Problem with BMW 530i Business CD head unit upgrade

[sktn77a]

Hi there:

I have a 2001 BMW 530i with the OEM Phillips Business Cassette radio. It has the standard (Non-DSP) sound system with the addition of 2 10" M5 subs and a Blaupunkt Tripath amp driving them. The signal taps for the subs come off the front audio outputs from the head unit, just before they go into the amp. I upgraded this head unit over the weekend to the OEM Alpine Business CD radio I got from BSW a while back. Install went fine except for 1 thing. I ain't got no bass from my subs any more (?!). I have audio to the front and rear speakers but nothing to the subs. I plugged in an MP3 player to the sub amp input and got bass from them so it appears to be something to do with the signal from the head unit to the sub amp.

Any ideas? Is there any fundamental difference between the Alpine head unit LF output and the Phillips?

Thanks

Keith

Well, I swapped out the Alpine Business CD head unit for the original Phillips Business Cassette and I have the bass back! So it looks like a bad head unit maybe? I'm sending it back to the seller on eBay and he's going to exchange it. I guess my concern is that it might be something to do with the (supposedly) balanced low level audio outputs from the BMW head units. Maybe they're slightly different on the Alpine than the Phillips and this is causing a problem with the sub amp (straight into the amp, presently, no Line Output Converter). I would imagine BMW would spec the head unit identically from all the different OEM manufacturers (?)
Anybody..... Bueller....... Anybody???
Keith

[sktn77a]

Took the car in to the shop today This is what they found at the input to the sub amp (output from the BMW head units):

OEM Phillips Business Cassette: 0v DC offset at idle, 3v DC offset at full power.
OEM Alpine Business CD: 3.5v DC offset at idle, 6.5v DC offset at full power.

Their diagnosis was probably a problem in the output stages of the CD head unit. Remember, though, both head units are working fine with the BMW amp - just the sub amp that's a problem.

Any other possibilites? Would this cause the problems I'm seing with the CD head unit and not the cassette?

Thanks

Keith

[12v Electronics]

Have you checked for power at the remote turn on wire at the amp?

[sktn77a]

Yes, and there's power to the sub amp - the light is on, I get a "thump" when I plug in the RCAs. If I unplug the RCAs to the sub and plug in an MP3 player, it works fine so I interpret this as everything good from the RCA sockets on the sub amp through to the subs.