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Analogue Systems Apprentice

Modular Analogue Synth & Integrator Synth Modules By Paul Nagle
Published June 2002

The Apprentice — a keyboard-less wooden casing designed to house synth modules — is the latest addition to Analogue Systems' fully modular Integrator series of analogue synths. We test one fitted with some of the company's new modules...

Analogue Systems Apprentice.Photo: Mike CameronAnalogue Systems' Integrator range of modular synth systems continues to expand like The Vicar Of Dibley's waistband at Christmas. Having covered the basic essentials of a modular synth over the last few years, the Cornish company are now starting to release rather more eclectic modules, which are designed to bring a little extra spice to your system. The most recent of these include an analogue frequency-shifter and a vocal/phase filter. These were sent to SOS for review in one of the company's new keyboardless Apprentice modular cabinets, supported by other newbies such as a voltage meter, MIDI/CV interface, and an improved version of the system's main sound source — the VCO. The review system also contained several older modules already reviewed in SOS (see SOS June 1998, January 1999, and October 2000 issues respectively.

The Apprentice

At the last roundup of AS modules in October 2000, SOS looked at the Sorceror keyboard controller with its integral MIDI interface and joystick, plus empty space to house your choice of synth modules. The Apprentice is essentially just the upper section of a Sorceror and offers an integral power supply and space suitable for fitting Analogue Systems Integrator, Analogue Solutions Concussor or Doepfer modules (all of which are built to the same dimensions to allow you to assemble synths made up of modules from several manufacturers). The casing provides a much more luxurious alternative to Analogue Systems' own metal rack cases and is made of high-quality polished American walnut. All round, the Apprentice is almost classically beautiful, recalling stylish EMS synths of yore.

RS190 Meter/Inverter

We'll start our look at the review system with one of the simplest modules. The RS190's minimal panel includes the meter itself, an input socket and two outputs (one of which has its phase inverted). The module is 18HP in width — in case you've forgotten, all AS modules are measured in Horizontal Pitch units, and use 3.5mm mini-jack connectors. The Apprentice, by the way, offers a total of 168HP of space for modules of your choice.

A selector switch with 'CV', 'Sig' and 'Off' options determines whether the meter is optimised to measure control voltages, audio signals or whether you want to switch it off entirely. The meter ranges covered are ±5V or 0V to 10V. To 'see' the voltage curves output from LFOs, envelopes, and so on, you select the 'CV' option; alternatively select 'Sig' and the meter displays the RMS value of AC signals. If this seems unexciting, any modular owner will tell you just how handy it is to be able to plug in a signal source and get instant visual confirmation of what's happening. I also think meters look cool — hence my own modular has one similar to this.

With visuals in mind, I would like to have seen a backlight included for the meter, not least because it would greatly increase the RS190's value in a live situation (for those of us mad enough to patch modulars on stage — and yes, I do).

RS140 16-bit MIDI-to-CV Converter

This module (pictured on the next page) processes incoming MIDI signals, its LED flashing cheerfully when MIDI is present. It produces up to 10 outputs in the form of five Control signals (each with independent sources and ranges), three triggers and two CV outputs. With four buttons (Up, Down, Select and Back) and a small (2 x 20-character) backlit LCD, you navigate intuitively through various screens, saving your settings courtesy of 64 onboard memories. These memories may be selected via MIDI program-change messages or, if your needs are simpler, a default user area stores each tweak you make automatically into memory location 0, retaining them after power-down. Helpfully, there's also a MIDI Thru socket.

Within the menu hierarchy, the top level has the following six sub-menus: Misc, Memories, LFO, CV Output, Trigger Outputs and Controller outputs.


From this menu, you set the base MIDI channel and display contrast. Also here is an option to display incoming MIDI events — ideal when trouble-shooting or when checking an incoming MIDI controller before mapping it to an output voltage in the Controllers sub-menu. Finally, the unit's firmware version may be found here (1.0).


This menu is used to store or recall up to 64 internal sets of configurations. You are even informed if overwriting a location that is not currently blank — a helpful safeguard.


The interface boasts an internal software-derived LFO with a range of 0.2Hz to 12.9Hz. This isn't vast in scope, but is adequate as another modulation source. You can specify the LFO's depth from 0 (no LFO output) to 127 (maximum) or, better, you can delegate this task to the MIDI controller of your choice (it would have been nice to set the speed in this way, too...). The LFO has six waveforms: random (sample & hold), sine, square, triangle, sawtooth and reverse sawtooth, and can be sync'ed to MIDI Clock.


CVs are fixed at the octave-per-Volt relationship used throughout the whole Integrator range (and indeed, the majority of CV/Gate synths). Of course, this means you won't be using this converter to play any synth that utilises Hertz-per-Volt control, such as the Korg MS10 or Yamaha CS10. Output scaling allows you to set the standard 1V-per-octave scale or a so-called 'stretched' scale of 1.02V per octave, where notes are sharpened slightly as you play higher on the keyboard. The pitch CV output from CV1 and CV2 usefully responds to the MIDI portamento commands On/Off and Rate. It's in this menu, too, that you specify the the maximum LFO depth that can be applied and the response to pitch-bend. The remaining entry of interest is high/low note-priority for the (monophonic) playing response of your preference.


For each trigger's output, there are three settings: 'Trigger', 'Gate' or 'S-Trig'. The most common within an AS modular will probably be 'Gate', which generates a variable length pulse based on receipt of both Note On and Note Off; typically you'd control envelopes with this. 'Trigger' generates a quick pulse with a fixed length whenever a Note On message is received, and is thus suitable for clock-type duties, such as driving a step sequencer. 'S-Trig', of course, is a negative gate found in Moog, Korg and Yamaha synths.

A further addition, 'MIDI Clock' generates a stream of pulses based on incoming MIDI Clock data. The rate of these pulses is determined by the 'Clock Output Rate' value, and ranges from breves to semi-quaver triplets. I would have welcomed longer divisions too, such as multiples of bars.

Triggering may be set up as Multiple or Single although, annoyingly, either setting affects all three trigger outputs globally. Multiple triggering results in a trigger output for each incoming MIDI Note On. Single triggering produces trigger outputs only when no previous notes are held down, so you can make expressive use of legato playing.


Up to five controller routings can be defined within a patch memory. Sources are selectable from any MIDI controller number, aftertouch, velocity, pitch-bend, or (in the case of Controller 1's output socket only) the converter's internal LFO. A built-in slew generator smooths the controller signals, thus improving the translation of the 128 steps of a MIDI controller into voltages. Each controller has an independent range setting, selectable from 0V to +5V, -5V to 0V, -2.5V to +2.5V and -5V to +5V. These cover pretty much every range in common usage (certainly in an Integrator system). Nevertheless, I'd still have liked fully user-definable ranges, and to be able to exceed the +5V maximum.

RS360 Vocal/Phase Filter Bank

The Vocal/Phase filter bank (above) has three parallel filters and is aimed at creating phasing effects and vocal-like textures. It is significantly cheaper than its predecessor, the stand-alone FB3 filter unit (reviewed in SOS June 1995) but, of course, it lacks the latter's built-in LFO, sturdy case, power supply and quarter-inch jacks, forsaking these for the bare AS module format. The RS360 features a single input with an LED to show that a signal is present.

Each of the filters has a separate Cutoff and Resonance control and a knob to set the amount of input signal. Furthermore, the filters each have their own CV input (at the 1V-per-octave standard) so that they can receive different amounts of filter sweep. The module has four outputs, all of which can be used simultaneously: low-pass, high-pass, notch- and band-pass. A single master frequency control can be employed to sweep all three filters, keeping their relative cutoff displacements intact. An overall CV input, with a depth control, can be routed to all filters simultaneously too.

This is a filter that offers a wide variety of applications. I got great results when treating string pads, recalling some of the lush phasing of early Jean-Michel Jarre albums. With such a module, you soon learn the value of having lots of LFOs in your modular system. The rich stereo swooshes obtained from sweeping each filter at slightly different rates, and taking the notch- and band-pass outputs and routing them to separate VCAs, put a wide smile on my face of the kind more usually associated with illegal states of mind.

A vocal-type effect can be produced by feeding equal amounts of a sawtooth wave into each filter, setting their frequencies to around an octave apart, and using keyboard tracking to carefully modulate cutoffs whilst playing. This works very effectively when the filters are each close to self-oscillation, and tweaking each filter frequency yielded a impressive range of formant-style vocal burbles. 

RS95 Advanced VCO

The RS95 VCO is an improved version of the RS90, reviewed back in SOS June 1998. The most significant enhancements include a variable sine-wave output and a tweak to the oscillator sync facility. This allows you access to a wider range of sync-type sounds that are far more responsive to both the wave and its level at the sync input. The review Apprentice had the RS165 mixer module supplied for me to experiment with, but I also found it useful to patch in a VCA and use a dynamic source to vary the input waveform level.

The VCO frequency pot now covers a range of ± one octave in 'Normal' mode (it was limited to about seven semitones on the RS90) and there are several cosmetic changes such as the labelling of the oscillator range and CV input level pots. If you check the picture below, you should see that, unusually, the saw/triangle waveform output socket also doubles as the external CV input control for the new variable sine wave. I asked AS designer Steve Gay to comment, and received the following reply:

"The heart of the VCO is a sawtooth waveform, and I found it almost impossible to make a sine wave from the sawtooth. I had to use the more traditional triangle output to convert to a sine. However, our triangle is only a triangle when the sawtooth waveshape pot is at 12 o'clock; so to achieve a true sine wave, the sawtooth shape pot must be left at 12. If the shape is changed, either by manually adjusting the pot or by voltage control, the sine output becomes distorted, producing a whole new set of waveforms that can be used as audio sources (albeit unintentionally). This is not true sine-wave shaping, but sine-wave distortion. If, however, a voltage is applied to the triangle output socket, the sine-wave output is then modulated, as in a true sine-shaping circuit. This is not actually a switched jack as it breaks into the triangle-sine converting circuit, allowing a DC offset to be applied to the sine-shaping circuit. So, in effect, we get two ways to modulate the sine output, achieving different results. In fact a dual modulation can be used simultaneously into both sockets at once."

One of my criticisms of the original RS90 oscillator was that only two waveform outputs were accessible. With a third output jack now squeezed into its design, the RS95 is a definite improvement over its predecessor, but I couldn't help feeling that a completely new oscillator, fully redesigned to feel less crammed, would be worthwhile. However, the gentle sounds of sine-wave distortion and modulation were a welcome enhancement.

RS240 Frequency-Shifter

The RS240 (shown right) is very powerful processor, whether used as part of a modular synth or as a stand-alone unit. For the purposes of this review, it was supplied in its own walnut box complete with power supply and RS270 jack adaptor. Gordon Reid recently covered frequency-shifters (not to be confused with pitch-shifters) in Synth Secrets (see SOS January 2002), so for now, it should suffice to say that the purpose of these modules (sometimes known as 'Bode' shifters in honour of the man who built the Model 1630 frequency-shifter for Moog modular synths) is to transpose each harmonic component of an input signal by fixed amounts in Hertz. No manual was available for this module at the time of review, but I was supplied a photocopy of the original Moog 1630, on which the RS240 is closely based. Indeed, AS claim that their Bode shifter is a direct copy, component for component, of the Moog — although since the original module is as common as the output of rocking horses, I'm unable to verify this.

The 24HP wide RS240 Frequency-Shifter module (right).The 24HP wide RS240 Frequency-Shifter module (right).

At 24HP wide, this is quite a large module, dominated by the 1.75-inch Frequency control knob. There is a single input jack for the audio signal, plus no less than three CV inputs. I would have liked at least one of these CV inputs to feature a Depth control, although if you use an LFO from the AS modular, the waveforms have their own individual level pots anyway. As on the original Moog, the up-shifted output appears at a jack marked 'A' and the down-shifted output at 'B', although unlike on the Moog 1630, there is but a single one of each of these jacks (the Moog has two). The mixed output is available simultaneously at three output points (one more than on the Moog) and the A/B mix ratio is controlled by a knob. I would have liked to see this ratio also controllable by external voltage input, because if you need to dynamically morph between the up and down-shifted spectra outputs, you would otherwise need to employ several additional modules.

Five ranges of shift are available, selected via the Scale rotary switch: 'Zero', 'Exponential', '5', '50', '500' and '5K' and are labelled as on the Moog 1630. 'Zero' is meant for calibrating the 'amount of shift' pot so that zero on the scale actually is zero. 'Exponential' is an extreme setting in which the shift initially covers the range 2-2000Hz and a 1V increase in the control input doubles the amount of frequency shift. The remaining four positions of the scale set linear relationships between the control input sum and the shift amount.

The delightfully-named 'Squelch' option features On/Off and Threshold controls. Essentially, this has been implemented so that you can turn off the frequency-shift effect when the input signal passes below a certain level. Turn it on, set the threshold to match the level at which you want the effect to stop (an LED gives visual feedback of this) and you get a very clean, natural-sounding result. Conversely, setting Squelch to Off means that the effect is always present. This can have noise implications with low input levels.

The most obvious applications of the Bode involve subtle or dramatic shifts to produce chorus or phasing effects, but of equal interest are its clean and pure ring-modulation-type sounds or, using the separately shifted outputs, a variety of rich stereo effects. As with the DACS Freque II unit that I reviewed in February 2002 issue, the quality of the effects on offer is reflected in the price but, given the high desirability and non-existent availability of the original Moog module, the RS240 offers something just a little special to the discerning audiophile.

Here are some further suggested applications of this module:

  • Feed in two sine-wave oscillators, one to the signal, one to the CV input. You thought you needed a DX7 for FM synthesis? Nope.
  • Add the Bode between a mixer and a PA, and apply a small amount of shift so the sound appears unchanged, but the regenerative effect (which leads to feedback howl) is greatly reduced.
  • Shift the frequency spectrum of speech and, although its quality and pitch are drastically altered, the legibility is unaffected.
  • Apply gratuitous shifts to everything! It's not the most subtle approach, but it's my favourite. Again, you can hear some of what I achieved at the SOS Soundbank web page.


As a modular cabinet, the Apprentice looks superb, although its length means you might need to think carefully about the placement of your own modules in it. The review model had the MIDI/CV converter positioned at one end and the Envelope Generators at the other. Thus, with no internal buss system to connect CV/Gate signals to commonly-used modules (oscillators and envelopes), I had to dig out some of my extra-long patch cables which then trailed the length of the instrument and generally got in the way. That said, it is a simple enough job to reposition modules, although it isn't something you'd want to do very often.

In the system reviewed, the new modules are all excellent in terms of sound quality and interfacing. In particular, the Bode frequency-shifter is a gem — although its price will deter the casual enthusiast. The RS140 MIDI/CV Converter is an improvement on the one found in the Sorceror keyboard, not least because of its 64 patch memories and built-in LFO. The RS95 oscillator also improves on the RS90 it replaces, offering an additional sine-wave output and improved oscillator sync. RS90 owners should contact AS for upgrade details.

Ultimately, as with all modulars, you can pick and mix configurations that suit your own needs. With the Analogue Systems range growing at the rate it is, you have a very wide choice indeed.


  • Improved oscillator sync and additional variable sine wave on the RS95 voltage-controlled oscillator.
  • Basic but well-thought out RS140 MIDI-CV converter with no superfluous features.
  • Handy visual feedback from the RS190 VU meter.
  • The awesome RS240 Bode shifter offers a wide range of processing applications, from subtle to mind-bending.
  • Rich-sounding, desirable RS360 triple filter module.


  • It could be time for a remake of the VCO module, as even on the improved RS95, things feel a little too tightly packed in for comfort.
  • More in-depth user-tailorable options (and a Hertz/Volt CV output) would have been nice on the RS140 MIDI/CV converter, as would independent settings for multiple/single triggering on each output.
  • The RS190 meter is perhaps a little expensive and lacks a backlight.
  • The RS240 is another expensive module — but it's worth it for the more experimentally-minded.
  • The RS360 filter is also slightly expensive!


Analogue Systems have produced some excellent new modules to complement their existing range, including the RS95, that welcome makeover for the RS90 oscillator. The Apprentice case also looks great and would make a classy addition to any studio or stage rig.


Apprentice case £395; RS95 VCO module £85; RS140 MIDI/CV converter module £199; RS190 VU meter module £99; RS240 Bode frequency-shifter module £550; RS270 phono/jack socket converter £35; RS360 vocal/phase filter module £175. All prices include VAT.

Analogue Systems +44 (0)1726 850103.