Eurorack power supply

I am working on fitting a Raspberry Pi as a Eurorack module in the EEGSynth. A previous post shows the completed case. Besides the Raspberry Pi which needs 5V, it will also hold a CV/Gate controller and some other modules for interfacing between the digital and analog parts of the synthesizer. The operational amplifiers and some other ICs on those modules require a symmetric positive and negative rails.

As I am not planing any critical parts that require an very stable voltage (such as a VCO) in my enclosure, I decided not to go for an expensive linear power supply, but rather construct one myself on the basis of two 12V switching power supply that I salvaged from some old wall-warts that once served some external 3.5 inch USB hard disks. The AC-DC converters have the 220V side isolated from the 12V side. This allows to connect the positive DC rails of one to the negative DC rails of the other, resulting in +12V and -12V from either converter relative to the common ground.

The Raspberry Pi requires quite a bit of current compared to most synthesizer modules, hence converting the 12V into 5V with a voltage regulator such as the L7805 would not be very efficient. Therefore I also added a 5V 2A AC-DC converter.

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For safety I made a small plexiglass enclosure using the laser cutter at the Techlab Nijmegen. All electronics, except for the connector, switch and three LEDs are completely enclosed behind the aluminum front panel.

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The connector with the synthesizer modules consists of a flat cable, wired according to the A-100 system bus.

The LEDs show the status for each of the three voltage levels. Surprising is to see that it takes a good 10 seconds for the capacitors of the +12V and -12V to completely drain when switching the power off.