Sorta OT: Wiring jacks

[nosamiam]

Ok, this isn't strictly a stompbox question, but the answer could be applied to stompboxes.

I have a couple "toy" synthesizers that I'm converting for more professional applications.  I'm not 100% sure how to proceed.

Synth #1)  Has internal speaker which I have disabled and don't intend to use.  I've wired in a 1/4" jack for it.  No prob.  However, it is a sampling keyboard and I want the option to use either the internal mic OR an external dynamic mic.  So what I'm looking for is a way to wire it so that if there is no 1/4" cable plugged into it, it will use the internal mic (has 2 wires).  But if I plug a mic cable into it, it would like it to disable the internal mic.  Is there a way to do this?  I'm looking for an "either-or" arrangement. Can someone please explain it?  Bear in mind, I'm a newbie who has built a few boxes, but has little clue as to how circuits actually work.

Synth #2)  Has internal speaker which I have disabled by wiring in a 1/4" jack.  However, I'd like to be able to unplug the keyboard and have the internal speaker working.  Once again, I'm looking for an "either-or" setup.  Can someone help me out with this?

Thanks a lot,
Brandon

[nosamiam]

bump

Anyone?

[Samuel]

You're looking for a "normally closed" jack. These have an extra solder tab connected to a strip of metal that runs along the tip connector. When the plug is inserted, the tip connector is bent away from this strip, breaking the contact. So what you do is to wire the internal mic's output to this strip, and then wire the tip connector to wherever the mic output would normally go. That way, with no plug, the signal travels through this metal strip, into the tip connector and on to the recipient of the mic signal. Plug a mic in, and this connection is broken, so that only the external mic is connected to the next stage. These jacks should be very readily available (I think even Radio Shack sells them).

A similar solution will apply to the speaker...

[niftydog]

You can buy "switched jacks" which have all the normal connections, plus a switch built in that is activated by the plug going into the socket.

[nosamiam]

A ha! Thanks much, folks.  I'll add some switched jacks to my next web order.