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Old 17th July 2010
Posts: n/a
Default Music player aux-in through CD-changer line-in

I posted this in the Lounge before but that doesn't seem to be a good place for any general technical questions. So I am re-posting here.

My '05 9-5 has the factory navigation system with the CD-changer. I currently have a Scosche FM modulator directly connected to the antenna-in at the back of the headunit but sound quality is pretty mediocre. I would like to add a music player/aux-in so I was browsing through the WIS and see what connections there are.

The CD changer is controlled through the i-bus but the audio connection seems pretty basic. Would it be this simple to tap into the line-out from the CD-changer to a 3.5mm jack on a music player? I know, it sounds too easy..

It seems the trick is to leave the rest of the cd changer connected so the head unit thinks the cd changer is sending the audio signals to the head unit, instead of the music player.

Would the audio signal be the same from an iPod as the cd changer? Are there better portable music players for balanced output (same as the cd changer)? I read up some on balanced vs unbalanced output bu I am just not familiar enough with it.

There was this thread a while back about the saablin project which seems very cool but it's more than what I need. I just want line-in to the head unit.
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Old 20th July 2010
gw0udm gw0udm is offline
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Join Date: Aug 2007                                                
Location: Birmingham, UK
My Saabs: Saab 9-5 Aero
Posts: 47

I should think that it would be quite easy to do what you want in the way that you suggest.

The main problem as you have identified is that you are wanting to feed an unbalanced source into a balanced input (ie the CD changer input on the head unit).

There are a number of ways of approaching this. I've not tried any of these actually in the car myself, but the principles are broadly applicable and any should work.

This site gives quite a lot of advice:

It talks about using a transformer as a means of interfacing the two, and quite a simple way of doing so is to use a common or garden ground loop isolator. These are in effect 1:1 transformers, and I believe people have used them with some success to convert unbalanced to balanced. THe problem is that you do lose quite a significant amount of signal. Whether this is enough to cause a problem I guess depends on your equipment, but it's not an ideal solution.

You've seen the Saablin project, and I can see that it is overkill. However, one part of it is quite a neat solution to this problem. The project has developed a fairly simple but effective converter - details here:

I believe you can order the custom PCBs directly, and a guy on there is offering some for free (dunno if he has any left though):

If you were up for the soldering this would provide a really nice solution. You could plumb this board into the CD changer audio connections as above, and just leave all the control wiring in place.

One final option is to use off the shelf kit. Converting unbalanced to balanced is quite commonly done in professional audio, as all professional mixing desks use balanced inputs and cables where possible. If you have something with an unbalanced output (eg a guitar or keyboard) you use a 'Direct Inject' or DI box to convert from one to the other. I see no reason why this shouldn't work for the car. DI boxes are readily available, but you would need either two boxes, or one with two channels.

Something like this would be good:

The disadvantage would be that you'd need quite a lot of bulky wiring - you'd need to terminate the CD changer connection in XLR connectors, and the output from each of the two stereo channels from your Ipod with 1/4" mono jacks. However, you could easily hide this away in the boot somewhere near the changer if you wanted.

I reckon any of these would be viable options. I'd be interested to hear how you get of if you try any of these.

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Old 20th July 2010
Posts: n/a

Thanks very much James, that was really helpful info. I'll need to research the options you suggested and see how I can make it work.
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