Doepfer A100 | CHRIS CARTER
An edited version of this text also appears in
Vol.13 No.9. July 1998

Review by Chris Carter


Analogue modular systems are getting like buses, none to speak of for ages then loads, all at once. In the April/May issues of SOS Paul Nagle reviewed the Clavia Nord, a hardware/software modular synth, last month I reviewed the Analogue Systems RS Integrator, this month it's the Doepfer A100. On the horizon is the massive and scary looking Technosaurus modular synth from Swiss company Selector and various software modular solutions are on the way for Mac's and PC's. If you aren't too sure what all this modular stuff is about check out last months review of the Analogue Systems RS Integrator, which includes an explanation of the theory behind modular synthesisers and a list of terms and abbreviations.

The Doepfer A100 system and modules have been available for a while now and is building up quite a reputation. Various configurations are available and the new EMIS catalogue lists Doepfer A100 systems based on classic analogue modular 'wallpaper' systems such as the Roland System 700, Moog 15, 35, 55 and 3C and an Arp 2600 configuration. These don't come cheap though, the gargantuan A100/Roland S700 configuration (about 70 modules in 7 racks) will leave a hole the size of £4215 in your pocket and that's without a keyboard.

Currently two A100 base systems are available, the A100 CV and the A100 MIDI. They are essentially the same system but the A100 MIDI omits the A150 and A162 modules and instead includes the A190 MIDI to CV module. Because the A100 CV doesn't include a MIDI module EMIS supplied us with the Doepfer M.A.U.S.I MIDI to CV/SYNC interface, a free-standing version of the A190 (see box elsewhere).

Analogue circuitry is used throughout (except in the A190 MIDI module) and the CV/GATE system used in all A100 systems is the standard 1v/Octave scaling with a positive trigger (V-Trig). To integrate the system with a Moog set-up (S-Trig) you need to use the A165 Trigger Inverter module and to use it with a Hz/Volt system you will need to purchase the M.A.U.S.I MIDI converter or go for the A100 MIDI version.

The A100 modules live in a (heavy) 19" rack case, 6U high and conforming to the Euro/HP specification. The sturdy aluminium construction includes a built-in power supply, with a rear mounted power socket and switch. All the modules use 3.5mm jack sockets and grey knobs, with small but legible lettering throughout and lots of bright flashing red LED's, nice!

The A100 includes two of almost everything as many of the modules incorporate dual circuits and this base system holds 23 modules of various HP widths. The A100 CV includes: A110 (X2), A114, A115, A116, A118, A120, A121, A130, A131, A138 (X2), A140 (X2), A145 (X2), A148, A150, A160, A161, A162, A170, A180. Other configurations are available using smaller and larger racks, including flight cased, wooden and custom versions. The current EMIS catalogue list approximately 50 Doepfer modules, with more on the way (see list/box). Each complete system comes with a large, informative ring bound manual, which includes full construction details, just in case you purchased the kit version. It also contains instructions for ALL the current modules, which might just be included to tempt you into buying more modules but will definitely make your mouth water once you start reading about all those fab modules you DON'T have.

A110 VCO
The VCO's supplied with the A100 are the lower specified 'no frills' A110 but don't let this put you off, this is still a creditable oscillator. The audio range covers about approximately 1Hz-5KHz, not great but fine for most purposes. There are two CV inputs, a SYNC input, a CV pulse width input and four simultaneous waveform outputs: Sawtooth, Pulse, Triangular and Sine. An 8-way rotary switch selects which octave range the VCO functions in and there is a coarse tune control covering +/- 1/2 Octaves. In the lower registers the VCO can be used as an VC-LFO source.

For general use a keyboard CV signal would be plugged into CV input 1, which is a direct connection and any modulation source (eg. an LFO) would be fed into CV input 2, via the input level knob, a slight quirk here is that CV2 has an exponential FM input (as opposed to linear). The problem with using exponential modulation is that trying to introduce vibrato (from an LFO sine wave) can make the VCO 'trill', rather than the required vibrato effect. The shape/width of the Pulse wave can be modulated (PWM) from an external CV source such as an LFO or ADSR generator, useful for fatter chorus effects.

The Sync input is a 'hard' type and works best when fed with a saw or pulse waveform from a second VCO (the master) which is set at either a higher or lower frequency than the synced VCO (the slave). Some interesting timbral effects can be achieved using the sync input, which works by superimposing the harmonics of the master VCO over the waveform of the slave VCO. Add modulation to either or both VCO's and some complex, dynamic waveforms can be conjured up. It's worth noting that because this is an analogue instrument the VCO can take a little while to 'warm up', usually about 15-20 minutes. Of course you can use it from cold but the tuning will probably drift slightly over time.

This frequency divider can mix an original signal (usually a VCO waveform) with up to four square wave sub-octaves signals. The octaves are fixed, with the input being halved, quartered and so on for each output. The front panel consists of an input (monophonic only), an output socket and five knobs for mixing the audio signals. In theory you can use any monophonic input source: VCO square wave, sine wave, even a keyboard or mike (through a pre-amp) but any signal will be converted to square waves at the output. Fed through a VCF this module can sound quite impressive particularly when used in conjunction with the A116 module below.

The Voltage Controlled Waveform Processor is capable of producing quite complex and unusual effects from a standard monophonic VCO waveform. A good analogy would be to describe this module as a kind of voltage controlled overdrive. There are five controls: Input Level, Clipping Level, Clipping CV attenuator, Symmetry and Symmetry CV attenuator. There's a single audio input and output and two CV inputs (Clipping and Symmetry). The Input knob can attenuate or boost the input signal, into overload if required and the Clipping control adjusts a +/- 10v clipping threshold on the input waveform (which makes the sound softer or harder). With only two basic VCO's in this system the A116 module is useful for strengthening (or mutating) the sound of a vanilla waveform.

A120 VCF1 and A121 VCF2
Two VCF's are included, the A120 and A121. The A120 uses a so-called 'transistor ladder', 24dB Low Pass design, as pioneered by Moog, while the A121 is designed around a CEM 3320 chip and is a 12dB multi-mode type filter. The A120 includes 3 filter frequency CV inputs (one direct, two via input attenuators) and the usual audio in and out. The resonance control permits the filter to be pushed into self-oscillation, which allows it to be used as a sine wave VCO. The A121 module takes this feature a step further by including two CV inputs for controlling resonance, but only includes 2 filter frequency CV inputs. However the A121 gives you 4 separate (and simultaneous) outputs, Low Pass, Band Pass, High Pass and Notch. These outputs work particularly well for 'stereofying' a mono signal, and some nice psycho acoustic effects can be obtained using different output modes on right and left mixer channels. My only concern is that both filters lack a certain amount of warmth and character. I would expect this of the A121 as it's only a 12dB type but the A120, which I had high hopes of, sounds...dare I say it, slightly clinical. If filters were in Technicolour a Moog VCF would be a deep and luscious red, an old Roland or Korg VCF would be less deep but still a nice bold red, while the A120 is a shade of orange.

A131 VCA (Two types, Log and Lin)
These are standard fare VCA's with two audio inputs, two CV inputs (with level controls) and a single audio output which also has a level control. Of the two types the A131 Exponential type would usually be used with audio signals and the A131 Linear VCA would be used for mixing and controlling CV signals, although as is the way with modular systems either type could be used with either audio or CV signals. Both VCA's work as they should and are essentially transparent and free of artifacts or noise.

A138 MIXER (Two types, Log and Lin)
These are basic, four channel attenuating mixers (they don't boost the signal), with four input sockets and associated knobs and a master output level control. The only difference between the two models is that one uses linear and one uses logarithmic response control pots. Each mixer can cope with either control voltages and/or audio signals.

As with the VCA's these are run of the mill ADSR envelope generators, no CV control inputs or built-in trigger generator I'm afraid. The front panel has, in addition to the ADSR knobs, Gate and Trigger inputs, two normal and one inverted CV envelope outputs (with LED indicator) and a three position ADSR Range switch (for standard timing, milliseconds or minutes).

A145 LFO (X2)
I hope I'm not repeating myself but these are also pretty standard offerings. The A145 has five separate outputs: Sawtooth, Inverted Sawtooth (with LED indicator), Sine, Triangle (with LED indicator) and Square. The LFO frequency of one cycle every few minutes to approximately 5KHz is controlled by a three-way Range switch and a Frequency knob. There's no CV input but there is a reset input which allows the LFO cycle to be synced to to an external trigger such as a keyboard or sequencer gate output. With such a wide frequency range (almost as high as the VCO) I would like to have seen a voltage control input included (and PWM for the square wave) but for that you will have to invest in the A146 LFO2 module.

This module includes two ring modulators (RM) on one panel, no controls, just sockets, an X and Y input and a summed output, for each RM. I found that the A114 wasn't as sensitive to slowly moving control signals as some RM's I've used and there was more signal breakthrough when only one signal is present than I would have liked, however the A114 does its job well enough and to help you along there a couple of interesting example patches in the instruction manual.

The A148 dual Sample and Hold is almost identical in layout to the dual RM, however this is an entirely different type of module. The two inputs: Trig and Smp and the S&H control output work in conjunction with external triggers/gates and high level signals to produce random or staircase control voltages. For example, if a white noise source is fed into the Smp input and an LFO is used to trigger the Trig input a regular, rhythmic random voltage will be generated, suitable for controlling the frequency of a VCO or VCF. If the noise signal is substituted for a slowish sine, sawtooth or triangular signal from a VCO or an LFO then a staircase or glissando control voltage is generated instead. Which brings me to the A118 NOISE+RANDOM module. This works alongside the A148 and incorporates a noise generator and a random clock pulse generator. The noise section includes a direct white noise output socket, a coloured noise output socket and two knobs for red and blue noise levels (basically a high and low pass filter). The random output section has a Rate control which governs the randomness of the clock speed, an output level knob and two LED's to show the speed and polarity of the random voltage output. A quirk not mentioned in the manual is that even though the two sections are supposedly independent the Red noise level knob interacts with the random voltage generator, a lot, and to get a decent random output level you need to turn the Red knob fully clockwise.

Slew Limiters are normally used between a CV keyboard and VCO and allow you to introduce an adjustable portamento effect. In this dual module each section is slightly different, the upper Slew Limiter has the usual CV In and Out sockets, a knob for adjusting the slew Time and a couple of LED's to indicate the level and polarity of the CV output. The lower Slew Limiter has a couple of additional features which increase its versatility, these include a 3-way slew Range switch and two Time knobs, one for adjusting the Rising Slew time and the other for Falling Slew time. With careful adjustment and a suitable input (such as a gate signal) this section can even produce basic AR envelopes, very useful in a tight situation.

This module contains two identical trigger delays, each includes a gate/trigger in and out socket, a Delay knob, trigger Length knob and an LED to show the on/off state of the trigger output. The length of the delay is adjustable from instantaneous to approximately 10 seconds.

Another dual module, this time with two voltage controlled bidirectional switches. Each switch includes a control input, a common i/o socket, two sockets marked i/o 1 and i/o 2 and two LED's to indicate which i/o is on or off. Because these switches are bidirectional the i/o sockets can be used as inputs OR outputs and can accept either control voltages or audio signals. The switching control input can use any signal from -8V to +8V and anything above 3.6V switches it one way and below 3.6V switches it the opposite way. This is a versatile little module and can be used for all sorts of switching and triggering effects, such as switching between modulation sources, VCO output waveforms, multi-mode VCF outputs etc. It also functions well with the following two modules.

These two work as a team and although the A160 will function without the A161, the A161 will only function when internally connected to the A160. The A160 Clock Divider is similar in concept to the A115 module, however this module takes a clock/LFO (or gate/trigger) signal and divides the frequency into 6 related sub-divisions, in this case half the original clock, 1/4, 1/8, 1/16, 1/32 and 1/64. There are no controls just a clock/trig input, a reset input and six gate/trigger outputs, each with an LED.

The A161 Clock Sequencer is a basic 8-step trigger sequencer, with its input trigger sourced from the halved output (socket 1/2) of A160 module. There are 8 trigger outputs (each with an LED) and for as long as any clock signal is present at the input of the A160 the A161 output sockets will step through a constantly looping, sequential stream of triggers.

While these two modules may not add up to a fully fledged sequencer they do allow for some quite complex rhythmic effects to be set up (if you have enough ADSR's, VCA's etc.) and the instruction manual contains some excellent example patches to try out.

The A100 has the features and capabilities for producing some impressive sounds and there's no denying that this is a fine hands on system to work with. Although I wasn't entirely happy with the supplied grey patch cords. They didn't connect as positively as they should and on a few of the sockets they were unquestionably loose. Also, not using colour coded patch cords can be a nightmare when you are trying to troubleshoot a problematic or complex patch and Doepfer don't help much as they haven't implemented a colour coding scheme on the modules either. I had to resort to using my trusty old colour coded Roland patch cords more than once, which fitted nice and snugly. But this is all just ergonomics, how does it fare as a day to day modular synth ?

Well there are a few modules I was surprised to see in a base system, such as the trigger delay, Clock Divider, Waveform Processor and VCS. I would expect users to add these modules later, as they expand their system and crave new challenges. Also, this configuration would benefit immensely from an additional VCO. After all the VCO is one of the essential building blocks of modular synthisis and you quickly find yourself running out of sources using only two VCO's. However the A110 VCO's do their job well enough, as do most of the other modules. Though as I mentioned above, I found the sound of the filters slightly character less, it would be interesting to compare them to the forthcoming A124 VCF5 and A127 VCF6 modules. I've always found the sound of filters and VCF's to be a somewhat subjective area and one persons liking for a particular type of filter could be another's total indifference.

One glaring omission is the lack of access to the internal CV/Gate buss, for controlling the VCO's and ADSR's from a single pair of CV/Gate sockets, to achieve this you need to fork out £30 for the A185 Buss Access module and loose an existing module in the process.

When the Doepfer A100 arrived I had only just finished reviewing the Analogue Systems RS Integrator and as both systems are so similar technically and physically (right down to interchangeable modules) it's impossible not to compare the two. Ultimately the main differences boil down to how particular features are implemented and how the instrument sounds. Some of the modules supplied in the A100 base systems lack a few features I would regard as fairly essential, such as voltage controlled ADSR's, LFO's and Slew Limiter.

My impression of the overall sound of the A100 is that it's lacking just a little at the bottom end but possibly has more presence and a more up front, if slightly colder sound than the RS Integrator. But this is a purely subjective impression and depending on the type of music you produce the Doepfer A100 is a very capable and exciting instrument, particularly for pure electronic, experimental and 'out there' dance music.

Considering the amount of engineering that goes into any decent sized modular system the £999 price tag seems quite reasonable but for anyone new to modular syntheses they might consider starting with the smaller A100 MINI at £699 which is based on the same system and just as expandable as its bigger brothers.

Some of my observations may have come across as slightly negative regarding a few of the modules but I really am quite a fan of Doepfer. If you don't believe me check out my earlier reviews of the MS404 Synth and MAQ 16/3 Sequencer. In the rest of Europe (and the US) Doepfer are quite well established and have made a lot of fans, with some famous users too (Kraftwerk for instance). Doepfer may have suffered from some UK distribution problems in the past but that has changed now that EMIS are sole distributor.

The A100 looks like it is meant to be operated by a someone in a white lab coat and a degree in applied mathematics, don't let that put you off. With a little time and effort almost anyone can coax some amazing sounds out of it, just don't expect instant results.




Price: £999 incl. VAT

Tel/Fax: 0117 956 1855



EMIS: The Old School House, Cossham Street, Mangotsfield, Bristol BS17 3EN


A respectable and complex system that's capable of exciting, unique and totally outrageous sounds. A few of the modules aren't quite the bees knees as far as features and sonics go but the system is easily expanded with affordable and higher specified modules from Doepfer and other manufacturers. A very involving experience, the phrase hands on was invented for instruments like this.

Analogue though and through, complete with 20 minute warm-up.

Pleasant analogue sound, but not quite a classic Moog or Roland.

Open architecture means endless patching and expansion possibilities.

Well designed and built.

Expandable using standard HP modules (with custom cable).

Over 50 different modules available, A100 also available in kit form.

Reasonably priced.

VCF's could sound better.

Would benefit immensely from a third VCO.

Some modules lacking features.

Direct CV and GATE buss only accessible via separate module.

Provide your own MIDI to CV converter (only applies to A100CV).

Supplied patch cords not up to the task.


At the present state of play this is a two horse race between Doepfer and Analogue Systems, the two systems are VERY similar technically (and physically). To my tiny twisted mind Analogue Systems are a nose ahead with the sound and features of their slightly cheaper base system (I can hear Doepfer fans screaming for my blood already). However Doepfer are galloping up fast with the sheer number of different modules available, a substantial user base and a good track record. The A100 and its DIY oriented racks, modules and accessories are a great way for electro musicians to build customised systems from scratch and expand them as finances allow. It's important to note that Doepfer also use the same HP rack system as Analogue Systems (and Maplin), so in this race everyone's a winner because users can mix and match preferred modules from each system. Go on, go on, go on, go on.


VC: Voltage Control.

VCO: Voltage Controlled Oscillator.

VCF: Voltage Controlled Filter.

VCA: Voltage Controlled Amplifier.

ADSR: Attack, Decay, Sustain, Release.

LFO: Low Frequency Oscillator.

Clock: A basic LFO, square wave only.

RM: Ring Modulator.

S&H: Sample and Hold.

Gate: An on/off control signal sent for as long as a key is pressed.

Trigger: A short on/off pulse similar to Gate but only sent at the beginning of a note.

FM: Frequency Modulation.

PWM: Pulse width modulation.

Noise: A rushing sound, also red noise, pink noise and blue noise.

Log: Logarithmic scale.

Lin: Linear scale.

1V/Oct: Chromatic control standard used by Moog, Arp, Roland etc.

Hz/Volt: Chromatic control standard used by Yamaha and Korg.

Slew: A type of portamento, sometimes called an Integrator, acts like a low pass filter on audio signals.

Resonance: Filter resonance, sometimes called Q or Emphasis.

Null Point: Zero output.

Buss: System of internal connection between modules.


EMIS is the exclusive UK distributor for the German made Doepfer products. There are now 50 different modules available for the A100 system and more due. All prices include VAT :

A-100 MIDI Modular System (22 Modules, incl. MIDI) £1079

A-100 CV Modular System (23 Modules, no MIDI) £999

A-100 Mini Modular Mini System (10 Modules) £699

A-110 Standard VCO £69

A-111 High End VCO £115

A-112 8-bit Sampler with CV control and MIDI dump £199

A-113 Harmonic Wave table Generator/VCO £159

A-114 Dual Ring Modulator £49

A-115 Audio Divider £39

A-116 Voltage Controlled Waveform Processor £49

A-117 Digital Noise/Random Clock/808 Sound Source £59

A-118 Noise/Random £39

A-119 External Input/Envelope Follower £49

A-120 VCF-1 (24dB Low Pass 1) £59

A-121 VCF-2 (12dB Multi-mode) £69

A-122 VCF-3 (24dB Low Pass 2) £59

A-123 VCF-4 (24dB High Pass) £65

A-124 VCF-5 18dB Filter with resonance envelope control £69

A-125 Voltage Controlled Phase Shifter £69

A-126 Voltage Controlled Frequency Shifter £159

A-127 VCF-6 Four fold Band-Pass with LFO's £199

A-128 Fixed Filter Bank £119

A-129 1/2 Vocoder Analysis & Synthesis £269

A-129 /3 Vocoder Slew Limiter / Attenuator / Offset Generator £79

A-129 /4 Vocoder Slew Limiter Controller £59

A-129 /5 Vocoder Voiced / Unvoiced Detector £69

A-130 Voltage Controlled Amplifier - Linear (CV) £49

A-131 Voltage Controlled Amplifier - Exponential (Audio) £49

A-132 Dual Voltage Controlled Amplifiers £39

A-134 Voltage Controlled Panner £69

A-135 Voltage Controlled Five Channel Mixer £115

A-138a Linear Mixer (CV) £35

A-138b Exponential Mixer (Audio) £35

A-139 Headphone Amplifier £?

A-140 ADSR Envelope Generator £39

A-141 Voltage Controlled Envelope Generator £89

A-142 Voltage Controlled Decay/Gate £59

A-145 Low Frequency Oscillator £39

A-146 Low Frequency Oscillator 2 £49

A-147 Voltage Controlled Low Frequency Oscillator £69

A-148 Dual Sample & Hold £39

A-150 Dual Voltage Controlled Switch £35

A-151 Quad Sequential Switch £35

A-155 Analogue/Trigger Sequencer £179

A-156 4 X Quantizer £?

A-160 Clock/Trigger Divider £35

A-161 Clock/Trigger Sequencer £29

A-162 Dual Trigger Delay £39

A-165 Dual Trigger Inverter / Modifier £29

A-170 Dual Slew Limiter £39

A-171 Voltage Controlled Slew Limiter £49

A-174 (X2) Joystick Module £69

A-175 Dual Voltage Inverter £29

A-176 Control Voltage Source £39

A-177 External Foot Controller Module £49

A-178 Theremin Control Voltage Source £69

A-179 Light to CV £?

A-180 Multiples 1 £19

A-181 Multiples 2 £25

A-185 Buss Access £29

A-190 MIDI-CV/Sync Interface £139

A-191 MIDI-CV Interface / Sheppard Generator £139

A-195 MIDI interface for Vocoder module £159

G3 3U Base Frame, with bus board, power supply and owners manual £199

G6 6U Base Frame, with 2x bus boards, power supply and owners manual £229

EMIS G32 Micro rack in a wood finish £50

EMIS G12 Studio rack with a wood finish equivalent to 2x G6 £449


A Doepfer M.A.U.S.I. unit was supplied with the A100 system and the following text box was submitted to SOS with the A100 review but not included because of lack of space.


The Doepfer M.A.U.S.I is a MIDI to CV / SYNC interface is a single channel unit containing two independent CV outputs, a single GATE output, a SYNC 24 output and MIDI in and thru sockets. The unit is small (102mm X 140mm X 45mm) and light with a neat front panel containing 4 small push buttons for accessing menus and modes and 8 LED's to indicate the various edit modes and the status of the CV, GATE outputs. Power is supplied by a 9V wall wart. The M.A.U.S.I has a battery backed memory and can store your favoured setting ready to be recalled the next time you switch on, alternatively the factory defaults can be recalled at any time.

A MIDI controllable LFO is included, with variable frequency and depth. Other MIDI controllable functions are portamento (on/off and time), pitch bend, retrigger time, note assign (highest or lowest note priority), all controllers off and all notes off. In addition to all this the M.A.U.S.I can output a standard 1v/Octave CV signal, a V-Trigger, an S-Trigger and can be programmed to output a Hz/V CV signal. The CV1 output has a resolution of 12 bits and is meant for accurate keyboard control, while the CV2 output is only 7 bit and is best used for velocity, aftertouch and other non-critical CV signals. The SYNC24 output responds to MIDI clock start/stop and can be reprogrammed to produce negative clock pulse and higher or lower clock frequencies than the standard Roland 24 ppqn, useful for triggering arpeggiators and analogue sequencers.

Working through the basic LED menu system can be a bit hit and miss the first few times you use M.A.U.S.I just keep the informative instruction manual close at hand to get you out of trouble. In use the interface worked fine, covering about 5 octaves with the CV tuning showing no signs of drift at either extreme. For such a diminutive unit the M.A.U.S.I includes a host of features at a very reasonable price. In terms of features and functions the A190 modular version is identical but also includes direct internal CV/Gate buss connections and a MIDI Start/Stop trigger output.

M.A.U.S.I MIDI-CV Interface (2x CV & Gate) with Sync 24 £99

Copyright © 1998 Chris Carter / SOS Publications.