checkmate1996

Jim,

I always stay away from snake oil products like suppresoors's, etc. To me, they are just band-aids for a bad install or something failing. I would try and trace your grounds. Remove components, i.e. amp and see if things get better. I always make sure I am using a defined ground point on the 928, large gauge ground wires, clean grounds and heavy dty, insulated RCA wires. I don't run electric and RCA wires together. My 79 sounds crystal clear.

However, when I first picked up my 79, the PO used the the negative post of the battery as the ground! Uggggggggggggggggggggggggggggggh! This caused MAJOR WHINE! I was laughing my butt off when I realized this ...

Alan

Chuck - the bridge is just a shorting plug to replace the supressor - it certainly won't help - at least - not unless you swap the supresssor to the other supply after installing the bridge.

An alternator/regulator that aren't working perfectly can create noise without many other side effects - if your alternator droops right to 12V at idle with just the cooling fans on you may have a problem. The best way to test it in the car is with an oscilloscope monitoring the voltage at the jump post - looking for a major spiky noise ripple. This can also be related to a weak battery as that affects the smoothing of the regulation - in this case weak means permanently damaged with higher internal resistance - this would likely manifest itself as notably slower cranking when starting...?

Assume this is on your GTS? stock radio head or upgrade? & had the radio ever been swapped for something else?

Many installers seem to like to rewire the 928 radio connections... Note that rewiring the radio feed from the CE panel somewhere creates noise almost every time - note there is no fuse in the normal supply that comes straight from a special terminal on the ignition switch, (yet one more reason to keep the installer monkeys away from your car).

Alan

Chuck Z

Thanks Alan. Yes, it is my GTS and it is the stock head unit and I am 99.9% nobody has been in that area before. I have all the alram cards and misc info associated with the stock radio. I will look into getting the alternator tested.

Alan

Brad,

Not sure where you get this 'snake oil' idea - your car likely already has a supressor and it has a Porsche part # stamped on the side... This is an effective and standard way to block noise - which is actually pretty inherent in a car (8 spark plugs shooting off at high speed and energy just a short distance away - and in this case not even shielded with steel).

As to grounding - avoiding ground loops would suggest ideally a star topology from the battery ground post - in practice this is a pain to do and the chassis is usually a solid enough ground that a remote star connect to the chassis is good enough...

I'd suspect that whoever connected to the ground post of your car was attempting to fix a noise issue. It may indeed have done no good at all if it was in fact +ve supply induced noise (e.g. the alternator possibility or a lack of a correctly wired supressor).

Stock the 928 isn't strictly wired as a complete star as above - but as I noted above for a persistent issue it could be a way to reduce ground induced noise.

Most often using (& if needed cleaning) the stock ground points is solution enough.

Alan

pcar928fan

My S4 went in to the shop once and they were screwing with the climate control module and some othr stuff and it came back with a damn whine. I changed the radio from the broke A$$ CD-1 to a CDR-220 and STILL have the whine. Would love any more thoughts on this. I didn't realize there was a noise suppressor in line so I might check/change that...

Any other new thoughts on this guys???

depami

They messed up a ground while screwing with the climate control.

I have always run my audio power (+ and -) directly to the battery and have never had a problem.

SQLGuy

There is supposed to be a choke in line (it's mounted to the torque tube hump under the center console)... could have been bypassed by later wiring.

Grounds are the other question. What are you using for amp(s), and where are they getting their ground(s)? An easy solution (though good ones can be a bit pricey) would be to install ground loop isolation transformers on the signal lines between the head unit and the amps.

Schocki

Had the same problem in my GTS. Installed two in line noise supressors from WalMart with RCA cables. Since then no noise problems. Cristal clear sound.

Pagnobito

Car I worked on updating the head unit to a newer version, replacing speakers and adding an amp resulted in noise. First thing I used was a different source at the RCA lead head unit end and no noise, ruling out the amp, speakers, x-overs and wiring between so the head unit was being affected.
I installed a choke on the permanent live to the head unit and problem solved.

There are far too many earths to be checking and alternator stuff to think about on someone elses car when a choke fixes the issue. RCA filters can affect the sound, chokes on the power smooth the ripples you hear as whine.

SQLGuy

One other thing you can try in these situations is changing the signal cable grounding to be from the signal source end only.

A lot of times this noise is caused by current flow looping along the grounds between the amp and the head unit (head unit is grounded to chassis near it; amp is grounded either to chassis near it or back to battery; signal cables have ground shielding running between the head unit and the amp - this allows current to loop around through chassis and back through the signal shielding, inducing noise into the signal).

Anyway, an easy way to see whether this is the cause is to disconnect all but one channel of the RCA connectors at the amp. Then, with the volume up a bit, the engine running, but no music playing, you should hear noise; pull the remaining RCA connector out a bit until its ground (outer metal layer) is no-longer in contact with the amp's connector. If the noise goes away, play some music and verify that this sounds OK (with the connector still almost disconnected). If this solves the problem, the more permanent solution is then to open the connectors at the amp end and cut the shielding where it's soldered to the connectors' shells (note that not all cables are suitable for such modification - a lot of them, especially the cheaper ones, have molded connectors).

pcar928fan

We will check these, but the stereo was 100% stock till I changed it out after the buzzing had started. I replaced the stock CD-1 (or was it CD-2??? The ones that are not fixable and most don't work anymore) with a CDR-220 and hoped we would fix the noise... Didn't... We need to get back in there and see what is up. Maybe change up a ground to start and see how that goes. Then maybe filters.

pdejong

I had the same problem for a long time. I don't know much about stereo systems, but here's what I did and that fixed the problem in my '90GT:
I did 2 things so I don't know which fixed it:
1. I added a separate ground wire from the radio frame directly to the chassis.
2. I separated the power wire from the speaker wires and the RCA wires (to a separate amplifier). They were run together and I moved them about 8 inches away from each other

I never knew what to do, but I wish I had thought of this sooner. It took care of an annoying alternator whine I had for years,

Peter deJong
'90 GT-TT

TheoJ

place an interference filter?
Don't know why but some cars do not have those...