Digging through a junk drawer (one of my many junk drawers, I should add) I came across an old MP3 player I had forgotten about, and figured I could probably rig it as a replacement for my noise-emitting PDA. It's a stick type portable player with a USB plug on the end which allows me to load and delete MP3 files just like a thumb drive, a bit like this one here. It takes a AAA battery to run it though, not actually a problem as I have a ready supply of rechargeable AAAs but it meant I'd have to keep on swapping batteries as it would only run for a few hours at a time on each charge. See "high-maintenance" as mentioned above.
"Ahah!" I said, "I'll bodge it to run off a mains 1.5V supply!" Except there's no socket in the player to accept an external power supply... so I made a dummy AAA cell from some plastic scrap and fitted it into the MP3 player's battery compartment. Hooking up a spare AA battery to the wires from the dummy cell made the MP3 player work. Great! Now all I needed was a 1.5V... power... pack... ummm.
5V power supplies? got plenty. 9V, 12V, 14V, 17V, 25V yep yep yep but nothing with a 1.5V output. I tried diode drops, resistors etc. wired up to a 5V supply but nothing worked for various abstruse and arcane reasons. I thought about building a regulated 1.5V power supply but the only circuits I could find were based around a regulator chip I didn't have, the infamous LM317 adjustable voltage 3-pin regulator device and I didn't want to buy something that I could fake otherwise from what I already had to hand.
It was only after I had another cup of brain stimulant (aka instant coffee) that I remembered this MP3 player had a USB plug... Sure enough, hooking it up to a USB power brick proved it would happily run as an MP3 player while powered via its USB connection so it's now playing ambient noise in the background. Problem solved.
Now all I have to do is find another USB power brick that I can use to charge the PDA...