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Business RDS schematics

2371 Views 3 Replies 2 Participants Last post by  M.Pankov
Hello all,

I am new to this forum and happy to find so many BMW enthusiasts!

My name is Mario Pankov, I am from Bulgaria, EU ( as could be seen from my profile ) and I own a 97 E39 fitted with the m52b20 engine ( aluminum block ).

I got my car stereo stollen just a few weeks ago and now I got back to my original head unit. I was looking for this back conversion for a long time as I did not like the way my dashboard looks with an aftermarket cd player and I prefer to keep the car in its stock look.

The problem is the performance of the BMW`s factory sound system. I did replace the front door speakers with a 2-way Focal Polyglass 130 V2 component system, I added an 8" B&W subwoofer ( made for home use, but I was looking for a high SQ sound system ) and two Audison LRx2.80 amplifiers in my trunk, one for the front speakers and one bridget for the B&W woofer. The interconnects came from Audison as well. The big problem is the stock head unit - it really makes all these expensive components useless.
What I would like to do is to remove the stock power amp and cassette player mechanism and to get RCA leads out of the stock preamp. Then I will connect my power amps directly to the original preamp of the car.
Has anyone done that, if yes what are the results in SQ and does the stock preamp kill the sound ( in this case I would need to completely replace it with a good diy preamp :) )?
Could anyone be able to provide the schematics of the preamp and amplifier sections of the Business RDS unit ( no external amplifier in the trunk version )?

If there are other people interested in such modification ( note it will also work on the X5 ), I will post my results.

The thread is more likely to be for the Sound forum, if true, i would ask you to excuse me and to move it to the correct place.
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I have a suggestion for you. If you plan to hook up an outboard amplifier to the factory head unit I recommend something like JL Audio's Clean Sweep. It essentially corrects the preamp curves of the factory head unit and allows you thee ability to properly tune outboard amplifiers.

I saw one of these installed on an E60 iDrive system with JL Audio slash series amplifiers, mids, highs, and subs and it sounded ridiculous. I highly recommend looking into something like this.

There are also other products similar to this:
MTX Audio re-Q

However, I do believe that the JL Audio CL441dsp is what you're going to want. It is truly the best OEM integration unit on the market right now and it will give you the same tuning abilities that an aftermarket head unit would give you.
Thanks for the input, this is truly a helpful device.
However this is not what I need, once the signal goes through the inbuilt crossovers it will get the crossover`s artifacts. Then, the unit will try to flatten the response curve and the result will be even worse. Once the signal goes through the factory preamp and power amp of the head unit, all will be lost as it is now just because they are rubbish.

What I need is the schematics because I want to check on the preamp circuit they have used, but now I do not think I need it. I will just throw all parts away and will completely rebuilt the preamplifier inside the stock head unit, it will have a preamp section only. I have to measure the specs of the regulated supply they have used and to see If I could adopt it for a tube preamp circuit. Otherwise a new supply should be built.

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