Kitchen soldering: Adding a line-in to the Audi Concert II head unit.

8 04 2011

OK.  Love the Bose factory stereo.  Head unit has a CD changer in the head unit, and a 6 CD autochanger, but no line-in or MP3 support.

So I’ve been burning CDs for the first time in about a decade in order to get my fix of Let It Bleed and my usual podcasts…

There are a number of products designed to let you add line in to factory stereos but they all appear deeply average, with no real ID3 tag support – plus you lose the autochanger.  Not good enough.  I’ll settle for managing the media on my beloved HTC Desire, and a decent line in.

So, line-in is just a couple of connections from the autochanger, right?

So once we’ve identified which connections on the big fat plugs on the back of the head unit are left/right in, it should be fairly straight-forward.  Hmm.

Then I came across Jeff Bipes’ stuff here:

Great – it’s doable.  I read this then hit up the kitchen with a bench PSU that my Dad made for me about 25 years ago…

After a quick trip to Maplins, I decided to use a DPDT relay rather than the 3PDT one Jeff used.  Makes the wiring simpler, too.


Basic premise is you find the L/R outputs from the CD changer and use a relay to allow you to connect either a line-in or the OEM CD changer to the head unit’s CD changer line in connections.  I used a micro toggle switch, and a 3mm red LED to indicate line-in selected.  This way you get to keep your autochanger, and fit a neat little toggle in the ashtray to fool the head unit into playing a 3.5mm line-in input when you click the toggle.


Checked it out on the kitchen worktop and it looks good: click the switch and the relay switches the input.

I test-removed the TT’s head unit using some £3 eBay-sourced removal keys and it came out OK.  Tomorrow, time permitting, we’ll start hacking the OEM loom to wire this in.

The idea is to fit the jack plug , LED and switch similarly to Jeff’s example.






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