You are here

Erica Synths Syntrx

Analogue Synthesizer By Rory Dow
Published March 2021

Erica Synths Syntrx

The Syntrx is not a clone, but its inspiration is clear. Can it recapture the spirit of the legendary EMS Synthi?

It’s a fact — the EMS VCS 3 and its portable cousin the Synthi AKS are among the most revered synthesizers ever built. Released at the tail end of the 1960s, the Synthi was quickly adopted by progressive musicians like Brian Eno, Pink Floyd, Jean‑Michel Jarre, Hawkwind and Tangerine Dream. Its unconventional interface and distinctive pin‑matrix patching system encouraged experimentation, resulting in an exotic, ‘far out’ sound.

The Syntrx wears its inspiration proudly but it is not a clone. No part of the circuitry is copied from EMS’s schematics, it’s all been newly developed by Erica Synths themselves. On the other hand, the choice of modules, the front panel layout, the pin matrix (albeit now 100‑percent digital), the parameter naming, the joystick, the VU meter, speakers and even the name, mimic the EMS designs. Erica Synths want to give you as close to the experience of an EMS Synthi as possible without entering the murky and contentious waters of cloning. The question is can the Syntrx keep the magic alive without the EMS engine firing under the hood?

Into The Matrix

The Syntrx, and the Synthi before it, are semi‑modular analogue monosynths. There are three oscillators (the third works at lower frequencies for LFO duties), noise generator, ring modulator, low‑pass filter, two input amplifiers and a spring reverb. For modulation sources, there’s a trapezoid envelope generator, sample and hold module and the joystick. The sample and hold circuit, along with oscillator sync, a gate input and of course MIDI, was not something that featured on the Synthi, although they could all be done, and often were, with skilled modification.

Erica Synths Syntrx digital pin matrix.The digital pin matrix.All modules are logically laid out on the front panel and in the middle, impossible to miss, is the pin matrix. I call it a ‘pin’ matrix, but the resistive pins used by the Synthi are gone. Instead a grid of LEDs replaces the pin‑holes and two endless encoders are used to move around the matrix like an Etch‑A‑Sketch. On the vertical axis are sources and on the horizontal axis, destinations. Line up the intersection between a source and a destination, and click the encoder to insert a virtual pin. In the Synthi, each pin had a resistor soldered within it. Different coloured pins used different resistors to vary the amount of signal that was passed from source to destination. The Syntrx emulates this with successive pushes of the encoder, the brightness of the LED dimming with each click indicating the level of signal being passed through.

The digital nature of the matrix opens up the opportunity for patch storage and although it’s not possible to store the values of the parameters themselves, you can store up to 256 matrix patches (one for each slot in the matrix). This is useful for storing templates. For example, one might store the basic routing for a simple monosynth (oscillators > filter > amp) to use as a starting point. Or perhaps a template to route the two external inputs through the ring modulator then into the spring reverb. I couldn’t imagine ever needing 256 templates, but the ability to save is definitely a welcome addition. If you’re quick with your hands, you might even be able to use the templates in a live situation, to help recall completely different setups between songs — it would take some practice though.

Another nice nod to the Synthi is the ability to temporarily insert pins. This was a common technique used to alter the sound by inserting and removing pins during a performance. By hitting the Shift button and clicking the encoder a temporary connection is made that lasts as long as the encoder is held down.

Sound Sources & Processing

Syntrx’s three oscillators use three‑turn vernier dials for tuning, which feel great and allow for easy fine‑tuning without the need for additional controls. Oscillator 1 can output sine and sawtooth waveforms, with a separate level control for each and the sine wave can be wave‑shaped. There’s also a +/‑1 octave switch. Oscillator 2 offers square and triangle waveforms, with the Shape knob taking care of both pulse width on the square and wave‑shaping on the triangle waveform simultaneously. The switch here enables hard sync to Oscillator 1, which wasn’t a feature on the EMS Synthi but was often installed as a mod. The third oscillator offers the same waveforms and wave‑shaping as Oscillator 2, but its tuning range is much lower and the switch disables keyboard tracking so you can use it as a fixed‑rate LFO.

Erica Synths Syntrx oscillator controls.Erica Synths Syntrx oscillator controls.Other potential audio generation sources are the noise module, with controls for level and colour, and the two external audio inputs. These two inputs each have gain control and share a mic/line switch. Like the oscillators and the noise source, these inputs are fed directly to the pin matrix, where they can be routed to any other module or output.

The low‑pass filter is an original design. It’s capable of self‑oscillation, but it doesn’t track 1V/Oct. Overdriving the filter is easy thanks to the generous gain on the oscillator outputs causing the resonance to disintegrate in a very pleasing way. The filter has been designed to respond to audio rate modulation very nicely too. I had wondered if Erica Synths might include the oft‑installed ‘Filter slew mod’ from the Synthi — a switch which bypassed a capacitor filtering the high frequencies of CV sent to the filter, giving you a very different filter characteristic — but alas not. I suspect the Syntrx new filter design makes this irrelevant, but it was always something I enjoyed on my Analogue Systems RS‑500E Synthi Filter module.

The ring modulator was a big part of the sound of the Synthi, especially when used to treat external signals such as guitar or voice. The two inputs and one output appear on the pin matrix and there is just one physical control for the output level. It sounds as deliciously clangorous as you would hope.

The spring reverb tank offers two controls, Mix and Feedback. The reverb input and output appear on the pin matrix, as does CV control for the mix amount. Most spring reverb tanks generate a fair amount of noise with a dash of electrical hum mixed in, and this one is no different — it’s all part of the charm. At high values, the feedback control will cause the spring to self‑oscillate, which can be a wonderful source of otherworldly drones and feedback effects. If you use the on‑board speakers, they too will cause mechanical interference with the spring, which can be equal parts annoying and interesting, but that’s the nature of mechanical effects. And of course, if you give the tasteful wood sides a good slap, you’ll be rewarded with the appropriate boing, twang and schplooong.


On the face of it, the Syntrx design doesn’t offer a huge amount of modulation sources when compared with more modern synthesizers. A sample and hold module, trapezoid envelope generator and the joystick are the only dedicated modulators, but there’s also the third oscillator which offers triangle and square LFO shapes. The two MIDI CCs could also be counted, but they are added to the joystick CVs in the pin matrix so you can’t use them independently. The point of the Synthi/Syntrx is that anything can be a modulation source, if you’re brave enough, and in use you never feel like you’re running out of options.

The trapezoid and ring mod controls.The trapezoid and ring mod controls.The trapezoid envelope is worthy of some explanation. Its design makes it more useful than the average ADSR. It is made up of four stages: Attack, On, Decay and Off. The envelope can be triggered by MIDI note, CV gate input or by the Attack button next to the joystick. It can also self trigger, making a looping envelope. There are two modes, AD and ASR. In AD mode, once a trigger is received, the envelope will go through the Attack stage, then hold high for a length determined by ‘On’, after which it will go to the Decay stage. This mode is useful for percussive or drum‑type sounds of a fixed length (although you can modulate Decay length in the pin matrix).

In ASR mode, the trapezoid envelope will loop as long as the Off stage isn’t at its maximum setting. A trigger will start the envelope at its Attack stage, hold ‘on’ for as long as the note is held and, once released, move to its Decay stage. Then, if the Off stage isn’t at full value, it will hold a zero value for the length of the Off parameter before it loops again starting at the Attack stage. ASR mode is flexible, either as a more traditional AHR envelope or as a looping trapezoid shape, which can be used for LFO‑type duties, or as a repeating pulse.

The envelope section also contains a somewhat hidden VCA. By routing audio or CV signals to the ‘Envelope’ on the pin matrix, and then routing ‘Env. Signal’ elsewhere, the signal will be amplitude modulated by the envelope.

The sample and hold section allows for either VCO3 or the noise generator to be used as the CV source with an internal clock used to trigger the sampling. There are physical controls for the rate and output level. Because of the limited number of slots available in the pin matrix, the sample and hold output has to share a row with VCO3. A three‑way switch allows you to select what appears at the pin matrix output: VCO3, sample and hold or an equal mix of the two.

The final, and in my humble opinion, most important source of modulation is the joystick. Something changes fundamentally in any patch when the joystick is brought into play. Huge sonic changes can happen with the smallest of movements and because there is no zero point or spring to return it to a default position, you always feel like you’re exploring some new part of a vast sonic vista. Functionally, it’s very simple, two dimensions — X and Y — both freely assignable in the pin matrix. As well as the joystick itself, there are two attenuators to change the CV output level going into the matrix.

Where a normal synthesizer encourages you down familiar paths, the Synthi begs to go off‑piste. The great news is that the Syntrx manages to hold on to this wonderful sense of exploration.


There is something undeniably special about the original EMS Synthi design. It gives you almost all the sonic potential of a much larger modular system without the cabling mess or the bewildering possibilities. The pin matrix encourages you to make new connections, try new things, experiment. It also urges you to make more connections because, unlike modular, a single source can be easily connected to many destinations and, conversely, a single destination can be linked to many sources. Sometimes it can feel like playing a piece of lab equipment but a deft knob‑twiddle or joystick tweak always brings the musicality into focus, and a ‘pin‑drop’ in the matrix can take a sound in wild new directions. Where a normal synthesizer encourages you down familiar paths, the Synthi begs to go off‑piste. The great news is that the Syntrx manages to hold on to this wonderful sense of exploration.

The Syntrx measures 309 x 457 x 115 mm and can be rackmounted with a pair of optional ears.The Syntrx measures 309 x 457 x 115 mm and can be rackmounted with a pair of optional ears.

It’s difficult to compare the sound of the Syntrx to its spiritual mentor. I had hoped to throw it in the car and visit one of my SOS colleagues who is lucky enough to own an EMS Synthi AKS, but Covid‑19 laid waste that plan (see ‘Comments From A Synthi AKS Owner’ box). The Syntrx is undoubtedly more stable than the Synthi. The oscillators will keep their tuning far better and track over a much wider range. Also, the Synthi pin matrix suffered from an unbuffered design. This meant that adding more pins to the matrix could affect the tuning of oscillators in a detrimental way. The Syntrx has no such problem. It’s also not subject to all the decrepitudes that age can bring.

In much the same way the Korg does with some of their reissues, it’s great that Erica Synths included some of the popular mods — the sample and hold circuit, oscillator sync and CV/gate. Plus there’s the basic but nonetheless useful MIDI implementation. All these are small but welcome improvements that don’t detract from the fundamental design.

Somewhat amazingly, EMS are still going, run by Robin Wood who was with the company back in 1970. At the time of this review, you can still put your name down on the waiting list for a genuine, brand‑new Synthi A or VCS 3. The price listed on their website is just shy of £6000. Output seems glacially slow however and the waiting list is long. A genuine vintage model, well‑kept and serviced, will set you back £9000‑£12000. The Syntrx, on the other hand, is available now and really does retain all the fun of the Synthi without the price tag or the worry of maintaining a 50‑year‑old instrument. It is also far more portable and, I suspect, forgiving of the rough handling that a live gig or a full tour might bestow. To answer my opening question, ‘Can the Syntrx keep the Synthi magic without the same electronics?’, the answer has to be ‘hell yes’. I had a blast with it and whilst some of the resulting sound might not fool a Synthi owner, it is every bit the madcap machine you would hope it to be.

Round The Back

Erica Synths Syntrx rear panel.

The rear panel is home to sockets for 12V DC power, headphones, dual audio inputs and outputs, MIDI In and Thru, gate input and two CV inputs (1V/Oct). The small push button next to the Gate In socket is used to set MIDI preferences for the internal MIDI CV converter such MIDI channel, MIDI CCs to control the joystick CV or velocity response (filter only).

MIDI Implementation

One thing you certainly won’t find on a 1971 EMS Synthi is a MIDI port. The Syntrx, on the other hand, offers basic but welcome functionality. With a MIDI controller connected to the MIDI input port, a note‑on will trigger the Trapezoid envelope and the oscillators will track pitch (the third oscillator can be set to Free mode if you wish to use it as an LFO instead). The MIDI input is added to the 1V/Oct CV inputs, which means you could use an analogue sequencer to play a melody, and a MIDI keyboard to transpose it — not a trick the original Synthi could pull off.

Velocity can be enabled or disabled although its only potential is to control filter cutoff, and you can’t control the amount. Finally, two MIDI CC numbers can be set and are converted to CV and added to the joystick X and Y CV.

Some may think that adding further MIDI support might be straying from the core concept of the Synthi/Syntrx, but I couldn’t help daydreaming about the possibilities of having complete MIDI control over all parameters. Combining sequencing of multiple parameters with hands‑on tweaking would produce staggering results I think — perhaps Erica Synths could consider it for a Mark II?

Comments From A Synthi AKS Owner

Despite Covid ruining my plans for an in‑person comparison, I sent SOS reviewer and Synthi AKS owner Paul Nagle a 25‑minute audio demo of the Syntrx. Here’s what he had to say:

“It definitely manages to evoke the Synthi vibe. Its reach is somewhat wider in some respects. The resonance has a harsher edge, more chirpy than wibbly, but it covers melodic stuff in a way that my Synthi would struggle to match. It’s cleaner than my clicky, buzzy, snarly and occasionally temperamental beast, but that’s to be expected. Sounds like it can cover a range of normal tones, which is all to the good. Reverb sounds nice. When I close my eyes for some parts of this, it’s surprisingly close. Even before hearing your demo, I suspected I’d love one — now I know!”

Click on the link below to hear the demo:


  • As close to the spiritual Synthi experience as you’ll get.
  • Sounds marvellous in its own right.
  • Solid build.
  • A few nice ‘mods’ from the original: S&H, oscillator sync and gate input.
  • Pin matrix presets.
  • MIDI, albeit basic.


  • As long as you don’t expect the exact sound of the Synthi, none.


The Syntrx mimics the experience of an EMS Synthi very well. Although its inner circuitry is entirely different, it still manages to capture the unique approach to sound design that made the Synthi such a hit. It doesn’t sound the same, but it retains the capacity for off‑the‑wall sonic journeys that made the original so beloved.


£2699 including VAT.