At this point in the project, it was time to start moving across from crudely constructed circuits in project boxes, to something more professional. The popular Eurorack standard seemed like the obvious choice, primarily due to the abundance of other compatible modules for my creations to work alongside.
Eurorack is a standard first introduced by Deopfer in 1996 with their A-100 Series modular synth, and the market for compatible modules, both professionally manufactured and DIY, has exploded over the past few years. The standard comprises of three areas that I will need to be aware of in my design and constructions work:
- The physical size of modules is to be 3U (rack units) in height, and measured in HP (horizontal pitch) units of 0.2″. Common module widths are multiples of 4HP. The depth is also an important consideration, and although there is no set standard here, modules deeper than about 3-4″ may have difficulty fitting into many cases.
- Power connections must be made by a 10 or 16 pin ribbon cable, supplying +12VDC, -12VDC and GND, as well as an optional +5VDC if the 16 pin cable is used. This extended cable also houses the option for Pitch and Gate busses, although these are not commonly seen outside of Doepfer’s early modules. The 5V rail will be particularly useful for my Arduino chips.
- Signals are sent between modules via 3.5mm TS jacks, and use different voltage ranges depending on the type of signal. Generally, audio signals will output between -5V and +5V, bipolar CV (LFOs for example) at -2.5V to +2.5V, unipolar CV (pitch) will be in the range from 0V – 8V with 1V/Octave, and triggers or gates are digital 0V – 5V pulses.
There is tons of information on the A-100 system and suggested circuits layouts, technical information etc on the Doepfer website, and referencing this will certainly become an important part of my project write-up further down the line. Annoyingly, their website does not allow linking to individual pages, but if you click the link below and then go Products>DIY Page (in the A-100 System) you can find this.
