Make 728
Octopart’s hardware blog has a dual channel music player amp (in an Altoids tin, of course)…

Have you ever seen a couple sharing a single pair of ipod buds, each listening with only one ear? That was the problem I wanted to solve when I started building dual channel headphone amplifiers while I was back in grad school. After a long day of soldering krytrons and high voltage capacitors in the plasma physics lab I would come home and…solder some more.

Octopart – Link.

From the pages of MAKE:
Make 729
Mint-Tin Amp. Pocket amplifier punches up headphones. MAKE 04 – page 141. Subscribers–read this article now in your digital edition or get MAKE 04 @ the Maker store.