Replace Concert I Head Unit With Aftermarket Unit

[Peter Lavoie]

Hello All,

I have a 1999 Audi A4 with a Concert I Head Unit (single DIN), CD Changer (which had failed) and a Bose 8D0035225A amplifier. I love the car but wanted to change to something more modern on the communications/entertainment side of things so I could use bluetooth streaming, handsfree telephone, digital music, DVD, satellite radio and navigation. The idea was to use the OEM speakers and amplifier. This is not for those who wish to have window-neighbour-bolt-rattling superbase.

Attached is a colour-coded schematic of the terminal blocks of the Concert I, the Bose 8D0035225A amplifier and an illustrative replacement head unit. The schematic indicates which wires to cut on the Concert I terminal blocks to have the replacement head unit communicate with the Bose 8D0035225A and produce acceptable sound out of the speakers.

When wiring to the speaker inputs at the dash of the car it is important to use the pre-amp outputs of the replacement head unit which are typically RCA style female phono connectors. Also, there is only one "common" ground wire at the terminal block (for the shield wire on the RCAs) which I connected to all four male RCA terminations that I made after cutting the wires off the back of the Concert I head unit terminal block. I am not sure if this is necessary but my thinking was that the amplifier should have a common reference ground voltage level for the four input channels, otherwise the ground level could "float".

I have not yet solved the mysterious puzzle of getting the high frequency front door speakers to operate, but I believe these to be powered by an amplifed signal directly from the head unit. I think they are LF and RF in the Concert I terminal block but are not wired as indicated with a + and a - terminal. If anyone gets this solved let me know.

I hope this helps those who want to perform a similar upgrade, happy motoring.

[Yoyo42]

Thanks for that, I was trying to figure out which Autoleads lead to get but I might just make my own now.