What Is Eurorack?

Eurorack is the most popular format for modular synthesizers — a system where individual electronic modules (each performing a specific function) are connected by patch cables to create custom signal paths. Unlike a conventional synthesizer where the signal flow is fixed, in Eurorack you decide how everything connects.

The format was standardized in the 1990s by Doepfer and is defined by: modules that are 3U tall (about 133mm), measured in HP (horizontal pitch) wide, and powered by ±12V and +5V rails. Today, hundreds of manufacturers produce Eurorack modules spanning every imaginable synthesis function.

Why Go Modular?

Modular synthesis isn't for everyone, but it offers capabilities that no fixed-architecture synth can match:

  • Complete signal flow freedom — route anything to anything. Use a filter as an oscillator. Use an envelope as an LFO. Use audio as a control signal.
  • Scalability — start small and expand your system over time, one module at a time.
  • Unique sounds — the combination of modules you own and how you patch them creates sounds no one else has.
  • Hands-on, tactile experience — patching cables is an immediate, physical form of music-making.

Understanding the Core Module Types

Before buying anything, understand what each module category does:

  • VCO (Voltage Controlled Oscillator): Generates the sound. The fundamental source module. Look for one with multiple waveform outputs.
  • VCF (Voltage Controlled Filter): Shapes the tone. Essential for subtractive synthesis.
  • VCA (Voltage Controlled Amplifier): Controls volume. Every voice needs at least one VCA.
  • ADSR / Envelope Generator: Creates the volume/filter shape over time. Usually paired with a VCA and VCF.
  • LFO: Provides modulation — vibrato, tremolo, wobbling filter effects.
  • Sequencer: Steps through a sequence of control voltages, creating melodic patterns or rhythms.
  • Utility modules: Mixers, attenuators, multiples, and logic — the "connective tissue" of a patch.

The Essential Starter Setup

A common recommendation for a first Eurorack system is called a "voice + modulation + utility" approach. Here's a minimal but functional starting point:

  1. A case/power supply — a 84HP or 104HP powered case is a good starting size. Never skimp on power — budget for a quality power supply.
  2. One or two VCOs — having two oscillators allows detuning, which immediately sounds richer.
  3. One multimode VCF — a filter with LP, HP, and BP modes gives you flexibility.
  4. One or two VCAs — a utility module with a built-in VCA is efficient.
  5. One dual ADSR — for filter and amplitude envelopes.
  6. One LFO — ideally with multiple waveform outputs.
  7. A MIDI-to-CV interface — so you can play your modular from a keyboard or DAW.

Critical Advice Before You Buy

  • Use VCVRack first — this free, open-source software modular synthesizer lets you experiment with Eurorack concepts at zero cost before spending any money on hardware.
  • Plan your rack on ModularGrid.net — the community resource for planning Eurorack systems. Check power consumption before purchasing.
  • Don't overbuy early — a small, cohesive system teaches you more than a large, incoherent collection. Limitation breeds creativity.
  • Budget for cables and power — patch cables add up. Budget at least 20–30% of your module cost for cables, a case, and power.

Your First Patch: A Simple Voice

Once you have the basics, here's how to patch a simple monophonic synthesizer voice:

  1. Connect a keyboard/MIDI interface CV output → VCO 1V/OCT input (this controls pitch).
  2. Connect the keyboard GATE output → ADSR trigger input.
  3. Connect VCO output → VCF input.
  4. Connect ADSR envelope output → VCF CV input (filter opens with each note).
  5. Connect VCF output → VCA input.
  6. Connect a second ADSR → VCA CV input (controls volume shape).
  7. Connect VCA output → your audio interface/mixer.

Press a key and you'll hear a synthesized note with a proper envelope. Congratulations — you've built a synthesizer from scratch. From here, the possibilities are genuinely limitless.