Danger

This is a preview of the elektrophon website, the content may not be accurate and is subject to change without any notice.

In this article, we look at how to build modules that can be mounted in a eurorack. The international standard 19" rack system (DIN 41494 / IEC 297-3 / IEEE 1001.1) is the base for the dimension. These standards define all the parts needed to build a complete rack. here only the rails to mount the modules are used. The rails will be screwed to side panels made from wood.

Danger

This is a work in progress module and might not work as expected. Feel free to file a bug report on the github page.

pcb size

The size of the modules is described in U (Rack Unit) and HP (Horizontal Pitch). U is the height of the module. One U is 1.75" = 44.45mm. The modules are 3U, the total height would be 3*44.45mm=133.4mm. This would be too large when rails with lips are used. Therefore the height of the modules is 128.5mm. The HP is or 1/5" (5.08 mm). The real sizes are slightly smaller because of the tolerance of the PCB production process.

Figure 1: Eurorack Size

All the placement of the potentiometers and jacks follows a grid of 5.08mm. Configure the grid in Kicad to ensure the correct position. In the template, there are helper lines to see the placement.

Figure 2: Mounting rails

panel mounting holes

The positions of the panel mounting holes are odd. 4HP and 8HP modules have one. 12HP and 16HP have two but on different locations. 20HP would have three. Of course, the amount doubles one on the top and one on the bottom of the panel.

Figure 3: Panel mounting holes

The panel mounting holes are placed 7.5mm from the left side of the panel and 3mm from the top and bottom. The mounting holes must be in steps of 5.08mm. There is always one mounting hole on the left of the panel. On the right side, there is one when the panel is equal to or larger than 8 HP. To assemble the modules on the rails M3x6 cap screws are used.

Figure 4: Stacking PCBs

PCB stacking

To use more than one PCB, for example, one for mounting jacks and pot and one for the main circuit, the PCBs are stacked. There are mounting holes on the PCB and connected using standoffs.

Figure 5: PCB mounting holes

The mounting holes for stacking the main and mount PCB are 1 inch or 2.54mm from the sides. Modules are only stackable if the width is equal to or larger than 8HP. For stacking the modules M2/15mm standoffs and screws are used.

Figure 6: Panel Mount

construction summary

In this table, there is a summary of the sizes and panel mount hole positions. The lines marked as bold are the sizes usually used to construct modules.

Module width [HP]	calculated width [mm]	width [mm]	Mounting Holes [mm]
1	5.08	5.00
1.5	7.62	7.50
2	10.16	9.80
4	20.32	20.00	7.5
6	30.48	30.00
8	40.64	40.30	7.5
10	50.80	50.50
12	60.96	60.60	7.5, 50.8
14	71.12	70.80
16	81.28	80.90	7.5, 71.12
18	91.44	91.30
20	101.60	101.30	7.5, 50.8, 91.44
21	106.68	106.30
22	111.76	111.40
28	142.24	141.90
42	213.36	213.00

side panels

The side panels are made of wood and the rails hold them together. The construction of the panels can be done with the PDF template.

References

Doepfer A-100 construction details.
Schroff Eurorack Datasheet Information about eurorack components.
Rack Openscad files for the rack
Schablone Template for cutting the rack side panels

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