So, being an audio person, I have been having a secret love affair with thermionic valve (vacuum tube, for you 'mericans) technology. Well, I've decided to come clean about it. This is my valve preamp:
Built from a kit, with power supply and input/output modifications from myself. Originally ran of two sets of batteries, a 9v supply and a 3v supply. So the board on the left has a pair of LM317s on it in parallel to supply those. The whole circuit has a pretty low current draw (70 hours out of 1 9V battery originally), so efficiency isn't a big concern for me. The toggle switch on the back is a bypass switch. Because there's nothing like a/b comparisons to prove that valves are wizards trapped in glass bottles.
For those of you wondering, the little glass things with the rubber rings around them are the valves, in the last picture.
Also, it sounds amazing~