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June 2, 2006

Add Aux Input to (Hacking | Modding) the Bose SoundDock

Update: I have succesfully built an auxiliary input cable for the Bose SoundDock, a project that was requested by several folks. The sound quality is much better running auxiliary sound through the SoundDock without having the iPod attached (as required for this hack). You can also buy the cable at CableJive.

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[[digg this]] Several months ago I was in a real quandry about what to do about portable sound for my iPod. I wanted something for my home office, but also something that I could take to the workshop or wherever.

I spent a lot of time thinking about it, and made several trips to more than one Apple store where they have all the options lined up. It boiled down to the Klipsch iGroove, Bose SoundDock and iPod HiFi. There's a lot of debate, but truthfully they are all very close. The iGroove had great sound, but I couldn't get used to the form factor so it boiled down to the HiFi and Bose. Listening in the store at pretty close range the Bose sounded just a bit better so I went with it, despite some of the missing features like battery power and aux input.

The Bose SoundDock has been great, I do really like the sound. It sits on my desk in my home office about three feet from where I sit. You can really hear the good audio quality at that distance (seems to be less quality with greater distances).

The one limiting factor that has haunted me is the fact that it doesn't have an auxiliary input, everything I listen to must be cone from the iPod. The iGroove and iPod HiFi both had an aux input feature. I spend a good deal of time at my desk listening to music, podcasts, audiobooks etc and it really has gotten annoying that if I want to listen to anything it has to be on the iPod and I have to use the iPod navigation to find stuff. It's good for on the go, but if I have iTunes right there I'd much rather use that to control what I'm listening to.

So I started thinking . . . and looking . . . and got an idea.

The first idea was to figure out the location of the pins on the iPod connector for line out audio and try to figure out a way to build something to plug into the iPod mount on the SoundDock. The wikiPodLinux has a great document on the iPod connector pinout. You can even purchase male and female adaptors (not sure they are Apple-authorized).

After thinking on that for awhile I decided to look at the SoundDock itself to see if there was a way to inject audio without using the Apple iPod connector. Turns out that you can see a bit of the circuit board on a fully assembled unit by just looking down in the slot where the iPod sits in the dock. The part you can see looks like a row of pins, which raised my curiosity enough to explore more and in the end led to a working aux input for the SoundDock.

It starts with pulling the two bottom covers off of the SoundDock. The first one is attached with four phillips screws, the second one is attached with three Torx screws (requires size 8 Torx). When I pulled off the first bottom cover (with phillips) there was a ribbon (about 8 inches long) folded over once. This connects the circuit board from the iPod connector to the SoundDock electronics.

When I pulled off the second cover the circuit board with the iPod connector could be pulled out. This circuit board is attached with a ribbon that is long enough to allow you to stretch the circuit board a few inches in front of the SoundDock to work on. When I initially pulled it out there was a black cover over the board, but it's only attached with some stickiness on the bottom of the black piece of thin plastic so was easy to remove. What's underneath is a circuit board that has the connections between the iPod dock connector and the SoundDock input ribbon. This board has the volumn adjustment controls as well.

Looking closely at the circuit board I could see that the connections on either side of the ribbon were numbered 1 and 24. At first I thought these would correspond to the iPod connector pinout, but it's fewer pins and when I connected audio to pins 1, 3 and 4 to match the iPod audio connector it didn't appear to do anything.

A little trial and error using some multitester probes revealed that the audio is sent into the SoundDock using connector 13 and 14 on the ribbon. 13 is for right audio, 14 is for left audio, and number 24 is ground.

At this point I realized that it's likely that the SoundDock is turned on and off by having the iPod attached. There's no on/off switch, so something about having the iPod docked turns on the SoundDock. Perhaps it's the 3.3 USB volt charge on pin 18 . . . as you'll see I never get to the point of making the SoundDock work with auxiliary sound without having the iPod docked. To put it another way, you must have the iPod docked in order for this aux input hack to work. Sending audio on pins 13, 14 and 24 isn't enough to trigger the SoundDock to come on.

Back to the hack. If you follow the connections on the board out about 1/2 inch from where the ribbon is soldered to the circuit there are spots where a wire can easily be soldered. I used unshielded, 24-gauge solid wire, but something even smaller would probably work better. I had to shave down the tip of the wire to get it to slide down into the circuit board. Perhaps 28 or 30 gauge would fit better. I soldered an 8" piece of wire for right (red), left (white) and ground (black) and send them to the left of the circuit board. In retrospect, if I had to do it again I'd get a shielded headphone cable or something similar to make the hack a little cleaner and ensure optimal audio quality (although I haven't noticed anything horrible about the wiring I used).

Before closing things up I tested by hooking audio up to the wires just to be sure that the wires were connected solidly and things were still working.

I then put the second cover back on (the one I removed second, with the Torx screws), pulling the wires through a small area near the screw base on the lower left of the cover.Then I put the first cover back on (the first one I removed, with the phillips screws). As I put the first cover back on I pulled the wires through the most obvious opening which put the wires running into the small cavity uner the left side of the SoundDock.

Again, I tested the SoundDock aux input by connecting an audio source just to be sure I hadn't disrupted something in putting the covers back on. I also tested the iPod sound to be sure that was still working as it should. Still looking good.

The last piece of the hack was to make a decent interface to the aux input. A quick trip to radio shack netted a 1/8" audio jack ($2.99 for a pack of 2). Another quick bit of soldering, drill a small hole, and use some serious glue to affix the body of the jack under the body of the SoundDock and I've got a nice place to plug in a 1/8" from my headphones out jack on any device.

Now I'm using the SoundDock to listen to whatever strikes my fancy, not just stuff from my iPod. This means I can watch movies on my laptop and listen using the SoundDock. Cool.

And the sound is good, I haven't altered the structure of the sound dock or the way it processes audio so I can get the same audio quality that I get with the iPod with other devices.

A Few Warnings (or things to note)

Posted by mike at June 2, 2006 9:26 PM