put the in line converter in?  The best ground I can find is the
> wire that goes to the original head unit...it is a very good ground.
> --Calvin

No, the problem was there before I installed the line converter.Not sure about it before new head unit since
the original head unit was code locked. Since my Alpine head unit has only 2v preamp outputs and not the 
required 4v to run the preamp/RCA/patchcords-style connections through into the line converter 
(as required by the converter) it is all speaker line-level wires from the deck to the 
converter to the factory (repaired) wiring.

> My 200 had very bad ground loop feedback with an aftermarket head unit 
> hooked up to the Factor Bose amplifiers. The problem turned out to be that 
> I had grounded the line-level shields to the chassis ground when I 
> repaired the harness (it was butchered). Removing that ground connection 
> and using only the RCA grounds solved the problem for me. Depending on how 
> the line-level shields on your head unit are grounded, you may also need a 
> ground loop isolator.
>      -Kurt
   Well, I was thinking the factory line-level shields might be a problem however the Bentley
wiring diagram shows that those line-level shields for both front and rear are connected
directly to the common chassis ground through wiring harness #133 which is also connected
to a ground connection wiring harness #33 behind the instrument panel along with the ground
connections for the Speaker Power Supply relay J225, 2 grounds for the head unit T8/2 & T8/8,
and the ground connections for all three amps.

Maybe this ground connection needs a bit of repair or possibly some of these have been butchered
to be grounded independantly. From what little I know about ground noise it is caused from feedback
through multiple ground connections.

I bought a ground loop isolator and hooked it up to the head unit power supply and nothing, noise persists. Since I
can't use the RCA preamp connectors I couldn't use a RCA style ground loop isolator like radioshack sells which
I assume goes between the head unit and the amp. This one I got is actually a power supply ground loop isolator
with an in, and out and a ground wire. I tried it with the main power supply line to the head unit, maybe I need
to try it with the ignition/accessory turn on lead to the head unit?? Or would I need one before each amp as well?
It just seems a bit odd like the factory wiring is not quite back to factory yet since not that many other people
running the same setup as me have had this problem. I would rather fix it right than bandaid patch the problem with
an isolator.

My line-level converter has a ground in and out so maybe grounding that may help!!???

>> -----Original Message-----
>> From: s-car-list-bounces at audifans.com
>> [mailto:s-car-list-bounces at audifans.com]On Behalf Of Aaron Ryba
>> Sent: Thursday, March 01, 2007 8:25 PM
>> To: s-car-list
>> Subject: Re: [s-cars] stereo upgrade
>>
>>
>> I am running a new alpine head unit to the stock amps and speakers through
>> the stock wiring using a fabricated connector.
>> The volume/gain and pop turn on problem was solved with an in-line converter
>> for about $25.
>> The problem I am having now is bad ground noise. I have tried grounding the
>> head unit directly to the chassis but no change.
>> I assume there is a bad ground in the harness somewhere for the three amps
>> in the stock "BOSE" system.
>> I had to piece back together the factory wiring since a previous owner had
>> cannibalized the stock common ground speaker wiring to use as speaker leads.
>> Has anyone had this bad ground noise problem with a new head and stock amps
>> and speakers? Maybe it is just my crapped out wiring.
>>
>> Thanks,
>> Aaron Ryba
>> 95 S6 138k

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