If you have a traditional regulated power supply that you want to make adjustable, you’ll have somewhere in the circuit a feedback line driven by a potential divider across the output. That divider will probably incorporate a variable resistor, which you’ll adjust to select your desired voltage.
The problem with using a standard pot to adjust something like a power supply is that a large voltage range is spread across a relatively small angle. The tiniest movement of the shaft results in too large a voltage change for real fine-tuning, so clearly a better means of adjustment is called for. And in many cases that need is satisfied with a ten-turn potentiometer, simply a pot with a 10 to 1 reduction drive built-in.
[Dardo] had just this problem, and since 10-turn pots are expensive to buy and expensive to ship to his part of the world he built his own instead of buying one.
His 10-turn pot is a fantastic piece of workbench improvisation to deliver the goods from what is at hand. A capstan and shaft from an old radio tuner drives a small rubber belt and pulley from a CD-ROM drive. This in turn has a gear which drives a much larger gear coupled to the shaft of a standard potentiometer. All the drive components are mounted on a frame made from an old aluminium heatsink.
To be strictly accurate it’s a 13-turn pot rather than a 10-turn one, but the principle is the same. And it’s an extremely effective component, especially for the price. We like it!
If you are inspired to put a 10-turn pot in your supply then this project provides a blueprint. It’s worth saying though you could take a look at an off-the-shelf component instead.