Do you want to enter the incredible world of Eurorack modular synths with a small rack but are held back by the price? Even for a mini 50hp rack, between the cost of the case, rails, and especially the power supply and power distribution systems, you have to spend over 150 euros. Without any modules... Fortunately, here I provide you with a way to build a mini rack for less than 50 euros!

Here are my choices for the case, rails, and power supply.

The Cheap Eurorack Case

On this side, the handiest among you can make a makeshift case out of thick cardboard, wood scraps (plywood, MDF, etc.), metal (aluminum, steel, etc.), plastic (PVC, ABS, etc.), or thick cardboard.

Are you one of those who think a hammer is a kitchen tool? Or maybe your toolbox is more decorative than functional? Don't worry, you're not alone!

You need only find a box with a height between 14 and 15 cm, 6 inches, since the height of an Eurorack module is 13.3 cm or 5.25 inches.

I found a somewhat stylish bamboo box on Amazon for 7 euros:

• Bamboo box 15x15x7cm
• or Bamboo box 9x6in

This 15x15cm box is suitable for holding a few modules, totaling 26hp. Alternatively, there are wider variants measuring 23 or 30cm, accommodating up to 60hp. If you find other boxes with a depth of 15cm/6in, I would be grateful if you share the references in the comments below (IKEA boxes?).

Eurorack rails

Eurorack rails are used to secure and align modular synthesizer modules within a standardized frame. They hold the modules in place and allow them to be easily connected.

Printing rails rather than buying them off-the-shelf can be advantageous for several reasons:

1. Cost: 3D printing can be less expensive, especially via the many print-on-demand services available.
2. Customization: You can adjust the dimensions, which will be crucial in our case, because of our not-so-standard box 😊
3. Experimentation: This allows you to test different designs and materials without investing in expensive parts.

For the rails, I found two interesting designs to print:

• Modular Rails
• Richard Lawler Rails

I opted for the 1st one, which I had printed at JLC3D for 10 euros, but the second design looks even better.

For our 15 cm case, we'll have to cut them off because they're too big. I glued a small 2mm balsa shim at the top and bottom to get the right height. Here's how it looks after gluing:

A mini Eurorack power supply

A Eurorack power supply must supply three standard voltages:

1. +12V: To power analog and digital modules.
2. -12V: For modules requiring a symmetrical power supply, which is the case for almost all modules.
3. +5V: For digital and logic modules.

If you have a lot of modules, and therefore need a lot of power, the DIY community suggests using a MeanWell RT65B power supply, to be connected to a bar bus. This power supply would be too big to fit into our little 15x15 box...

That's why I'm proposing a compact design based on a Meanwell DCWN03E-12 module connected to a USB C port for power. It fits easily into our Bamboo box, and the USB C power supply is really practical, so you can even use a power bank. But you're limited to 125mA on each 12-volt line.

Here are the components used, which will cost you less than 10 euros, the most expensive being the Meanwell module at around 7 euros:

• USB C Aliexpress trigger board
• PCB Stripboard 60x40mm
• Meanwell DCWN03E-12 module
• Two 2x16 pins connectors
• Possibly capacitors to smooth the power supply, and wires to solder it all together. A 500uF chemical capacitor at both input and output will give a cleaner voltage, but this isn't necessarily necessary as the DCWN module is already fitted with a PI filter. To be seen if you have a module that is very sensitive to power supply noise.

A few soldering operations later, following the diagram above, you'll get this. Just stick the module in a corner and cut a hole for the USB-C port.

Caution! The Meanwell module is limited to 125 mA of current on both the +12V and -12V rails. This is sufficient for a few Eurorack modules, but likely not enough for a larger case. Please verify the total power consumption of your modules on ModularGrid.net. Typically, fully analog modules consume less power. For higher current requirements, you could consider using two Meanwell modules for 250mA on each rail. Alternatively, an external power supply may be necessary. While the X can be used in place of the Meanwell for higher current, tests indicate that its voltage stability is not ideal.

P.S.: Another idea for increased current: use a Meanwell DCWN06A-12 (250mA max) but then you need a 9v input which is not a problem with the USB C trigger board. In that case, an additional 5v regulator will be needed.

Now with a small budget, you can start with Eurorack. The hardest part is actually finding the right case, so if you have other sources for €10, feel free to share them in the comments below. To continue your journey, I recommend building your first modules on a stripboard or breadboard; there are countless circuits available in communities like Reddit's diypedals, diyeffectspedals.com, and others. Have fun!