Strange car stereo problem - please help !

[maltloaf]

Hi all,

I'm in the middle of trying to install a Kenwood head unit to my Audi TT.

The TT has an amplified system driven by a Bose amp, which takes a set of RCA from the stereo and a power on signal wire just as any amp would.

I got the right adaptors and powered everything up and it worked fine, the amp was coming on and it sounded fine EXCEPT I was getting some alternator hum and also a loudish "Crack" noise whenever I changed source or turned the ignition on/off.

I have had that before and knew that a ground loop isolator would help so I went off to Maplin to get one.

Plugged it in and everything went weird. I got a weird screwed up reverb effect which sounds like you are listening in a church hall or something.

I thought that there may be a problem with the GLI (even though there isn't much to go wrong) so I went and swapped it for another one, which was exactly the same. I got a refund for it and bought one from elsewhere which was also the same.

I have been through stripping the amp etc this morning and checking all the connections especially ground connections and can't find anything wrong

I have taken two videos of the problem, one without the GLI in which the sound is normal and one with the GLI in which the reverb effect can be heard.

I am completely flummoxed by this. Haven't had anything like it before. The ONLY difference between the two is the introduction of the GLI, same stereo, same settings etc.

First video WITHOUT GLI (sounds normal)

https://www.youtube.com/watch?v=fSp3Zs8a2tQ

Second video WITH GLI (sounds like a church hall!)

https://www.youtube.com/watch?v=KEHrKv9Mapk

Does anyone have any clue what's going on here ? I am completely puzzled by it. Other TT users use the exact same solution (same leads, with a GLI) without issue.

Thanks,

malty

[evilsatan]

I had the same problem with my A3 but GLIs sorted my problem, but other people on audi-sport forums have the same problems even with GLIs installed. Do you have another HU you can try as a test? General consensus was a floating ground or something like that but I don't know how to hunt those down.

[maltloaf]

I don't have another head unit to try sadly, except the original Audi chorus 2 unit which works fine.

I have checked and grounded everything I can think of including the amp which is a bit of a cow to get to. I haven't run a separate earth to the head unit itself but I can't see why it would need it. I will try when I get home.

I can't get straight in my head why installing a gli would cause that effect and if I don't understand it I can't fault find it and I find that frustrating!

Cheers,

Malty

[evilsatan]

I find that frustrating too! Out of interest did your harness have RCA plugs attached to connect to the back of the HU? It took me ages to finally get a harness that worked with my full Bose. Shame you can't just run a standard RCA cable to test.

Just thought of one thing, I am sure when I was getting my ICE installed that I read about removing/relocating a pin from the Audi quadlock to resolve a sound issue, it might be that you need to do the same thing. On top of your chorus 2 should be a wiring diagram to help you identify the pinout, maybe note down which pins are connected on the Audi wiring and also check the same pins are connected on your ISO harness, post the list up and then search some of the wires to see if you get results?

I had to reconfigure some of my pins in the quadlock and also added the RCA section myself. Does your ISO harness have the pins labelled too?

[maltloaf]

The Audi harness is is in two parts, the first is adapted using an Autoleads PC9-410 which gives you traditional rca connections and a blue wire for amp control.

The other connector is half an ISO connector and plugs straight into the corresponding connector on the Kenwood's supplied harness. The RCAs from the Autoleads harness go straight into some RCA terminals on the back panel of the Kenwood (or via the ground loop isolator).

There's no quad lock interface on this TT.

I have been through the pinouts a zillion times but because I have looked so much I might be overlooking the same thing over and over.

When I next get out into the car I'll take some pics of everything and post them up, I still can't work out wtf is going on with this GLI though...

[maltloaf]

I have had a bit of a breakthrough! I used the HU to provide the power on signal for the amp BUT I fed in my iPhone via a 1/8" jack to 2x RCA lead via the GLI and it worked 100% without any noise so I began to suspect the head unit (which was second hand).

I then started earthing various points of the leads and the chassis and happened to touch a screwdriver between the HU RCA output and the HU chassis. It suddenly burst into life and sounded perfect with no noise, crackling, hum or otherwise so I think I know now what has been happening but not why it has occurred.

It would seem that there is no electrical connection between the head unit earth and it's RCA outer. I therefore presume to complete a circuit it needed the electrical path all the way to the amplifier and with the GLI in place that circuit was no longer there.

Is it normal for a head unit RCA outers not to be connected to the HU ground connection ? seems a bit odd to me.

To get this head unit working I am going to have to solder a flying earth lead onto the shield part of the cable on the HU side of the GLI and then attach it to a chassis screw on the head unit, or open the head unit and do the same internally.

A very strange one !

[evilsatan]

I know you got this sorted but here is the thread on Audi-sport, not exactly the same problem as yours but others finding your thread here might find it useful:
http://www.audi-sport.net/xf/threads.../#post-2508058

[Over Carl]

Never understood ground loops myself (never had any reason to) but here is my basic guess at what's happened (Please note, there is a fair chance I may be talking complete bollocks).

The Kenwood doesn't have chassis earth joined to RCA earth to separate the earths to prevent this kind of issue by isolating them. However the Amp doesn't. I'm guessing if you send the RCA's from the Kenwood to a domestic amplifier not powered by the car, it would work fine, but as the car's amp has earths joined but Kenwood doesn't, you have ended up with this issue.