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7 Series - E38 (1995 - 2001)

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  #1  
Old 02-28-2014, 10:34 PM
CitizenOfDreams CitizenOfDreams is offline
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Mein Auto: 1998 BMW 740i
E38 (DSP) radio upgrade

I gave myself a promise to stop spending time and money on my car and just keep driving it. Like most promises, this one did not last long...

I decided to investigate why the radio sound in my car was so lousy, even by 1998 standards.

The main reason: the foam on the door woofers has decomposed.



The second reason: all four "subwoofers" - as BMW calls them - were missing.



So the first step was obvious: I went and bought the best speakers I could afford, spending a hefty sum of 120 dollars. The midrange speakers and the tweeters seemed to be OK, so I decided to keep them.



That made the radio sound pretty good, even with the pathetic 4-inch "subwoofers" still missing. But now I wanted more...

I took a long look at the factory amplifier. Expensive, sophisticated, loaded with the bleeding edge DSP technology from 1990s. And just as lousy as any other factory car amplifier.



So I decided to replace it with an Alpine MRP-F320 I saved from my last car. It's an old and inexpensive amp, but it's well built and has plenty of power for my needs - 4 channels at 40 watts RMS each and a subwoofer channel at 120 watts RMS.



Problem is, the new amplifier did not fit on the original bracket in the trunk. It is wider and taller, and of course the mounting holes don't match. So I made some adapters...





Next step: the head unit. My plan is to reuse the original car wiring, without pulling new wires or cutting/splicing the existing ones. This car had its share of sloppy repairs, I don't want to hurt it any more.

So I bought a harness adapter on eBay and rewired it for my needs:



Then I pulled the radio out...



There is very little free space inside the single-DIN pocket. It was challenging to make all the wiring and the connectors fit behind the new radio. I had to pull the DSP, MID and IHKA to get my hands in there:



Well, that's all for now. Stay tuned, I will keep reporting my progress for the next few days.
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  #2  
Old 03-01-2014, 05:29 PM
CitizenOfDreams CitizenOfDreams is offline
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Public service announcement.

When you are working on your car - or on someone else's car - PLEASE do not use any "insulation displacement connectors", also known as "Scotchloks":



This is what the wire looks like inside when you use them:



Half of the strands are completely broken, others are badly mangled. This is NOT what you want in your audio signal path, especially in the high current circuits (power and speakers).
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  #3  
Old 03-01-2014, 09:28 PM
CitizenOfDreams CitizenOfDreams is offline
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Moving on...

I murdered the factory amplifier and stole its connectors.



The new amplifier is mounted...



... and powered.



That's all for today, more to come.
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  #4  
Old 03-02-2014, 08:53 PM
CitizenOfDreams CitizenOfDreams is offline
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All the wiring harnesses are made, waiting for crossovers to arrive.



Unfortunately, I have a big problem. Unshielded wires don't work too well. You can hear the noise from the I-Bus bleeding through. Not too loud, but you can hear it if you turn the music down to minimum volume.

At this point I have two options.

Option one: Run 2 channels of audio instead of 4 so I could use the existing twisted pairs. But then I would lose the fader function and the individual speaker delay adjustment.

Option two: Run a new shielded cable from the dashboard to the trunk. Sounds like a huge pain. Has anyone here done it? What does it take?
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  #5  
Old 03-04-2014, 08:37 PM
CitizenOfDreams CitizenOfDreams is offline
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Twisted pairs didn't work too well, the I-Bus noise still bled through. So I pulled new shielded cables. It was time to clean the center console anyway.
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  #6  
Old 03-05-2014, 02:21 PM
CitizenOfDreams CitizenOfDreams is offline
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Shielded cables solved the problem, as expected. The installation continues...
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  #7  
Old 03-05-2014, 03:46 PM
CitizenOfDreams CitizenOfDreams is offline
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Installation in progress, a pile of wires and crossovers. The subwoofers are still missing, but the system already sounds good. I'm happy.

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  #8  
Old 03-07-2014, 06:14 PM
CitizenOfDreams CitizenOfDreams is offline
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Crossovers mounted in a more organized manner...

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  #9  
Old 03-08-2014, 06:44 AM
First740i First740i is offline
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So you have had to do all this for new speakers?

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  #10  
Old 03-08-2014, 06:47 AM
miguel740i miguel740i is offline
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After seeing these pictures I'm having second thoughts about audio upgrades
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  #11  
Old 03-08-2014, 07:30 AM
First740i First740i is offline
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Same I'll pay for this.

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  #12  
Old 03-08-2014, 07:52 AM
CitizenOfDreams CitizenOfDreams is offline
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Quote:
Originally Posted by First740i View Post
So you have had to do all this for new speakers?
I didn't have to do it, just one thing led to another... You know how it works with repairs and improvements. The most important skill is knowing when to stop.
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  #13  
Old 03-08-2014, 08:07 AM
CitizenOfDreams CitizenOfDreams is offline
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Quote:
Originally Posted by First740i View Post
Same I'll pay for this.
A problem with paying for audio installs is that a paid mechanic will not spend hours soldering wire harnesses and taking apart half of the car interior to route them properly. He will more likely add an amplifier to the speaker outputs of the original audio system, clip wires on with Scotchloks, tuck the cables under the carpet and move on to the next customer. I'm not a perfectionist, but I can't tolerate %^*** like this in my car:

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  #14  
Old 03-08-2014, 03:30 PM
miguel740i miguel740i is offline
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I agree with your above statement, if you're gonna pay someone pay them to do it right. Otherwise you're better off doing it yourself
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  #15  
Old 03-11-2014, 10:11 PM
CitizenOfDreams CitizenOfDreams is offline
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The rear shelf is now repopulated with subwoofers.

Here is an old speaker again:



And here is the same speaker repaired (new rubber surround by SpeakerWorks) and installed into the rear shelf:

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  #16  
Old 03-11-2014, 10:19 PM
CitizenOfDreams CitizenOfDreams is offline
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Final view of the amplifier/crossover assembly. All 14 speakers are wired, all cables are neatly tied (except for that thin blue wire which I will take care of eventually). The factory wiring is intact in case the car ever becomes collectible and I want to put the original radio back.

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  #17  
Old 03-13-2014, 03:50 PM
CitizenOfDreams CitizenOfDreams is offline
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Okay, one more dose of fail.

I took the best microphone I had laying around and tried to do some (pseudo)scientific measurements.





Unfortunately, as soon as I played some 1kHz tone, I immediately heard something bad: nonlinear distortion coming from the front speakers. A quick look at the spectrum confirmed it: instead of a single 1kHz peak I saw a trail of harmonics.

A short investigation revealed the source of the problem: the 3-way crossovers I used for the front doors. You wouldn't think that a circuit of capacitors and inductors can be nonlinear, but apparently it can with a careful selection of lousy components.



The capacitors look and measure fine, but the big coils... This is the weirdest-looking ferrite I have ever seen:



I suspect that it's the ferrite core going into saturation and causing the nonlinearity. Can't think of anything else, but I'm open to ideas.
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  #18  
Old 03-14-2014, 09:38 AM
umewes umewes is offline
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Great post! Keep going. Thanks!
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  #19  
Old 05-25-2014, 10:38 PM
blindgoro blindgoro is offline
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awesome but its been months where are the updates!
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