BM24 radio module RCA preouts - Write-up

[voodoomelon]

EDIT: This does not work as expected. Read down the page for more information!

Hey all.
I've successfully managed to extract 4 pre-out signals from my E38s BM24 radio module. This of course means that I/you/whoever can now use an aftermarket amplifier to bypass the factory one, or if like me you have a dodgey radio module which has dissappearing audio, you can bypass the amplifier chips which have the bad solder joints.
Just to add, Jochen at Navcoder was a great help in describing what I needed to do, that man is a wealth of information!

I haven't seen this written up anywhere else on the web, believe me I searched high and low and the only details available are for the newer BM54 module, which has an entirely different layout. I simply found the datasheet for the amplifier chips online, got the pinout diagram and traced back the chip inputs to x4 capacitors on the board, each one acting as a stereo channel. I took a risk as I wasn't 100% sure what i was doing, but I have moderate electronics knowledge and this method works great.

You do not need to be a skilled soldering expert, i'm a novice when it comes to soldering and I managed this in about 20 minutes. All you need is:

- A soldering iron with a thin tip
- Solder
- x4 female RCA connectors
- x4 lengths of wire
- Lots of light
- A magnifying glass (i didnt use one but it would have helped)

Here is where you need to solder the x4 cables:



To access this area, you need to remove the heatsink, which slides up off the voltage regulator and two amplifier chips. Its only held on by friction by the clips on its underside.

Once you have the heatsink off, you're looking for x4 tiny capacitors side by side. They're located below the 4 larger cylinderical capacitors:





The voltage flows from the bottom side to the top side, the top side being beside the cylinderical capacitors. So you want to solder the wires to the top side of the tiny capacitors as the signal is leaving them.

However, after much testing, one of my wires that was soldered to one of the caps actually ripped off the top side of the cap. I through I was screwed until I soldered it to the bottom side of the cap where the signal enters, and it works just great. So i'm not sure it matters what side of the capacitors you solder to.

The best way I found of soldering them, was to put a tiny amount of solder onto the iron's tip and drop this solder onto the capacitor. Then tin the end of the wire and then heat both of them together. You need to be quick as you could dislodge the entire capacitor if you hold the iron there too long.

Here are the RCA connectors:





I simply drilled x4 7mm holes and passed the wires through and soldered the rear of the connectors. The module casing acts as the ground so no need for the ground rings what were included. I passes the wires though as shown and re-attached the heatsink:





Thats all there is to it!
Here's me testing the new set up, I have it connected to my Alpine PDX-F6. Its all tidied away now and the sound quality is definitely better that it was before with the speaker level converter I was using.



Hope this helps someone.

[sbender121]

Nice write up! I bet someone can put this to use, I might do this over the summer because my amp is going out.

[voodoomelon]

No problem, its much trickier to solder these wires than to do the BM54 as there's no space to move the iron about, it has to go straight down without touching anything else.

None the less, its not too difficult.

[Strahan]

Sooo.... does doing this mean all signal now routes out through the preamp connection you made, or does that just become an "extra" output? I was thinking of buying the BSW sub system, but I was reading their install directions and it uses a line output convertor. I used one of those once, wasn't impressed with the quality. I could do your mod to get preamp connection to it, but if I lose my amplification of the cabin speakers I'd have to factor in buying a second amp for them too.

[Edwin NL]

Great stuff!!

[voodoomelon]

Sooo.... does doing this mean all signal now routes out through the preamp connection you made, or does that just become an "extra" output? I was thinking of buying the BSW sub system, but I was reading their install directions and it uses a line output convertor. I used one of those once, wasn't impressed with the quality. I could do your mod to get preamp connection to it, but if I lose my amplification of the cabin speakers I'd have to factor in buying a second amp for them too.

Its an extra output. You aren't actually breaking the connection to the factory speakers, you're just tapping into the signal before it gets amplified. So you get a cleaner signal for connecting a sub whilst still maintaining your factory speaker outputs.

Or, as the main purpose of this mod is to do, is take the factory amplifier and speakers out of the car and replace with better aftermarket gear.

One thing I only noticed today was that I have no sound on my TV anymore. The TV tuner must input into the amplifier chips on the radio module board, hence they've been bipassed by my new RCA outputs. I'm sure theres an easy way around it.

To be honest i thought there would be more interest in this thread, this time last year everyone was chirping on about using aftermarket gear, this is the most effective mod to make this happen.

EDIT: You don't loose TV sound, just a temporary glitch or reception problem, sound for TV and navigation is still present.

[Strahan]

Well, I'm sure happy about your thread

I can keep my stock amp and decent sounding door speakers and get a clean signal to my sub amp. Yay

[Mless5]

Good stuff mate!

Sorry, but which one is BM24? I have a small navigation screen in my car, I am assuming the radio that I have is not the same as your's? I'd love to have a set of RCAs...

Thanks!

[cazal740i]

Genious!!!!!!!!!!!!!!!!!...Good job.. I wish I could figure this out ...Much Props!!
^
Negative again Bigblksevn

[voodoomelon]

Good stuff mate!

Sorry, but which one is BM24? I have a small navigation screen in my car, I am assuming the radio that I have is not the same as your's? I'd love to have a set of RCAs...

Thanks!

Here is a link to a year 2000 radio module from a US spec 740i E38:
http://www.realoem.com/bmw/showparts...62&hg=65&fg=05

Here is a link to my year 2000 radio module from a Euro spec 728i E38:
http://www.realoem.com/bmw/showparts...62&hg=65&fg=05

As you can see, there are many more options for the Euro models. The Becker BM24 was the best radio module of the lot.
Courtesy of Jochen in navcoder, here are the 3 radio modules that BMW produced, from worst to best:

Reverse RDS
PHilips or Becker
Single tuner, no CD changer control (only for non-nav cars)
Lowest of the range model

Business RDS (PHxxxx)
Philips
Single tuner
No CD list
No dynamic station list
With RDS and some with TMC
Mid range model

Professional RDS (BM24)
Becker
Double tuner
Shows CD disc number
Shows dynamic station list
With RDS, and some with TMC
Top of the range model

All of the above will work in any E38, however the lower models have less functionality. I'm not sure what radio module you might have, the only way to find out is to remove it from the car and check the label. If you have the professional RDS model, then thats the Becker BM24.

[Mless5]

Oh, I see thanks. I did not know we are talking about the unit in the trunk.

[330Ci78]

Hi!

Very great stuff.

So, i'de like to do the same job on my e46 330 with 16/9 head unit and bm24.
Could you tell me where i have to weld the cable on the main card and where are located the right an left channels?
The pictures you made are excellent, but i can't determine exactly on which 'pins' i have to make the solders.
I can see 2 lines of 8 points... Perhaps you could make a draw???

best regards... from France!

[voodoomelon]

Sorry, it turns out that this does not work 100%. The signals which i tapped into are not full range signals. Yes, you will get sound out of the signals, however there is very poor bass response. I would not recommend doing this.

If you want to get a clean, full range signal, just solder RCA connectors onto the speaker cables. These signals are already 5v balanced signals, this is what I am using now and it sounds fine.

[330Ci78]

Thanks for your response... I really thought you had have THE solution!
I already have bought Jlaudio Cl441dsp, and i'm not really satisfied!
Do you think it is possible to have better? Like Focal Hilo for example...
What's the deal with people who send modified bm24/54 with rca outputs on ebay?
Anyway, your idea was(is) very good... really!

[voodoomelon]

To be honest, I tried the same kind of filters and high-lo converters and they're all crap. You don't actually need them anyways, as I said, simply solder RCAs directly onto the speaker wires leaving the BM24 and plug them directly into your amplifier, it works great.

I don't know what those eBay guys do, they do the same mod as above no doubt, but probably tap into a different area of the board, possibly after the amplifier chips and not before.

[jwheels]

will that method work even if the amp is not producing sound. I have no sound and I belive my amp is bad

[voodoomelon]

The radio module is a four channel amplifier. So disconnect your DSP amplifier and the radio module takes over.

[jwheels]

thanks

[wbpatron]

Sorry, it turns out that this does not work 100%. The signals which i tapped into are not full range signals. Yes, you will get sound out of the signals, however there is very poor bass response. I would not recommend doing this.

If you want to get a clean, full range signal, just solder RCA connectors onto the speaker cables. These signals are already 5v balanced signals, this is what I am using now and it sounds fine.

Please post a picture of your method so I can know exactly which wires. I want to use your method because it sounds simpler and I don't want to mess it up.

[voodoomelon]

Just follow the yellow and blue speaker cables that come out of your radio module.

Snip them after about 18 inches and simply solder on some female RCA cables:





In the pic below, ignore the RCA cables leaving the side of the radio module. You can see the yellow and blue speaker wires coming out of the back of the radio module that you need to snip.

[osc911]

This is a great mod, and I was surprised at the end when you took line out straight from the speaker output without tapping of the signal. Are you still happy with this method and able to confirm it's full range. I'd like to keep the stock amp for door speakers and use this tap for a sub. Any idea if I can do this and retain the output to the rear door speakers?

[S.Hafsmo]

*Subscribed*

[voodoomelon]

This is a great mod, and I was surprised at the end when you took line out straight from the speaker output without tapping of the signal. Are you still happy with this method and able to confirm it's full range. I'd like to keep the stock amp for door speakers and use this tap for a sub. Any idea if I can do this and retain the output to the rear door speakers?

Technically, I don't know if its full range as I don't have measuring equipment. But the tweeters do produce real highs and the mids produce decent enough bass with the bass on the stock car Tone setting set to near the max.

BUT, I have to say, with this $600 Alpine amplifier and $800 odd worth of Boston components, the sound is *average*. I really think the only ideal way to get a good source is to ditch the factory gear completely and go with a dedicated headunit, which I really don't wanna do. It does go LOUD, very loud, and its very clear, however the bass response is extremely lacking.

I'm not too sure if a component set is meant to have a decent bass response, can anyone clear that up?
Regardless, I have a Pioneer WX77A going in this week to bulk it up, add a bit of punch. http://www.caraudiogiant.co.uk/shop/.../prod_412.html

[Playdrv4me]

On my early build 2003 Range Rover with the DSP audio system (pre-Logic 7) the sub behind the rear wall sounded like crap, so I decided to try an experiment and disconnect the factory sub and then splice off the lead to an Alpine 10 inch Sub that I had laying around. Surprisingly enough, not only did it work, but it sounded fantastic. The factory amp had plenty of power for the aftermarket sub, and the sound was finally full and balanced.

As soon as I lasso up another subwoofer I am going to try this again with the E38 (if possible).

[fiveseven57]

Hi,

When soldering the wires to the resistors I have damaged one of them. Does anyone know the resistors value for a replacement?
Thanks.