Intro to Eurorack Part I: Doepfer's Beginnings and Power Supply Basics

From modest beginnings in the mid-1990s to its current beloved presence in the world of gear, the Eurorack synthesizer is firmly established as an important contemporary instrument. Bubbling up from the underground, the independent world of Eurorack has been a revolutionary player in keeping live hardware electronic music thriving and essential. Eurorack has always been about responding directly to needs of the musicians themselves who desired creative immediacy instead of an impenetrable workstation interface or mouse and screen.

History of the Eurorack

Charting 20 years of innovation in electronic instruments must begin somewhere, and Doepfer is that beginning. Dieter Doepfer started his company and began developing a voice card modular system in the early 1980s. Development wrapped up in 1982, but by 1983, MIDI was standardized and the DX7 was released. The market for synthesizers shifted rapidly. Doepfer carried on, however, and developed a reputable line of MIDI controllers.

Doepfer A-100

By 1992, Doepfer turned his attention back towards analog, designing the MAQ16/3 Sequencer with seminal electronic outfit Kraftwerk. This was followed by the successful MS-404, a rackmount analog monosynth module, in 1995. Doepfer then revisited his designs from the early 1980s and by the fall of 1996 released the A-100 Analog Modular System, a complete complement of analog modules housed in a standard 19” rackmount enclosure. The continued collaboration with Kraftwerk resulted in the system's distinctive all-silver appearance.

Significant to the establishment of the Eurorack standard in 1996 was the case itself. The mechanical specification for the Eurocard enclosures was adapted by Dieter Doepfer, who then designed the power supplies and bus boards for plugging in the modules, which could easily be fit into existing rack cases commonly found secondhand in Europe at the time. The modules themselves adhered to specifications from this industrial standard. The module height was three rack units and the width was measured in the Eurocard-specific Horizontal Pitch standard, where 1HP equals 0.2 inches, or 5.08 mm. The modules were largely low cost, compact, and had some components on their boards which were socketed instead of soldered down, so the user could, for example, upgrade to a better op amp IC.

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Eurorack Basics

Emphasis on DIY options is crucial to understanding Doepfer and the Eurorack, and getting a little comfortable around electronics is key. Those new to the format first need to familiarize themselves with power specification and be ready to do a little technical work and some basic math.

The Doepfer-designed power system consists of two components: the power supply and bus boards. The power supply is currently the A-100PSU3, updated as of 2015. However, most used Doepfer cases floating around will have the A-100PSU2. This is important, as the two have different specifications.

Second are the bus boards, where the modules are plugged in within the case. The Doepfer bus board allows for a maximum of 14 modules to be plugged in. A standard Doepfer case, either rackmount or portable, consists of two rows of 84hp, 6U high, containing one PSU and two bus boards. The modules connect to bus board via a 10 to 16 or 16 to 16 pin cable, depending on the design of the module. The 16 pins on the bus board are arranged in pairs and carry the following signals, from top to bottom: Gate, CV, +5V, +12V, GND (3 set of pins), and -12V. The bottom 10 pins do most of the work, providing + and -12V to power the modules. The top two pins are for Doepfer's optional internal CV and Gate routing. The +5V rail is used on a select number of modules requiring some extra power.

Learning How to Power Up

The two things newcomers to Eurorack need to know is how to plug in the modules and how to calculate the power consumption of the modules. Plugging the modules in seems easy enough, but in reality, special attention is required. Experienced Eurorack users will double and triple check their connections before powering up, no matter how long they've been working with the system. The standing convention is that the (typically) red stripe on the ribbon cable connecting the modules to the bus board must line up with -12V. This should be labeled on the module, and is always labeled on the bus board.

Although many manufacturers build some type of protection into their circuits now, tales of poor souls plugging a module in backwards and frying it have plagued forums for years. Doepfer boards have open pin configurations, but some manufacturers offer shrouded or keyed headers on their bus boards. In this case, be sure to still check the red stripe as there is a possibility for flipped connectors on the bus cable itself.

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Planning Power Consumption

As for power consumption, anyone familiar with putting together a pedal board has likely done the same type of math. First, check the power supply. As mentioned, the Doepfer A-100PSU2 is common, which provides 1200mA of current to both the +12V and -12V rails. After that, check the specifications for the modules. The manual or manufacturer’s website should let you know how much current in mA is required to power up the module.

Next, check the specs on all the modules in the system and calculate how much power is needed. Finally, make sure it falls under what your PSU specifies, and leave a little headroom if possible.

With the classic Doepfer case, a user would need to fall in under 1200mA on both rails. It’s good common sense to split up the modules pretty evenly between the two bus boards. If a module requires +5V, most manufacturers, including Doepfer as of 2015, include that in the power specification at this point. However, with the older Doepfer cases an adapter must be used, which pulls current from the +12V rail. Keep in mind that the mA required on the +5V rail will be subtracted from the available current on the +12V rail.

Even after 20 years, the power specifications in Eurorack are not technically standardized, but most manufacturers take after Doepfer. With a little technical dedication and some easy math, anyone can get a system powered up. Once the boring work is through, the best part follows: learning about synthesis and making fascinating, original sounds.

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