shooks

Hey-
Does anyone know of a clever way to get an analog/aux input into the C230k bose audio system? I realize the system uses the D2B optical bus, but I was wondering if anyone knew of any tricks. Right now I see my options as a tape adapter or an FM modulator. The tape adapter would sound okay, but looks like crap. The FM modulator sounds bad, but looks seamless.

I thought about using a tape adapter with the wire running out the back of the radio chasis. Then I would permanently leave the tape inside head unit. Then I could close the front cover and no one would ever know about the tape. This is definitely not the best solution, but it could work pretty well. Does anyone know how to remove the head unit?

I'm trying to use my iPod in my car. Any ideas or help would be greatly appreciated.

Thanks,
Spencer

BrabusCClass

You should ask this in the C class forum. There are a lot of poeple there who have taken their headdeck off. I use the RF modulator for my RCA outputs and thats ok, Im not sure if you are asking abou that.

shooks

Thanks for your reply. I figured the Audio section would be the best place, but I'll try the C-Class section as well.

You're right that I am basically just trying to get an RCA input into my system. Are you satisfied with the sound quality from the RF Modulator? Have you ever compared the RF modulator to a simple tape adapter?

BrabusCClass

Modulator is fine. Works good. I took the speaker inputs from the rear sub. It was really easy. Much easier than taking out the headdeck which is a big pain. To take out the headdeck you need to go thru the a/c vents. After you take those out there is screws. Then the trim comes off. There is also a screw under the ashtry. Look up the C Class forums, it is up there step by step.

Cryptnotic

An FM modulator will probably sound better than a tape adapter. Most of the tape adapters I've used sound like crap. You get noise from the motors spinning the spindles around. An FM modulator should sound slightly better than a local high-powered FM radio station.

I'm going to try to use one to hook up to a Phatnoise Car Audio System (see http://www.phatnoise.com ).

Liming

To take out your headunit, you can order the headunit remove tool from becker of north america for $2+ shipping.
www.beckerautosound.com

Cryptnotic

For a modern Becker/Mercedes head unit, you do not need that removal tool. In fact, that tool won't help you at all since there's nowhere to use it.

You need to remove the center air vent. Do a search on this forum for "head unit removal" for the directions. After the vent you can take off the surrounding trim around the radio. After that, the radio is held in place by two screws, one on either side. Remove the screws and the radio just slides out. disconnect from the wiring harness and you're done.

I'm working on a way of modifying the radio to add line outs and aux input (via the tape interface). I've found a way to access the front and rear outputs before they get amplified. However, I'm not sure if the levels are appropriate for running accross RCA cables to an amplifier. I will find out what the levels are tomorrow when I hook them up to the oscilloscope at work.

Liming

I used that tool to remove the head unit on my car. (5 seconds) I have a 98 c280.
Does your radio unit has two narrow holes on the face plate?

For the signal, Bose use 2.5 volts diffential (floating ground) signal. You can use it as standard RCA level output if you transfer it to common ground signals. You can also use speakerlevel-rca level converter. I think peripheral makes them. If you want to buils it by yourself, audio transformers (10k-10k counts) might works.

Liming

check this, it is a becker cd player. Can be ordered by phone.
http://www.beckerautosound.com/4602specs.html

Liming

BTW, if you need mounting kits for new mercedes, a british store might carry them. I was looking for mounting kit for my car, but the staff of that store told me only new mercedes needs mounting kits.

http://www.alcestercaraudio.co.uk/

shooks

Cryptnotic: Can you give me more info about how you're planning to add the aux input? Are you trying to figure out a place on the circuit board where you can solder in an aux input? Or are you doing something else?

Cryptnotic

Yep, I've opened up the head unit and I'm in the process of figuring out how to get an input.

I'll probably try to use the tape interface for an analog input. I want to find the pinout of the 21 pin ribbon cable connecting the tape mechanism to the main board. The tape mechanism is most likely a Shinwa tape mechanism (they make something like 90% of the world's tape mechanisms), although it doesn't look like any of the ones on their web sites.

Finding preouts was amazingly easy, since they were labelled on the amplifier board (the vertical board at the back of the unit). The pins there are labelled "FL FR S-GND RR RL", or front left, front right, signal ground, rear right, rear left. They're not in that order though, I think.

Some other people here at work are using the oscilloscope, so I can't analyze the preout levels just yet.

Liming

Are you trying to add Aux in and keep using the OEM head unit, or you just want to replace the head unit with aftermarket ones and feed into the stock amplifier?

For the first choice, how about insert a piece of extension cable between stock amp and your head unit, and put a four-channel switching circuit in? You can get the aux signal into the amp througn the switch. Of course, the first problem is to find the extension cable. I hope becker would have them.

For the second choice, I am doing it now.

Liming

As of the 21 PIN cable( in the trunk for amp?), I think 8 of them are used as signal feed in, 2 big ones (big leads) are DC power and ground, and the rest of them are for speakers.

Here is the PIN out for some head unit model, hopefully it is the same as yours.
http://www.beckerautosound.com/1492.html

shooks

Cool. Definitely keep me posted on your progress.

I thought about opening up mine as well, but unfortunately I won't have enough free time for a couple weeks at best. I think I'm going to go ahead with the quick and dirty FM modulator so I can get some decent tunes for now. My iPod is feeling neglected.

This should definitely be possible. It might require some extra analog circuitry to match the aux input level to what is coming from the tape mechanism. Although, in my case I might just be able to use the volume knob on my iPod. It all depends what the levels are. I'd love to ditch the FM modulator ASAP...

I'm just not willing to give the asthetics and integration that the factory head unit provides.

Cryptnotic

I'm very tempted to try to contact Autoleads (http://www.autoleads.co.uk/) and try to get them to send me a facia adaptor (yes, it's spelled "adaptor" in UK english). I found several .uk web sites that carry them, but none of them ship outside the UK. With that, I could just put in a nice aftermarket head unit with pre-out's and AUX inputs like a Nakamichi CD-45z w/ amber display.

On the other hand, I have already figured out how to get line-level outputs from the head unit. Getting a line input should be relatively easy. I'd also like to figure out a way to wire the fast forward and rewind mechanism of the tape deck to signals that go out to control my MP3 player. That way it would work through the steering wheel controls.

Liming

For Line out converter, scosche FAI-3 and Peripheral VEN 4.5 will do the job. www.sounddomain.com has them.
I just received my mp3 player this afternoon. (Alpine CDA-7894). It's RCA pre-amp output is refering to the chesis ground. I am not sure if I can feed it into the amp directly. I will install it on saturday.

Cryptnotic

It is normal for the preouts on a head unit to share ground with the head unit chassis. Note that on a cd changer or external amplifier, the RCA grounds are not connected to the external device's ground, but instead get their ground level from the head unit across the RCA cable. That way the audio signals are connected to ground only at one place (inside the head unit).

If you didn't do this, you would get what is called a ground loop where noise would creep into the system from the power circuits. On a home system, you get a power circuit hum (either 60Hz or 50Hz depending on where in the world you live). In a car, you get a alternator whine in sync with the engine speed.

Liming

I see.
Now I am having the Bose amp in front of me. I can not find the bypass capacitor for each channel. Do you know what could happen if I feed the common ground pre-amp signal into the bose amp? I know the bose amp takes floating ground differential input.

Cryptnotic

Bose amp? It's best not to mess with the Bose system. Take it or leave it as a whole.

I don't have the Bose system, so I can't really comment.

Liming

All right, I will use line out converter first.
The max film capacitor I can found is 10 uF, can't be a good bypass capacitor. Hopefully I will build a floating ground converter later.

shooks

Just an update on my situation:

I had the FM modulator installed yesterday (I was feeling lazy) and I'm actually really impressed. It sounds much better than I was expecting. I was starting to think the Bose system was kinda lame after listening to only radio stations and some 10 year old tapes, but I was wrong. With my iPod hooked up it sounds great. I'm completely happy with it now. The iPod has many EQ settings, which helps.

Everyone complains about the lack of bass in the Bose system, but I think the system sounds fine. I had two 10" subs in my car for years, but I just don't really need ridiculous levels of bass anymore. The Bose system doesn't give me the nice back massage that I used to get, but I can live without it. I think the low end sounds good.

Liming

I have opened the bose amplifier, it accepts four channel input. But inside the amp, there is an extra chennel for subwoofer.
I think the bose amp are OK. Head unit upgrade will always a good idea.

Liming

Finally changed my headunit.
Replaced the OEM headunit with Alpine CDA-7894. It comes with 4V pre-out. Tried using coupling capacitors between headunit and bose amp, but I got engine noise. Replacing them with two ground loop isolators, everything works fine now.
Just noticed that Aux signal is connected through CD changer cable for CDA-7894. Maybe OEM MB headunits also do.