Originally Posted by Volktronic
I was under the impression with the correct harness, nothing like that was needed, the signal just goes right into the amp and out to the speakers.
I'm only referring to what Technic and I did in this project. The Tech is mistaken in this regard, I believe.
In the Stereo cars, the speaker interface isn't the issue, it's the correction.
But it's incorrect to say "all that's needed is the right harness". 97% of all aftermarket amplifiers sold are NOT compatible with the signal out of ANY BMW audio system with ANY harness. Even HiFi system signals are only usable by amps with balanced inputs.
A few amps can take the woofer signal directly in without distortion in a Logic 7/HK add-a-sub arrangement.
But most amps on the market are common-ground RCA input, and if they have a "speaker-level" input, it's a balanced input with a lot of attenuation in front of it (which usually ruins your noise floor with a lower-voltage preamp signal which needs no attenuation). Common-ground RCA input means the outer ring of the RCA is grounded, and this shorts the (-) clamped DC leg of the HiFi audio output.