[DR51FTA]

ok basically i have a 3 series professional stock head unit...i have this amp http://www.justkenwood.co.uk/stock01/kac9104d.asp taken out already from my old car, used to power two x 12 inch rockford punch subs..can i hook this up onto my bmw prof. head unit. i dont have the hi fi upgrade or the logic 7 i jus hav the stock loudspeaker system so there is NOT a amp in the boot or anything. how do i wire this up to my headunit? its a single channel amp. i would like to keep the same headunit also. and i do not have steering controls to worry about.

[gerbil_b]

Easiest way mate, get the conversion harness from BMW to ISO find a live to take a feed off for power, get a facia plate and then get a decent head unit with amp/sub control on it. If you get the right head unit will look a lot better, i have a flip out DVD player but still not commited to put it in yet haha.

For parts i used car audio centre. google them.

[richd]

What are you trying to drive with the amp?? The same subs?

The problem you have is that you can only pull a speaker level (not line level) signal from the existing head unit, so you either need to use a different amp that supports speaker level inputs, or use a speaker to line level converter.

In either case you would need to tap into either the front or rear feeds from the head unit.

However, that said, there are plenty of things I would do first before just adding an amp/sub.

[DR51FTA]

ok cause im new to wiring ive just clocked this..
i connect the power wire with a fuse to the battery. i connect the ground GND wire to the chassis. i connect the remote wire to the head unit. and i use a line converter to the line-in in my amp by tapin into the rear speakers? and then amp connect to sub?

and then it should work?

[DR51FTA]

my amp supports speaker level inputs btw

[richd]

Originally Posted by DR51FTA

ok cause im new to wiring ive just clocked this..
i connect the power wire with a fuse to the battery. i connect the ground GND wire to the chassis. i connect the remote wire to the head unit. and i use a line converter to the line-in in my amp by tapin into the rear speakers? and then amp connect to sub?

and then it should work?

You can tap into the backs to drive the sub, but to be honest, you are going to be very bass heavy, especially as the standard setup doesn't have any top end (no tweeters).

Up to you, but I would suggest upgrading the rest of the system first before throwing a sub in the boot. The Alpine upgrade would make sense, then just add the sub if you want more bottom end.

[richd]

Originally Posted by DR51FTA

my amp supports speaker level inputs btw

One other thing, you need to consider the impedance of the rear output from the head unit. The head unit is only stable down to 4ohms, which will match the impedance of the rear mids. Adding a feed to the amp in parallel to the rears will reduce the impedance down to below 4 ohms (probably 2 ohms) which will mean the Head Unit won't be stable and will cause you issues.

You will probably need to disconnect the rear mids completely to be able to drive the amp.

Have you read the E90 stereo system guide? Explains all the setups including the stock system. Send me a PM if you need it as I have it.