So I took apart an old car radio a while back, looked at the datasheet and made a small boombox for my shed (I have lead acid batteries charging from wind and solar so the chip was quite happy without regulation)
The radio had two separate chips in it and I was wondering what to do with it for a while now but then my girlfriend mentioned that she had speakers from a surround sound system (but no controller strangely enough) so sooner than dumping them, I made a second amplifier circuit and I'm just going to show the assembly here..
Step 1: The Enclosure
I cut the back out of an ABS enclosure so I could screw the chip onto the heatsink. As you can see the box is screwed straight onto the heatsink too.
Step 2: The Circuit
The amplifier chip is a TDA7375A, a quick look on the datasheet shows some example circuits for it so I picked the most suitable design and bought a few capacitors which I didn't readily have.
I also bought a step down buck converter as I'm powering it with an old chrapbook charger, which outputs more voltage than the chip can take. I did buy multiple at a time so the cost of one was minimal..
Step 3: Somewhat Compact..
I definitely could have done with a bigger case but I managed to squeeze it in anyways. Also there is thermal grease between the chip and the heatsink so it should last a good while before going thermonuclear ;)
And that's it! Sorry it's not a full instructable but I'm pretty sure anybody could do this if they looked at the datasheet, also if you can't find old car radios anywhere I'm fairly certain ebay would sell similar if not better chips (I say better as the two chips I pulled were out of a radio with a cassette player haha)