Modular synth power supply

Every modular synth needs a power supply (except systems containing only blanks and Giskies 12 HP Bottle Openers). Switched power supplies sometimes casuses problems (when you have a lot of small modules, all with input power filtering caps), so I moved to a proven solution. My power supply unit is based on Doepfers Modular PSU, but has few little upgrades:

  • uses more popular, cheap heat-sinks,
  • better quality capacitors,
  • protection diodes,
  • changed connector spacing for easy operation,
  • 2 x 1,5 A output @ 12 V (tested), but will go to over 2 A on each rail.

Total cost of the PSU is about 20 euros.


The schematic

The schematic is very simple – just a popular linear power supply based on LM317/337 pair. Finally I used toroidal 2 x 15 V, 2.1 A transformer. Notice there is no fuse holder on PCB – it should be right after mains socket and before on/off switch. Filtering capacitors C1-C4 are 25 V rated which is correct if PSU is loaded. If no current is draw from outputs, the input voltage can get close to 25 V, therefore is is a good idea to use higher rated electrolytic capacitors, f.e. 35 V.

Euro synth PSU schematics
Eurorack modular power supply schematics



I always start the PCB design with fitting major components on printed PCB layout. There is nothing more annoyng then see that componets don’t fit after you spend 2 hours on cutting, etching and drilling. It takes only few minutes and can save a lot of time later.

Modular synth PSU layput tests
PSU layout tests

PCB was made with Bungard FR4100X160/3500 laminate with light-sensitive coating. Size of the board is 100 x 160 mm. All project files are added as attachement at the end of the post.

Modular PSU and busboards PCBs
Etched PCBs, ready to drill


The build

Vertical-oriented heat sinks make PCB size smaller, but at the cost of its hight. Most of the PCB is occupied by toroidal transformer.

Modular synth PSU top view
Finished PSU

6.3 mm outputs are marked with pieces of heat shrink. You can connect up to 3 bus boards. The small red LEDs inform you that there is something on power output, but what is more important, they let linear voltage regulators work properly when nothing is connected.

Modular synth PSU back view
Back view of the PSU

Silicon isolators under linear regulators ensure there is no eletrical connection to heat sink. They are not needed if you are 100% shure that the heat sinks will never touch. But you never can be 100% shure 🙂

Modular PSU front
PSU view from high voltage side

Before you do anything, remember: ~230 V can kill you with no problem. If you don’t have experience with mains voltage, leave it to someone who has. You are using the project files for your own responsibility.


6 thoughts on “Modular synth power supply

  1. Hey! If you change R1 and R3 to a 2k7 and put on a 2x18v transfo, Can you make this psu into -/+ 15v? 🙂

    1. Hello, if you calculated R1 and R3, it should work. Don’t forget to change capacitors rating to 35V!

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