I want to remove the DC component and boost to a line in level the mic signal of a regular headset plugged into a mobile phone while still allowing the mic to be used by the phone at the same time:
I need this to work with any standard headset and mobile phone; i.e. I want the preamp box on the diagram to act transparently, not affecting the interaction between the mic and the phone. For example, it shouldn't modify the impedance since iphones measure that impedance to detect whether a microphone is connected or not.
What is the simplest way to achieve this bias removal and amplification so that I get a low-noise line in version of the mic signal that I can use for other means (e.g. feed to a computer for monitoring or recording)?