Any way to use a switching jack to turn off circuit(test oscillator)?

[jimmybjj]

I want to install a oscillator circuit in my "circuit testing box" that has the normal input and output jacks. What I want is when the input is unplugged it activates the oscillator circuit, or visa versa when the input is plugged in the oscillator is activated. Its tedious to strum your guitar and trouble shoot the guitar but I want to final test with a real guitar. I know that I could just use a SPDT switch but I would prefer to use the jack. Any ideas?

[R.G.]

I want to install a oscillator circuit in my "circuit testing box" that has the normal input and output jacks. What I want is when the input is unplugged it activates the oscillator circuit, or visa versa when the input is plugged in the oscillator is activated. Its tedious to strum your guitar and trouble shoot the guitar but I want to final test with a real guitar. I know that I could just use a SPDT switch but I would prefer to use the jack. Any ideas?

Sure. If you use a stereo jack, the ring connection is grounded when a plug is inserted. I used that as a signal, not a ground for power here:
http://geofex.com/FX_images/splitter.gif
Grounding the jack ring contact provides current into the 3904, which pulls current through the bases of the 3906 and second 3904.

You can use a simple NPN or PNP which has its base connected to ground to turn it on (PNP) or off (NPN) and then use the current through the transistor to turn something on or off. This could be power to the oscillator or the bias to a JFET that is letting the oscillator go through.