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Analogue Systems RS Modular

Synthesis Modules By Chris Carter
Published November 2003

Analogue Systems Synthesis ModulesPhoto: Mark Ewing

The monster AS modular synth system continues to expand with the launch of another batch of new sonic tools.

It's only been a few months since those Cornish techno-boffins Analogue Systems were gracing these pages with the Spawn monosynth (see SOS April 2003 issue). Well, here they come again with a new batch of small but perfectly formed electronic marvels — yes, it's a fresh crop of RS modules, the ever-expanding, weird and wonderful range of plug-and-play synthesizer boxes that populate Analogue Systems' modular cabinets. In this review we'll be taking a look at a selection of analogue modules made under license from EMS, a couple of retro effect modules, and, first, a module that puts a whole new spin on sampling and delay-based effects...

RS290 Sampler/Delay

The RS290 is a 16-bit digital Sampler/Delay module offering extended sample/delay times, 50 user memories for delay presets, and extensive analogue control of digital parameters. It functions in one of two modes — sampler or echo/delay — and its specifications aren't bad for such a small unit. It features a variable sampling rate, from 9.8kHz right up to 46.9kHz, and a switchable bit rate that starts at a CD-friendly 16-bit and steps down (in single bits) to an almost unusable 4-bit level. Both sampling and bit rates can be set independently of each other, and the playback pitch can be modulated by an external control voltage, in sampler or delay modes. The RS290's CV control adheres to the 1V/oct standard, which means that samples can be played chromatically using a CV keyboard or a MIDI-to-CV convertor.

RS290 Sampler/Delay and optional RS295 expander module.RS290 Sampler/Delay and optional RS295 expander module.Photo: Mark Ewing

The memory available in sampler or delay mode is a respectable 5.6 seconds at the top sample rate and an incredible 26.8 seconds at the lowest. The downsides to all this nice RAM are that only a single sample can be held in memory at once, sampling is in mono, and playback is monophonic (see 'RS290/295 Quirks' box). However, in Echo/Delay mode a mono-in/stereo-out configuration is available.

Although small compared to most hardware samplers, the RS290 is one of Analogue Systems' larger 12HP-wide (Horizontal Pitch) units, and as a result the layout of the controls around the display is less cramped than on some RS modules. The yellow backlit LCD is large, bright, and easy to navigate, and none of the menu parameter adjustments is more than two levels (edit clicks) down, so there's little chance of getting lost in the bowels of some arcane menu system.

Parameter editing and navigation is carried out by way of a red 'Cancel' button and a single 'Edit' knob, the latter being a combined continuous data controller and a push 'enter' switch. Pushing the Edit knob selects a function, mode and/or parameter, while rotating it changes parameter values, moves the cursor or scrolls the menus. Continually pressing the Cancel button always brings you back to the initial display screen — very handy. Apart from showing the current preset or mode, the LCD can also display audio input or output levels, though there's basic input- and output-level metering via two tri-colour LEDS too.

The RS290 includes a dedicated LFO, although this is software based and (with the current firmware) is only available in Echo/Delay mode. However, it's quite well featured and does offer useful programmable (and externally controllable) parameters, such as speed and various output waveforms. Modulation destinations comprise delay time, output panning, left/right delay offset, feedback, and sample size and pitch. The LFO will also sync to the Trig1 and Trig2 gate inputs, or to a MIDI clock if you have the optional RS295 module installed.

To examine the controls of the RS290, apart from a self-explantory Input Gain knob, we have knobs for:

  • Repeat Speed/Sample Start: for adjusting the length of time between delay repeats or trimming the start point of a sample.
  • FB Gain/Sample End: adjusts number of delay repeats or trims sample end point.
  • Wet/Dry Mix control and Bypass switch: these are active in Echo/Delay mode only.
  • Assign1/Sample Pitch: while in Echo/Delay mode this is a programmable controller and can be assigned to alter parameters such as damping, bit rate, LFO speed or depth, and so on. In Sampler mode, adjusts sample playback speed and external modulation depth.

Of the above controls, Repeat Speed/Sample Start, FB Gain/Sample End and Assign1/Sample Pitch each have a dedicated input socket for external modulation via a standard 1.0V/octave Voltage Control source. Very usefully, these modulation inputs work in addition to modulation offered by the internal LFO.

Whoa Trigger!

Two trigger/gate input sockets (Trig1 and Trig2, as mentioned above) are included. These innocuous sockets give access to some pretty fancy triggering and gating options, as the RS290 can be programmed to respond to a variety of trigger on and off states. For example: sample record start and stop can be initiated (independently) by either an on (high) or an off (low) gate signal, as can sample playback. In Echo/delay mode the Trig1 and Trig2 sockets can also be used for connecting an external clock source to synchronise the delay BPM times of the RS290. The sync source can be anything that produces a regular gate output, such as a drum machine, LFO or MIDI clock.

If Trig1 and Trig2 are used in conjunction with the voltage control inputs, an analogue sequencer and an LFO or three, you can configure complex delay effects and experimental sampling and playback patches that would be near impossible with a regular MIDI sampler or soft sampler application.

Voltage Controlled Sampling & Editing

Sampling is straightforward, and can be initiated by pushing the Edit knob to begin and to end a recording (in Record Start mode). Alternatively, you can start and stop sampling (and playback) externally, using trigger/gate signals, as I mention elsewhere.

Sample editing is basic, using just the Sample Start and Sample End knobs, but it is also easy and fast, and both parameters are voltage controllable. One problem you encounter, however, is that the longer the sample time, the coarser the Start and End control-knob resolutions become, so that (for example) fine editing of long rhythmic loops, in particular, becomes very hit and miss. Then again, this unit isn't really aimed at loopists, who have far more accurate looping tools at their disposal. Talking of loops, there are five sample playback options: Once, Reverse Once, Loop, Reverse Loop and Alternate Loop. Some interesting and quite bizarre effects can be heard if the Sample Start and End parameters are modulated by an external LFO or analogue sequencer while an alternating sample is played back.

Sound & Character

At its highest sampling rates, the RS290's sound is dynamic and clear of digital artifacts. Even down to about 33kHz it sounds very good. However, between 29kHz and 16KHz there's a noticeable drop in clarity, and below this the sound loses a lot of top end. But it's a case of swings and roundabouts, because at 29kHz you get the luxury of about 10 seconds of decent-sounding delay/sample time.

The most noticeable drop in quality occurs when the bit rate is below 12-14 bits. However, reducing bit rate is great for emulating early digital drum machines, delay units or analogue tape echos, and for adding grungy special effects to delay patches or samples. A useful feature is that both the sample rate and bit rate can be changed during playback.

ECHO...echo DELAY...delay

With its wealth of modulation possibilities and extended delay times, Echo/Delay mode is extremely versatile and can produce anything from regular echo, chorus and flanging effects to comb filtering, pitch shifting, tape echo, analogue delay simulations, Fripp-type loops and long, mutating sound-on-sound effects.

The standard output configuration is a mono-in/stereo-out ping-pong delay. The L/R delay ratio can be adjusted from 100 percent Left or Right (mono) to an equal 50/50 left and right mix, or anywhere in between. The L/R ratio parameter can also be modulated internally by the LFO, or externally using the RS295 module (more below).

The Right output socket serves two purposes and is labelled F/B Send. If it is used with the F/B Return socket and the External Feedback menu option it can be configured to direct the incoming signal 'pre or post' the delay feedback loop. This send/return method would usually be used with an external effects device, and is a nice option to have.

Before I move on to discussing the optional extra RS295 module, I should mention that I eventually ended up receiving three RS290 modules for review. There was nothing physically wrong with the first two units, but not being a PC user I couldn't run the PC-only AS firmware application to update the 290's operating system. The only solution when the OS was updated was for AS to send replacement modules. AS are hoping to overcome this problem by possibly adopting a standard MIDI file format for future updates.

Optional RS295 Module

The RS295 expander module isn't necessary to use the RS290, but it does offer some useful additional features. For a start, it includes MIDI In and Out sockets, which are essential if you intend updating the RS290 firmware. It will also allow you to save and load your own Echo/Delay presets and dump and retrieve samples using MIDI sample dump standard (I know it's slow but it works!). Once the RS295 is in place, you can also change Echo/Delay presets using MIDI Program Change messages from a keyboard or sequencer. The module also includes an additional programmable Assign2 control knob and CV input socket.

RS500E 'EMS Synthi' Filter Module

The RS500E module — or, to use its full title, 'EMS Synthi Filter' — is a voltage-controlled low-pass filter based on the design used in the original EMS VSC3 and portable Synthi AKS synthesizers from the early '70s. Analogue Systems have tried to keep as close to the original circuit designs as possible, and any differences are primarily so that the filter will interface with other RS modules.

The filter is a standard RS 12HP-wide module with a sensible layout of sockets and controls, including audio Signal Level in and out, filter-frequency knob, two filter-frequency CV inputs (a 1V/oct input and a variable one), and a Response control (Response is EMS terminology for resonance). The Response control also includes a CV input, something not available with the original EMS version. Two additional switches not part of the original design are also included, namely CV Slew and a filter slope selector. The original EMS circuit was slow to respond to fast or short percussive control voltages (due to a capacitor in the circuit), and the CV Slew control switches this capacitor off. It doesn't change the filter's sound as such, just makes it able to be more responsive and snappy.

The original (and some say the best) EMS filter circuits had a frequency response that rolled off at 18dB/octave. In 1974, and to fall in line with what other synth manufactures were producing, EMS changed their filter to a 24dB/octave design. Analogue Systems have thoughtfully included a switch marked 'Pre-1974 18dB/Post-1974 24dB' so you can decided for yourself which sounds best.

RS500E EMS Synthi Filter and RS510E EMS Trapezoid Generator modules, shown in case with Ring Mod and Multiple modules.RS500E EMS Synthi Filter and RS510E EMS Trapezoid Generator modules, shown in case with Ring Mod and Multiple modules.Photo: Mark Ewing

So what does it sound like? As I don't currently have an EMS synth I couldn't do a direct A/B comparison, but I've used half a dozen or so since the 1970s and I'd say this filter sounds pretty authentic, probably about as close as you're going to get without spending some serious cash on an original VCS3 or Synthi AKS. OK, so EMS filters weren't exactly renowned for their outstanding character — well, not in the same way that some US and Japanese filters were. I doubt I'm the first to mention that the character of the original filter (pre- or post-'74) could be described as restrained, and the same applies to this authentic-sounding reproduction; to my ears, at least, it doesn't have the musicality of some low-pass filter designs.

I hope I'm not giving out mixed messages, because these aren't really criticisms, just subjective observations. I've a real fondness for EMS synths and this is a very good sounding filter, especially in Pre-1974 mode with the Slew switch on Fast. But it also exhibits a few annoying classic EMS characteristics too! One is that the Response control drastically reduces audio output as the resonance is increased, then pushes the filter into self-oscillation almost without warning. (As an aside, the RS500E sounds great used as an oscillator, in self-oscillating mode, producing a stable, smooth sine-wave output.)

So, all in all this is a nice-sounding filter (and part-time oscillator). Couple that with the CV inputs and other RS modifications and the RS500E makes a worthwhile addition to any RS rack.

RS510E EMS Trapezoid Generator

This is the second RS module made under license from EMS, and is fundamentally an envelope (or contour) generator combined with a VCA. The original EMS circuit used in the VCS3 and Synthi AKS was rather confusingly referred to as "Envelope Shaper with a Trapezoid output". This was probably one of the reasons for a certain amount of the head-scratching it caused — and it wasn't very intuitive to use either. However, it was worth persevering with, as it could be quite a flexible envelope generator if tweaked enough. Fast forward 30 years and here we are with the new RS510E module, an updated but authentic reproduction of the original circuit with a couple of useful RS additions.

One of the main differences between this trapezoid envelope generator and a regular ADSR envelope generator is that the RS510E doesn't need triggering from an external gate to produce an envelope-control voltage output. It can generate a free-running four-stage voltage contour using just its own Attack, On, Decay and Off controls (A/On/D/Off). If the Off control is set to Manual (full clockwise) and the RS510E is triggered from the front-panel Attack button, or an external positive gate signal, it will perform in a similar manner to an ASR (Attack, Sustain, Release) envelope generator, with an Attack of between 2ms and two seconds, a Decay of 3ms-25s and an On time of up to four seconds. However, turning the Off control anti-clockwise introduces a repeating trigger element to the envelope; with the control fully anti-clockwise, the re-trigger speed is around 30Hz or so. We're now entering LFO territory, where it becomes possible to adjust the A/On/D/Off controls to automatically generate waveforms such as triangle, skewed triangle, sawtooth, square, pulse and other trapezoid shapes. These waveforms can be further modified or modulated using the Decay CV input. A variable control allows you to adjust the Trapezoid Output Level between -5v and +5v, and this is then suitable for modulating and triggering all kinds of CV and gate modules.

Control options for the VCA are limited to audio in and out level knobs and there's no way to independently modulate it using an external voltage, only via the trapezoid output. The attack time is a bit less snappy than most contemporary envelope generators, but otherwise a VCA is a VCA.

On first impressions, the Trapezoid Generator may seem unexciting, but it's also bit of a dark horse, as it can be pressed into service as an envelope generator, a trapezoid generator or an LFO, and can simultaneously be used as a VCA too. It's a nice bag of tricks, and would be at home in many an RS rack.

RS290/RS295 Quirks

As I mentioned elsewhere, the RS290 samples in mono, has a single-sample memory and offers only monophonic playback, which you learn to live with. More annoying is the volatile memory — if you turn the rack off or it loses power, your sample is also lost without warning.

I've discussed this problem with Analogue Systems, but it seems that short of a total redesign, adding non-volatile sample memory would involve costly hardware changes and make the unit too expensive to produce. My advice would be to invest in the optional RS295 expander (which uses MIDI Sample Dump) if you desperately need to save and load samples you spent a lot of time working on.

A feature I was surprised not to see as part of the optional RS295 expander was sample playback (or triggering) via the MIDI input, which I think would be useful and add to the appeal of the module. Unfortunately, there are currently no plans to include this feature, as I don't think Analogue Systems see it as essential in a primarily analogue-controlled environment — but maybe pressure from RS295 owners may change their mind. During the review period I found the guys at AS very open to suggestions for new features.

RS390 Echo

The 12HP-Wide RS390 Echo is a new spin on the classic analogue and tape-delay effects of the '70s and '80s. When disco reigned, most delay-based effects devices, such as chorus, flanging, phasing and short slap-back echo units, were powered by the popular but oddly-named Bucket Brigade Delay device, an analogue chip. The BBD was pre-DDL (digital delay line) technology and is usually associated with a warmer sound than that of digital time-based effects units.

To get an idea of how far we've come from the few hundred milliseconds that lo-fi BBD technology gave us, let me point out that to achieve its analogue-sounding mono-in/stereo-out digital effects the RS Echo module uses 24-bit DSP technology, has an audio frequency response of 22kHz and offers a maximum delay time of three seconds at full bandwidth. Impressive!

This device has six control knobs: Delay Time, Delay Range (three steps), Dry/Effect Mix, audio Input level, Repeat Damping and Repeat Depth. CV inputs are also available for modulating Delay Time and Dry/Effect Mix. Most of the controls are self explanatory, but the Repeat Damping control and Delay Time CV input are the secret weapons for achieving authentic-sounding analogue and tape delay effects. For chorus, flanging and phasing effects, a short delay time is needed, modulated by a slow external LFO sine or triangle waveform applied to the Delay Time CV input. Depending on how 'analogue' you want the effect, you may need to increase the amount of Repeat Damping, which will dull the sound. For longer analogue delay and tape delay effects, Delay Time is increased, modulation is reduced (to almost zero) and Repeat Depth increased for more echo repeats. For really grungy-sounding 'tape' delays, copious amounts of Repeat Damping and CV modulation could be applied.

This module can be a lot of fun, and I whiled away many hours recreating old tape, analogue delay and flanging effects. Admittedly, with only a ping-pong stereo output it's not going to recreate the sound of multi-headed tape machines such as the Copicat and Echorette — for that you'd need to invest in a few more RS390s — and a built-in LFO would be useful for modulation, but nevertheless this module is capable of a wide range of analogue emulations and quality delay-based effects. It gets my vote.RS400 Phase Shifter and RS390 Echo modules, shown in case with phono adaptor module.RS400 Phase Shifter and RS390 Echo modules, shown in case with phono adaptor module.Photo: Mark Ewing

RS400 Phase Shifter/LFO

The last new module on this list of RS retro effects is the RS400 Phase Shifter, a title that describes it exactly. This module (also 12HP wide) uses an analogue four-stage circuit design that also includes a built-in LFO. Controls are minimal but functional: Phase Frequency, Emphasis (filter resonance), an external CV input and Level control (to modulate Phase Frequency), and LFO Rate and Depth knobs. Apart from the mono audio input and output sockets, there are connections for two CV inputs (fixed and variable) and an LFO CV output, with a bi-colour LED indicator for the LFO rate.

Apparently, the sonic benchmark for RS400 is the 1970s Electro-Harmonix Small Stone phaser. The oddly named Small Stone was a classic of its time but many owners substituted its two-way feedback switch (filter resonance) for a variable knob, and it is this version that the RS400 sound is based upon.

And it sounds very good too! The phase effect is deep and wide ranging at all frequencies. The Emphasis control just holds back from self-oscillating at maximum, which is probably a good thing for a phaser, and the LFO rate goes from a leisurely 0.2Hz to a bubbly 10Hz. An audio input-level LED would have been useful, and I missed not having a dedicated effect on/off switch or effect/dry knob, but extensive modulation options make up for this, as the internal LFO waveform can be mixed with the two external CV inputs, for complex multi-modulations. Also, usefully, the module has an LFO CV output, so it can double as a triangle waveform LFO within a modular system.

As with all phasers, the effect of the RS400 works best on harmonically rich audio and complex waveforms. A deep effect at slow speeds is great for adding colour to pad sounds, while a faster, shallower effect is good for Leslie organ cabinet-type sounds. The RS400 sounds a bit classier to me than the Small Stone, and thankfully lacks the noise and grunge I remember from the original. To me, it sounds slightly more MXR than Electro-Harmonix, which isn't a bad thing in my books. Another thumbs-up for AS.

Modular Anthropology: Final Thoughts

In my experience, modularists (is that a real word?) tend to fall into three categories. First there's the purist, who's only interested in analogue modules. MIDI? forget it — if it's not CV, they're not interested. Then there are the experimentalists, who'll mix and match any module, always looking for new and ever-more fiendish patches and sounds. And lastly there are the completists, the catalogue hounds who have to have all the modules, the newest modules and the limited editions, they live and die by E-Bay. I'll stand up and say I fall into the middle category, though if money and space were no object I'd be scarily close to the last type.

The good news is that amongst this new crop of RS modules there's probably something for all three types. Classic retro effects, authentic-sounding analogue EMS recreations and digital sampling combined with analogue control. And you know what? Not one of them is a duffer. My biggest problem is that I've got to return them all to Analogue Systems, damn!


  • High-quality sound.
  • Versatile modulation options.
  • RS390 stereo output.
  • RS390 extended delay times.


  • No input-level indicators.
  • RS390 does not include an LFO.
  • RS400 does not include a wet/dry control.


An experimentalist's dream, combining versatile analogue control of high-quality digital sampling and delay-based effects. Looping and editing can be tricky, and the optional RS295 Expander is pretty essential, but the RS290 is capable of real-time sound modulations that would be impossible with any other unit.


RS290 Sampler/Delay £345; RS295 Expander £45; RS500E EMS Synthi Filter £99; RS510E EMS Trapezoid Generator, £125; RS390 Echo £199; RS400 Phase Shifter/LFO £120. Prices include VAT.

Analogue Systems +44 (0)1726 850103.