Oh dear - don't know where to start with this really - I was hoping for a simple 'plug and play' scenario.

Where exactly are the capacitors and resistors - are they part of the plug assembly on the back of the Aux In itself?

This is going to be way beyond me I think, unless there is some sort of idiots guide thing - any suggestions / help ?

 

Alright, here we go:
1. Remove glove box compartment and big piece of plastic cover between glove box and compartment above.
2. You'll see a very long AUX cable.
3. Take out AUX cable
4. Cap and resistor is next to the AUX plug wrapped with plastic
5. Cut it off and connect the remaining wire to the AUX plug and wrap with electrical tape. To make it better, solder those wire connections.
6. Test it before putting it back
7. Reverse the installation process.

If you don't like the sound connect those cap back to the wire. Here are the pic of the cap and resistors

 

Can someone please post the pdf's on how to remove the glove box compartment and trim needed to access the aux wiring.

 

Wow, my530i, I could make love to you all night!!! Okay, maybe not make love... but rather thank you so much for such a genious idea. After two hours of frustrating work in trying to get to the wires behind the glove box, I finally removed those EVIL caps and resistors which were easy to locate (big bulges from the cloth-wrapped bundle of wires) only a few inches right behind the AUX 3.5mm jack. The result? Just what you said! Improved sound quality and most importantly... BASS!!! I can actually hear the underseat subwoofers thumping away! I had my XM Satellite Radio receiver plugged in but never listened to it anymore since it sounded like (crap) through the AUX input... but now I'm going to be using it everytime I drive thanks to you!!!

It just makes me wonder why BMW decided to put those resistors in the first place.

For those who want to reap the rewards of cap and resistor removal, this is what I did:

1. Open the glove box
2. Look into your glove box and look up towards the front. See those screws? Remove them! You'll find more screws on the side. There's also one more screw on the bottom of the glove compartment on the left.
3. Carefully pull down the compartment.
4. Behind the AUX jack in that area, you should find a long cloth-wrapped bundle. Mine was zip tied. If yours is zip tied, remove the zip tie!
5. Go to the AUX jack, remove the bottom and top screws, then unscrew the middle jack screw.
6. Reach your hand in the back and pull out the jack. If it doesn't want to budge, then go back to the front and push it out... if you can't with your finger, then use a pen or something. I used the tip of a nose plier.
7. Bring out the bundle. At the very beginning is the jack, of course. A few inches down the bundle and you will notice that there is a long bulge... kind of a like a snake that recently swallowed a mouse. That bulge contains those caps and resistors. Take some scissors and cut out that bulge.
8. Now that you are bulge-free, you need to reconnect the wires. There are three: red, blue, and brown. Carefully splice the wires, and connect red to to red, blue to blue, and brown to brown.
9. Insulate with electrical tape. If you have the time, solder the wires before you insulate (to prevent yourself from having to take everything apart again should the wires come apart).
10. Turn on the radio, set it to AUX Input, turn on your input device, and "oooo and awwww" at the improvement you just made to your system.
11. If all sounds good, put everything back together.
12. Good luck. It was a very stressful procedure for me... took me about two hours... but it was well worth the work!

 

Use this DIY with caution.

The caps and resistors are there for a reason. They reduce the power levels down so that you don't affect the main amp of the car, at the cost of reduced quality...agreed.
You can buy similar caps and resistors moulded into an RCA plug in any good sound shop to plug between your CD player and a sensitive amp.

However this is mainly needed if you use high powered outputs from most walkmans Headphones out.
If you strictly use the Line Out feed from your device you 'should' be OK.

 

I use the Line Output from my 60 gig, 4th generation iPod.

I have never felt that the bass response was lacking.... only that the bass is muddy, and less distinct than the same music played from CD.

I'd like to try this DIY out, but it seems like a lot of trouble.

 

Thanks for the steps! Just what the doctor ordered.

woohoo.

 

The first time it you'd take you 2 hours, but the second time, it might take you only 20-30 minutes.
Caps and resistor are there serve as high pass filter which pass frequency higher than the one specified.
Take a look at the circuit below and you see what I mean. The reasons they are there are to reduce gain coming from headphone jeck instead of line-out, and filter out low frequency. The second reason is the side effect of the first one.

To avoid clipping, set your MP3 equalizer to flat if you connect to your MP3/iPod/DVD player headphone jack.

I'm glad that people are happy with the outcome. Let me know if you guy have any question.

 

As I said best to avoid the headphone jack altogether and use Line Out when doing this. If using the headphone out keep the volume as low as possible (less than half should do) with the equalizer flat as mentioned on the iPOD and increase it on the car amp.

 

potatoaddict and my530i - thanks so much you are heroes.

my530i for finding the answer and potatoaddict for writing it down so that I can not only understand it - but have enough courage to attempt it.

Next chance I have I'm going to snip the little b*ggers (caps and resistor) out !