This guy has built his into a biscuit tin. Its powered by a single PP9 battery and while it isn't going to setthe world of hifi alight it will certainlyplay back the music from his iPod/Generic MP3 player.
If you have never made one they give it a go, once you have the bits the whol thing takes less than two hours to build and you will be suprised where you can use it.
I have one, built into an old radio case, which I use with my Casio CZ-101 synth to get that fantastic Jan Hammer "Miami Vice sound".
Othe ruses have been
- Testing synth (and other electronic) music circuits as I build them
- Linked to my MP3 player when camping or working in the garage.
- Giving a nice overdriven sound with synths and electric guitars.
- Pluged into my MP3 player, to play back drum patterms while I play acoustic guitar away from the house
- Providing a bit more volume from teh speakers of my netbook computer.