Getting Started with Modular Synthesizers

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Doepfer A-100 modular system
The Doepfer A-100, the system that started the Eurorack format. Image: Wikimedia Commons

What is a modular synthesizer?

A modular synthesizer is a synth split into separate building blocks (modules), each doing one job. You connect them with patch cables to decide how sound and control signals flow. Three kinds of signals travel through those cables:

  • Audio – the sound itself.
  • CV (control voltage) – a changing voltage that controls a parameter, like pitch or filter cutoff.
  • Gates and triggers – on/off signals that start and stop events, like notes or envelopes.
Eurorack 16-pin ribbon cable
A Eurorack ribbon cable: the red stripe is −12V

The Eurorack format

Eurorack, introduced by Doepfer with the A-100 system, is the most popular modular format today. Every module follows the same basic standard:

  • Height: 3U (panels are 128.5 mm tall).
  • Width: measured in HP (1 HP = 5.08 mm). Cases are usually sized like 84 HP or 104 HP per row.
  • Power: +12V, −12V and (optionally) +5V, delivered over a 10-pin or 16-pin ribbon cable.
  • Orientation: the red stripe on the ribbon cable is always −12V. Plugging a cable in backwards can damage a module, so always check it.
  • Signals: 3.5 mm mono jacks; pitch usually follows 1 V per octave.
SequencerVCOVCFVCAEnvelopeto speakerspitchgateaudioCVgate
Illustration: the classic synth voice.

Core building blocks

  • VCO (oscillator) – generates the raw tone.
  • VCF (filter) – shapes the tone by removing frequencies.
  • VCA (amplifier) – controls loudness, or the amount of any signal.
  • Envelope generator – creates a shape over time (attack, decay, sustain, release) when triggered.
  • LFO – a slow oscillator used for movement and modulation.
  • Sequencer – plays back patterns of notes and gates.
  • Utilities – mixers, multiples, attenuators and offsets that make patching flexible.

See how they connect in our Patching Techniques guide.

Your first 5 modules

A simple, complete voice needs only a handful of modules. These five types make sound, shape it and play it. Together they take about 40–50 HP, so they fit in an 84 HP row with room to grow.

Module What it does Typical width
VCO (oscillator) Makes the raw sound: a waveform at a pitch set by a 1 V/oct control voltage. 8–14 HP
VCF (filter) Shapes the tone by removing high or low frequencies. 8–12 HP
VCA (amplifier) Controls the volume. Without it, the oscillator never stops sounding. 4–8 HP (often dual)
Envelope (ADSR) Turns a gate (key press) into a volume and tone shape over time. 4–8 HP
Utility: LFO, mixer or mult Slow modulation, combining signals, sending one signal to several places. 4–8 HP

To play the voice you also need a source of notes: a MIDI-to-CV interface for your keyboard or a sequencer. See complete example systems with HP and power on Configure Your Modular Synthesizer, and try this exact chain for free in VCV Rack.

What does it cost?

Rough price ranges, so you know what to expect. Prices vary a lot between brands; use these as a starting point, not a quote.

Route What you get Rough cost
VCV Rack A virtual modular on your computer Free
Semi-modular synth One complete voice with patch points, no case needed €250–€700
Ready-built modules Per module, new €100–€400 each
DIY module kits Per module, you solder it €40–€200 each
A basic 5-module voice Ready-built / DIY kits €700–€1,500 / €300–€600
Ready-made powered case Case, rails and power supply €300–€1,000+
DIY case with our parts Rails, threaded strips and the Case Power Kit (from €73.30), plus wood about €100–€150
Tools to start soldering Hand tools starter set (€15) plus a temperature-controlled iron €50–€120

Tip: building your own case is the biggest saving. The money you save on the case often pays for your first module.

VCV Rack: virtual Eurorack modules connected with patch cables
VCV Rack: a free virtual Eurorack on your computer. Read our VCV Rack guide

Ways to start

  1. Try it in software first. VCV Rack is a free virtual Eurorack, perfect for learning patching and trying modules before you buy them. Read our VCV Rack guide to get started.
  2. Build a case and power it. See our guides on case building and powering with the RT-65B.
  3. Build your first module from a kit. Kits include all parts and instructions – a great way to learn soldering. See How to Solder.
  4. Move on to PCB + panel builds or your own designs using our parts & components and a breadboard.
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