battery switch for mono jacks?

[dschwartz]

hi all:
i would like your help on finding out how can i make a switch that turns off the battery power when a mono jack is unplugged..
I use these little plastic mono jacks:


they have a switch that connects to the tip when unplugged (i use them to ground the input when unplugged to avoid oscilations)

i tried simulating a transistor switch, but i couldn´t get good voltages. The principle was to ground the base of the transistor when no plug is in, but didn´t work so well..
any ideas?