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The Age Of Eurorack: An Interview With Dieter Doepfer
On Eurorack's Origins, Present, and Future
Few people have shaped the contemporary landscape of electronic musical instruments as profoundly as Dieter Doepfer, the German engineer whose A-100 system effectively established the Eurorack format in the mid-1990s and helped bring modular synthesis into widespread use. Maintaining his passion for music throughout his physics studies, Dieter’s path led him from repairing band equipment and building DIY effects to becoming a household name for anyone immersed in analog synthesis over the last three decades. To his own continued surprise, he helped lay the foundation for a community-driven ecosystem that now spans thousands of modules and hundreds of manufacturers worldwide.
In this interview—offered as Dieter cheerfully eyes his retirement—he reflects on the origins of the A-100, the technical decisions that defined Eurorack, and how early experiments grew into a vibrant global network of artists, engineers, designers, and makers. We discuss his trajectory, his thoughts on the industry, and the unexpected hits and misses across Doepfer’s vast catalog, all delivered with his signature mix of dry humor and directness.
The Making Of A Synth Designer
Perfect Circuit: Hi Dieter. Thank you for chatting with us. Surely, you don't need much of an introduction for our audience. However, since this is your first interview with us on Signal, we’d love to begin with your background. How did you first get involved with electronic music, sound synthesis, and eventually instrument design?
Dieter Doepfer: During my physics studies I was playing in a band and began to repair the band equipment and to develop effect units like phaser, wah-wah, distortion/fuzz, tremolo and so on. It turned out little by little that I was very interested in any kind of electronic sound generation and processing.
And at that time there was some rumor about a new instrument called the "Moog Synthesizer" that was used by bands like Emerson, Lake, and Palmer, Yes, the Doors, the Monkees, Simon & Garfunkel, the Beatles, and many others. I was totally impressed by the sounds of this new machine and tried to collect as much information about the technical details and how this unit works. It helped a lot that I had the chance to service the Moog modular system of Gershon Kingsley (of "Popcorn" fame), as it was located in Munich at that time, and Mr. Kingsley was looking for a technician to service the machine. He contacted Bob Moog and a few weeks later the service manual arrived (remember: at that time there was no internet and the documents came in printed form via mail). And the electronic magazine Elektor published the DIY project FORMANT. In each issue a new module was presented (power supply, keyboard, VCO, VCF, VCA and so on). I designed a few Formant-compatible modules which were not published by Elektor (e.g. a voltage controlled phaser, an envelope follower, a frequency divider, and a few more). I also designed a polyphonic modular system (PMS).
A few years later I met Doug Curtis and had the chance to take over the representation of CES in Europe. Based on Doug's circuits I designed a new synthesizer, the voice modular system (VMS), which also included a sound sampler.
PC: If we're not mistaken, the first modules from the A-100 system emerged c. 1995. What were some of the biggest technical or conceptual challenges you faced in getting the format off the ground during those early years?
DD: The challenges were manageable. The circuits of the first modules were taken from the MS-404, which was a very successful stand-alone synth. It was released in 1993, and the demand was incredible. We had to find a way to manufacture the MS-404 at subcontractors, as we could not manage the quantities in-house. The success of the MS-404 was one of the reasons why I decided to start the A-100. The other reason was that I, myself, wanted to have a modular system with smaller dimensions.
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PC: The decision to adopt the 3U format was originally driven by practical standards in Germany, but it ended up defining the physical identity of Eurorack as a whole. Looking back now, with decades of hindsight and a vastly expanded ecosystem, would you still make the same format choices—or are there aspects of the size, layout, or power design you might approach differently today?
DD: Looking back I think I would leave the mechanical specifications as they are—it was already an international standard at that time, and I modified only a few things like the variable depth and dimensions of the pc boards behind the front panels. But I would use boxed pin headers at the bus boards right from the start. When I began the A-100 the plan was to offer only complete systems. But it turned out after a while that users wanted to compile their own systems, especially as other companies began to offer A-100-compatible modules.
And I would probably use power supplies with higher voltages (+/-15V or +/-18V) and add a few more signal lines to the bus board—not only CV/Gate, but also for digital communication between modules similar to the I2C or SPI bus.
Reflections on the Doepfer Catalog
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PC: Over the years, you’ve developed a vast catalog of modules, covering everything from foundational building blocks—VCOs, VCAs, filters, utilities—to more experimental modules like the A-196 Phase-Locked Loop, A-174-4 3D Joystick, and A-152 Addressed T&H / Switch. What kinds of projects do you personally enjoy working on the most, and why?
DD: Most of the modules are standard designs and not very challenging for an electronic engineer. But some of the modules are based on new ideas, and it took a while to realize them. And just those were the most exciting designs for me and Christian (he does the programming for modules which include microcontrollers).
A few of these more ambitious and interesting modules were e.g. A-107 (morphing filter), A-137-1 (wave multiplier), A-188-1 and A-188-2 (BBD module), A-126-1/2 (frequency shifters), A-108 (48dB Moog type filter), A-112 (sampler), A-121s (stereo filter), A-198 (ribbon controller, especially the mechanical concept of the manual), A-178 (Theremin), A-154 (sequencer controller) and a few more.
PC: One particularly unique aspect of Doepfer designs is how often they're inspired by ideas from the community. Can you walk us through your design process and how it has evolved over time?
DD: That differs each time. The first modules were nothing but the corresponding circuits of the MS-404. For newer modules it's about a 50:50 mixture of our own ideas and suggestions coming from users.
PC: Has there ever been a feature or module idea that you personally loved—but the community didn’t respond to the way you expected? What about the other way around?
DD: Indeed I'm a bit disappointed about the sales of e.g. A-121s (stereo filter) and A-157 (trigger sequencer). On the other hand, I was amazed by the sales of some simple modules suggested by customers like A-138s (stereo mixer), A-151 (sequential switch), A-183-1/5 (attenuators) or A-180-3 (bufferd multiple).
Unique Doepfer Designs
Modular Synthesis Then and Now
PC: When you look at what Eurorack has become—thousands of modules, hundreds of manufacturers, and a truly global community—how do you feel about the role you played in shaping this ecosystem? Did you anticipate that it would be so widely adopted? Do you feel a sense of stewardship for the format?
DD: It was really a lot of good luck. When I started the A-100, I had no idea how it would evolve. I expected the typical life span of a few years for a new product. In the first interviews I said that I would be happy if it lasted more than 5, maybe 10 years. I never expected that it's still alive after 30 years. Apart from the basic idea of a modular musical instrument (which was not my idea), probably the most important reason was the affordability of the system. And another important reason is that so many other companies offer compatible modules. Customers do no longer depend on one supplier only but have the possibility to buy alternative products from other sources. This also causes a safety feeling. If one company disappears from the market many others are still available.
PC: We imagine the format has evolved in ways you couldn’t have fully predicted.
DD: Definitely!
PC: What aspects of today’s Eurorack landscape surprise, inspire, or perhaps even concern you the most?
DD: Surprise—the multiplicity of manufacturers and modules; inspire—the never-ending suggestions of users; concern—the half-baked designs of a few low-cost switching power supplies and bus concepts on the market, which result in needless service inquiries and dissatisfaction of customers.
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PC: What do you think draws people to modular synthesis today? Is it a similar or a fundamentally different motivation from what drew people in during the early days of the A-100?
DD: I think there are several reasons: the manifoldness of the available modules and the unique possibilities to create sound with these tools, the "user interface", i.e. the direct manual access to all parameters (no sub-menus accessible via computer mouse) or how Hans Zimmer mentioned when I met him in his studio: "the playfulness with devils candies".
PC: Are there any designers or companies in the Eurorack scene today whose work you particularly find inspiring?
DD: Our company philosophy is based—apart from fundamental ideas of the inventors (Moog, Buchla …)—on our own ideas and customer suggestions. To speak the truth, we do not trace very much products of other companies. When customers ask me about another product I have to reply very often that I don't know the product.
PC: Many newer Eurorack makers lean heavily into DSP-based synthesis, exploring things like granular or spectral engines. Do you see a role for Doepfer in that space in the future?
DD: Not really. It has to do with the manpower in our company. There are only 2 guys in the development: I'm a "pure" analog designer and Christian is dealing with microcontrollers, but not audio DSPs.
PC: More broadly, speaking about the rise of high-complexity digital modules—do you feel this shift risks taking away from the tactile and immediate nature that makes analog modular synthesis so compelling?
DD: It depends upon the particular design. Digital designs are indispensable also in the analog modular synthesis. But the user interface should have an analog feeling as much as possible and not approach the handling of a computer. The best digital interface is one that you do not recognize as a digital interface.
What the Future Holds
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PC: What are your thoughts on the future of Eurorack?
DD: I decided to answer this question no longer because I was always wrong when I was asked this question in the past.
PC: Is there a next frontier for modular synthesis that excites you personally?
DD: Yes, my retirement :)
PC: And finally, could you share a bit about what you're currently working on, and what projects you're particularly excited about at the moment?
DD: Meanwhile, I'm no longer the CEO and owner of the company. But I still work as a freelance consultant and my main job is to support the company with the realization of new products. We are working on a few projects like a new ribbon controller, a new quantizer, a combined Shepard/Morphing/Quadrophonic controller, and a few more.
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