A smaller project I've spent a couple days on is modifying an old receiver for wireless headphones to work with normal RCA plugins and using power from the wall instead of batteries. The proof of concept was very easy and took less than an hour. Basically cut out the headphone speakers and hooked up male RCA cables to each. Also for the power I checked it with a multimeter(It was 4.5 V) and then found a wall plugin that matched. For the current I started by trying to use the current of one AAA battery(Roughly 1000mA) and found that worked fine so left it at that. I did have problems opening them up and made some dremel cuts on it till I figured out where the screws were.
Next the long part was compressing it down into a smaller package. This involved taking out the wires that went between the headphones and replacing them with shorter wires, and eliminating wires not needed anymore(Like the headphone's internal amp to the headphone cup). Also hooking up the power to the switch and cutting out the battery pack holder. Picture below is about 1/3 of the way through:
The finished product turned out okay. The two cups didn't quite match up, so there is a large gap on one side. Also the tool marks from the original attempt at opening the headphones. Hot glue was use to hold the wires in place(And avoid any shorts from moving wires) as well as keep the cups together. All the buttons(Power, amp, freq) and LEDs still work and are easily accessible. I also ran the antennae wire to the outside so I could improve reception and avoid it contacting any of my wires on the inside.
The finished 'setup' is an old torn apart stereo system, with speakers positioned to project sound below(This is all up in my work shop in the loft). I'm using my vaulted ceiling to try and redirect the sound to hit both ears, which has been working pretty well, except the left speaker sounds like it's coming from directly above instead of to the side. I've been using it all day with no problems, and it sounds much clearer and better than the crappy TV speakers, even with them being on a different floor.
In the future I want to splice out the IR receiver on the stereo and position it so I can change the volume downstairs without moving(Right now I'm using the transmitter's amp). Also I need to change around speaker position to get better left and right separation, as well as tweak all the amps. There are now 4 amps that come into play which is the TV, the transmitter, the receiver, and the stereo, so it takes a fair amount of fine tuning.