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Doepfer A100

CV Modular Synthesizer By Chris Carter
Published July 1998

Doepfer A100

Analogue modular synths in the late '90s are something like the old bus joke — none for ages, then loads all at once. Chris Carter catches the latest arrival.

In the April and May 1998 issues of SOS Paul Nagle reviewed the Clavia Nord Modular, a hardware/software modular synth, last month I reviewed the Analogue Systems RS Integrator, and this month it's the turn of 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 Macs and PCs. If you're not too sure what all this modular stuff is about, you should certainly check out last month's review of the Analogue Systems RS Integrator, which includes an explanation of the theory behind modular synthesizers.


The Doepfer A100 system has been available for a while now, and is building up quite a reputation. Various configurations of modules are available, including 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 seven 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 Dual Voltage Controlled Switch and A162 Dual Trigger Delay modules and instead includes the A190 MIDI‑to‑CV module. Because the A100 CV (which is the system under review) doesn't include a MIDI module, EMIS supplied us with the Doepfer MAUSI MIDI‑to‑CV/Sync interface, a free‑standing version of the A190, so that the A100 could be checked out with MIDI.

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 setup (which uses S‑Trig) you'd need an A165 Trigger Inverter module, and if you wanted to use an A100 with a Hz/Volt system you'd need to buy the MAUSI MIDI converter or go for the MIDI version of the A100.

HP Source

The A100 modules live in a sturdy 6U aluminium rack case, conforming to the Euro/HP (Horizontal Pitch) specification, with a built‑in power supply and a rear‑mounted power socket and switch. All the modules have 3.5mm jack sockets and grey knobs, with small but legible lettering throughout and lots of bright red LEDs — nice! The A100 base system holds 23 modules, of various HP widths, and includes two of almost everything, as many of the modules incorporate dual circuits. The A100 CV features: A110 standard VCO (x2); A114 Dual Ring Modulator; A115 Audio Divider; A116 Voltage Controlled Waveform Processor; A118 Noise/Random; A120 VCF‑1 (24dB Low‑Pass 1); A121 VCF‑2 (12dB Multi‑mode); A130 Voltage Controlled Amplifier (Linear, CV); A131 Voltage Controlled Amplifier (Exponential, Audio); A138 Mixer (x2); A140 ADSR Envelope Generator (x2); A145 Low Frequency Oscillator (x2); A148 Dual Sample & Hold; A150 Dual Voltage Controlled Switch; A160 Clock/Trigger Divider; A161 Clock/Trigger Sequencer; A162 Dual Trigger Delay; A170 Dual Slew Limiter; A180 Multiples 1 (single panel with eight sockets for linking things together if you run out of sockets on other modules).

Other configurations are available using smaller and larger racks, including flightcased, wooden and custom versions.

A110 VCO

The VCOs supplied with the A100 are the 'no frills' A110, but don't let this put you off — the A110 is a creditable oscillator, with an audio range covering 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 the VCO's octave range, and there's a coarse‑tune control covering +/‑ 1/2 Octaves. For general use, a keyboard CV signal would be plugged into CV input 1, and any modulation source (an LFO, for example) would be fed into CV input 2, via the input level knob. A slight quirk here is that CV2 has an exponential, rather than linear, FM (Frequency Modulation) input, which can make the VCO 'trill' when you're trying to introduce vibrato. The shape/width of the Pulse wave can be modulated from an external CV source such as an LFO or ADSR generator, useful for fatter chorus effects, and some interesting timbral effects can be achieved using the Sync input, which works by superimposing the harmonics of one VCO over the waveform of another. Add modulation to either or both VCOs 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 15 or 20 minutes.

A115 Audio Divider

This frequency divider can mix an original signal (usually a VCO waveform) with up to four squarewave sub‑octave signals (halved, quartered, and so on) derived from the input signal. The front panel features a monophonic input, an output, and five knobs for mixing the sub‑octave signals with the original signal. In theory, you can use any monophonic input source, even a keyboard or mic (through a pre‑amp), but any signal will be converted to squarewaves at the output. Fed through a VCF this module can sound quite impressive, particularly when used in conjunction with the A116 module below.

A116 Waveform Processor

The Voltage Controlled Waveform Processor is capable of producing quite complex and unusual effects from a standard monophonic VCO waveform. A good description of this module would be a kind of 'voltage controlled overdrive'. The five controls on the unit relate to Input Level, Clipping Level, Clipping CV attenuator, Symmetry (a kind of waveform width control which has an effect on the tone) 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 VCOs in the A100 system, the A116 module is useful for strengthening (or mutating) the sound of a 'vanilla' waveform.

The A100 is capable of producing some impressive sounds, and is a fine hands‑on system.

A120 VCF & A121 VCF

Two VCFs are included in the system, with the A120 using a so‑called 'transistor ladder', 24dB low‑pass design, as pioneered by Moog, and the A121, designed around a CEM 3320 chip, being a 12dB multi‑mode filter. The A120 includes three 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 sinewave VCO. The A121 module takes this feature a step further, by including two CV inputs for controlling resonance, but only has two filter‑frequency CV inputs. However, the A121 does give you four 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 psychoacoustic effects can be obtained by 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 red, but still nice and bold, and the A120 would be a shade of orange.

A131 VCA (Log & Lin)

These are standard‑fare VCAs 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 (Logarithmic) type would usually be used with audio signals, and the Linear type for mixing and controlling CV signals, although — as is the way with modular systems — either type could be used with audio or CV signals. Both VCAs work well, and are essentially transparent and free of artifacts.

A138 Mixer (Log & Lin)

These are basic, 4‑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‑response and one uses logarithmic‑response control pots. Each mixer can cope with control voltages and/or audio signals.

A140 ADSR Envelope Generator

The 140 is a run‑of‑the‑mill ADSR EG — 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 an ADSR Range switch which alters the time over which the envelope develops.

A145 LFO

I hope I'm not repeating myself, but these are also pretty standard offerings. The A145 has five 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 Range switch and a Frequency knob. There's no CV input for voltage control, which I'd like to have seen, but there is a reset input which allows the LFO cycle to be sync'ed to an external trigger, such as a keyboard or sequencer gate output.

A114 Dual Ring Modulator

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

This configuration would benefit immensely from an additional VCO.

A148 Dual S&H/A118 Noise+Random

The A148 dual Sample & Hold is almost identical in layout to the dual RM but, appearances aside, this is an entirely different type of module. The two inputs, Trig and Smp (Sample), and the S&control output work in conjunction with external triggers/gates and high‑level signals to produce random or 'staircase' control voltages. (The latter acts as a kind of arpeggiator; a staircase generator gives the same effect as an arpeggiator, but is not controlled from a keyboard.) 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 by a slowish sine, sawtooth or triangular signal from a VCO or an LFO, a staircase or glissando control voltage is generated instead.

The A118 Noise+Random module 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 high‑ and low‑pass filters). The random output section has a Rate control which governs the randomness of the clock speed, an output level knob, and two LEDs 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 quite significantly with the random voltage generator, and to get a decent random output level you need to turn the Red knob fully clockwise.

A170 Dual Slew Limiter

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 LEDs 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 (Attack Release) envelopes, very useful in a tight situation.

A162 Trigger Delay

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.

A150 Dual VC Switch

This is another dual module, featuring two voltage‑controlled bi‑directional switches. Each switch includes a control input, a common I/O socket, two sockets marked I/O 1 and I/O 2, and two LEDs to indicate whether the I/Os are on or off. Because the switches are bi‑directional, the I/O sockets can be used as inputs or outputs, and can accept control voltages or audio signals. The switching control input can use any signal from ‑8V to +8V; anything above 3.6V switches it one way, while a signal of below 3.6V switches it the opposite way. This is a versatile module which can be used for all sorts of switching and triggering effects, such as switching between modulation sources. It also functions well with the following two modules.

A160 Clock Divider/A161 Clock Sequencer

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 Audio Divider. However, the A160 takes a clock/LFO (or gate/trigger) signal and divides the frequency into six related sub‑divisions (1/2, 1/4, 1/8, 1/16, 1/32 and 1/64 of the original clock). 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, whose input trigger comes from the halved output socket of the A160 module. It has eight 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. These two modules don't add up to a full sequencer, but they do yield some quite complex rhythmic effects (if you have enough ADSRs, VCAs, and so on), and the manual gives some excellent example patches.

A Chip Off The Old Block

The A100 is capable of producing some impressive sounds, and is a fine hands‑on system, 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're 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, and these fitted snugly.

Ergonomics aside, how does the A100 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. Also, this configuration would benefit immensely from an additional VCO. The VCO is one of the essential building blocks of modular synthesis, and you quickly find yourself running out of sources if you have only two VCOs. However, the A110 VCOs 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 lacking in character. Mind you, the sound of filters and VCFs is a subjective area. One glaring omission is the lack of access to the internal CV/Gate buss, for controlling the VCOs and ADSRs from a single pair of CV/Gate sockets. To achieve this, you need to fork out £30 for the A185 bus Access module.

The Doepfer A100 is a very capable and exciting instrument, particularly for pure electronic, experimental and 'out there' dance music.

Mad Scientist

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 them. Ultimately, the main differences are how particular features are implemented and how the instruments sound. Some of the modules supplied in the A100 base system lack a few features I would regard as almost essential, such as voltage‑controlled ADSRs, LFOs and Slew Limiter. My impression of the sound of the A100 is that it's lacking a little at the bottom end, but possibly has more presence and a more up‑front (if slightly colder) sound than the RS Integrator.

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 anyone new to modular synthesis might consider starting with the A100 Mini, at £699, which is just as expandable as its bigger brothers.

Some of my observations may have come across as slightly negative regarding a few of the A100 modules, but I really am quite a fan of Doepfer. In the rest of Europe (and the US) they are well established and have amassed a lot of admirers, with some famous users too (Kraftwerk, for instance). The A100 looks as though it's meant to be operated by someone in a white lab‑coat with a degree in applied mathematics, but don't let that put you off. With some time and effort, almost anyone can coax some amazing sounds out of it.

Terms & Abbreviations

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, with a single‑waveform output and a limited range, so called because they used to be used for clocking sequencers
RM: Ring Modulator
S&H: Sample and Hold, a circuit for sampling an input voltage when given a trigger. That signal will then be held at the output until re‑triggered. It's a bit like a sampler, but just for voltages
Gate: An on/off control signal. When you press a key, a gate signal will be sent out for as long as you keep your finger on the key
Trigger: A short on/off pulse, similar to Gate. The difference is that a Trigger signal is sent only at the beginning of a note, and is unaffected by how long you hold a key down
Log: Logarithmic scale
Lin: Linear scale
1V/Oct: Chromatic control standard used by Moog, Arp and Roland. A change of one Volt in the control signal would mean a change of one octave in pitch. Each Volt is sub‑divided into 12 for the notes of an octave, with each sub‑division corresponding to one semitone
Hz/Volt: Different chromatic control standard used by Yamaha and Korg
Slew: A type of portamento; acts like a low‑pass filter on audio signals

Doepfer Modules

There are 50 modules available for the A100 system, and more are due. We can't list them all, for reasons of space, so here's a selection. Prices include VAT.

  • A110 Standard VCO: £69
  • A111 High End VCO: £115
  • A113 Harmonic Wavetable Generator/VCO: £159
  • A114 Dual Ring Modulator: £49
  • A115 Audio Divider: £39
  • A116 Waveform Processor: £49
  • A117 Digital Noise/Random Clock/808 Sound Source: £59
  • A118 Noise & Random Generator: £39
  • A119 External Input/Envelope Follower: £49
  • A120‑124: VCFs priced from £59‑£69
  • A125 Voltage Controlled Phase Shifter: £69
  • A129 1/2 Vocoder Analysis & Synthesis: £269
  • A130 VCA (Linear, CV): £49
  • A131 VCA (Exponential, Audio): £49
  • A135 Voltage Controlled 5‑Channel Mixer: £115
  • A138a/b Linear and Exponential Mixers: £35 each
  • A140 ADSR EG: £39
  • A141 Voltage Controlled EG: £89
  • A145‑147: LFOs priced from £39‑£69
  • A148 Dual Sample & Hold: £39
  • A150 Dual Voltage Controlled Switch: £35
  • A160 Clock/Trigger Divider: £35
  • A161 Clock/Trigger Sequencer: £29
  • A162 Dual Trigger Delay: £39
  • A165 Dual Trigger Inverter/Modifier: £29
  • A170 Dual Slew Limiter: £39
  • A171 Voltage Controlled Slew Limiter: £49
  • A177 External Foot Controller Module: £49
  • A178 Theremin CV Source: £69
  • A180 Multiples 1: £19
  • A185 bus Access: £29
  • A190 MIDI‑CV/Sync Interface: £139
  • A195 MIDI interface for Vocoder module: £159
  • G3 3U Base Frame (buss board, PSU, manual): £199
  • G6 6U Base Frame (2 buss boards, PSU, manual): £229
  • EMIS G32 Micro Rack, wood finish: £50
  • EMIS G12 Studio Rack, wood finish, equivalent to two G6s: £449
  • MAUSI MIDI‑CV Interface (2x CV & Gate) with Sync 24: £99

A100 modules are also available in kit versions.

Two‑Horse Race

If you're looking for an affordable modular, at present it's 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 coming up fast with the sheer number of different modules available, a substantial user base, and a good track record. The A100 and its DIY‑orientated 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 racking as Analogue Systems (and Maplin), so users can mix and match preferred modules from each system.


  • Analogue through and through, with a pleasant sound.
  • Endless patching and expansion possibilities.
  • Well designed and built.
  • Expandable using standard HP modules (with custom cable).
  • 50+ modules available.
  • Reasonably priced.


  • VCFs could sound better.
  • A third VCO would really help.
  • Some modules lacking features.
  • Direct CV and Gate buss only accessible via separate module.
  • You need your own MIDI‑to‑CV converter (only A100CV).
  • Supplied patch cords not up to the task.


A respectable and complex system that's capable of exciting, unique and totally outrageous sounds. A few of the modules aren't quite the bee's 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.


A100 CV system (23 modules) £999 including VAT; A100 MIDI system (22 modules) £1079; A100 Mini system (10 modules) £699. Prices include VAT. See 'Doepfer Modules' box for individual module prices.