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[PolyPhuckin]

In pretty much most pedals nowadays, if a pedal is run on batteries, when a jack is inserted the unit turns on and when unplugged, turns off.
How is this achieved?

[Gordonjcp]

Stereo socket, sleeve connected to chassis ground and battery connected to ring.

When you plug a mono jack plug in, it shorts sleeve to ring, connecting the battery.  Simple, but clever.

[Bogus Noise]

As mentioned, it's a nice little bit of component design. When you buy jack sockets, make sure you get the 'switched' ones.

If you buy them shaped like the image below, they're easily identifiable by having solder points on both sides of the plug.

[PolyPhuckin]

i think i get what you mean, like this?


Dont you just love my Illustrator skills 

[Gordonjcp]

Usually the battery negative and circuit negative are the other way round, but yeah, that's it.

[PolyPhuckin]

That is an ingenious idea 

[hoffy]

That's pretty much exactly what you'd do to turn the speaker on/off as well...

... right?

[Gordonjcp]

Nope, that's what you use a jack with two rows of contacts for.  Looking at the picture of the stereo jack a little up the page, you'll see that the contact fingers touch the second row of terminals when there's no jack inserted.  So, what you'd do is, you'd wire the output of the amp to the "tip" contact on the jack, and wire the speaker to the tag opposite.  When you put the plug in, the tip of the jack lifts the contact finger off the other terminal, breaking the circuit with the speaker.

A long long time ago, you could get gauge B jacks (used in some patch panels, and old telephone exchanges) that had little pushrods that operated switches with NC and NO contacts when a jack was inserted.

[goldenbaby]

K, about the switched jacks we've turned our attention to, we'd wire the sound signal to the fingers, right?  since when the jack is pushed in, they will be the only contacts touching it, while the side ones will go to the speaker?

[Gordonjcp]

K, about the switched jacks we've turned our attention to, we'd wire the sound signal to the fingers, right?  since when the jack is pushed in, they will be the only contacts touching it, while the side ones will go to the speaker?

Correct.  It's easiest to visualise this with 1/4" jacks, where two terminals go to the contact fingers and two terminals go to the "break" contacts.  If you were wiring up an external speaker socket you'd wire the speaker across the break contacts and the output from the amp across the fingers.  If you were wiring up an input, you'd wire the break contact for the tip of the jack to ground, so that with no plug in, the input is shorted.  That would stop it buzzing.