Installing new stereo while keeping factory amp?

What is the best way to install an aftermarket stereo system to a 1995 325i BMW without bypassing the factory amp installed. I read you can use the Metra Integrated harness with the RCA plugs, however the reviews were bad. I do not want to bypass the amp, nor do I want to put another crap BMW OEM radio in my car ever again.
Do I have any other choices here? Please help.

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This post was auto-generated based upon a question asked on our tech article page here: Pelican Technical Article: BMW Radio Head Unit Installation

[Wayne 962]

I'm not sure how the factory amps were wired - if they simply have RCA inputs, then you can hook it up to your new stereo quite easily. If they are integrated with the wire harness and plug then it might be a bit more difficult. I haven't had an issue with the Metra harnesses - they have worked well for me in the past.

- Wayne

[Manolito]

I have not messed with a standard amp- just the HK, but both of them process a speaker-level signal from the head unit so yes, you should be able to use the existing amp, and that will be easier than bypassing or replacing it.

Since the BMW amp amplifies speaker-level signal, not line-level signal, you will use the speaker connections from your new head unit, not the RCA jack line-level connections. Actually, I may be mis-speaking. I assume that all head units put out line-level from their RCA jacks, but that may not be universally true.

On an HK, four speaker channels go from the head unit to the amp, where they are frequency-split down, creating one channel for each of the 12 speakers.


Trivia for the Day:
This works only on 3-series. I read that on the 5- and 7-series, there is two-way communication between the amp and the head unit so they have to be matched. If you replace the head unit, the amp has to go as well. I have not confirmed this, nor do I know in what model year this started.

[airbikeman]

The factory amp takes two channels and makes them four, sends them to fader and back out to speakers. If you think you can tell the difference in the sound from this arrangement and the sound from four channels out of your aftermarket radio, then keeping the factory amp may not be for you.

However, if you want to keep the factory amp, here is how to hook up another radio. My example is a CD43, a lot like an aftermarket unit, but with BMW looks and logo. It should work for any radio though.

INSTRUCTIONS for wiring the CD43 to existing E30 circuitry and hardware, seamlessly.

This will leave you with the same or slightly better sound quality as the original radio.

There are only four wires coming from the existing original E30 radio concerning sound. These are the ones going to the amp.

BLUE- - Right Channel
YELLOW - - Left Channel
BROWN/BLACK - - Ground -- Splits to 2 wires from one coming out of old unit
WHITE - - Amp On Switching -- Splits to 2 wires from one coming out of old unit

SPEAKER LEADS pigtail and BLUE wire from POWER pigtail

The RIGHT FRONT + from the adapter pigtail attaches to BLUE
The LEFT FRONT + from the adapter pigtail attaches to YELLOW
The RIGHT FRONT – and LEFT FRONT -- from the adapter pigtail get tied together and capped. They attach to nothing.
One of the WHITE wires from the original radio turns on the antenna and the other turns on the amp. The BLUE (ANTENNA) lead from the POWER LEADS pigtail attaches to these two.
The BROWN/BLACKS that came from the old radio get tied together and capped. They attach to nothing.

POWER LEADS pigtail

Connect the YELLOW (MEMORY) pigtail lead to constant power.
Connect the RED (POWER) pigtail lead to switched power. (VIOLET/GREY)
Connect the ORANGE (LIGHTING) pigtail lead to a line that comes hot only with the light switch.
Connect the BLACK (GROUND) to a body ground of your own making. I highly recommend this in order to avoid potential problems with specific equipment grounds.
The BLUE (ANTENNA) has previously been attached.
This hookup will utilize all existing equipment including the fader. The fader on the radio menu will not be operative, but all other menu options will. The fader option is switched to the hardware fader above the radio.

This hookup should work for any off-the-shelf radio. Just follow the leads that would equate to the CD43 installation adapter pigtail leads. The basic element is that the original E30 amp only accepts two channels and only the positive side of each. The amp splits the signal, making four channels, positive and negative, one channel to each speaker. Since only what goes into the amp is the installer’s concern, there is no need for removing any panels. The radio mounting area provides all the necessary leads.

[BmwNiteRyder93]

Where is the factory amp? Speakers are good but i cant hear anything out of them. The guy at this radio store said that it maybe my facyory amp just off of a guess. He checked speakers and said they where fine. I have a. Bmw 93 325is