Take a couple of intake valves from a Harley-Davidson Shovelhead engine, a few blocks of (thick) plywood, a cheap stepper motor and a handful of other leftovers and what do you get? Why, a mellow sounding, home-made record player, of course.
The Altmann DIY turntable and tone-arm are built from such parts. The Harley valves make up the bearing, the wood goes into the base and the platter, and the stepper motor is fed a sine wave to keep it spinning at a constant speed. Wait, what? A sine wave?
Charles Altmann, for whom the setup is named, needed an analog way to run the stepper motor at a constant speed. By generating a 50Hz sine wave on a computer, running that to an old amplifier and then connecting the speaker outputs from that to the two coils of the stepper motor, Charles can get the motor running at just the right speed to turn the platter at 33 1/3 rpm. Tweaking the frequency allows fine adjustment if you need it, and you could then load the resulting sound file onto an MP3 player.
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