Originally Posted by
StereoInstaller1
My favorite trick to interfacing an aftermarket deck to a stock BMW amp is simple: use chassis ground on the speaker level negative inputs.
Basically, I do not connect the aftermarket decks speaker negatives to anything, simply insulate them. Once the positives are connected, grounding the amp input negatives drops the aftermarket decks voltage to a far more acceptable level. The deck then runs cooler and overall SQ is improved by not overloading the input stage of the amp.
If you meter the output of your stock deck, you will see all 4 speaker negatives are chassis ground anyway, so all it does is replicate the factory systems output.
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