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Date: Mon, 31 Aug 1998 11:46:21 -0400
From: Bob Hazelwood <>
Subject: Re: Jason's '93 325is stereo dilemma (Long)

> Jason asked:I have a 1993 325is with the 10-speaker factory system (non HK). I recently bought a Sony ES CDX-780CD head unit, and ordered the (supposed) correct wiring adapter from
> Crutchfield. I thought everything

> was going quite smoothly, soldered the harnesses together and used shrink wrap, etc. Put the key in, hit
> power and - no sound.
> <snip>Crutchfield guy told me
> that their harness would by-pass the factory amp, and I have the two groups of wires and connectors (one
> white, one black) ready to be plugged together so I can enjoy my CD's. Does anyone have the
> necessary pinout so I can by-pass the factory amp? Or is there a ready-made by-pass adapter? <snip>
> I called Crutchfield back, and was told that my only options were to:
> a) wire the speakers myself from the back of the head unit
> b) buy a $40 wiring adapter that will STILL use my factory amp (which is one of the reasons for the
> upgrade).
> Out of these two options, I'd choose (a), but really don't want to tear apart all the interior panels.

Hi Jason,
Unless you are prepared to replace the amp, and or speakers, you're stuck with option B. Here's why: BMW has taken an unorthodox (although logical) approach to the system architecture on E36 and E34 models. The factory amp is a simple 4-channel 15W x 4 amplifier, but with all the passive crossover circuitry for the speakers inside the amp. The reason this is logical, is that by simply replacing the amp module with one which has 10-channels and an electronic crossover they can offer a system upgrade option (Like HK) using the same harness. The problem is, if you replace the amp, the crossover circuitry goes with it. If you try to drive the speakers directly, you'll end up blowing out all the tweeters and mids, since they can't handle the low frequencies. Note that this is not the case with the small system in your friends 318, only with the 10 speaker systems. That's why his works.
So you're left with the following options:

  1. Keep the factory amp in and modify the wiring of the adaptor so it works with the Sony.
  2. Replace the factory amp with a multichannel amp with built-in electronic crossover ($$$)
  3. Buy or build a passive crossover to replace the one you lose when you take out the factory amp.
  4. Replace the speakers with ones which come with their own passive crossovers and wire them directly to the head unit.
  5. Replace both the amp and the speakers.

Of course, as the VP of a company that makes amps and speakers I'd love it if you went with E, but I'll assume you want to avoid that because of cost. That leaves B, which can get expensive; C, which is a lot trickier than it sounds to get good results; D, which may also be more than you want in terms of cost and complexity; and A, which is the quickest/easiest and most predictable.

Assuming the Crutchfield adaptor is not defective, I think the problem you're having is that the Sony radio is floating ground (each channel speaker - wire must be isolated from the other channels), but the input to the BMW factory amp is common ground. As a result, the short circuit protection circuitry built into the Sony radio is probably killing it's output in order to keep the radio's amp from blowing.
The workaround is simple:
First, disconnect all 4 of the speaker - wires coming from the Sony. Insulate them with tape and don't connect them to anything. Connect the four previously connected wires from the Crutchfield harness adaptor together and to a screw on the Sony radio chassis. Connect a 470uF _at_ 16V (or greater) electrolytic capacitor in series with each of the speaker + wires between the Sony and the adaptor. Connect the + lead of the capacitor to the Radio side and the - lead towards the adaptor.

Put the factory amp back in and try it. BTW, make sure the white wire from the factory harness goes to the remote wire of your Sony (probably blue). This is the wire which turns on both the factory amp and the antenna amplifier.

Best regards,
Bob Hazelwood
VP Product Management, a/d/s/
'93 525i 5-sp