Using the iPod Touch 2G with the AUX input

I was disappointed to learn that the inspiretech dock connector-to-3.5mm plug audio cable, which worked great with my iPod nano, no longer worked with my new iPod Touch 2G (2nd generation).

Turns out that the software in the Touch 2G looks for a specific resistance value on one of the dock connector pins before allowing the audio to be routed out the LINE OUT pins on the dock connector. The LINE OUT signal is a better choice for connecting to the AUX input on the Prius (or any other system, for that matter), because it bypasses the headphone amplifier and eliminates the need to adjust the volume on the iPod.

So naturally I looked online for a dock-to-3.5mm cable that is compatible with the Touch 2G, but could not find any. There were cables that came with warnings about not being compatible, but otherwise, no dice.

That leaves us with a few options:

- get more sophisticated with an integration kit ($$)

- contact manufacturers to find out if their products are compatible and/or if they will be introducing any soon (ugh!)

- modify the existing cable to make it compatible (yesss!)


I'm an electronics engineer, so guess which one I chose...

With a little research, I discovered that it is rather easy to modify the inspiretech cable (inspiretech.com: Apple iPod Classic Dock to 3.5mm AUX Cable, iPod Classic Auxiliary Cable, iPod Classic Dock to AUX Cable, iPod Classic 3.5mm AUX Cable). Here's how:

1. Remove the plastic backshell. This is easy--it just requires lightly prying the latches (four places) with a small flat jeweler's screwdriver and separating the two halves.

2. Remove the metal shield material, making sure to note how it fits together for reassembly.

3. You will find three unused terminals sticking out the back of the connector. With a needle-nose pliers or strong tweezers, carefully pull two of the unused terminals straight out the back, then re-insert them fully into positions 15 and 21 (counting from the end where the three audio wires connect, which are at pins 2, 3 and 4).

4. Solder a 1KOhm resistor between the pins you just moved (positions 15 and 21). I recommend an 0805 or 1206 surface-mount resistor package or a 1/8-Watt axial leaded resistor. There is a fair amount of room in there for the resistor. Some soldering experience is recommended since it is all a bit on the small side, but nothing a decent pair of tweezers, a fine-tip soldering iron and a magnifier (if needed) can't deal with.

5. Re-assemble the metal shielding and the plastic housing--it all pretty much just snaps back together. Make sure you seat the wire strain relief back into the backshell properly before snapping it together.

Pin 21 is the "Accessory Indicator" pin, and depending on what's connected to it, apparently the iPod software responds in different ways. Pin 15 is a ground pin. The 1KOhm resistor tells the software that it's connected to a dock, which enables the LINE OUT functionality. More information about the dock connector can be found here: Apple iPod and iPhone dock interfaces pinout and signals @ pinouts.ru

I think this mod will also work for the iPhone 3G, although I haven't tested it. Provided you don't connect to any other pins on the back of the connector, the risk of damaging your iPod is pretty low to zero.

The inspiretech cable is available from Amazon.com for $5. Be warned that cables claiming compatibility with iPod Touch, unless they specifically indicate the Touch 2G, will most likely not work without this modification. If anybody can confirm otherwise, please let me know.

- Doug