Hi, all.

I am in need of the pinout of the round CD Changer socket on the back of the stock head unit. In particular, I am looking for the audio signal pins. Does anyone know? What I am really looking for is those same audio signal pins on the Alpine CD changer that I have plugged into the stock head unit via the adapter. I am trying to make a device that will tap into the CD changer audio inputs on the stock radio as an auxiliary input with generig RCA or stereo plugs. I want to play my iPod through the radio and both FM transmitter and the tape adapter proved bad in various respects, not the least of which is audio quality.

Thanks!
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Vladimir. '98 S70 base, 5-speed manual - his, '93 945 (approaching 200K miles and rolling on...) - hers

Though for an 850, should be the same for our cars:
http://www.volvospeed.com/Repair/radiocon.php
You might also check this forum as I know a lot of people have tried some or all of what you're trying to do: http://forums.swedespeed.com/zeroforum?id=22
BTW, I have a USA SPEC device in my S70 that allows my iPod to be played through my Volvo radio and controlled by the Volvo Head Unit! Sounds great and it isn't very expensive. You'll read about it in the Swedespeed forum. I got my at Crutchfield's.
Regards,
MIJ
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1998 S70 T5 Emarald Green Metallic, 2004 V70 2.5T Ruby Red, Previous Owner of Black '94 850 Turbo Wagon

Thanks, but that is not what I asked for. I have this diagram, it is for the radio connector. What I want is the round CD Changer socket that's below and to the right. If I know which wires are audio inputs I can construct a box that will splice in there. With one of those clever guitar amp 1/4" stereo sockets I can make the CD audio to be disconnected when the external device is plugged in. I believe this is possible for our radios. The thread you pointedme to talks about the newer HU head units (2001 and newer?) that use the digital stream between the CD changer and the head unit. I do not believe this is the case with our cars from the previous century. I believe the audio signal that comes from the CD changer is analog and feeds into the pre-amp section of the head unit whereby it gets affected by the volume and tone controls. What I am plotting is to splice into the CD changer auidio output with my clever socket and REPLACE the CD changer signal with the signal of whatever I plug inito the spliced wire. The head unit will still think it's playing the CD changer audio. I just need the wiring diagram of either the Alpine CHM-620's cable or the Volvo head unit's CD changer socket. If, however I am wrong in my assumption that the audio output of the CD changer is analog, all bets are off.

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Vladimir. '98 S70 base, 5-speed manual - his, '93 945 (approaching 200K miles and rolling on...) - hers

I spent a good while looking for this. It is not to my knowledge the same as the standard Alpine M-bus but has some pins different. Here is the closest I found. It is for an Acura which also at one time used Alpine audio components. Alpine has also appeared in Jaguar cars.


Alpine Pin# Acura Pin# Pin Name Pin Function Wire (ext) Wire (int.)
8 8 GND Ground Black Orange/White
6 6 BATT +12V Yellow Blue/White
7 7 ACC Accessory Red White
1 1 BUS Bus Green Red/White
3 3 B.G Bus Ground Black Orange/White
4 2 R Right Signal Red Blue/White
2 4 S.G Signal Ground Black White
5 5 L Left Signal White Red/White
Shell Shell Chassis Chassis Ground Black Chassis

Since you have a scope and/or meter you may be able to verify this without damaging anything. The problem I had was that when I connected audio sources to the signal leads I heard nothing, regardless of how I set the stereo controls. I suspect that some particular bit stream has to be sent on the bus between the cd drive and the main unit to get it switched over to external inputs.

I assume you have googled "alpine m-bus" or similar, which is how I got the above.

I put in an FM modulator from Audiovox which has line inputs. This one is hard wired between antenna and antenna input and has a dash-mounted switch to enable/disable. It does not work with the headphone outputs of an iPod or portable cd player because those outputs are about 10x lower than line level. My plan is to build a little booster/preamp for this.

Well, I did it and without knowing the pinout. See, I have an alpine changer with Peripheral adapter. That adapter consists of an aluminum box with a PCB and the two cables (in from Alpine and out to Volvo). I cracked opened the aluminum box and there was the mother lode. The two cables go into these great molex-like connectors where it's easy to probe with a scope. I burned a CD with two tracks that I created using CoolEdit. Track one had a 440 Hz tone at full scale only on the left channel and track two had the same thing only on the right channel. I made each track 30 seconds long. I loaded that CD into the changer, powered up the scope and started probing. Pretty soon I came upon a nice 440 Hz sine wave and after making sure track one was still playing, I marked it "Left", skipped to the second track and repeated the procedure and found "Right". That's all I was looking for. I then took the adapter to the work bench and spliced in a 12" lenght of patch cord into it connected to a 1/4" stereo amp plug, the kind that disconnects one side when the male end is inserted into it (under $2 at PartsExpress). I then connected the CD changer to the end that gets disconnected and the Volvo end to the other side. Now, all I have to do is to load the cd changer and let it play, then just plug in the iPod into the plug I spliced in and I have iPod feeding the preamp of the head unit. You are absolutely correct about the fact that you must have the changer present and playing something for this spoof to work. I specifically wanted to keep the changer AND have the ability to add iPod as an option, so this worked out for me. If you want to add aux in and don't have a changer, then you need to do what you did or go the Monster Cable route. They actually have an ellegant iPod solution. But this is fine for now. You are also correct about the signal level of the iPod. It's low. I didn't measure it, but the signal to noise is not nearly as good as it is on the changer. What's up with that? Or maybe the impedence of the circuit I presented to the iPod headphone output is too low. I don't know, but it works well enough. I have made a patch cord that has a 1/8" stere plug on one side and 1/4" on the other and this can now accomodate most devices, but I was really only looking for iPod.

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Vladimir. '98 S70 base, 5-speed manual - his, '93 945 (approaching 200K miles and rolling on...) - hers

In my car I don't have a CD drive to supply the logic signals as you do. So that I guess explains why you get a result and I did not.

The input impedance of your auxiliary inputs is almost certainly high, 10K ohms or more. The low signal level is due to the small power output of iPods, etc, which is just 3 milliwatts or so. Typical headphones of these units have impedances of about 16 ohms. Using P=I^2*R you find the peak current output would be close to 6 mA. Using Ohm's law you get about 0.1V. At best this same voltage would be developed by the iPod at higher load impedance, and it is very marginal for a line level input, not enough to mask background noise.

My son bought an iPod charger from Belkin which plugs into the cigar lighter. It contains also a built-in amplifier which should give you line levels. I have not tried it as to the signal quality it can deliver. He uses the charger and also a casette adaptor which provides a very inferior result.

Ah, that was my next question. The audio output that is connected to the docking connector, is that the same as the headphone or is it conditioned/amplified? It bypasses the gain (volume) control, that's for sure. I did see a few chargers out there that provide access to the line out. I'll look into that. If the bottom output is a line out, then it may give better voltage levels at the same power due to higher impedence of the line input. As it is, the quality is acceptable if not stupendous. It's certainly superior to the tape adapter and possibly the FM modulator. And it wasn't too difficult to achieve.

Thanks!
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Vladimir. '98 S70 base, 5-speed manual - his, '93 945 (approaching 200K miles and rolling on...) - hers

Nice hack! Great job! Wish you would post your findings with some pictures over on Swedespeed's audio section. I know there are folks there that would eat this stuff up.

By the way, I like your picture...you look like the evil scientist...and having lots and lots of fun...LOL.
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1998 S70 T5 Emarald Green Metallic, 2004 V70 2.5T Ruby Red, Previous Owner of Black '94 850 Turbo Wagon

Thanks, I am very happy with the hack myself. Unfortunately, I did not take pictures as I went along. I was also using this as a teaching opportunity for my 9 year old son to show him how the scope works and what the difference is between digital and analog signals. We had fun making and burning the test CD with sine wave tones and seeing the same waveforms on the scope later in the car. We also looked at music waveforms and how that was different from pure sine wave tones. So, I neglected to photo-document the process. I may still do that because I did not figure out which pins on the Alpine cable and Volvo socket the audio signals live on. I was happy to just splice into the adapter since the wires are already exposed there. For the info to be useful to the Volvospeed crowd I would need to tell them which pis carry the audio. From all the info I have it wouldn't take long with a continuity meter, but I would have to take the adapter apart again and that would be a good time to take pictures of everything I did.

Glad you like the picture. This was taken in '99 when the car was still pretty new. both the car and I are older now. But still as crazy as ever (me, that is).
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Vladimir. '98 S70 base, 5-speed manual - his, '93 945 (approaching 200K miles and rolling on...) - hers

I'm sorry but this is the only diagram I know of any part of the Volvo pins. Did you search Swedespeed? Anyway, good luck!
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1998 S70 T5 Emarald Green Metallic, 2004 V70 2.5T Ruby Red, Previous Owner of Black '94 850 Turbo Wagon

No apologies necessary! I also have the same diagram from years ago. This is why I posted. The Volvospeed mostly talks about the HU units that I know are different than ours. I also found a pretty interesting solution from Monster Cable. They sell a little box that talks M-bus as do our head units and CD changers as far as command interface. They charge $150 for the box and then about $30 for the cable that goes from the box to the head unit. Then another cable from the box plugs into the iPod and then you control the iPod from the head unit as if it were a CD changer. Instead of disks you change playlists and you can use CD changer controls on the head unit to skip through songs in the playlist as if they were songs on a CD. It's cute, but a) pricey and b) you must loose the CD changer. If what I am thinking about works, the CD changer will stay put and you will be able to switch the aux piece of equipment (not just iPod) in and CD changer will automatically be taken out of the audio path. The controls will need to be worked on the aux piece of equipment, not via head unit. I will be blowing dust off my oscilloscope shortly to find out if my plan will work. If it does and I have a prototype, I'll report.

Thanks!
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Vladimir. '98 S70 base, 5-speed manual - his, '93 945 (approaching 200K miles and rolling on...) - hers

The Monster Cable solution sounds a lot like the USA-SPEC solution( PA10-HON with Volvo Cable...all totalled about $130), which also uses the head unit via the CD-Changer. Didn't know if you knew this but the USA-SPEC unit also has aux. input, but you do loose the original CD-Changer unless you can somehow ingeniously splice in a switch along with other connector. I know that someone over at Swedespeed was successful in doing just this with newer cars but I haven't read anything for our cars. I was thinking that possibly that information, although for different head units, would be helpful in your application. That's why I posted.

Good luck with your endevours and let us know of your developments.
Regards,
MIJ
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1998 S70 T5 Emarald Green Metallic, 2004 V70 2.5T Ruby Red, Previous Owner of Black '94 850 Turbo Wagon