Allen was the brains behind this. We used this schematic and he added in an LED and a rheostat to control gain.
Because it has a magnet in it, the speaker conveniently sticks to the altoids tin while still being detachable. The indicator LED is inside (the red dot on the right).
The point of building this pocket amplifier was to listen to the output of a coil of thin gauge wire--ie, read magnetic fields. However, we built it kind of messily and it turned out to be more of a feedback machine. I did get some interesting results though, especially when holding it up to chargers and then unplugging them.
Later on, I found the following bit of treasure in a dumpster near the old Lucas building. It is a piece of old recording equipment, basically a magnetic tape reader attached to a 1/4" audio plug. I plugged it into my real amplifier, and achieved my original goal with much less extra noise.
I imagine it as a stethoscope for my computer.