speakie

New to this so go easy.

Took out the concert unit in my A3 1.8T. Fitted an ISO adapter for installing aftermarket head-unit. All worked well except, whenever I connect the 12v supply for the stock amplifer for rear speakers and sub, I get a buzzing noise through rear speakers. Does this even if headunit is off or even removed from ISO adapter.

Took it to an installer to check over. Told that this happens in one or two of the cars and they cant to anything. Tried new earthing for amp etc.
Someone must have seen and beatten this.

Please help!!

HIS4

Need a little more information about the installation to diagnose the problem but this might be a possibility. The rear speakers have their own amplifier and are fed a low level signal from the stock head unit. So now that you've installed an aftermarket head unit, what kind of signal is the rear speakers getting. If they are hooked up to the speaker level outputs of the head unit, you are giving the amp a signal it wasn't meant to handle. You would either have to make a modified set of RCA cables so that you can send low level signals to the rear speakers or just disconnect them. Just a guess but I hope it helps.

speakie

The buzzing occurs when supplying the rear amp with the + supply - even when the head unit is removed if the amp supply is powered up the buzzing ocuurs. Even the installer couldnt do anything with it - claiming it was an incompatibility that occurs in or or two cars.

I have more or less decided to bypass the rear speakers and amplifer and fit decent speakers set in a new parcel shelf anyway.

WClark

You might try an experiment. Jumper the line level + leads to the grounds (brown wires probably) at that adapter with the head unit disconnected. Try powering up the rear amp and see if the buzz goes away. If it does then the adapter or head unit probably isnt cleanly connecting the line level + leads to a low impedance source.