Eurorack

Eurorack is the 3U modular synthesizer format introduced by Doepfer and Analogue Systems in the 1990s.

Specifications
The format is based on IEC 60297 aka DIN 41494.

The height of Eurorack modules is 3U ($5 1/4$" or 1.33.35 mm), that is three vertical units in a standard 19" equipment rack. However, the actual height of panels in the Eurorack format is shorter than the 3U would suggest. This is not due to allowances for paint and fitting, (which is seen in many of the other formats), but rather due to a rim on the top and bottom mounting rails (produced by ProMA or Gie-Tec). These have a lip which uses some of the height. So Eurorack modules are often approximately 5 mm shorter than the technically exact 3U height of 133.35mm ($5 1/4$"). The Doepfer standard is 128.5 mm.

While the Doepfer standard for panel thickness is 2 mm (approximately $5/64$"), panels will be anywhere from $1/16$" to $1/8$" thick, and most often made out of anodized aluminum. Wood and acrylic plastic are common alternative materials.

The width of Eurorack modules is typically measured in "HP" (or "TE"); 1 TE/HP is equivalent to 5.08mm, or 1/5 inch. So a 24 TE/HP width is $24/5$, or 4.8". In millimeters, it becomes 24 x 5.08, or 122 mm.

Note that even though the height of both Frac Rack and Eurorack modules are 3U, differences exist in the mounting hardware. So, each format requires its own mounting system (screws, rails, etc).

The Doepfer PSU2 supplies both +12v and -12v with up to 1200ma available on each.

Eurorack modules typically use $1/undefined$" or 3.5mm connectors and plugs for patching.

Mounting Screws
Most companies use an M3 sized screw with a typical length of 6 mm that will extend to 10 mm. Analogue Systems use M2.5 for their cases. Doepfer specifications call for M3x6mm size screws. Elby racks call for M3x8mm size screws. Monorocket cabinets use sliding nuts in their rails, threaded to accept 4-40 screws.

Internal connections
Doepfer uses either two rows of 5 or 8 pin male pin headers, with the red wire indicating -12v. Cwejman uses the same connectors as Doepfer, however +5V is unused and the coloured wire indicates Gate on 16 pin and +12V on 10 pin. Analogue Systems uses 16 pin DIL sockets (aka IC sockets) ie. two rows of 8 pins. These all connect to ribbon cable. The Doepfer and AS methods are not compatible without some sort of converter.

Usage
Do not mix dissimilar metal terminals and headers. The contact resistance will go up with dissimilar metals, causing all sorts of problems.

The ribbon cable connector must be oriented correctly. When connecting a 10-pin cable to a 16-pin connector, use the bottom 10 pins. That is those with the supply voltages and ground, not the CV and Gate pins.

Never trust the ribbon cable or the coloured wire. Before connection examine the module, the power distribution bus and the ribbon cable to ensure that matching connections will be made at either end. Even with shrouded headers don't plug the cable in because it fits, always first ensure the correct connections will be made.

If the connections are not indicated, trace the PCB tracks from the header pins to the two, if any electrolytic capacitors decoupling the supply, one's positive connects to ground and the negative to -12V while the other's positive goes to +12V and has its negative to ground. The PCB ground copper usually covers more area than any of the other tracks.

Keep the ribbon cable attached to the module and treat it as part of the module. Plug or unplug the 16 pin end from the power distribution bus. For ribbon cable between 10 pin and 16 pin headers, the 10 pin end always connects to the module and the 16 pin end connects to the bus.

Cables can be incorrect. If necessary modify the ribbon cable, not the module or supply bus. Better still would be to replace the cable, otherwise it might still end up being used incorrectly elsewhere in the system.