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The Secret World Of Modular Synthesizers

Weird Science - The SOS Guide To The Modular Synth Underground
Published April 2013
By Al James

Bedroom-based boffins the world over are manufacturing increasingly bizarre and esoteric synth modules. Come with us as we step away from the modular mainstream and take a look at some of the more eccentric Eurorack synth modules this weird world has to offer.

Eurorack synth modules.Welcome to the wild west. Far below the slow-moving product cycles of music tech's big-brand behemoths, a small yet busy branch of synth technology is creating some of the strangest, deepest and most inspiring ideas in synthesis, and turning them into products you can actually buy. Products both designed and bought by an increasing legion of musicians who, in a corner of their studios keep a box, filled with wires, that makes visitors remark: 'I know what this stuff is, but what in heck is that?' The synth is modular, the format is Eurorack.

Don't get me wrong, I love my fixed-architecture synths dearly. A fixed architecture synth will give you fast, repeatable results from a perfectly complementary set of 'modules'. Sounds that could take minutes on a modular might be the work of seconds on a fixed architecture synth and you'd probably keep more money in your bank account while doing it.

But a modular synth can be a wonderful addition to an electronic music setup, especially if you already have other analogue gear. You can add step sequencers, wild oscillators, filters and modulation to existing machines, or process audio from computers, guitar and mics beyond recognition. And it can be, by itself, a machine that offers a lifetime of sonic and melodic exploration and creativity. You will struggle to repeat the same sound on it twice, but it will constantly surprise you with new sounds, rhythms and melodies that could form the germ of a new track. With enough modules, you could produce an entire track on a modular without ever touching a computer.

Modular Revisited

Tiptop Audio's Z3000 MkII oscillator.

It has been four years since 'The SOS Guide To Choosing A Modular Synth', in which Jyoti Mishra described the decision making process involved in assembling his first modular system. In that period, the Eurorack modular synthesizer format has grown from a handful of manufacturers to over 80 by some counts, and there are over 700 modules currently on the market. An explosion of small and creative manufacturers, and more customers than ever, mean that Eurorack is experiencing a golden age. It seems that nearly every week a new module is announced that tempts you into the dangerous territory called 'just one more module'.

Jyoti's article is an excellent primer for the format: as well as looking at some of the more obscure options, he focused on modules available from the forefathers of Eurorack synthesis, Doepfer Musikelektronik, Analogue Solutions and Analogue Systems. These are great and well-established manufacturers who can provide complete systems made entirely from their own modules, but when I came to put together my own Eurorack modular, I allowed for choices from the wider mass of options. I think that this is where the format starts to get particularly interesting; with the smaller, lesser known manufacturers whose products are blurring the lines between analogue and digital in a way that opens up what is possible under voltage control. It's a handful of these manufacturers, their philosophies and their modules, that I'm going to investigate today.

Jyoti rightly observes that the process of building a modular can be endless, and working out your system could be a journey that encompasses many years, many bought and sold modules, and much experimentation and solicited advice. There is much to learn, and an open mind is the key to connecting with something you may previously have regarded as not for you. In my own continuing modular quest, I've found this to be the case several times over.

Manufacturers & Modules

Intellijel's Dixie II oscillator.

There are, to generalise, two schools in modular synthesis. On one side you've got what is referred to as the 'East Coast' style: the simpler, fixed-function world of Moog, ARP, Oberheim and the like. Subtractive synthesis is the standard, and an LFO is pretty much always just an LFO, perhaps getting up to audio rate, but generally having only a single function. In many cases, that's a welcome thing. These simpler machines are often quick and easy to work with and sound fabulous doing pretty much anything.

On the other side of the fence is what's referred to as 'West Coast' thinking, an approach championed by brands such Buchla, Serge and Wiard. Here you may not recognise the names of the functions so easily, because they aren't strictly dedicated to just one purpose. For example, a 'Quad Function Generator' could, depending on how you had it patched, be several different things. Many West Coast modular synths do not have filters; instead, much like the Yamaha DX7, through complex timbral controls, frequency modulation and wavefolding, they produce 'complete' sounds that simply don't require further sculpting or refinement. Both different, both equally valid, and both available in Eurorack. Let's make some waves!


Intellijel's Rubicon is unusual for being an analogue, through-zero FM oscillator.

Tiptop Audio

Somewhat philosophically east (but physically west), you'll find Gur Milstein's Tiptop Audio of Hollywood, USA. After making his debut in 2008 with the Z5000 Multi-Effects Module, Milstein now employs a team of people to produce a small but functionally broad range of modules and power distribution systems. When asked where he draws his inspiration from, Milstein doesn't cite other manufacturers: "It's actually musicians/DJs that influence my work, like Sven Vath, Kraftwerk and others.” There is a sense of polish in his modules, with solid-feeling pots and a carefully chosen set of features rather than the entire kitchen sink.

One of Tiptop's flagship modules is the Z3000 MKII (£189$245), a so called 'Smart' analogue oscillator with the novel feature of a digital frequency counter built into the panel. This comes in handy due to the precision and range of the module's pitch tracking, the latter going from LFO-rate cycles all the way up to 30kHz, and there's also an input to check the frequency of other sources. Truly analogue at heart, it's a beefy, classic sounding oscillator. Its stability, combined with the frequency counter and its ability to support Linear FM, make it highly useful for FM synthesis (although, sadly, not the through-zero style of a DX7). Additionally, its chunky sound, combined with the 'Hard Sync' input, is good for creating ripping tones when sync'ed to another oscillator. Sporting a solid East Coast feature set with some bells on, this was my first oscillator!

Intellijel Designs

The Cyclonix Cylclebox oscillator.

Moving philosophically West (but physically East, to Toronto, Canada), we come to Intellijel Designs, founded by Danjel van Tijn. Danjel has built up a spare-time business to the point where he has literally quit his day job. With a core staff of three, local manufacturing businesses, PCBs from the Far East and their own hands, Intellijel produce a range of compact, functional and well-considered modules. In Danjel's own words, "I have always admired the forward thinking, solid engineering and creativity of Buchla and Cwejman.” With only a few functions now left to cover, it is possible to build a largely complete and deep modular synth from Intellijel modules alone.

Intellijel's Dixie II oscillator (£202.58$220) is notable as a highly accurate and wide-ranging 'classic' VCO and LFO (0.01Hz-24kHz with a pitch stability of 0.1 percent over eight octaves), and plenty of simultaneous waveshapes. Given that it comes in at only 6HP wide, it's also exceptionally compact. (A Eurorack module's height is set at 128.5mm, but width is measured in Horizontal Pitch, one HP being equal to 5mm.)

Intellijel have recently released a new oscillator that may make quite a stir: The Rubicon (£353.44$399) is nothing less than an analogue through-zero FM oscillator, capable of tuned DX7-style FM synthesis (in combination with at least one another oscillator). With this comes a world of musical, tuned, melodic FM sounds.


Make Noise's Buchla-inspired Dual Prismatic Oscillator.

Let me introduce our first digital module, the Cylonix Cyclebox (£474.13$500), which is the brainchild of Canadian Professor Jim Clark, now partnered with Intellijel. Built under license by their manufacturing team, the Cyclebox is a small module with a remarkable set of abilities: dual oscillators plus sub-oscillator, multiple waveshapes (from traditional waveforms to scannable wavetables), through-zero FM, wavefolder... But the ace in the hole is the four switches at the bottom which enable 16 separate modes of operation. These include modes to allow the dual oscillators to emerge separately from both outputs (with individual tuning possible, this is a true dual mode), as well as numerous fascinating wave-combination and interleaving functions that generate complex new timbres at the flick of a switch. A selector for 'Mega-mode' stacks eight detuned copies of Oscillator 1 together (with the detune amount controllable by both a knob and CV input). Sending a pulse into the sync input immediately aligns all waves, which then drift back out of sync again, for a huge 'springy chaos' detuned sound. As you'd expect, a host of inputs are provided to put this all under voltage control.

The Cyclebox's sonic complexity makes it an excellent LFO, and its speed can range from over one minute per cycle up to the dog-bothering heights of 40kHz. Given the level of options available, this is certainly one of the most sonically broad and functionally capable single modules in the Eurorack format, and, dare I suggest, in perhaps any? Filters beware: this is almost a complete synthesizer in itself.

Make Noise

The Livewire Synthesizers Audio Frequency Generator — a beast of an oscillator.

Now we find ourselves arriving at the shores of the west coast, with arguably the kings of this philosophy, Make Noise. Conceived, designed and built by Tony Rolando and a small team in Asheville North Carolina (home of Moog Music Inc — indeed, Rolando worked on the production lines there), Make Noise modules are feature packed, with a unique 'punk-Egyptian hieroglyphic' panel styling created in the same program with which Rolando designs his PCBs. Many Make Noise modules are strongly influenced by the work of Don Buchla: "I've always been very inspired by his user interfaces,” says Rolando. "Additionally, the sound of his 200-series modules just blows my mind.” For sheer functionality per pound, these designs perhaps represent some of the best value in the format. "My dream system is quite small,” continues Rolando, "a powerful electronic instrument that I could carry with me on journeys. For this reason, I prefer functionally dense modules.”

Tiptop Audio's Z2040 four-pole low-pass filter.Make Noise have only recently begun the process of shipping their first dedicated oscillator, the no-holds-barred Buchla-fest that is the 'DPO' Dual Prismatic Oscillator (£547.40$599). The DPO is a complex dual analogue design, true to the spirit of West Coast legend Don Buchla. In this case, the DPO is in many senses a Eurorack take on the Buchla Complex Waveform Generator 259, but peppered internally with vactrols (more on vactrols later...) and a few twists. Like its forebear, the DPO features two interlinked analogue oscillator cores (one able to frequency modulate the other, but with a lag control in between), CV-controllable wavefolding (see the 'Effects' section for a full explanation of wavefolding), 'harmonics' controls and a plethora of other modulation inputs. As one would expect from such a configuration, it excels for a broad spectrum of sounds, from classic-voiced analogue traditional tones to the complex, 'complete voice', brassy, bonky, metallic timbres of Buchla (hence 'prismatic' — lots of scintillating, pointy waveforms). And with so many different modulation options available, it's exceptionally deep.

The Harvestman

Intellijel Designs' Korgasmatron, a wonderfully named filter inspired by the Korg MS20.

Scott Jaeger, aka The Harvestman, grew up in Seattle surrounded by thrash metal — an influence at odds, perhaps, with time spent on his brother's then-revolutionary Casio SK1 sampler. Inspired in around 2006 by the more West Coast-style modules coming out for the Doepfer Eurorack system he had just bought, he took his love for circuit-bent sounds, digital grit and metal, and made his first module. That was the 'Malgorithm', and only the start. Harvestman's 1991 Piston Honda (£283.61$395) is a digital wavetable oscillator with only mild concessions made to taming digital aliasing, fizzing and grit at extreme registers — these are 'features'! It contains two ROMs as standard, containing 256 wavetables in 16 banks (which are further expandable with an optional board). Beyond an innately fizzy, aliasing-accepting character, a key signature of the Piston Honda is that both the banks and wavetables themselves can be scanned independently by voltages in a hard or smoothly blended manner. This timbre-morphing characteristic, combined with its intrinsically 'vintage '80s sampler' tonality, makes wonderful grist for feeding into analogue filters and complements traditional oscillators.

Livewire Synthesizers

The Doepfer A124 WASP filter.

The designs of the late Mike Brown of California live on in his Livewire Synthesizers company and his grand analogue oscillator, the Audio Frequency Generator ($399$399). Both a wide (28HP) and physically deep module (it is comprised of three boards and actually requires two power cables to be connected!), the AFG combines five classic traditional waveform outputs with all the trimmings. It departs from the norm in two ways. Firstly, a bevy of CV inputs and offsets/attenuator knobs control additional outputs for 'Animated Pulses' and 'Alien Saws' — unconventionally shaped mutations of what we know as Saws and Pulses. These animation controls, when under modulation, pull at the waveforms and give these extra outs a uniquely ripping, chewy, monstrous quality that is similar to PWM, but sonically completely unique to the AFG. The sonic possibilities are then doubled by the 'Matter/Anti-Matter' switch, which mutates every output into a new variation of itself, for a complete total of 27 possible waveforms. And, as with any modular oscillator, one can tap all eight outputs simultaneously!

Who said function generators were dull? The Make Noise Maths.

Honourable Mentions

Other notable oscillators must include the R2D2-on-a-night-out voltage-controlled speech synth chip module that is the German made Flame 'Talking Synth', and Harvestman's wild 'Casio Buchla' dual oscillator, the Hertz Donut, which heavily influenced the design of the Cyclebox. There are, of course, many, many more and you may wish to look into the Analogue Solutions range, the Analogue Systems RS95E, the Bubblesound VCOb, Cwejman's VCO6, Doepfer's range, the Kilpatrick K3020, the Metasonix R55, MFB's Triple VCO, the Pittsburgh Generator, the Synthesis Tech E350 Morphing Terrarium and E340 Cloud Generator and, finally, the Wiard/Malekko Anti Oscillator.


The ADDAC Systems Marble Physics CV generator.

Tiptop Audio

Small but well formed, Tiptop Audio's Z2040 (£162.93$199) is a 24dB, four-pole, analogue low-pass filter, similar in response to the SSM2040 filter chip found in the Sequential Circuits Prophet 5. With a built-in VCA, this is a compact, classic, bassy and sweet sounding filter. A nice touch is its ability to retain punch by applying additional gain to compensate for the inherent volume drop that occurs at high resonance settings.


Intellijel have three filter products available, the most complex of which is the Korgasmatron filter (£335.34$340). This is a multi-mode, Korg MS20-inspired dual filter system with a unique Q-drive knob that takes the resonance response from polite to rude. A carefully designed set of CV inputs and controls allows one LFO to act on both filters in precise opposition to one other — useful for creating vocal formant effects. The two filters are able to operate both in series and in parallel, with a crossfade ability and voltage input to control a fade between them at speeds up to audio rates, tapping the 'mix' output for the results. A pair of 1V/Oct inputs are provided for both filter-frequency inputs, as the design is precise enough that both filters can operate as pitch-accurate sine-wave oscillators at high resonance settings. These sine waves are perfect for frequency modulating one side with the other, or for use as raw material for feeding into wavefolders (we'll look at some of these later). If you're looking for something that's a genuine attempt to recreate the flavour of a Korg MS10, Manhattan Analog's MA35 aims to bring the Korg 35 VCA and VCF to Eurorack, in one module.

Tiptop Audio's Z8000 Matrix Sequencer.

The Harvestman

A Harvestman analogue filter is available in the form of the notoriously wild-sounding Formanta Polivoks filter (£174.90$200). The Polivoks VCF is fully licensed from original designer Vladimir Kuzmin, and uses original schematics and new old-stock parts. Surprisingly polite and sweet-sounding with low input volumes and resonance settings, it is naturally able to go fully into the same speaker-destroyingly states as the original Polivoks. An equally authentic Polivoks oscillator, the Polivoks VCG, is also available from The Harvestman.

Livewire Synthesizers

Livewire's Frequensteiner ($225$225) is an authentic take on the Steiner Parker Synthasystem filter, an elegantly simple yet juicy-sounding design that does not exhibit bass roll-off characteristics at high resonance settings — good for dancing to. It also includes truly cutting BP/HP modes, making it an all-rounder with a voice of its own.


The Make Noise Pressure Points sequencer.

Doepfer have celebrated a truly unusual design with their A124 WASP Filter (£70.31$110), and it deserves mention here. A re-creation of the filter in the British-made EDP Wasp synthesizer, it is of the resonant, 12dB, multi-mode variety, and in the words of Doepfer, "abuses digital inverters as analogue operational amplifiers, leading to distortions and other 'dirty' effects”. The A124 WASP is characterised by a curiously sizzly, driven and raspy character, and at high resonance settings the filter starts to warble and waver unpredictably. This can work very well on snarling and strange acid-style sequences, but with a flavour that is most certainly not that of a 303. It's perhaps not the only filter you would want in your system, but its low cost and unmistakable character certainly make it worth investigating.

Flight Of Harmony

The preceding entries are all recreations, but don't let that make you think that there aren't lots of original filters in Eurorack. One highlight is Flight Of Harmony's Plague Bearer (£104.59$119), a dual filter that is really as much a scorching, wild, CV-able distortion unit as anything else. If gain and the selectivity of a filter can be said to focus our attention on an aspect of the source material, then the Plague Bearer has enough gain and selectivity to show us the source material at an atomic level, and then completely tear it to pieces.

Honourable Mentions

The above is just the tip of the Eurorack filter iceberg. Also worthy of investigation is AMSynth's range, the Analogue Systems RS500e, Cwejman's range, Bubblesound's SEM20, Doepfer's range, the Harvestman Bionic Lester, the Intellijel Dr Octature, the Metasonix R52, the Pittsburgh Modular Filter, Toppobrillo's Multifilter, the Wiard/Malekko Borg/Boogie and the WMD Sychrodyne/Micro Hadron Collider.

Function Generators

The author's current Eurorack system, much of which will be familiar to you from the text. Perched on top you can see the worky bit of a Doepfer A199 spring reverb.

Make Noise

If you think this section sounds like it should be the most boring thing ever, you couldn't be more wrong. A case in point is the Make Noise Maths.

Deep breath. The Maths ($280$280) is a single module that can be, depending on how it is patched, a CV-controllable, free-running dual LFO; a dual AR or ASR envelope generator; a dual bass-frequency range oscillator; a dual slew (portamento) generator; a voltage and audio mixer; an attenuator and inverter; an envelope follower; a comparator; a DC offset generator; and a logic gate and combinations thereof. Phew. Borrowing heavily from the work of near genius that is the Serge DUSG, a Maths module is often the solution when you find yourself short of a function. There's an extraordinary range of repeatable envelopes, CV processing and free-running modulation to draw upon.

Both sides of Maths can operate independently or can be self inter-modulated for more complex behaviour. Using the 'OR' logic output while having one side wait for the other to finish before repeating can create interesting flip-flopping effects, even while modulation is being received from elsewhere. As esoteric as it may look, remember that, like all the modules in this article, the inputs and outputs use the 1V/Oct 'Moog' standard CV voltage ranges and will chat happily with external analogue synths (assuming that they too obey this standard).

... And it's companion in crime Brains.To introduce some randomness, Make Noise produce a Eurorack version of Wiard Synthesizers' truly eccentric 'Wogglebug' circuit, itself descended from the Buchla 265 'Source Of Uncertainty' Module. This is simultaneously a fascinatingly odd dual random voltage generator, dual VCO and ring modulator, but with the bizarre 'woggle' CV out. The best way I can explain this is as a sort of smoothed sample and hold with sine wave wiggles in-between. It's difficult to predict what a knob turn will do, but could that be half the fun? The WoggleBug (£228.51$270) is excellent as a non-repeating-yet-oddly-sentient random modulator for patches, and as it can create audio-rate drones, it's also capable of producing 'unique' music all by itself!

Make Noise's René sequencer.

ADDAC Systems

I'll cover some more traditional ADSRs and LFOs in this article (as we'll see in a moment), but it would be remiss not to mention the ADDAC Systems 'Marble Physics' (€330€330) , a Eurorack modulation source that derives voltages by simulating the physics of a marble rolling and bouncing around on a tray. Knobs and external inputs are provided for tilt and bump, to affect elasticity and further control the simulation. What else would we expect from the company who brought us a voltage-controlled FM radio module?

Honourable Mentions

For further function-generator fun, one should check out the 4MS PEG, Analogue Systems' RS510e, the Bubblesound uLFO, the Circuit Abbey ADSRjr, the Flame C3 Knob Recorder, The Harvestman's Double Andore, Intellijel's Quadra and Planar, the MFB Dual LFO, the Pittsburgh ADSR, Synthesis Tech's E355 Morphing Dual LFO and the Wiard/Malekko Envelator and NoiseRing.

Sequencers, Clock Dividers & Pitch Quantisation

The 4MS Pedals 'RCM' Rotating Clock Divider and 'SCM' Shuffling Clock Multiplier.

Tiptop Audio

Tiptop's Z8000 Matrix Sequencer (£309$395) is effectively 10 sequencers in one. It has a 16-knob matrix of voltage sources with 30 clock inputs to drive, reset and change the direction of sequences (which share knob settings), and the sequences can advance both vertically and horizontally at the same time. With so many outputs, the Z8000 is highly flexible and a treasure trove of modulation to send off to your various inputs. However, be aware that, with 30 inputs, a large number of clock sources are required to unlock its full potential!

Make Noise

Although it's eminently possible to wrangle sequencer-like behaviour from a self-patched Maths module, Make Noise also offer two unusual dedicated Eurorack sequencer products.

... And the 'SCM' Shuffling Clock Multiplier.The first is Pressure Points (£160$215), a module with four contact-sensitive plates, each beneath a corresponding trio of knobs. CV outputs are provided at the end of each row of knobs, with a separate output corresponding to the amount of skin contacting the plates. One row could be controlling oscillator pitch, the others controlling modulation, with 'pressure' controlling timbre and the gate firing an envelope. An expansion module called Brains (£104.59$120) allows Pressure Points to receive a clock and cycle through stages like a traditional step sequencer (but with touch-sensitivity to allow you to add manual variation, and more). Brains will accept audio-rate clocks, so if you patch the CV-out of a Pressure Points row directly to the modular audio output, Pressure Points becomes a triple-output oscillator, whose timbre can be adjusted by turning the knobs! It can also be used as a keyboard. There is, of course, no requirement to tune each key/plate to well-tempered tuning. You're free to choose whatever set pitches you require, thus eliminating the possibility of ever playing a duff note!

The Intellijel µScale pitch quantiser.Up to six Pressure Points can be chained together to make a simple and performance-led keyboard and step-sequencing system. Additionally, an 'Analog Memory' expander is available, which internally connects to Pressure Points to add a further five tuned voltages per touch-plate. A sequential switch module (such as a Doepfer A151), allows the rows to play one after another, turning a single Pressure Points/Brains combination from a four-step sequencer into an eight or 12-step one.

Make Noise's other sequencer system is René (£379)$500). While Pressure Points is inspired by the Serge Touch Keyboard Sequencer, René has no such historical counterpart. Called a Cartesian sequencer (and named after the mathematician), it features a 4x4 grid of 16 knobs alongside a corresponding matrix of touch plates, which, unlike the Pressure Points', lack pressure sensitivity. By sending gate pulses into the inputs for the X-axis, you can advance the sequence horizontally and vertically for note variation, with active steps (and more) configured by modes selected on the touch plate. As with Pressure Points, it is possible to force the sequence to skip to different stages by touch, but with René you can also constrain the sequence to whichever notes are selected at any one time. A pitch-quantised CV output is provided, as well as a non-quantised output (useful for modulation). It is also possible to preserve the knob's quantised CV outputs in memory, which leaves you free to re-position them and allows for a whole new set of control voltages to emerge from the un-quantised output. This extra output could control filter modulation, timbre controls, the rate of the clock driving René itself (for sequences that slow down and speed up) — anything you like. René is one of the most functionally dense sequencer modules available in the Eurorack format, and can provide an effectively limitless supply of melodies and ways to re-order them.

The Make Noise Optomix.

4MS Pedals

4MS Pedals, known to the guitar community as builders of bizarre and unique pedals, have expanded into Eurorack. While they produce modular versions of their Atoner and Swash pedals, their 'RCD' Rotating Clock Divider (£166.99$179) and 'SCM' Shuffling Clock Multiplier (£166.11$179) modules are the ones that have perhaps found their way into the most modular systems. These panels receive clocks or LFOs, and then spit out musically divided or multiplied variants of the input clock. This concept is rather powerful, as one single clock source could, via an RCD or SCM, be polyrhythmically firing off complex drum patterns, opening envelopes and advancing sequencers, all locked to a master tempo.


The Intellijel Designs Mutamix.

Another important building block in the construction of a sequencer is pitch quantisation. Intellijel's offering in this area is called the µScale, but there are many different approaches available. The µScale (£206.54$220) is a compact representation of the well-tempered keyboard, and gives the user the ability to input a control voltage and click the keys to determine the notes that the quantiser will round up or down to. This would allow you to turn a sine-wave LFO into an up/down arpeggiator with user-defined scales. The µScale also lets you rein in the outputs of random voltage generators such as the Wogglebug, Wiard NoiseRing and sample and hold modules. Up to 144 user-generated scales can be saved to memory, and CVs can be used to pitch-shift the resulting outputs up or down by as much as 12 semitones, allowing extra modulation sources to add musical variation to your sequence.

Honourable Mentions

It's also worth checking out the following. Pitch Quantisation: the ADDAC 207, Flame's Tame Machine and Chord Machine, the Doepfer A156 and the Toppobrillo Quantimator. Sequencers: the Modcan Touch Sequencer, Intellijel's Metropolis and µStep and the Doepfer A155. Clock Sources/Dividers: Flame's Clockwork, the Doepfer A160 and the 4MS PEG.

Mixers, Low-pass Gates, Utilities & Logic

The Tiptop Audio Z5000 multi-effects unit.

More traditional audio and voltage mixing (and many utilities) are widely available in Eurorack format, so here I'll give just a taste of the extremes.

Make Noise

Make Noise offer two forms of unusual VCA/Mixer. The most curious of these is perhaps the Optomix (£192.48$215), a so-called 'Low-pass Gate' and two-channel mixer which utilises vactrols. Vactrols are essentially slow-reacting resistors made from light-fast capsules containing an LED shining onto a light-sensing photocell. If you feed a sharp 1ms CV click into a traditional VCA, you'll hear the snap as it opens and closes in an instant; just as a light bulb glows after being turned off, the LED in the vactrol does not immediately darken, adding a natural decay to the signal. If you feed a click into the Optomix's CV input, you'll hear the input material burst into audibility, then fade out, as if being acted on by an exponential triangle wave. This behaviour is useful for creating kick drums or percussive tones without tying up an envelope in order to create an extended decay. With the closing of the gate also comes a natural rolling off of high frequencies (hence the term Low-pass Gate). The LPG is key to the West Coast palette — a woody, warm, percussive tonality. In contrast to the relaxed approach of the vactrol, Make Noise also offer an ultra high-speed dual VCA/RingMod/Mixer called the ModDemix (£122.17$140). This allows for incredibly fast amplitude-modulation, and also manages to squeeze a ring modulator and summing mixer into a relatively small space.


Tiptop Audio's ZDSP, an open-source digital multi-effects module.

Intellijel's Mutamix ($250$250) is a six-channel, slider-based CV and audio mixer, capable of far more than just blending inputs. Triple outputs and selector switches on each channel allow sources to be routed to three destinations with a click. But 'X-MODE' allows for an inputted voltage to cycle through six saved mute 'snapshots' in different ways, and if it's used on control voltages, sequencer-like behaviour can be achieved!

There are many handy utility modules in the Eurorack format. Compact by nature, Intellijel offer an entire range of 'micro' utility modules: µAtt, µMod, µFade, µVCA, HexVCA and µStep. While perhaps not that exciting on their own, utilities help unlock the potential of other modules in your system. This is also true of their logic modules, Plog and Flip Flop. The Mutamix has real depth, intermingling control voltages from LFOs, sequencers and more in mathematically determined ways, and so building complex gestalt functionality (DIY sequencers, in effect) from separate modules, or perhaps just call-and-response switching between multiple voltage sources. Modules such as Plog and the Doepfer A151 can also run at audio rates to combine separate waveforms into new hybrid tones using logic operations. Who knew logic could be so creative?

Honourable Mentions

Also worth seeking out and prodding are Doepfer's range of utility modules, the Fonitronik MH01, Intellijel's Unity Mixer/TriAtt combo, the Manhattan Mix, the STG .Mix and Synovatron's CV Tools.


Tiptop Audio

Make Noise's Echophon is about as unusual as effects modules get.

The Tiptop Z5000 is a simple DSP-based multi-effects unit, much like the rackmount multi-effects units of the '90s, but in Eurorack format! Its 16 programs provide reverbs, delays, a flanger/phaser, pitch-shifting and a single CV control input for simple modulation.

But that's not all: Tiptop also make the ZDSP ($435$435). This is an open-source stereo DSP-processing Eurorack module; a platform on which users can create custom functionality and effects. The module itself has a healthy set of inputs, allowing external control voltages to affect parameters, the wet/dry mix, feedback and the switching between programs themselves. The ZDSP can also be fitted with expansion cartridges. Tiptop offer two pre-programmed cartridges, the multi-mode 'Bat Filter' and 'Dragonfly Delay' ($65$65 each), but blank ZDSP cartridges can be written with the separate 'Numberz' burning kit. Programs are available for free on the Tiptop Audio web site, as well as elsewhere in the SpinASM language forums and beyond.

The Harvestman

The Harvestman's Malgorithm (£276.26$330) is a voltage-controlled bit-depth and sample-rate reducer. It is capable of effects ranging from a mild digital bite up to extreme digital destruction — once well-behaved waveforms will end up sounding like a 1980s arcade game being thrown down an escalator. The 'Volvulus Mode' section allows eight bizarre extra modes to be engaged for voltage-controlled digital waveshaping and also to act as a low-fi oscillator with no input source connected. Perhaps Malgorithm's manual sums it up best, with the unapologetic and uncompromising mission-statement, "This module is also used to bring external signals into aesthetic compliance with the Harvestman system.”

Make Noise

No, wait, the Make Noise Phonogene is just as peculiar.

Make Noise have some of the most unique modules available. Reversing the trend for recreations of analogue hardware in software, they've paired up with DSP guru Tom Erbe of SoundHack plug-ins, to put software under analogue control. Echophon (£344.46$399) is a 16-bit, pitch-shifting delay module based on the esoteric Springer Tempophon, which, for those who don't know, is a vintage tape-based, granular pitch-shifting device. A maximum delay time of 1.7 seconds is available, as are CV inputs for literally every function. An input is also provided for timing, allowing delays to sync to clock sources from elsewhere in your modular. Remarkably, the pitch of the echoes is controllable via standard 1V/Oct CV input, so you could use a sequencer to play tuned melodies from delays, without affecting their timing! CV-controllable 'freeze' is provided for flamming/stutter effects, and you can also patch into the feedback paths, to further tweak, filter or decimate the delayed audio. If this sounds like fun, Harvestman's 'Tyme Sefari' delay/looper module is another one to check out.

Also available from Make Noise is the digital 'tape-slicing' machine of Phonogene (£457.55$530). Inspired by the methods of tape splicing pioneers of the last century, Phonogene makes it possible to capture and rearrange digital audio under voltage control. You can input a drum loop, manually set slicing points by tapping a button, and then rearrange them wildly with an LFO. Featuring 2MB memory, it is much more of a sampler than Echophon is capable of being, and lower bit-rates are available to extend recording time. Phonogene also, appropriately, includes a 'Sound On Sound' input for overdubbing recordings.

Two different approaches to wavefolding: the Intellijel µFold...


Back in the analogue domain, the Intellijel µFold (£142.44$160) and Toppobrillo Triple Wavefolder (£220.14$250) are simple and complex wavefolders respectively. A wavefolders is, effectively, the opposite of a filter. Rather than making a complex sound simpler, a wavefolder literally folds the wave back upon itself, making a simple wave more complex. Because of this, the effect is only really pronounced on simple waveforms. To process complex external audio (such as guitars and the human voice) through a wavefolder, it's helpful to try low-pass filtering the audio before folding. Sonically, wavefolding has a certain FM-synthesis quality — a growly, vocal-esque metallic character. Using a VCA (under control of an envelope) to control the amount of wavefolding allows for time-based timbre shaping to occur, and with only simple tools as the starting point, sonically interesting 'complete' waveforms can start to appear. This is West Coast synthesis in action. In fact, through a combination of Intellijel Dixie, µFold, µVCA and µFade, the functionality of a complex West Coast dual oscillator starts to emerge from constituent parts. The effects of wavefolding can equally be applied to control voltages themselves: both µFold and the TWF are DC-coupled to allow for this. Processing slow-moving control voltages through a wavefolder can turn simple LFOs into complex modulation sources. For a more vicious and lo-fi take that verges on a distortion effect, see Doepfer's A137 Wave Multiplier.

Doepfer/Analogue Solutions

Now for a word on spring reverbs. There is something inherently marvellous about mechanical spring reverbs combined with modular synths; equal parts of nostalgia, character and practicality. When experimenting with sound design, a little ambience can really complement the dry, raw sound of the machine, and this can well be provided by external hardware or software. But we need only look into the past to see that analogue modular systems often shipped with built-in spring reverbs — the ARP 2600, the EMS Synthi and the Buchla Music Easel, to name a few. And if Buchla, Zinovieff and Pearlman felt that modular systems needed a little reverberation, who am I to disagree? Doepfer's A199 (£94.96$180) and Analogue Solutions SR01 (£145£145) are the key units in Eurorack format, and there's also the possibility of swapping out the included spring tanks with compatible alternatives for different reverb characteristics.

Honourable Mentions

For other interesting Eurorack effects, check out the Flame FX6, Doepfer's BBD Delay Modules, the Pittsburgh Analog Delay, Flight Of Harmony's Sound Of Shadows, the Snazzy FX Ardcore, Synthesis Tech's E560 Deflector Shield and the WMD Geiger Counter.

A Few Final Words

... And the Toppobrillo Triple Wave Folder.

Hopefully, this article will have given you a flavour of the more exotic side of the current Eurorack market, but with over 80 companies and more than 700 modules out there at the time of writing, this is only a tiny fraction of what's available. So, in your search for modular Nirvana, I urge you to please look up the full catalogues of the brands mentioned above, and explore the resources listed in the 'Further Info' box.

For intrepid explorers entering the world of Eurorack, I have a few words of caution: build a system slowly. You'll be able to better understand what capabilities your system has and what elements you might be missing, because with so many fascinating options available, it's hard to resist the pull of a new module. To quote musician Stretta (the owner of a truly epic Eurorack modular): "When you get a new module, your old instrument is entirely new again.” Just remember the spirit of modular is as much about building functionality from combinations of existing modules as it is about finding the 'right' ones. If you're creative before you reach for your wallet, you will find fresh sounds in old circuits. The journey is endless, and you might find that your finished system is very different to how you first envisaged it.

The experience of patching a modular can be very 'zen', and for many, simply enjoying the process of discovering new sounds is the only goal, although it can be a distraction from the flow of writing music. Perhaps we should take a leaf from the book of Vince Clarke (a man of many modulars), and write the song on guitar first, then fire up the synths?

No matter how you look at it, for boundary exploration, woofer destruction and discovering ideas you'd never have worked out on a keyboard, a modular synth is the ultimate way to complement an electronic music studio — or perhaps even the ultimate electronic studio. And if you fall deep enough down the rabbit hole, you may never turn your computer on again, except, of course, to hit record. Never forget: once that patch is made, capture it. We will never hear anything like it again.  

Power & Cases

If you're considering buying a modular system, your exciting new modules will need some power and somewhere to live, so the first thing to decide is which case and power supply.

Doepfer offer a fairly priced three-row wooden case called the LC9 (£241.72$460), which represents about the most cost-effective medium sized, off-the-shelf Eurorack case. If that's still a little too rich for your blood, an LC6 (£207.19$390) with two rows is also available. Further reduced, Tiptop's Happy Ending metal frame kit ($149$149) is, at 3U, the smallest and least expensive Eurorack case that includes both power and a frame.

ADDAC have relatively inexpensive power-not-included 3U and 6U rack cases available, made from wood. These would go well with Tiptop's µZeus (£65$85), a tiny power module with a wall-wart and 10 connectors for modules. Unless you combine µZeus with a pre-made case, you'll have to purchase Tiptop Z-Rails (£31.99$35) to screw modules into (or screw them into wooden strips), and then build a frame! You can also buy Doepfer's bus boards and power section 'naked', in a product called the DIY Kit 1 (£103.60$195). This is the equivalent electronics (plus rails) of a Doepfer LC6 Case, leaving you free to build your own case. You can also buy additional bus boards and rails to create a three-row case.

Higher-end alternatives include portable suitcase cases from Monorocket in the USA, Tiptop's Buchla-esque folding Station 252, and wooden cases from a handful of bespoke modular synth case makers. Of these, probably the most well-known are Matthew Goike in the US and Ross Lamond in the UK, whose work borders on fine art.

Further Info

There are Eurorack dealers scattered throughout the world. Visit the various web sites for the brands mentioned in this article and investigate their dealer locator pages for retailers in your territory. Some of these will have demo systems, so give them a call and see what they can show you.

As far as online resources go, is an invaluable directory for the Eurorack format, and, at the time of writing, provides an incredibly comprehensive database of over 80 manufacturers and 730(!) modules. Also useful is, a new but promising graphical web-based app for conveniently planning and re-arranging a Eurorack modular synth layout, which allows users to add, edit and browse modules.

Web sites such YouTube, Vimeo and SoundCloud are essential resources for research. Just input the name of a module and you can probably find a video or sound clip of it in action.

No place on the Internet is more vocal on the subject of modular synths than a forum called (named after the fuzz pedal, before you ask!). The Eurorack sub-forum is one of the key online communities for the format and it's common to witness products being discussed and announced there by the companies mentioned in this article.

Computer Love

British company Expert Sleepers have carved themselves a niche by bridging the gap between our DAWs and our analogue synths. Their flagship Silent Way package allows your computer to communicate with your analogue synth — and vice versa — via an audio interface. The catch used to be that specific audio interfaces (ones with DC-coupled outputs) were needed to deliver the required voltages, but Expert Sleepers have come up with the ES1 and ES2 Eurorack modules to convert the signals from any audio interface into ones calibrated for the job.The ES3 and ES4 modules plug into your audio interface's ADAT Lightpipe and S/PDIF outputs respectively, putting them to work delivering Silent Way's outputs to modular-calibrated 3.5mm jack outputs located on the modules. One caveat is that a license for Silent Way software must be purchased in addition to the modules, but, at around £40 for V2, it's unlikely to break the bank.

The Future?

NAMM 2012 saw functioning prototypes of an ambitious project previewed: Tiptop Audio are pioneering a Eurorack-based, polyphonic analogue modular system. Utilising eight-core cables, it is an attempt to create a standard that others can develop modules for. This is in addition to their continuing work bringing analogue clones of the TR808 and 909 drum machines to Eurorack.

But what about using your modular system to control and interact with your computer? With an Analogue Solutions RS300 CV-to-MIDI converter (or Expert Sleepers Silent Way), this is becoming daily more meaningful for Eurorack users.

Published April 2013

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