Tim Escobedo was this wildly creative force in the early DIY Stomp Box community. His circuit snippets page was had a lot of really great ideas. One of the ideas there was the PWM, which stands for pulse Width Modulation.
This circuit converts your input signal into a square wave and varies the amount of on and off time or duty cycle of the wave.
I had these boards manufactured through PCBWay.com. The quality is great. Ignore the bad silkscreen that was my fault. The cost was $5 USD for 10 boards which is very reasonable.
I designed this board to fit a 1590B enclosure in landscape. The cutout is for the power jack. I thought it would work well… After getting the boards I realized I would have trouble getting 500k 9mm pots that mount at 90 degrees. I going to have rethink this project. I also botched up the silkscreen. This is going to need a second try.