Hello everyone!
1 - audio signal to headphones connector (R)
2 - Vcc after power switch ON
3 - connected through 10k resistor to pin 2 of DB9 for normal operation. Disconnected for headphones use.
4 - GND
5 - Potentiometer cursor
6 - audio signal to headphones connector (L)
7 - 20 Vcc from...