You fried an audio output chip, and if you are unlucky as well the on board multi IO chip as well, as it is connected there as well for detecting headphone insertion and line or headphone output levels. Not easy to fix, as the chip is small, and buried in the non removeable main board. Applecare might replace the motherboard if you have the extended support option, but if they do not cover it the Macbook is going to have no audio built in any more.
Solution is to buy an external USB sound device and use it ( cheap at $2 for the simplest Skype dongle with mic and headphone outputs), and use a spare one for your sound experiments.