For a couple reasons I had been wanting a headphone amplifier to use with an electric guitar or bass guitar. I wanted to hear myself play, but not use an amp. I like my neighbors and didn’t want to keep the whole neighborhood awake.
I decided to build it since the electronics part is easy. I used a very simple amplifier based on a LM386 op amp chip. You can get them at Radio Shack. I basically built the schematic that is on the chip’s packaging. No rocket science involved. I changed the output slightly in hopes of reducing some hiss, which I thought worked. But there is a lot of hiss now that it is packaged and plugged into the bass guitar.
The interesting part is the packaging. I used a wall wart transformer from the junk pile and put the amp into it. This way the battery could be inside. Here are a couple photos. Since the battery is inside I added a switch and a pilot led to make things easy.
The two things left to do, which are related, is the get the battery to be stable and not rattle around. I used the PC board to handle most of this but need some sponge of something glued into the cover so that it will be held in. And the cover is pretty loose. I will use a rubber band until I come up with a better solution.