Ok, some actual engineering

[atom]

I just got a new case. This one finally has front USB and front audio. I have an older motherboard, it does not support front audio. My sound blaster live does not either (at least I couldnt find a pinout for the connector on it)  I want to wire up these ports so that it gets the audio signal from the soundcard, and if I plugin my headphones, it shuts off the speakers. I believe this would be possible with like 3 or 4 transistors, but I do not know my gates. Can anyone help me with this? (10 bucks says Aidan has the best answer for this one.)

[atom]

After some consideration I have decided that because of the way transistors work, this would not be possible. Transistors usually need a 5 volt signal, which means its going to be a digital thing. Its possible there is an IC out there to do what i want, but I dont give a crud, Im hooking up a switch. That doesnt matter much either, my crappy hardware is all failing on me, you guys might not see me in a while. Anyone have a combo of mobo, cpu and ram to sell me at a good price?

[Aidan]

Normally the functionality you're asking for is actually done in the headphone jack with the contacts there, rather than any fancy circuitry. Depending on the cheapness of the case, you might find the jack in the case doesn't support that. How many wires go to the case's jack?

Oh, and transistors are quite happy working on signals much smaller than 5V. How else do you think that microphone amplifiers work?

[atom]

Yes someone else told me about the switching jacks, if my case already has them (havent looked yet) then I will rewire them, if not I will replace them. I have a jack for left right for both headphones and mic and i have a vcc for both. And I was under the impression that an analogue signal of varying voltage wouldnt properly trip the transistors. I dunno. Im no expert. Thanks for your help though.

[Aidan]

Transistors operate extremely well in amplifing small signals. They're not actually a switch per se, but can be used as one. Basically, the transistor watches the current into it's base terminal, and will output a proportionally scaled (ish) current through it's collector. The ish bit is because the signal isn't totally linear, but follows an interesting curve. This is why some amplifiers have different classes (like A, AB, B, C, D and H), as they have different methods for coping with the non-lineararity of transistors.