[s-cars] Bose audio system, iPOD interfacing via cassette in.

[Postupack, Jeff]

Hi

So I was obsessed over the weekend.

Several people wrote to me WRT my project to replace the cassette input,
with the iPOD output.
My initial goal was to retain the CD for now and add iPOD, or Philips
GoGear.

After spending an insane amount of time searching, I never did find the
schematic.

Ti Kan's site was very helpful to document the various Audi Bose models,
I had a thread from Frank Amoroso dating 1998, that was a deadend, no
schema in sight.
Turns out this headunit is built by Blaupunkt in Spain.

Anyway, I preceded to regenerate the schematic manually and now have the
cassette interface
written, I think it is accurate.

Trouble now is 2 fold.

1- There's a T.I. 4558 dual opamp receiving the L/R tape inputs and
amplifying it a lot.
Cassette head outputs are tiny and much lower signal than even the iPOD
headphone out. Therefore the iPOD can clip the 
Amplifier. Plus this circuit is unipolar, meaning a DC offset on the
audio signals. This is a bias for the tapehead I think.

2- Tape heads also require equalization ( high end boost) and this
interface has the typical curves built in.

I went ahead and fabricated an interface circuit anyway and plugged in
the iPOD.  

The sound quality was not good.

Making this work will require changing that cassette circuit to be lower
gain and flat EQ. Can be done as the SMT components are on one side.

<< My recommendation is to follow other S car owners who placed relays
at the CD Line outs, to select the iPOD line outs with a switch. >>

Check out the iceLINK from Dension for a well designed iPOD mechanical
adapter.

Personally, I am much more interested in the GT3071 rave that's going on
these days, and will go do that instead.

If you want the schematic, email me.


Jeff Posto