| Pin | Signal | Description |
| 1 | USB +5V in | USB 5V supply - in K750 not used |
| 2 | SP_REF | Reference / headphone gnd |
| 3 | Mic+/AUXIN_L | Microphone+ / AUX Input - left / Short to 4 for Answer button (*) |
| 4 | Mic-/AUXIN_R | Microphone- / AUX Input - right / Short to 3 for Answer button (*) |
| 5 | DFMS/SP_L | DFMS / headphone speaker - left |
| 6 | DTMS/SP_R | DTMS / headphone speaker - right |
| 7 | VIDEO/STB | Video / strobe |
| 8 | VPPFLASH | Short to pin 9 for handsfree detection (use a 130 ohm r) |
| 9 | GND | Ground |
| 10 | CTMS / USB DATA+ | CTMS / USB+ (data) - in K750 not used |
| 11 | CFMS / USB DATA- | CFMS / USB- (data) - in K750 not used |
| 12 | Charge In | Battery charging (+5V) - in K750 not used |
If you want to make a stereo converter with a SE socket, you should use pins 5 and 6. It may not work well with an amplifier due to low output i.e. just enough power for headphones . (May need pre-amp).
Suggestion:
To make a stereo-amp using the cell phone you must shortcircuit pins 8 and 9. Then connect the outputs (L) (R) (GND) using pins 5 = (L), 6 = (R) and 9 = (GND).
However, note that the Original Sony-Erisson Walkman headset is connected using pins 2 (GND), 5 (L) and 6 (R).
(*) Use a push button to shortcircuit pins 3 and 4 to pick up / hang up an incoming call