Power supply

An analog synth requires a very stable and well regulated power supply. My very first synth module was the power supply for the Elekror Formant. I built that in 1978, when I was 19 years old.
I didn't know how to etch circuit boards back then, so I made the board by taking an unetched board and grinding away the copper between the traces. The board look ugly, but this power suppy has been in use ever since, and still works perfectly.
For my new portable case, I wanted something more compact and I also wanted to retain the old supply in the workshop, for developing new modules.
I decided to design a new circuit board and use the same circuit as in the Formant. My new board is less than half the size of the Elektor board. To supply all my planned modules, I needed at least two units. That also enables me to put sensitive modules on one and noisy ones on the other.

On the prototype for my new board, I measured the load regulation to be within 100 mV from no load to 800 mA load. 100 mV might sound like too much variation for precision use, but remember that in reality load current doesn't wary between nothing and full load. Load current mainly change when you connect a new module. You can easily trim the voltage if it should be necessary then.
Maximum output current is measured to be 930 mA, but for best regulation, do not to go over 800 mA. With shorted output, the current is limited to 500 mA.
Temperature drift seems to be no more than a few millivolts, under normal operating conditions.

Circuit board layout (PDF-file)

Component placement (PDF-file)

On top of the power supply unit, there is a normal computer fan, which runs on reduced voltage, from the 10V supply. I used diodes to drop the voltage below 10V. The heatsinks are inside the channel, which the circuit boards and the plywood sides form.
The banana jacks are for monitoring the voltages and currents from each unit. By removing the brass links between the banana jacks, an ampèremeter can be connected in series with the load.

All my modules use the same connector for the power. This connector also contain two channels of keyboard control voltages and gates. These are normally connected to the two MIDI-to-CV-converters. Above is a pinout plan for the power connector.


This is the power distribution bus, which connectors for 24 modules.  The two rows of connectors are connected to the two separate +-15 volt supplies.