Here's the deal (really!) :) (archive)

Ron W's explanation is pretty logical, so I would look at that. I used to be an installer, used to sell the things. But I always saw factory amps the way an oncology surgeon sees tumors: Don't understand them, don't talk to them, don't work with them--remove them. :)

Most factory amps get their turn-on either from a specific turn-on lead, or from sensing a hot output from the radio. It IS possible that the BMW factory amp uses a strange turn-on circuit and it will need its own juice.

Personally, I say play it like the oncology surgeon, and here's why: A) The IC amp in that head unit is ten times better than the junk in the factory amp, I promise. You'll get more power and less distortion if you bypass the amp and run direct. You'll have to run speaker wires if you want to make it easy on yourself, but it's not too bad and you'll thank yourself. B) Once you do this and conceivably discover the radio does have a problem (which frankly would be very rare--usually quality control problems with car radios fall into the work/don't work category), you'll know for sure it's the radio.

In short, be the surgeon. There's no reason to keep the amp in the circuit. It'll sound better and be easier to troubleshoot if you just forget it's there. If you put the factory in later, just reconnect it.

HTH.

David
'88 535iS-"Hannah"
113k

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