An edited version of this text also appears in
SOUND ON SOUND magazine Vol.19 No.2. December 2003

Review by Chris Carter

DOEPFER A-100 - New Modules for 2003.

No sooner do I finish reviewing one modular system when an even bigger one turns up. But I'm not complaining, far from it. I'm in modular heaven right now, well until I have to send them back anyway.

Two 3U Doepfer racks containing 17 shiny silver modules arrived for review courtesy of UK distributor EMIS. A few of the modules have been reviewed before (SOS July 1998) or were duplicates but amongst them were eleven new modules that haven't graced these pages before:

A-102 VCF-9 (Diode Low Pass)
A-103 VCF-6 (18dB Low Pass)
A-105 VCF (SSM 24dB Low Pass)
A-108 VCF-8 (48dB Low Pass)
A-109 VC Signal Processor (VCF, VCA, VC Pan)
A-124 VCF-5 ("Wasp" filter)
A-135 Quad VC Mixer
A-136 VC Distortion/Waveshaper
A-144 Morph Controller
A-190 MIDI-CV/Sync Interface9
A-198 Ribbon Controller

As you can see from the list Doepfer now produce quite a few variations of analogue VCF module, which is probably a good place to start.

The VCF-9 fascia uses a standard Doepfer VCF layout with audio input and output, an audio level control, Cut-Off frequency, Resonance and one fixed and two variable frequency modulation CV inputs. The circuitry is based on an old analogue low pass filter design utilising an arrangement of diodes as an element of the filter control stage, as opposed to transistors or chips. This 18dB design is supposed to impart a particular (peculiar?) character to the filter and Doepfer themselves describe the sound of the VCF-9 as 'strange', to which I agree.
The filter has an unusual but not unpleasant sound. Fully open it exhibits plenty of top end, which can sound a little buzzy when using raw square or sawtooth waveforms. The bottom end isn't nearly as interesting until the resonance is turned up, when some unusual interactions come into play, due to the diode design I imagine. And adding more resonance introduces an increasingly more unstable quality to the sound. At maximum resonance the filter sounds like it is being overdriven but with a superimposed undulating whistling effect, like they said... strange. When it is self-oscillating (and without an input signal) it produces a regular sine wave output.

A-103 VCF-6 18dB LP
This is another 18dB low-pass filter with an almost identical feature set and layout to the A-103 but using the more traditional so-called 'transistor ladder' (or Moog ladder) circuit design. The range of this filter is narrower than the VCF-9 and the top end isn't nearly as cheeky. Also the bass has a tendency to tail off just when you need a bit more oomph. It comes to life a bit more when resonance is applied but it lacks character. The filter will also self-oscillate but it's nothing to get too excited about. Overall this is a more restrained and smoother sounding filter than VCF-9.

This is a classic 24dB low pass filter design incorporating the near legendary SSM2044 chip, as used in the Korg Polysix & Mono/Poly, Fairlight II, PPG Wave, EMU SP1200 and other such illustrious instruments. Quite a heritage. The VCF 'SSM' differs from the two previous VCFs by substituting the third frequency CV input for a resonance CV input. Otherwise the controls are basically the same.
This is a very nice sounding VCF. In the upper registers it is brighter than the VCF-6 or 9 and although it lacks some of the 'bite' of the VCF-9 this can be improved by adding a little resonance. The bottom end is nicely rounded, with or without resonance and can produce some powerful synth bass sounds using the right waveforms. Unfortunately the audio output does fall off quite a bit as resonance is introduced and although the level control can sometimes compensate for this it has to be used with care to avoid distortion. In oscillating mode it produces a clean and wide ranging sinewave. This filter has a distinctly more 'musical' character than either VCF-6 or 9.

This module is intended to emulate the filter section of an EDP Wasp synthisiser (SOS December 94). It is a 12dB multi-mode type VCF based on a unusual 1970s design that uses digital inverters as operational amplifiers (no it doesn't mean anything to me either !) but apparently this is what gave the Wasp filter its distinct character.
Layout and features are similar to the other Doepfer VCFs and although there are only two frequency CV inputs this module includes an additional Band Pass audio output and an LP/HP Mix control for the main audio output. This is a departure from the the original Wasp design, which included a three-way switch for selecting which of the three filter modes was active. By setting the Mix control to a 50/50 position and sweeping the Frequency you get a subtle but pleasing phasing effect (this is Notch mode), something the original Wasp filter wasn't capable of.
If you haven't heard a Wasp filter before I suppose you could describe its character as having a rasping, thinner quality compared to other VCFs. The band pass and high pass modes are particularly nasal sounding. The Doepfer A-124 version sounds very faithful to the original, including the fact that it won't self-oscillate (due to a built-in limiter). In some respects it sounds similar to the A-102 VCF-9 (Diode VCF), including adding a certain 'unstableness' to the sound when resonating. However, one feature I've always admired in the Wasp VCF is the relatively constant audio output level it maintains, regardless of the frequency and resonance settings, something many other VCFs designs aren't able to achieve but this module can.
With a handful of modules and ten minutes worth of tweaking it is quite easy to put together a patch based around the A-124 VCF that resembles the sound of an EDP Wasp. Actually it would be a good idea if basic instructions on how to do this were in the manual, are you listening Doepfer? To recreate the full Wasp experience it would be great to have a a flat, touch sensitive keyboard, which as you'll see further on can be emulated using the A-198 ribbon controller. But Doepfer users and owners of dead Wasps (there are many of us) looking to revisit the past should definitely invest in this module.

A-108 VCF-8 48dB LPF
The VCF-8 is the big daddy in this collection of filters and is housed in a wider 12HP module and includes similar controls and layout to the other VCFs already covered. It also has three Frequency CV modulation inputs. This filter is an 8-stage, 48dB low pass type featuring the 'transistor ladder' circuit design mentioned above, the so-called Moog ladder design.
The main difference with this VCF is that it includes five different filter slopes, all available simultaneously on independent outputs: 48dB LP, 24dB LP, 12dB LP, 6dB LP and Band Pass. Unusually these outputs can also be internally reconfigured (using jumper links) to produce 42dB LP, 36dB LP and 18dB LP filter slopes. There's also an additional 'external feedback return' socket that allows the insertion of other modules onto the resonance feedback path: eg. using a VCA for enabling voltage controlled resonance.
The sound quality is very good, far better than the other 'Moog ladder' filter (the A-103 VCF-6). Frequency sweeps in all modes is silky smooth without any unexpected peaks or dips. It has an even and consistent audio output with a clear bright top end. I found the 12dB LP output produced the fattest (phattest?) bass sound but ramp up the Emphasis (resonance) control in any mode and the VCF-8 can scream like the best of them, but watch those speakers!
Although it doesn't have a singular 'character' like the Wasp or Diode VCFs the A-108 VCF-8 is capable of taking on the guise of many types of VCF due to the various filter slopes available. This is undoubtedly one of Doepfer's most versatile VCF modules, unfortunately it is also the most expensive.

This versatile multi-purpose module contains separate VCF, VCA and VCPan sections. Because the design of this module is built around the now defunct Curtis CEM3379 multi-purpose chip (previously used in many Sequential, Ensoniq and PPG synths) there will only be a limited quantity of the A-109 available, which is a shame. However, it is certainly feature rich and well specified for the price.
The filter section is a 24dB, 4-pole, low pass design which includes two frequency VC modulation inputs and two resonance VC inputs. The filter also features a "constant amplitude versus resonance design", which means the output level will remain relatively constant even when resonance is increased. It has two audio inputs (one variable) and a single audio output.
The VCA has an audio input, two CV inputs (one variable) and a manual amplitude knob. The amplifier design uses a combined exponential/linear CV scale and a "rounded knee" response. This apparently allows a more natural envelope decay to zero when used with an ADSR generator.
The VC Panning section includes a single audio input, two audio outputs (L & R), two voltage control inputs (one is variable) and a manual pan control. This part of the module is actually two complimentary configured VCAs, which also use a combination of exponential & linear CV scales, depending on the voltage applied.
All three sections are hard-wired internally (VCF > VCA > VC Pan) so no patching is necessary other than connecting a source signal (VCO) to the VCF and the L&R outputs to a mixer or amp. However, all the audio connections are normalised so the internal audio path can be tapped into, or out of.
This is an ideal module for anyone starting out, on a budget, or tight for space in their A-100 rack as all you need to get it up and running are a VCO and an ADSR generator. The quality of the filter is very good, with a sound and character reminiscent of the A-105 VCF module. I've no complaints with the VCA either, which is transparent and yet punchy when used with short ADSR settings. The VC Panning feature is a bonus too and adds a lot to the module's appeal.

A-136 DIS (sic)
The A-136 DIS module is a voltage controlled Distortion/Waveshaper, whose purpose is complex manipulations and distortions of waveforms. The A-136 works its wonders by taking an incoming audio or CV signal and dividing it into three component parts: positive, original and negative. These components can then be controlled by external CV modulations using two CV inputs, or can be manually adjusted using five control knobs (+A, +L, A, -L, -A). The scope of distortion/modification stretches from basic soft clipping to extreme warping that renders the original tone unrecognisable.
It is hard to accurately describe the effect produced by the module because the same settings can sound completely different depending on the source material. Feed the A-136 with a square-wave and it is possible to get a decent pulse width modulation effect, however inputting a sine or triangle wave using the same settings produces a buzzy 'squeezed' kind of sound that has a tendency to disappear completely if modulated too deep. Sometimes it produces sounds similar to digital 'bit crushing', although more analogue sounding. It definitely produces the most interesting results with complex material, filtered waveforms, drum machine outputs and so on.
If there is one problem with this module it's that the controls don't always act as you would expect and some settings will produce absolutely no output at all with certain signals. Perseverance will pay off though, just don't expect instant results.

Although these modules are available separately the A-144 is considered an extension to the A-135 and is primarily intended to work in conjunction with it.
The Quad VC Mixer is in essence four linear VCAs who's outputs are mixed down to a single audio output. It has a relatively basic set of controls mounted in a 22HP wide module. The mono audio output is fed by four identical mono channels, each has an audio input, an input attenuation knob, a gain control, an external CV input knob and a CV modulation input socket. As you'd expect the sound quality fine with no colouration or strange audio artifacts.
The module is ideally suited to patches that require some kind of mono mixing e.g.: combining simultaneous VCO waveform outputs, mixing multiple VCOs into a single VCF, combining VCF multimode outputs and so on. However, even more interesting applications become apparent when you partner it with the A-144 Morph Controller.
With a name like Morph Controller you'd think this was some kind of futuristic Terminator module but what it does is essentially quite simple. It transforms a single incoming control voltage (0v to +5v) into four separate, displaced control voltage outputs. Which means that each CV output is progressively further offset from the original CV signal. Controls are kept to a bare minimum with just a CV input, an input attenuator, four CV outputs and a manual Morph control. At this point you're probably wondering what any of this has to do with morphing? Well that's where the Quad VC Mixer module comes into the equation.
The first stage is to connect the Morph Controller's four CV outputs to the Quad VC Mixer's four CV inputs. This gives you the ability to cyclically (using an LFO) or manually cross-fade (or morph) from one mixer channel to the next and the next and so on using a single CV source. The next stage is to input four separate sounds into the Quad VC Mixer. The final stage is to apply a CV source to the Morph Controller CV input, such as an LFO sine-wave, KB pitch CV, analogue sequencer CV output or an ADSR output. The so-called morphing effect is what you'll hear coming from the Quad VC Mixer's audio output, a continuous, cyclic and progressive cross-fading of the four sound sources.
The sounds can be anything at all but good 'morphing' material could be four VCO waveforms, four different VCF outputs (LP/BP/HP/Notch etc.), four different effects patches fed by the same source, four completely different patch set-ups (if you have enough modules!), of course the variations are endless. On a slightly different tack the instruction leaflet also includes a useful patch for configuring the Morph Controller as a auto quadrophonic surround panner by using it to control four VCA modules from an LFO.
With the right sounds the A-135 and A-144 modules are an effective and open ended combination that will allow the user some unusual audio configurations and hours of experimentation.

Even though this MIDI-CV module is only 10HP wide it crams in a surprising number of features, including two independent DACs (digital-to-analogue converters), MIDI IN and THRU, five analogue outputs and direct system buss connection for the CV and Gate signals to the Doepfer rack without using additional connections.
There is no LED display to speak of and editing is carried out by way of four (very) small push buttons and six red LEDs. I couldn't really describe programming and editing the A-190 as intuitive. You'll need the instruction manual handy at first, but once you've tried it a few times it doesn't seem such a big deal and anyway the default settings will be fine for most users.
DAC1 has a 12-bit resolution and only converts MIDI note messages to Pitch control voltages. Its output is hard-wired to the CV1 output and it is intended for precise 1v/Octave VCO pitch control. DAC2 is wired to the CV2 output and although it only has a 7-bit resolution it is fully MIDI assignable (e.g. pitch bend, aftertouch, volocity etc.). The CV2 output is suitable for non-critical modulations of VCFs and VCAs and the like.
The A-190 also features separate Gate, Clock and Reset outputs. Gate signals are automatically generated when a MIDI keyboard message is received and there are options for setting the gate to positive or negative polarities and single or multiple triggering. The Clock output is derived the incoming MIDI clock speed and the output pulses can set to generate positive or negative types. The clock divisions are programmable over a range of 4ppqn to 96ppqn (Roland drum machines and BassLines sync to 24 ppqn so no problems there). A Reset output is generated when MIDI start/stop/continue commands are received and this is intended to control the transport functions of Doepfer sequencer modules. Also included is basic MIDI controllable LFO, with variable depth and frequency (0.2Hz-20Hz) and programmable portamento (glide).
The A-190 is surprisingly versatile for such a compact module and apart from the fiddly editing I can find little to complain about. It's stable and was happy to track accurately across a 5 octave MIDI keyboard.

I've saved the most interesting of the new Doepfer modules for last. The A-198 comes in two parts: a ribbon controller (the part you rub your finger across) and a CV module. This pair also form part of the Trautonium range, an ongoing project using specially designed Doepfer modules to emulate various aspects of the Mixtur Trautonium electronic instrument, an invention of Friedrich Trautwein's in the 1930s. The Trautonium subject is hugely interesting but unfortunately there isn't space to cover it in this review. If you'd like to find out more the Doepfer website ( has an extensive overview of the Trautonium concept.
Most of the major electronic instrument manufacturers have produced ribbon controllers of some kind, including Moog, Korg, Yamaha and Kurzweil (reviewed SOS May 2000). They have been in use for a long time and the sound they are most usually associated with is a pitch sweeping glissando, Theremin like effect.
Doepfer's spin on ribbon controlling comes in the form of a (technically speaking) 50cm plastic coated, pressure sensitive, linear potentiometer, which is set into a sturdy steel frame (60cm x 20cm x 10cm). The controller is connected via a USB type cable to the A-198 module. The module contains two position sensitive control outputs (Gate & CV), a position Scale/Spead control and a Position Hold switch. There are also two pressure sensitive control outputs (Gate & CV), a pressure Scale/Spead control and a pressure Threshold control. Both the Gate outputs include LEDs for visual feedback while playing.

All you need to start producing sounds with the Ribbon Controller is a finger and a single VCO but you won't get the best out of it unless your'e a little more adventurous with your patching. The instruction manual includes some useful example patches and there are a few example MP3 files on the Doepfer web site too. A typical patch would include a VCO whose pitch is controlled by the Position CV output, a VCF controlled by the Pressure CV output and a VCA under control of an ADSR, which is triggered by either of the Gate outputs.
Depending on your style of playing you need to adjust the Position Scale control to give the correct pitch spread across the ribbon. For extreme pitch bending and warping (from very low to very high and vice-versa) the Scale would be set to a wide spread. For more accurate playing techniques Doepfer recommend adjusting the VCO pitch and Scale control to produce a spread of approximately one octave over 25cm (half the length of the ribbon). If set up in this way it is possible, with some practice to play pretty decent melodies, even if they do sound like they are played on a 21st Century musical saw! Also some very expressive vibrato effects can be achieved in this mode by gently wobbling you finger from side to side, a little like playing a violin. For more accurate pitching Doepfer recommend using their A-156 Quantizer module, which will chromatically smooth out any pitch instability, producing more of an arpeggio effect. Although I think this rather defeats the point of the Ribbon Controller's major feature, sweeping glissandos.
Anyway, couple these pitching techniques with its pressure abilities and the Ribbon Controller literally becomes an instrument that can be learnt and played, something along the lines of a single stringed fretless bass.
When the Pressure Gate output is used with a VCA/ADSR combination the controller can also simulate a EDP Wasp keyboard, by jabbing and poking your fingers onto the ribbon rather than rubbing across it. Some great trilling effects can also be achieved if you try this with your fingers at opposite ends of the strip. There are endless applications the ribbon controller can be applied to: filter sweeps, volume swells, morph controlling (using the A-135/A-144 combo), theremin impersonations and so on.

Doepfer still surprise me with their inventiveness and innovation. They are constantly coming up with ever more devious ways of manipulating CV and audio. And I can tell you (from experience) that getting into modular synthesis is habit forming. To be perfectly honest if I had the space (and the funds) I would probably buy all of these modules, and I'm guessing the same applies to you... the reader. Spoilt for choice, as the saying goes.

Doepfer deliver the goods yet again with an excellent selection of great sounding filters and innovative module designs. The interactive Ribbon controller is expressive and fun to use, particularly when in combination with the Morph controller.

A excellent range of fine sounding VCFs.
The Ribbon Controller is both expressive and fun to use.
The MIDI-CV module features an impressive number of features for something so small.
The Morph Controller/Quad VC Mixer combo allows for some unique effects.
Open ended system, full of potential.
The modules are sensibly priced.

The Ribbon Controller sensor requires excessive pressure.
The Ribbon Controller module suffers noticeable frequency drift.
Adjusting some modules doesn't always give predictable results.
The system is complex and not suited to everyone.
Buying modules can be habit forming.


I'm quite a fan of Doepfer modules and often impressed by their build quality but I hope the flight case these modules arrived is just a blip in their usual professional approach. To put it bluntly it is horrible! It's cheap looking, poorly designed, badly fitting and to cap it all the inside of the removable lids are covered in a deep purple 'fun fur' fabric. Imagine a 1970s funk bordello... yes it's that bad! And the shiny 'leatherette' outer finish won't last five minutes in an aircraft hold, a baggage carousel or in the back of a transit. If you need to flight case your beloved Doepfer rack my advice would be to invest in a professional road rack case, preferably a 'shock-mount' type. Expensive? yes but so is a new rack full of Doepfer modules.

Although I had great fun with the A-198 Ribbon Controller not everything in the garden is green and there are a few of points I wasn't entirely happy with.
If the Position Hold switch is set to Off the CV pitch drops to zero when your finger is released from the ribbon, this is normal. If however, the Hold switch is set to On the CV pitch is meant to be sustained by a S&H circuit and the Gate signal held on. What actually happens is that after a few seconds the CV pitch starts to drift downwards, noticeably. This is not something I would expect using state-of-the-art analogue technology and hopefully it is just a quirk of the review unit.
Which could also be the case with another problem I found, the pressure sensitivity just wasn't sensitive enough. I had to press down 'really' hard to get a decent response. Although this problem did seem to get a little better the more I used it maybe I was just subconsciously pressing harder, who knows?
My last point is purely a question of taste. The USB umbilical cable is connected to the right hand side of the ribbon controller. OK, so this may not seem like a big deal but if you 'strike a pose' with it as you would a guitar the pitch response is upside down, and running a finger 'up' the ribbon produces a 'downward' pitch sweep, the opposite of a guitar fret. Of course this could be corrected by patching in an A-175 Voltage Inverter to the CV ouput but it would be nice if the module included some kind of pitch inversion option instead.

There seems to be a trend at the moment to produce hardware modules which emulate features of particular classic analogue synths and effects units using original circuit designs and components. Moogerfrooger, Analogue Systems and Doepfer have all taken this route in recent years. This is fine but many designs rely on an ever decreasing supply of specific analogue components. When the source of those parts eventually (and inevitably) dries up the only alternative will be emulation using DSP technology or producing software versions, neither is a solution for analogue purists. Some of the modules reviewed here rely on such components and as the saying goes 'when they're gone they're gone'. Which is a shame as these are some of the best modules I've reviewed in years. My only advice would be... buy now, before it's too late!

EMIS/Doepfer Price list (Incl. VAT):

A-102 VCF-9 (Diode Low Pass) £65
A-103 VCF-6 (18dB Low Pass) £65
A-105 VCF ("SSM' 24dB Low Pass) £79
A-108 VCF-8 (48dB Low Pass) £119
A-109 VC Signal Processor (VCF, VCA) £99
A-124 VCF-5 ("Wasp" filter) £49
A-135 Quad VC Mixer £79
A-136 VC Distortion/Waveshaper £49
A-144 Morph Controller £39
A-190 MIDI-CV/Sync Interface £119
A-198 Ribbon Controller £149

 Copyright © 2003 Chris Carter / SOS Publications.
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