Chuck Z

Just did the foam repair on one of my rear woofers and the stock stereo system sounds really good..... with the engine off anyway!

Ever since I have had the car occaisionally there is engine noise through the stereo. Is there a fix for this problem? I do have another stock head unit (NIB with code cards I bought on eBay) as well as a stock amp if the only fix is to replace the original stuff. I am hoping there is a fix so I do not need to replace the original pieces.

Any help would be appreciated.

Thanks.

F451

Same problem for me with a stock (I think) stereo with cassette (cassette - wa-hoo!) on my '88 S4. I haven't looked into it yet as I have other more pressing issues, but I seem to recall there is a noise suppressor of some type that you can install on the power feed wire. Not sure if it is snake oil.

I'll have to do some research on it now that you mention it. Been meaning to look into it since I bought the S4. Will be monitering this thread as I'm sure the stereo experts will chime in soon.

bronto

I think this is an indication that something's not grounded properly(?).

camboinc

check your alternator. i just replaced mine and the wretched whine completely disappeared.

ROG100

Chuck,
On the s4's there was a supressor down near the amp next to the passenger seat.
I checked my GTS and there is NOT one there anymore.
Checked the 94 GTS wiring diagram and it shows a supressor, however it is not fitted with option M331 which is the combination CR1 with the rear CD changer.
Thats not much help I am sorry.

I am not an expert but maybe an in line noise filter (radio shack) in the power feed to the amp.

Someone like Alan would be a more helpful person to chime in here.

F451

Found this on Crutchfields site. Seems like useful info:

http://www.crutchfieldadvisor.com/IS...noise_faq.html

Kevin in Atlanta

I have been fighting a whine since I installed my MB Quarts. I had a whine at the speakers without them being routed to the amp. Ended up moving the x-overs from under the pass seat to next to the computers. That solved some of the whine, not all. Now the whine is coming from the rear speakers. Agravating.

Interesting that battery level can contribute to whine. I am going to look their tonight. I think mine is low or at least that was suggested by my ex-mechanic because it took several cranks of the starter to fire up ths GTS.

I would like a recomendation for aftermarket noise suppression.

Kevin

the flyin' scotsman

The noise could be from the 'unclipped' ac output from the alternator. The basic configuration of the rectifier output unless fully supressed results in noise in our more modern stereo systems.

Adding a noise suppresor to the main power feed as well as providing good grounds should cure the issue.

911Dave

The problem is that your exhaust isn't loud enough. Removing the muffler and resonator will resolve the issue.

John Speake

There are two possible causes of whine from the alternator being introduced into the stereo.

1) In the main battery feed, a series choke should be used.
2) By the stereo ground conenction having some common path with the alterator curret to the battery.

Try a series choke first, in the battery feed.

Chuck Z

On another board I found a similar post about this topic. The post refrenced a noise suppression relay XXI. Thoughts?



XXI Interference Noise Suppressor 928.618.223.00

F451

Interesting. Another possible relay trouble source for the 928. LOL!

Alan

Chuck - the one on the CE panel is a different supressor/ different purpose - forget it...

Whine can be casued by an alternator on the way out - if it once worked fine and all is still stock - this might be a suspect.

For aftermarket someone either screwed it up (often poor or badly placed grounding) OR the head unit works differently than stock....

There is usually either the supressor near the amp location or one in the console below & left of the radios slot (Roger your GTS has it here) - you can see it clearly (if its there) if you remove the LHS console carpet panel (looks like a transformer but with only 3 connections).

As John says you need an inductor(/choke*) in series with the supply to the radio to blobk noise. Some modern radios need a choke in the constant 12v line instead or maybe also with the switched 12v line... the stock config usually has it in the switched line only. You can buy inductors for this in audio stores - but the one in the car is a good one - use this one on the line that needs it most - it also has a diode spike protector to ground (hence 3 terms) - helps protect the radio.

* incidentally Porsche calls it a 'throttle' sometimes in the wiring diagrams - a bit of creative translation...

Alan

There are also other things you can do - like run a seperate ground back from the head to the battery (or Amp) and more... but start with the obvious...

If you have realy big power in the headunit or amps you may need a large decoupling capacitor for the audio - stock systems should not.

ROG100

Found this in the 94 wiring diagram.
Shows the supressor without the Cr1 and CD chager M331.
Also a bridge with M331.
Alan will be able to interpret that I am sure

Chuck Z

Jim B @ Eurowerks has mentioned a bridge as a possible fix in the past. Wonder if this is what he was referring to.

Alan, any other signs of an alternator issue? My car has done this ever since I bought it 7 years ago and has shown no abnormal electrical symptoms other than the radio noise.