Radio / amp upgrade

[Ckay5thou]

I just bought a 04 330ci (with HK without nav) all the speakers were blown / missing including the hk amp.. I’ve replaced the lower door speakers and I’m replacing the factory radio with a aftermarket radio. (Adding subs) so my question is do I have to have a HK amp or can I replace it with a aftermarket amp? I’m new to the bmw world & could really use the help!

[MarcoZandrini]

USA market E46s have a separate amp in the trunk. Regardless of the audio system the amp has built in crossovers. So, replacing the factory amp will require the installation of crossovers. The front crossovers (one for each door) are 3-way crossovers as there are 3 speakers in each door. The rear crossovers are 2-way. Be advised that the signals between the factory head unit and the factory amp are balanced differential signals. They are not line level signals! Balanced differential signals are a much higher voltage (2 or 3 volts) versus line level signals (~0.5 volts).