Kenwood Line Input
The Kenwood KD-SX991R is an in-car CD/Radio system which provides an external connector for either DAB, CD Changer or AUX input. Great system and all (although the graphics are a tad flashy), until I wanted to get an input for my minidisc player. After a quick call to my Kenwood stockists, I was quoted £45.99 for a AUX IN to standard 3.5mm socket. Balking at the price for ~50cm of wire with a fancy connector (I seem to balk at almost all prices nowadays, maybe I am just a cheapskate, or everyone else is happy to be ripped off) I set about working out how to make my own cable from some components I had lying around.
The first thing I did was look at the manual. Two reasons for this: first I wanted to see if it would give me any pinouts (you never know) for the connector, and second, it would tell me more about the AUX IN and other options available.
Anyway, after looking through, I found out that the Line In can be set manually through the menu. So after a bit of fiddling with the buttons, we had "Line In" as an option.
The Radio, all set up and running from a 12V Lead-Acid Battery and two Hi-Fi speakers set up. Was first tested using a CD to see if sound does indeed come out the speakers (always good to check).
Ok, so we got the system all set up, next we had to work out which of the connector pins dealt with the line input. The picture of the Kenwood adapter I was shown was nothing more than a 50cm wire with a "Kenwood" plug on one end, and a 3.5mm socket on the other. This meant that the "Kenwood" socket most likely had analogue LcGRc (Left channel, Ground, Right channel) inputs. I was originally worried that the reason the cable was so expensive was because the radio only took digital inputs (for DAB/CD) and the AUX required some sort of D/A conversion for inputs from external sources, so this was actually a good sign.
The next thing we had to do was look at the socket on the radio and test the pins (while the radio is on) with a multimeter:
The connection at the back of the radio. Note 9 pins (2 in the middle, 3 on either side, and one circular (GND) )
First we tested for voltages. Then for all those pins without high voltages (one was +12V) we used two wires attached to a signal generator. We would touch the selected pins and check if we got any sound out of the speakers.
After a bit of time testing I came up with the following:
Kenwood socket, top deals with audio in, middle is power, I think the bottom is digital IO (have not tested).
So the top is what we are working with. To make our connector I will use a piece of stripboard, as shown:
To facilitate a better connection, I melted some solder onto the three strips. This made them raised and curvy, as shown:
Once done, I then cut the three strips from the PCB, and attached wires to each pin (for testing). The wire is nothing special, so it probably does not give good audio quality, but this was only for the purposes of testing. Once everything was soldered, I pushed the PCB into the back of the radio and connected the ends to an audio source.
The PCB inserted into the radio, note I had to resolder the strips a few times to get the right shape of the pins
And there's it done! I tested it and the radio worked perfectly, no problems at all.
All in all the job was not too bad, and I saved ~£50 in the process. If you want to do this properly (i.e. use audio) I would recommend some higher quality cable, rather than the telephone wire I used.
