A gentle introduction to Eurorack modular synth hardware for hardware enthusiasts.
A Rack is a place to put components. A common piece of audio racking is called the 19” rack, because the space across the rack in 19 inches wide.
You see these at gigs, dance parties, sound studios, server rooms. All sorts of places. They come in many shapes and sizes. Depth, height and pitch can all vary wildly, but the space between the sides is 19”.
The other specific standard in 19” racks are the mounting holes on the sides. They are laid out at specific heights.
These heights are called ‘units’ or RU or U for short. A device that is 1 unit high is said to be 1U. A device that is 6 units, 6U etc.
The following diagram is in german, so HE = U.
This is a standard that Doepfer introduced, based off of rack standards from DIN and IEEE. Much of what I cover here is a more gentle introduction than Doepfer’s own.
A Eurorack is designed with the 19” rack in mind. A Eurorack is 3U high. This means that it is 5.25” or 133.35mm high.
Warning: Do not make your module faceplates 5.25” high! You have to account for the “Lip”. The section on modules later has more information.
Now lets insert some Eurorack rails to mount our modules.
The best definition I can find for one set of Eurorack rails is a ‘Row’. Which suits me fine.
A single row is a single 3U enclosure, regardless of whether it’s a Rack mountable enclosure.
For example. Here’s my Pittsburgh Module [48] case (the 48 is it's width, I'll explain later).
This case is 9.5” wide. it’s not designed for a 19” rack. It’s just portable and complies with the other Eurorack dimensions. I keep calling out the “Lip” and I promise I’ll get to that.
Now we have a space to put our modules. I hope you’re reading this because you want to make your own modules.
I only bought one module for my synth. An oscillator from Intellijel, I hope to make the rest myself.
19” racks have variable heights and fixed width, so they standardized the heights as ‘Units’. Conversly, Eurorack has a fixed height and variable widths.
The height of a face plate should be 128.5mm as stated in the Doepfer documentation.
The width of a module is measured in ‘Horizontal Pitch’ or HP for short. 1HP is ⅕” or 5.08mm. Leave a little bit of tolerance for each plate and make them approx 0.3 to 0.4 mm narrower. For example (again from Doepfer’s spec):
Warning: Go buy a metric ruler. If you get these parts engineered for you, make sure the ‘tolerance’ you specify is 0.05 mm or better.
The thickness of a faceplate can be whatever makes you happy. To the best of my knowledge, 2 mm is considered generous.
Depth is a whole other story.
Doepfer modules are up to 105mm deep. My little portable Pittsburgh Synth case? No more than 28mm is going to fit in there (unless it’s away from the backplane components, where you might fit 50mm).
For more information, including size and position of mounting holes, read the now much referenced Doepfer spec. Just remember to ignore the bus boards - I’ll cover those next.
Eurorack bus boards are not used consistently across all Eurorack synth modules or enclosures. I don’t know why, but to hazard a guess I suspect that it’s cheaper, more flexible and easier to use a ribbon cable backplane
I recommend ignoring the position of headers in the Doepfer spec because:
You can use ribbon cable jumpers in all enclosures.
Most other enclosures use a ribbon cable with well spaced headers.
Let's look at my minimalist synth:
You can see my Dixie OSC on the left, and heaps of room for the synth modules of my own making! The ribbon cable carries the power to your modules.
Above is the bus pinouts for the Eurorack. It uses a common IDC header on the boards, and female to female connectors on the ribbon cable.
WARNING: Not everyone uses keyed IDC headers. Get the orientation right or cry.
WARNING: Pin numbers are not always shown. Look for clear evidence of which way to orient the connectors before powering up!
Actually misorientation guarantees a short on 16 pin headers, so you might be lucky and just lose your power supply. On 10 pin headers you’ll probably be lucky. Surely folks use diodes right, they’re cheap!
Personally, I’d never risk it.
Learning Modular Glossary of Modular Terms
Coming up next time... All about Control Voltages and Gates.
prguitarman
janainaart
gummygunk
romaincrisis
tangentwithtanner
titsay
baratheonpilled
izzy806
