The common question in AudiWorld forum: "How install a new head unit with the Bose amplifier/speakers?" My original feeling was that it is not going to be easy - the Delta unit got a non-standard faceplate and using an external trunk-mounted Bose amplifier. Also I wanted that new in-dash CD looks the closest to the Audi red night illumination. Still, I am feeling ok with factory Bose amplifier/speakers sitting in my A4 97. Delta head unit - what was really giving me a pain.
Bose AmplifierThe power stage of amplifier deploys two TDA7393 Dual Bridge 30W ICs driving six Audi stock speakers. What is really puzzled me when I opened the assembling - the custom-built Bose preamplifier circuitry, the number of RC correction pairs prompting what a weird frequency EQ was implemented to make the stock speakers sound right! So, if you decide to toss away your Bose amplifier - you have to replace the speakers as well.
Delta head unitThe original Delta was custom-made by Blaupunkt and providing 4-channel preamp output for trunk-mounted amplifier. It also could be configured for non-Bose systems using an external amplifier only for rear speakers and with built-in for the front ones. The simplest way of replacing it would be getting Blaupunkt CD-Receiver from SkyLine, FunLine or T-Line series. They all are sharing the same output and antenna connectors as the original Delta unit. Although the connectors are the same the standard Blaupunkt pinout is not identical. The C2 subconnector is different and C3 is using for connecting an external CD-Changer, so connect only parts A and C1. I didn't test this solution, but it should work. However, you still need Scosche AU2300B faceplate installation kit.
The solution allows install any DIN-mounted CD-Receiver. Here is what you need:
I found Sounddomain is good source of parts listed above. The harness schematic is shown on the picture. The pin numbering for VW1 corresponding the Blaupunkt pinout, the Scosche numbering is different. Use the same pinout for wiring C1 subconnector.
Only one part of Scosche VW1 connector is using, corresponding to subconnector A.
The final touchWhen I mounted the new in-dash unit the first time I was puzzled by the loud booms coming from the rear speakers every time when I turned on my radio or just switched radio stations. The clue was in the circuitry of BPV 655. Blaupunkt designed the preamp outputs stages with the blanking transistors, grounding the output signals to eliminate the switching noise. That causing the input capacitors from Bose amplifier to play charging/discharging game, creating a loud booming in the speakers. I had to remove them but it didn't affect the sound quality.