Interference

[S3Steve]

I have justed started to get interference noise coming from the rear speakers of my S3. It appears to be alternator related as the sound/pitch changes as the revs increase. The noise is even present when the volume on the stereo is turned off. Its really annoying me

Has anyone come across this fault if so what was causing it?

 

[AndyMac]

If it's just the rears I'm assuming you have the standard non-Bose system. Also is it still present on radio and CD?
If it is then it's because the rear speakers (and sub) are driven off their own seperate amp inside the sub enclosure, which is why you still get it with the volume on zero.
It'll be an earth problem as 99% of all interference problems are, not helped by the fact that the pre-out wiring from the HU to the rear/sub amp isn't screened properly. The wiring is naked where it connects to the HU which is the closest point to the engine and I'm amazed everyone doesn't get the same problem. Easiest thing to try is earthing the HU:
If you can pull the HU out, or remove the glovebox, you can then get to the back of the HU. Try earthing the HU casing. Get a short piece of fairly thick cable, connect it to the back of the HU and then try different points on the car chassis with the engine running, HU on and volume at zero. Hopefully you'll find a point that stops the alternator whine (you will need to try different points on the chassis to get a good earth).
This worked for me when I had a similar problem with an aftermarket CD changer, and I even burned a CD with silence on it, so I could listen for the whine with the volume jacked right up.
If this doesn't do the trick then you'll probably need to investigate the wiring to the rear amp. Try moving the connector and wiring around on the top connector (multi coloured plug). The pre-out feed to the amp is the yellow part of the connector shown below:

It maybe the feeble screen connection isn't making proper contact.
If this doesn't work then unfortunately you need to get to the amp, which is buried behind a lot of trim in the boot.

 

[S3Steve]

Yes i do have the standard non bose system.

Strangely the problem not only occurs when the volume is at zero but also when the head unit is off. Is the audi amp wired differently to normal amps and not turned on and off with the head unit?

 

[AndyMac]

No it should go on/off with the HU. Are you sure a previous owner hasn't done a DIY job on your rear/sub amp? Sounds like they've wired it up to the ignition on rather than use the remote on from the HU.
Is there any seperate/additional wiring going to the red connector on the sub?
It's clipped to the front of the sub, so you should be able to see it just by shining a torch into the rear left cubbyhole.

 

[timps]

Yes i do have the standard non bose system.

Strangely the problem not only occurs when the volume is at zero but also when the head unit is off. Is the audi amp wired differently to normal amps and not turned on and off with the head unit?

When I checked the amp remote feed from my Concert II non-Bose (2002 A4 B6) with a multi meter I found the amp remote was only controlled by the ignition key and not by the head unit even though the wire comes from the head unit.

The head unit being on or off made no difference at all, only the key being removed made a difference, first I thought I made a mistake but I checked numerous times that I was correct before I used it to control my JL amps & crossover, I guess its one of the joys of the can bus system.

So it sounds like its the same on your 2002 S3 as it is the facelift model & IIRC it uses the Can Bus Concert II / Symphony II etc. same as my A4 although I have never personally checked a 2002 S3 only a 2002 Concert II on my A4 B6.

 

[AndyMac]

No it definately should be controlled by the HU on all Audi's. I've never seen a stock system where the amp switch on is controlled by the ignition, that is a bodge, probably resulting from either laziness or a duff remote on feed from the HU. The remote on is part of the same loom that feeds the rear pre-outs to the rear amp, so to by pass it for an ignition on feed is actually harder to accomplish, but nothing to do with the CAN-BUS.

 

[timps]

Andy I respect your knowledge on audio matters so this is a genuine question out of interest & not me being derisive in any way. Have you tested the remote from a 2002 Concert II with a multi meter switching the radio off & on by pressing the volume button alone and not using the key?

Or like me at first just assumed that it would switched off with the radio button seeing that this is where the wire comes from and the head unit supplies the power to this wire.

I tested my head unit and wiring several times as it struck me as odd and not the norm (nothing new to Audi then).

There was nothing wrong with my wiring or radio it was all stock no fault codes with vag com and the radio worked perfectly.

The radio is controlled by the bus system to switch on/off and You are correct that remote out is on the same plug that feeds the rear pre-outs to the rear amp but this is still live with radio switched off by pressing the volume button but leaving the key in the ignition on my car.

As far as it being a faulty remote amp feed that is still a possibility & I did think off that at the time but I discounted this because a faulty switch or relay would normally result in loss of power rather than constant power (unless they use a latch relay which I could see no reason for).

It was also killed by removing the key even though the radio was still receiving its own permanent power so unless it was drawing its power from the bus system the switch was working.

Seeing as S3Steve amp is also working with the radio off it’s either

1 how our 2002 Audi radios works
2 A faulty amp switch in the head unit
3 botch up job on S3Steve car

But without testing S3steve car we won’t know for sure but either 1 or 2 were definite in my case (I doubt no 2) so they also have to be possibility on his car as there is no botch up job on my car .

 

[AndyMac]

Well if that is the case then it's just plain wrong, unsurprising as you say on an Audi. Where did you check it at the HU or in the boot?
I've done about 20+ installs on A3/S3's and the remote on has worked properly on all of them. Can't remember if there were any Concert 2's but certainly Symphony, Delta and Concert 1's, and certainly on 02/03 vehicles.
All the CANBUS is doing is telling the HU when the ignition is on and when the keys are pulled out, just like a traditional accessory or ignition on feed to the HU. It's not changing the way the HU works, so can't understand:
1. Why they'd want it to work that way
2. How they could get it to work that way.
either way, even if the remote on is working incorrectly, the interference should not be there, which would seem to suggest there's something wierd going on with Steves system.

 

[S3Steve]

I will hopefully get some time to look at the car tomorrow so i will check the amp remote feed with a multimeter. I have checked all the wiring previously when fixing an aerial fault and can confirm it is all as it left the factory and not a botched up wiring job.

 

[S3Steve]

either way, even if the remote on is working incorrectly, the interference should not be there, which would seem to suggest there's something wierd going on with Steves system.

If the amp is permantly on with the ignition on then any interference it is picking up would be transmitted whenever the ignition is on.

 

[AndyMac]

Yes, but there shouldn't be any to start with

 

[S3Steve]

Yes, but there shouldn't be any to start with

Your not wrong there!

 

[timps]

I agree with you Andy it is just plain wrong, as to why they would do it I guess the same reason why the head unit capacitor discharges a negative voltage down the pre outs when you switch the head unit off.

As far as testing it was tested from the back of the head unit and in the boot I even checked for tracking across components that could fool a multi meter.

There was enough power to trigger one Sony crossover and two JLAudio amps to the on position.

Here are two different posts on Audi world with the same thing both with Concert head units (don’t always trust other peoples posts but seeing as I have tested myself)

http://forums.audiworld.com/audio/msgs/1265.phtml

http://forums.audiworld.com/audio/msgs/17163.phtml

So it does seem like it's by design or a very common fault.

As far as interference goes one other problem I came across was with one set of speaker wires which had worn out / been trapped behind a panel and one was grounding out on the chassis and this caused wine from an amp.

 

[S3Steve]

Had half the car in bits today looking for the fault. It turns out it is only coming from the passenger side rear speaker. I disconnected this speaker and the noise dissapeared. I subbed in another speaker to prove it wasnt a faulty speaker and the noise reappeared. so i now believe that it may be one of the channels of the amp that has gone u/s. ran out of time today to prove it for sure.