Eurorack Modular Synthesizers

by Florian Meindl July 12, 2019

Modular Synthesizer

You want to get into Modular Synthesizers?

In this article you will learn which components you need to get started with modular synths and what the most essential modules (Oscillator, Filter, ADSR, VCA, Mixer, Sequencer) are and what they do. Some tips about cases, cables and patches are included too.

Around 2002 I started to produce music on a PC and was creating loads of music in the box, which was very exciting around that time, because DAWs became better and better every year and computers were affordable. 

It was not only the technology though. Techno in the 90s was sounding very saturated and distorted, it was fast and mostly overloaded with sounds – pretty much like it is today – so the new possibility to produce very clean and minimal tracks was exciting. Labels like Minus from Richie Hawtin were on the forefront of this movement and distorted sounds were a bit old-fashioned at that time. Clean Sine waves, in the box digital sampling and high quality field recordings were the main ingredients of modern Minimal Techno tracks.

“THE STRONGEST FEATURE OF A MODULAR SYSTEM IS ITS VERSATILITY IN THE ANALOGUE DOMAIN, THE ONLY LIMIT IS YOUR IMAGINATION”

After a couple of years producing with this kind of setup I felt, that it was time to look for something new, something out of the box. The main reasons were, that I spent too much time on the computer. At daytime answering e-mails and managing all sorts of things and at night producing music in front of the computer, again. The other thing was the sound, there was something magic coming out from analogue gear. I didn’t exactly know what it was back then, but those two reasons grew my desire to make music with analog gear.

After working with more and more hardware synthesizers I finally arrived at the point where I decided to add a modular synth to my setup and this was probably a similar situation where you are currently in.

You can get certain sounds from hardware synthesizers and drum computers, which are simply not possible with a computer, but the main strength of a modular system is its versatility in the analogue domain, the only limit is your imagination.

“STARTING A PATCH FROM SCRATCH IS LIKE CLASSICAL PAINTING WITH A BLANK CANVAS, COLORS AND A BRUSH”

The first thing I have to tell you is, that you should know the basics of subtractive synthesis, additive synthesis and sampling. I strongly recommend to get a book from the list at the bottom of this page and work through it until you have an understanding of oscillators and until you know what and ADSR envelope is, what a filter does, what frequency modulation is and what a control voltage can do etc.

I assume you want to create music, but in the modular synth world there is also mathematics and electronics involved, there is no shortcut I’m afraid. If you don’t do your homework properly you will waste a lot fo time afterwards when you are in a creative mood and get stuck with a technical problem or a lack of understanding the functions.

Some might say, that the most amazing things happen when you don’t know everything and make mistakes. This is actually true most of the times, but believe me, it’s better to know what you’re doing and being able to forget and break the rules if you want – that’s true creative power – and modular synthesizers are so complicated you will never know everything and you will not be able to predict everything, so there is plenty of room for those lucky accidents!

The components

To get started with modular synthesis, you should get the following components. All modules are screwed into a modular synth case, which needs to have power supply inside. The modules are then connected via designated cables.

If your modular synth should sync to an external clock signal you need a MIDI interface which translates MIDI into CV and gate.

The audio output can be taken directly from the mixer module with a cable described below – later you can upgrade the case with an input/output module.

If your system grows—and especially if you use modules with tubes—it is advised to check the maximum power load of your case and sum up the power consumption of all modules. If the millivolt of the modules is higher, then you need to put out one or two modules.

Warning: Use blind plates (front plates without electric components) to cover free space. The power transformer operates on high voltage, you don’t want to risk your or anybody’s life.

MODULAR SYNTH CASE

If you want to start to get into modular synthesizers I would recommend a small low budget case, probably second hand from eBay. Just make sure it has got a working power supply, there are power buses inside which contain the connectors for the modules. Make sure the red colored power cable is pointing downwards, but this is described in the manuals as well. 

Later on, if you know where your journey should go, you can upgrade to a larger aluminum case or travel case for a proper live act.

My recommendation is this low cost case from DOEPFER, it will do for the start!

DOEPFER Low Cost Case

This A100 case has got 3U (standard hight unit for Eurorack format) and 84HP (horizontal pitch – the with).

Tip: Probably it’s better to buy a larger case right away, because you will most likely get a larger case very soon anyways.

OSCILLATOR (VCO)

A sound must have an origin and in case of an analogue, additive or subtractive synthesizer, it all starts with an oscillator. This module can produce a voltage (in Eurorack modular systems +-5 volt) which alternates in a steady frequency and a waveform. The waveform determines the sound character from bright and overtone-rich (sawtooth waveform) to clean and flute-like (sine waveform). The frequency of the oscillator and in some cases also the waveform can be modulated by an incoming control voltage, this way an oscillator can play a melody or form new waveforms with frequency modulation. The oscillator pitch is usually calibrated at 1 volt per octave, this standard enables you to play western scales if you plug in a sequencer. 

Oscillators can also receive CV (control voltage) from other sources than sequencers, but this will result in more experimental or percussive sounds or even noises rather than melodies. 

A simple A-110 oscillator from the most popular Eurorack brand DOEPFER will do here, they are good value for money and very reliable. They are also often available second hand on eBay if you want to get the most out of your budget.

DOEPFER A-110

The CV1 input is where the incoming CV should be plugged in and the PW CV (pulsewith control voltage) can alternate the with of the pulse waveform in order to get more interesting sounds. The outputs are at the bottom, you can take all four at once and even mix them in ratios you prefer.

Tip: You can create a steady frequency modulation already only with this module, simply patch the triangle waveform output back to CV2 and turn up the CV2 amount knob a little bit. If you listen to the signal coming from the sine output, you will notice the effect.

FILTER

This module does what its name says, it filters out frequencies. The three basic settings are low-pass (let’s through low frequencies), band-pass (let’s through frequencies in a certain frequency band only) and high-pass.

The cutoff frequency sets the point, from where the frequencies are being reduced, in case of a lowpass filter, the high frequencies. The slew rate in db/octave gives you information how abrupt the frequencies above or below the cutoff are being reduced.

All analogue filters have a resonance amount, if you turn that up it will highlight the frequency where the cutoff is. When turned up to maximum, some filters can go into resonance frequency and even become oscillators themselves. The most popular use of the resonance feature is the music genre Acid, which is created with the infamous Roland Tb-303 Bassline synthesizer, it sounds a little bit like tweeting birds (on acid).

A good choice for a multimode filter is the Wasp A-124 from DOEPFER, which is inspired by a 70s synthesizer and sounds quite wild and aggressive – it probably gives you the analogue sound you are looking for.

Wasp Filter

Tip: You can take the bandpass (BP) output as well as the LP/HP output, process it differently and mix it back together in order to create an organic moving synthesizer sound for example!

ENVELOPE (ADSR)

An envelope doesn’t create any sound at all, nor does it process audio. An envelope creates a control voltage!

ADSR stands for Attack, Decay, Sustain and Release and lets you shape the control voltage so that other modules, which are controlled by the envelope, can follow a certain movement. 

Envelopes are mainly used to control an amplifier level or filter frequency, but it can be used for anything accepting control voltage, for instance effect amounts, LFO amounts, oscillator frequencies etc.

This ADSR envelope from MFB is good value and has also got a loop function:

MFB ADSR

In addition to its normal ADSR function you can also modify the single amounts by an additional external control voltage, try routing in an LFO into the sustain level. 

VOLTAGE CONTROLLED AMPLIFIER (VCA)

Imagine a VCA as a volume fader and the control voltage tells it where the fader is, down means zero volt and full volume is 5 volt. 

The main use for this module is in a classic subtractive synthesizer, directly after the oscillator. Aa amplifier can influence the sound of the signal as well because when it is overloaded it will add overtones. Tube amplifiers are known for their warm sound and overtones.

As this article is for beginners and how to get started with modular synthesizers, we recommend this model from Manhattan Analog rather than an expensive tune amplifier. 

VCA Manhattan Analog

This VCA has got an additional feature, a so called “offset” which allows you to add direct current to the output. It also has got two CV inputs, which means you can have the volume being controlled by an envelope for instance and and LFO – then you can decide in which amounts they should influence the output volume.

MIXER

I assume you are familiar with a mixer, but in the modular world they are mostly simple modules with volume knobs per channel.

There are stereo mixers available, matrix mixers and also different models which work better for audio or control voltage, but in order to get started I would recommend you to get this one from Erica Synth or a similar one:

erica synth mixer

The big advantage of the PICO series from Erica synth is their small size, if you build a live modular system you will need to save space, so consider some of those to keep it compact and effective.

SEQUENCER

In order to get a melody out of an oscillator you need to feed it with notes, those notes come from, you guessed it, control voltages. If you have a keyboard which can send CV, you could play a melody with the oscillator, but in order to sync the notes properly to the tempo it’s maybe better to let it be done by a sequencer. It will also come up with melodies you would not play so easily and continuously. And electronic music mainly comes from sequencers anyways, I would say it’s an essential part of the genre!

A sequencer also sends gate signals, which are very short and high voltages – they function as note triggers if you want to play a melody.

I would recommend this sequencer from BEFACO, because it has got many useful modular features like direct access to the control voltages, single outputs for gates but also a mixed output and even a clock divider/multiplier.

BEFACO MUXLICER Sequencer

Tip: You can use the sequencer also for filter movements over a synthesizer or soundscape! The sliders would then simply tell the filter which frequency it should hit.

LOW FREQUENCY OSCILLATOR (LFO)

An LFO is used as a control voltage source and not audio source, it is focussed on the very low frequencies, mainly the ones we don’t even hear below 20hz. LFOs become really interesting if they can be clocked and reseted, because then they can control something like a filter in a rhythmical way to the tempo of the music.

This LFO from Eowave has got many different waveforms and the sync inputs function as resets.

EOWAVE LFO

EURORACK CABLES

The modules don’t connect magically, you need to connect them with designated cables – but this is where your creativity starts.

Ok this was a bit too simple, we would not be in the modular world if there would not be an option to connect them magically without cables. So, there are some modules which can send and receive CV for pitch via the power bus, also audio generating modules like the Tiptop Audio Drum modules can send the audio signal to a mixer of the same brand – but I would recommend using the cables, because then you can see the signal flow and take a copy of the signal, process it in between and so on.

The most useful cables are also the most costly ones, namely the so called “Stackcables” from Tiptop Audio. The big advantage is, that you can take a copy of the signal by stacking in another cable! A genius idea, taken from laboratory equipment.

Tiptop Audio Stackcables

Probably it’s best to get 5 short stackcables in order to be able to take copies of some signals and additionally some medium length normal cables. The format is mono 3.5mm mini-jack.

In order to bring the final audio signal out of the modular synth into a standard studio mixer or audio interface you can use cables with 3.5mm mono mini-jack on the one side and 6.3mm mono jack on the other side.

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