Hi, Glenn
Are you about pin 3 on the schematic ? You are right that is 4 pins connector, sorry for this missunderstanding.
Actually pin 3 just goes to short to ground when simple 3-pin jack is using and that is not weigh with work in this mode.
4-pins sockets are compartible with 3 pins Jacks,?
Put both theese Jacks close to each other and you will see how it works.
Sorry, I was sure that pin 3 is a "jack insertion detection pin" and nothing more. Actually it works exactly like this with using 3 pins mini jack.
