Originally Posted By: K447
Thinking about your resistor to ground comments, perhaps there is an issue with which ground(s) you have used.

I think there are separate ground pins for power, USB and audio within the iPhone connector. I do not know, but I suspect, that some of these grounds are NOT inter-connected together within the phone itself. Or maybe they are, but it may still be important which ground pin gets used for what.


There's one ground for everything, in effect BUT the audio has a ground *sense* pin. This senses the audio ground at the point of consumption (on a dock, that's usually at the audio output jack) and the system drives the signals with respect to that virtual ground. This means that changes in charge current, for example, which would be moving the system ground around (with respect to what the dock thought was ground) don't get coupled onto the audio.

The resistor can go to any actual ground - ie the power supply ground is fine.