If you really want to build a good headphone or lightweight amp, go to either headfi.org (http://www.headfi.org) or straight to tangentsoft (http://tangentsoft.net/audio/) Start with the CMOY and move up to the meta42 or PiMeta amps. You can order the parts directly from Tangent and the instructions are easy to follow for anyone with basic soldering skills. The result (in the case of the Meta42, PiMeta, or PPA) is an amp that will go head to head with the best commercial amps, can be portable (pimeta/cmoy) and will give you the satisfaction of building something yourself.

"Obviously this amp was made for the use of an iPod but it could also be easily used with any type of audio player using the standard 1/4-inch audio jack." Don't you mean 1/8"?

i'm getting sick of all these really neat projects that you can make at home. Reason why is, the require knwoledge of electrical engineering. Doesnt anyone realize that many people who would love to give some of these a shot have no idea about any of that stuff!? i think a good move would be for someone to find or make a website that explains as well as gives you little rudimentary projects to do in order to teach you about all this stuff well enough so that afterwards you would have enough knowledge to actually do some of these projects. Then afterwards, all of these sites which talk about building stuff at home could put a link to that site, on theirs!!!!

For less than that price you can just buy a T-amp well known for its audiophile quality. available at thinkgeek, target, amazon, etc.

Justin is right -- that oughta be "1/8-inch".