I’ve finally committed myself to the fact that I’m going to build a modular synthesizer so the first thing I need to build is a modular synth power supply. I also figure that if I build the synthesizer power supply it will kick-start me into finally building the rest. This is a project I’ve had at the back of my mind for years.

Since most of the modular circuits I’ve looked at seem to need dual supplies of 12V to 15V the LM317 variable voltage regulator looks like a good choice. I’ve already built a power supply based on the LM317 kit here so I’ve more or less made up my mind. It’s going to have to be a linear power supply due to the fact that I want it to be as clean as possible as it is going to be used for audio circuits.

While looking around at which case I could build it into I suddenly had an idea that will not only save me money but also time. Most of the holes are already in the right places so that will save me the most time-consuming part of drilling.

The idea I have is to use an old computer power supply. Open it up take the old computer PSU board and wiring out. Be aware though if you try this because some of the large capacitors on these boards can give you a nasty shock even after a few days without being powered up.

The old PC power supply that I’m going to use. It’s working but worth more to me as a case.

You can use the three-pin socket for the mains in and just wire it to the transformer and there’s already a large hole with a rubber grommet to use for all the power cables out.

Synthesizer power supply

There are a few power supply kits on Amazon that are excellent value and just what I’m looking for. I was initially going to build a power supply using the previously mentioned LM317 and design a board but there are already kits for exactly that using the LM337 for the negative supply.

It seems stupid not to utilise something that’s already available at a very reasonable price. It’s also going to save me loads of time in not having to design and build a custom printed circuit board, something that I’m quite slow at.

This is the kit that I decided to get. There are a few that are very similar with almost identical parts but different board layouts.

The construction of the kit is fairly straightforward. There are no positive markings for the polarised capacitors, instead, they use a shading screen printing for the negative terminal. It helps if you put a thermal transfer compound on the LM317 and LM337.

This is the circuit diagram of the kit.

Thermal heat transfer compound.

Apply it to the devices.

Smear it so there is a thin layer.

Bolt on the devices.

​I used a thermal transfer compound that I’ve had for years. You don’t use much up and a small amount will last a long time. If I was having to buy new stuff I would buy Arctic Silver 5 Thermal Compound 12g Tube for the reason that you can also use it for microprocessors in PC’s and laptops.

The completed, assembled kit.

The next stage was to strip out the old circuitry in my old PC PSU. Be careful that the capacitors are not holding a charge. You can leave the fan in place along with the mains in socket.

The completed modular synth power supply.

There’s plenty of space inside the case for a large transformer. Here I’ve just bolted it to the inside of the case. The mains is already taken care of with the socket. There are plenty of nicely pre-cut venting holes. I’m going to use some stripboard as the bus bars to supply the voltages to the individual modules. The multi-turn pre-sets make it easy to accurately set the output voltage. In my case, this was to be plus and minus 15V. When the lid is screwed on there is a large hole with a rubber grommet where all the original wires came through for them to go through. As you can see it’s not too hard to build a modular synth power supply. It’s the rest of it that’s going to be challenging.