I understand that most analog hardware phase shifting circuits seem to use OpAmps to get their job done. I am trying to build a tiny, non-powered in-line adapter for Mp3-players and such to quickly sum up multiple signals - which can easily be accomplished without external power using just resistor signal mixing. However, to make this adapter really nifty and interesting, a phase shifting switch would really make the icing on the cake. Now, this leads me to the question in the title of this thread: a passive audio phase shifter/inverter - can this be done?
Any input/idea/feedback/suggestion is greatly appreciated!