The same circuit as in Explain “Audio Loopback Dongle"; I wanted to know how it worked. Anything I couldn't figure out I found out via CircuitLab's time analysis:
This is how I plan to use it. I want to know ahead of time if there are any problems. Will it smoke the phones?
One thing I can't decide. Should the ground lines be connected?
Edit v1: Changed the 0.1 uF capacitor to 1 uF because the 200 Hz signal was too filtered. Compensated by reducing the 100 Ohm resistors to 50 Ohm to keep the microphone signal between the standard 5-50 mV. Hope this makes sense.
Edit v2: Well it works. Only the grounded version above. I have no idea. Why? Answer this and I'll accept. I hope it doesn't switch the jack from CTIA to OMTP and bypass the entire circuit. Also the ground and mic lines on the left have to be shorted for a headphone to be detected.