[Andrew]

There used to be a big "hobbyist" electronics movement in this country. I have watched this steadily decline over the past several years. You may be able to find a hobbyist area on the internet and get plugged in.

There were two magazines (Popular Electronics & Electronics Something) which merged into Electronics Now about four years ago. These magazines published circuits especially for audio applications. If you can dig back into that archive, you'll find some audio circuits to do the various tasks that Al mentioned.

You need to start with a condensor microphone element (available from Radio Hut or from Digikey). A condensor mic takes sound waves and converts them into a change in capacitance. You need a preamplifier circuit to take this change in capacitance and convert it into a voltage. Good luck on finding such a circuit. There were many in the Popular Electronics. Since Pop Elec is referenced in Applied Science and Technology database, you can probably do a real lit search and find one.

You might be able to find a data sheet for the condensor microphone which gives you a circuit to preamplify it.

The output side is the driver is best done with an LM386. I'm pretty sure this chip is not obsolete. If you want to find the circuit to do this, look up the Data Sheet and Application Note for the LM386 on National Semiconductor's web site (if they haven't spun off this part of there business to another chip maker).

You can find the "in between" stuff by looking up the patent for the noise cancelling ear phones. Somewhere out there is a patent search database (on the .gov net). You can acquire patents from any public library. If they don't have them, they can get them through interlibrary loan.

In terms of getting everything working, if you don't have an oscilloscope, I would abandon ship right now.

The LM386 part of the puzzle is the easiest to get working. You can get the parts and wire it up in a couple of weeks. To test, you can take the output of any CD device (CDROM drive for instance) and connect that as your circuit input. Connect the output of your audio driver to a speaker. If you get sound (and the LM386 doesn't heat up and start a fire), then you're good to go. Otherwise, check your solder joints and connections!