Eurorack modules typically require a +/-12VDC power supply. A few need +5VDC as well.
Eurorack Case Power
For power distribution, a Eurorack case would typically have a power supply connected to a distribution board that looks like this:
Each connector is a 16-pin DIP header that you connect a power cable to. Sometimes the headers have a keyed shroud around them that only lets you plug connectors into them one way. This helps prevent reversing/offsetting connectors and damaging your modules or power supply.
Eurorack Module Power
Modules themselves can have either 16-pin or 10-pin headers for power connectors (shrouded or unshrouded). Here are the pinouts for the connectors:
The 10 pin header provides the module with +/-12V and Ground, which is quite frequently all that is required.
Many modules also require a +5V supply, but since not all power supplies provide it, most of them create their own +5V from the +12V supply.
The Gate and CV buses are rarely taken advantage of, but can be used by modules to send signals to each other through their power cables without requiring front patch cables.
A module may use the 16-pin power connector if it needs the +5V, Gate, or CV signals.
Eurorack Power Cable
A Eurorack power cable is typically a piece of ribbon cable with a female 16-pin IDC connector on one end and a 16 or 10-pin on the other.
Note the stripe on one edge of the ribbon cable. This indicates the -12V side. Most power boards and modules indicate which direction to put this stripe in some way:
- “Red Stripe”
- “Stripe Down”
Note: Be very careful when connecting power to your modules! Unless shrouded/keyed headers are used, it is very easy to connect one of the connectors backwards. This could damage your module! Some modules use diodes for reverse-polarity protection, but unless you are absolutely sure, it pays to hook them up right.
Plus AND Minus volts? Where the heck do I get that?
There are a number of companies that sell power supplies that are perfect for Eurorack, or cases that have supplies built in. They can range pretty wildly in price and current capacity.
If you are just getting started, one way to make a cheap easy Eurorack power supply is to connect a couple of (regulated!) 12V DC wall power supplies together. Connect them like this:
All power supplies have a maximum amount of current that they can supply. In the Eurorack world, you should find a current spec for each voltage your supply provides. For example:
- 5V: 500mA max
- +12V: 2A max
- -12V: 2A max
This means that our imaginary supply can theoretically provide up to 0.5 amps (mA, or milliamps, are 1/1000th of an amp) on the 5V output, and 2 amps on the 12 volt outputs. This doesn’t mean that you should load it down that much though. It’s best not to draw more than about 80% of their rated capacity. This allows for things like startup current (where modules draw extra power when they’re first turned on), occasional current draw spikes over what the module is rated, parts getting hot inside stuffy Eurorack cases, etc.
How do you know how many modules you can put on a power supply? Manufacturers usually list the current draw figures for their modules on their sites. Another good place to look is modulargrid.net, where most modules in existence are collected in one easy to search place. Add up the current draw for each voltage, and stop plugging in modules when one of them reaches 80% of your supply’s maximum for that voltage.