I'm using a split supply, using 2x 9V batteries for a headphone amplifier. In lieu of an on off switch I'd like to just turn on or off when I put in the 3.5mm jack. Unfortunately the female jacks I've seen all have normally closed switches. When the user inserts, the switches open. I can't figure out a low power way to use a closed circuit to kill the power! I feel like this should be very simple but I'm coming up with complicated solutions like xoring the input and using a SSR, but SSR have 1-1.4V drops...ideas?
If the diagram to be believed, this 3.5 mm jack mates with a 3 conductor stereo plug, and also has an completely independent normally open switch:
Granted, these are rare; out of 170 3.5 mm audio barrel connectors at Digi-Key, this is the only one I could find in this configuration.