I’m slowly working towards a project, it’s still not ready to be disclosed though, but it needed a dual rail power supply. I’ve always bought Doepfer DIY kits for my Eurorack needs, but I needed a +14V/-14V for this project. Since I could use an extra +12V/-12V supply as well for future Eurorack work, I decided to build a power supply with variable voltage regulators so it could handle both.

The main layout is simple. A power transformer which brings down 220V AC to 2x18V AC, put that through a bridge rectifier add some capacitors and put the result  through 2 variable voltage regulators. Add a trimpot for the voltage regulator so you can finetune the voltage. Top off with some extra capacitors and you’re finished. I tossed a led in for a visual indication and added some fuses – safety is good mmmkay.

The ( LM317/LM337 ) combination can output anything between 1.2v to 37v according to the datasheets. They need a few volt of overhead, so that’s why I choose 18V. You don’t want the voltage being too high either to prevent the voltage regulators from heating up too much. So 18V to 14V seemed like a good plan. Nevertheless I provided some room in the pcb for cooling. You would be able to use this design for +12V/-12V applications or +15V/-15V applications as well.


disclaimer: This design features mains voltages which can be lethal, please take all necessary precautions. As always, double check your work, and mine. You should expect errors in my design. 

Some pointers
  • Adjust the trimmers until you reach the desired voltage output. A multi-turn trimmer will give you the precision you need.
  • Make sure the capacitors used are the right voltage rating. 50V should be adequate but a 16V rating will actually explode.