Homemade Kenwood Aux-Input Adapter
The Kenwood CA-C1AX adapter lets you plug an auxilliary input (like an Apple iPod or other MP3 player) into the CD changer port of a Kenwood head unit. I bought one and "reverse-engineered" it, and discovered that you can easily make this adapter yourself. Here's how.
I wanted to run the output from my MP3-playing "musicbox" computer into my Kenwood head unit (model KDC-7011), so that I could use the volume and other audio controls of the head unit, and also continue to use its CD player and radio. The head unit doesn't have an auxilliary input, but it does have a CD changer input, and Kenwood makes an adapter called the CA-C1AX (or CAC1AX or CA-C1AUX or CAC1AUX). This is just a 1-foot cable with a male 13-pin DIN connector on one end (for the head unit's female CD changer connector), and 2 female RCA connectors on the other end (which is where you plug your auxilliary source into). Normally, when you press the SRC (source) button on the head unit, it switches from the CD to the radio and back again. When you plug this adapter into the head unit's CD changer connector, the SRC button has a 3rd stop called DISC or AUX. Simple!
You can see photos and buy the adapter at Crutchfield for about $20.
Of course, since this is just a simple cable, there had to be a simple way to tell the head unit that an AUX source was present without buying this $20 cable. I got out my multimeter and tested the resistance between the 13 pins on the DIN connector and the 2 RCA connectors on the other end. I discovered that the adapter has a 10 kilohm resistor between 2 of its pins, and that's how it tells the head unit that a CD changer / AUX input is present. Here's a diagram:
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(Note that you probably want female RCA plugs (er, jacks) instead of male ones, but male ones were easier to draw and are more easily recognizable. And a pair of RCA couplers doesn't cost much either, so you could make them male if you wanted...)
On the DIN plug, the "V" at the top indicates the notch on the plug. Pin 8 is connected to the center of the red RCA plug, pin 12 to the center of the white RCA plug, and pin 6 is connected to the outer ring (audio ground) of both RCA plugs. There is 10 kohms of resistance between pins 3 and 9. I went out to my car, turned it on, and stuck a 10k resistor into the (female) CD changer connector on the back of my head unit, into the holes for pins 3 and 9. Sure enough, when I pressed the SRC button, I got a new choice -- DISC/AUX. Hopefully this information helps someone else out there who's searching for a schematic of this adapter's internals; knowing these pinouts, one could easily make such an adapter out of spare parts.