Thread: ipod hookup on factory installed system
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Old Dec 15, 2007 | 06:09 AM
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DickB
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Default Re: ipod hookup on factory installed system
Originally Posted by pgmikes
Here is some more information on the MP3 Adapter. It's designed to work with a Bose system. They may be able to modify it to work with our system, different pin out and plugs.

http://frontiernet.net/~dbipes/SLK/m...pter/index.htm

I put an email out to him asking.
Short answer: it may be adaptable, but I would need access to a car to work it out.

US-spec Mercedes 170 SLKs came with a Bose system, consisting of a head unit sourced typically from Alpine and a Bose amp and speakers. I believe some head units may have been sourced from Becker. I know that Mercedes has used heads units which appear identical but carry different part and model numbers and are in fact different and from different suppliers. Mercedes also built SLKs without the amplified Bose system, more common overseas.

The interface between head unit and Bose amp is two channels only, left and right. The Bose amp drives two pair of front speakers, tweeters and midrange, left and right out of two channels, and two rear speakers behind the seats out of two additional channels. There is no fader control; rather, Bose directs signals to these speakers at it sees fit, presumably tailored to the drivers characteristics and the cabin’s acoustic properties. The amp’s inputs are balanced 4 to 5 volt signals, which many confuse with speaker outputs on the head unit. Many SLK owners have swapped out their head units using aftermarket units by connecting the speaker outputs directly to the Bose amp input. This works, in that you get sound, but it’s not optimum. Typical aftermarket preamp outputs are 2 volt unbalanced signals, and these are not a good match for the Bose amp either.

The 99 and newer SLK Bose systems use a fiber optic interface for optional trunk-mounted CD changer and telephone interface. This system is independent from the head unit-amp interface.

The SLK adapter that I designed plugs in between head unit and amp. It is switched out of circuit when the head unit is used. The adapter senses when the head unit is turned off, then inserts itself into the circuit. It contains a preamplifier to boost a portable player’s unbalanced output signal and match it to the Bose amp’s balanced higher-voltage inputs. Volume, tone, and balance controls (if available) are from the portable player. Sound quality is quite good, due to the nature of the connection. The adapter momentarily powers down the amp when switching from MP3 to head unit or vice versa, to prevent annoying and potentially damaging pops and clicks.

The answer to the question of will the adapter work in a Crossfire depends upon how similar the Crossfire system is to the SLK Bose system. The adapter has proven compatible with a few other Mercedes vehicles, such as a ’99 M class. But others that at first blush appear to be compatible have proven to be incompatible. Unfortunately, Becker head units fall into this category. The usual symptom is that the stock head unit works fine, but the MP3 input never kicks in. I suspect some incompatibility in amp turn on signal, but without access to a vehicle I have been unable to diagnose the problem.

I also developed a modification to the Alpine-sourced head unit to add a true aux in. This is controlled by the existing head unit’s front panel switches, so the appearance remains stock. This modification is of course head unit specific.
 
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