Q:

Audio jack detection to turn on device without power loss

I'm trying to make simple headphones amp and I wonder - is there any way to use stereo jack connector with N-C switches like this: 
to turn on the amp so the battery is mechanically disconnected?
I mean that, if my connectors had N-O switches, it would be easy, but with N-C I have no idea, whether it's even possible to make such "smart" power on, without any power loss (i.e. powering some transistors/logic gates that detect open circuit etc.) or maybe should I seek for female connector with N-O switches?
Best regards!

A:

Not really for a stereo headphone, but you can do it for a mono jack by hooking the battery negative lead to the ring contact on a stereo socket... Classic guitar pedal trick. 
About the best you can do is a mosfet with a 22M resistor to bias the gate and use one of the headphone switches to pull the gate down when nothing is inserted. 
Regards, Dan.

