Doepfer MS404
An edited version of this text also appears in
Vol.13 No.2. December 1997

Review by Chris Carter


German synth manufacturer Doepfer Musikelektronik have been producing excellent, if expensive analogue synth gear for about four years now and while they may not have made too many waves over here they have left a few ripples. Because, unfortunately until now Doepfer have suffered from lacklustre distribution, little public name awareness and an almost non-existent UK profile. Hopefully this is all about to change now that Bristol based EMIS have been appointed official UK distributors and are re-launching the entire Doepfer range with a revamped pricing structure and a new mouth watering catalogue covering MIDI keyboards, hybrid analogue/MIDI sequencers, MIDI-CV interfaces and a full range of expandable modular synths based on their A100, 19" base frame with more than 40 individual, affordable and some quite esoteric synth modules available. As they say, watch this space.

The MS404 being reviewed here is a rack-mounting MIDI-controlled, monophonic, analogue synth module and is the baby of the Doepfer range, even so it still holds a few surprises considering the price. Apart from the built-in MIDI-CV interface the audio and CV side of the MS404 is pure analogue, no patch memories or system exclusive to bother with in this instrument.

Although officially called the MS404 MIDI ANALOG SYNTHESIZER you could also put the word MINI anywhere in the title, this synth is small. The fact that it's presented in a sturdy, pressed steel, 1U rack mount case that is only 80 mm deep is even more astonishing when you consider that it also contains a built-in power supply. The front panel is logically and clearly laid out with 15 control knobs, 6 small toggle switches, a couple of LEDs to indicate LFO speeds and a couple more to show MIDI input activity and GLIDE status (more on this later). Doepfer have also, rather thoughtfully, printed numbered graduations around each knob, making it easier to note down favoured patches and settings. The rear panel has all the usual suspects, MIDI in and thru sockets, mono audio output and input jack sockets, both working at standard -10 dB line level, plus a small audio input level control and two jack sockets labelled CV and GATE (see box). There is also a neat, combined IEC mains input socket/fuse holder/power switch, nice!

The front panel is divided into five sections: MIDI, VCO, VCF, VCA and ENVELOPE and gives a pretty good inkling of what to expect. The minimalist MIDI section includes just one small rubber push button labelled LEARN and two LEDs, with one labelled GLIDE (more on this section later). The first analogue section is the VCO (voltage controlled oscillator), this consists of knobs for GLIDE amount (from zero to 4 seconds), TUNE (plus or minus a couple of tones) and PULSE WIDTH (for varying the waveform shape), followed by a 3-way switch for selecting the VCO waveform: SAWTOOTH/OFF/PULSE. Next is a switch for choosing the VCO output signal, VCO (on), OFF (no signal) or NOISE (the white variety), unfortunately you can't have the noise signal and oscillator on simultaneously, shame. Next in line is LFO 1 which produces a triangular control waveform and is used solely to modulate the VCO, via the the modulation selector switch, which can be set to: FM (pitch modulation), OFF (no modulation) or PWM (pulse width modulation). PWM is only audible if the VCO waveform switch is set to PULSE and works by changing the shape of the waveform in a cyclic manner from a short pulse to a square wave. At slow rates PWM sounds like a chorus or detuning effect and is useful for fattening sounds, while at higher rates it takes on a more metallic edge and sounds like ring modulation. LFO 1 consists of a LEVEL control, for adjusting the depth of the triangular wave into the modulation selector switch, a FREQ control for adjusting the LFO speed and a 3-way frequency range switch, which defies convention by using a LOW/HIGH/MED configuration instead of the usual LOW/MED/HIGH. However, the range of the LFO covers an impressive (for an LFO anyway) 0.01 Hz, where one cycle takes few minutes, to 5 kHz, way up into audio range which allows for some useful inter modulations, drones and generally weird effects across the whole frequency spectrum.

The VCF (voltage controlled filter) has controls for FREQ (the filter cut-off frequency), TRACKING, a 3-way (HIGH/OFF/LOW) toggle switch for selecting how much of the keyboard CV (control voltage) affects filter frequency, and ENVELOPE, for adjusting the amount of ADSR CV feeding the filter frequency input. Next is LFO 2, which is identical to LFO 1 but solely for modulating the VCF frequency. Last in this section is the EMPHASIS control (also known as 'Q' or resonance) and is for emphasising harmonics at the filter cut-off point and adds that distinctive resonant peakiness we all know and love. As with most analogue filters, when this control is turned fully clockwise it pushes the VCF into self-oscillation, producing an almost pure sine wave signal and once oscillating becomes, in effect, a second VCO to be played by the MIDI or CV in, modulated by LFO 2.

The VCA is represented by just a single knob marked ACCENT, however behind the scenes the MS404 is summing CV signals from the ADSR generator, MIDI volume controller #7 (via the CV interface) and an offset control from the ACCENT knob, which in reality acts as a master volume control because decreasing the ACCENT control also reduces the envelope generator signal and any MIDI volume changes.

The ENVELOPE generator uses a standard ADSR configuration with four knobs marked ATTACK, DECAY, SUSTAIN, RELEASE and outputs a control voltage directly to the VCA and to the VCF (via the VCF ENVELOPE depth control). The ADSR controls cover a pretty good range, from super short Kraftwerk like blips to 20 second ambient attacks and decays and should be more than adequate for most situations.

Because this is a monophonic instrument with no programmable analogue functions Doepfer have only included a few basic MIDI features, giving you just a single but selectable MIDI channel converting MIDI keyboard information into various CV/GATE signals. These are: MIDI Note to VCO pitch and VCF frequency and Gate to ENVELOPE, MIDI Velocity to VCF frequency and VCA level, MIDI Pitch Bend to VCO pitch, MIDI Volume Controller #7 to VCA level, MIDI Sustain Controller #64 to ENVELOPE gate, MIDI Portamento Controller #65 to GLIDE on/off and one user definable MIDI Controller (usually Mod Wheel) to modulate the VCF or VCA. A further MIDI function is the use of Program Changes 0-5 to set the status of the VCF and VCA velocity response and the ENVELOPE highest note re-trigger on/off mode, e.g.: Prog #2 turns VCF velocity response off, while Prog #3 turns it on, etc.

To set any MIDI function couldn't be easier and simply involves pressing the LEARN button and the MIDI LED above it flashes until the MS404 receives a MIDI signal (this LED also acts as a useful MIDI status indicator). When you perform this "learning" process the MS404 also registers which MIDI channel you are transmitting on and remembers this and any MIDI functions you have set (such as velocity, re-trigger mode etc.) in a non-volatile memory.

Although the synth will respond to the full MIDI Note range (0-127) the VCO only has a range of 5 octaves (with an audio upper limit of 5 kHz, the same as the LFOs). This 5 octave window can be anywhere on your keyboard and is best set each time you turn on the unit. To do this just involves pressing the LEARN button (as above) and playing your lowest C note, from now on you won't hear any notes below this bottom C, or above the 5 octave ceiling.

Because this is an analogue instrument it responds to temperature changes and needs a warm-up period of around 20 minutes to reach optimum stability. If you bear this in mind and don't stick it in the fridge or oven the VCO has no trouble tracking a MIDI keyboard accurately over the maximum 5 octaves and will remain stable for hours on end.

The waveforms sound fine, the sawtooth has plenty of buzz and bite and the pulse wave sounds suitably reedy, thin, hollow or square depending on the position of the PULSE WIDTH knob, which can, if you wish, make the wave so narrow as to become inaudible. The pulse wave sounds especially good when being modulated by LFO 1, but it's a shame you can't use LFO 2 to modulate it while LFO 1 is used for a touch of VCO pitch modulation, for an even fatter sound. The MIDI switchable GLIDE is a handy feature and works particularly well for Roland TB303 impersonations. The NOISE generator sounds, well... white noisy, I would have liked the option of mixing the noise with the VCO, but as it stands it's either one or t'uther. Also, because the TUNE control has only a limited span, I must admit a longing for a stepped, octave control for the adjusting overall VCO pitch range (as on the A110 module). This became all the more apparent when the MS404 is used as a VC source (as opposed to a MIDI source), because when used with something like a Roland SH101 keyboard/sequencer or an analogue step sequencer there is no way of transposing the MS404 pitch other than reprogramming the sequence. However, most users will be hooked up to a MIDI system where this will be less of an issue because of the obliging way MIDI information can be transposed and edited.

The VCF is generally considered to be one of the most important ingredients when imparting character to a synth and the filter in the MS404 is no exception being a 24 dB low pass filter, using a "transistor ladder" design, the same type used in Moog synths. The MS404 filter sounds particularly sweet, with a nice musical quality in the mid frequencies and with the emphasis control whacked up to about 3/4, almost crystalline in the upper regions. In the lower octaves the filter looses some of its character a little but is still capable of producing a decent oomph (for want of a better word) that, in conjunction with the VCO, works particularly well for Mini Moog style bass lines and Roland TB303 peaky, resonant type bass sequences.

The inclusion of an external audio input is welcome, particularly with access to such a good sounding filter to warp your sounds through. I tried out a number of sources: sampler, drum machine and keyboards to see how accommodating the input level was and generally most stuff sounded great, digital synths in particular benefited from a touch of analogue warmth and when deliberately pushing the input into distortion, which can happen if you're just playing big chords on a keyboard, it sounded more like an overdrive effect that could be quite usable in the right situation.

The MS404 may look a little bland and if anything looks a bit like a piece of test gear, but once you start using and exploring it, it reveals an altogether different persona. Hooked up to a MIDI keyboard controller you could consider this as a serious alternative to a lot of second-hand mono synths of yore such as the Korg MS10, Roland SH101, Moog Prodigy or even a Roland TB303 BassLine, as it can match most of these sound for sound (and none of them have two LFOs). But without two VCOs it's never going to sound as fat as a Mini Moog, Roland SH2 or Korg MS20, although that could be remedied by feeding another VCO or keyboard through the external audio input.

Operationally it's a piece of cake as most of the controls will be obvious to anyone who's been near a synth before, even for relative newcomers to analogue. If you're an analogue purist you might cringe at the thought of mixing analogue and MIDI but bear in mind that the MIDI spec has been kept to a minimum and doesn't interfere with the audio side of things at all. On the other hand some may bemoan the lack of programmability, patch memories and MIDI SysEx but that would be missing the point... by about a million miles. This is, and is meant to be, an analogue mono synth (complete with 20 minute warm-up), with the option of controlling it from a MIDI keyboard. And don't be misled by the affordable price, this is a very capable, expressive instrument covering the full range of sounds you would expect from a quality analogue synth, due in part to the excellent VCF, and if this is a sign of what's to come from Doepfer then I can't wait to see more. I like the MS404 it's small, it's solid, and it sounds superb.


As I mentioned elsewhere the MS404 only utilises MIDI for basic keyboard control. What this means to the user is that the front panel control knobs are realtime analogue pots and not scanned digital controllers and hence don't produce that tell tale "zipper" stepping noise you get on some MIDI instruments. And because the MS404 doesn't offer you any patch memories or MIDI control of the front panel you tend to find yourself rediscovering the dying art of real time 'knob twiddling'. Start twisting and turning those knobs and chances are you'll never get the same sound twice, so hit the record button now and start flying by the seat of your pants.

The two rear sockets labelled CV and GATE need a little explaining as they aren't all they seem. Direct from the Doepfer factory the CV and GATE sockets are wired as outputs from the internal MIDI-CV interface and MIDI Note, Pitch Bend and Mod Wheel information appearing at the MS404 MIDI input are transmitted as CV/GATE signals through these two sockets. This enables the unit to be used as a stand-alone MIDI-CV interface even if you aren't using it as a synth.

However, the MS404 is quite capable of acting as a totally analogue, non-MIDI, voltage controlled mono synth module. But to work in external CV/GATE mode involves either ordering the unit preconfigured to CV/GATE input or returning it to EMIS for a small modification. Not a very satisfactory arrangement I'm sure you'll agree, particularly if you intend to control the synth from something like a Roland TB303 BassLine which only has CV/GATE outputs. However after voicing my frustration EMIS inform me that anyone ordering an MS404 can request a small modification which consists of a rear mounted toggle switch to select either internal MIDI control (CV/GATE out) or external CV/GATE control (no MIDI in). This will be an essential option for anyone considering using the synth in both MIDI and CV situations.

Interestingly the instruction manual (a very good read) states that it uses circuitry from the the Doepfer A100 modular system and is based on the following modules: A110 VCO, A120 VCF, A131 VCA, A140 ADSR, A145 LFO, A190 MIDI-CV.

Unfortunately Doepfer haven't published any technical specifications for the MS404, however after discussing this with EMIS I came up with the following:



1 x VCO. Sawtooth and variable pulse waveforms, range approximately 1 Hz to 5 kHz.

1 x VCF. 24 dB/Octave low pass with resonance, no further spec. available.

1 x VCA. Logarithmic response, -10 dB line level output, no further spec. available

1 x Envelope Generator. ADSR type, A: 0-15s, D: 0-23s, S: 0-100%, R: 0-23s.

2 x LFO. Triangular waveform (or square wave with internal modification), range approximately 0.01 Hz to 5 kHz.

1 x Noise Generator. White noise, fixed level.

1 x MIDI-CV Interface. 3 x CV (1v per octave), 1 x Gate (+5v), Glide switching, 5 octave range. 

MIDI in and thru, audio out, audio in/level control, CV in/out and GATE in/out (see box), 240v power in and on/off.

1U Rack Mount, depth 80 mm, weight 3 lbs.


Authentic, all analogue audio circuitry.

Great sound quality, particularly the VCF.

Built-in MIDI to CV interface, which can double as stand alone MIDI to CV convertor.

External audio input.

Easy to use, with a clear and logical layout.

Solid, compact case with built-in power supply.

Excellent value for money.


High note priority only.

VCO and noise signals can't be mixed.

Limited VCO/LFO modulation routing.

Noise and ADSR outputs can't be used as VCO modulation sources.

No CV/GATE inputs without internal modification (see box).


A true analogue mono synth with an authentic sound, plenty of features and just enough MIDI to make it easy to integrate into most set-ups. A second VCO and more flexible VCO/LFO patching would have been nice but would have pushed the price beyond a very reasonable £299. Recommended for both beginners and pros alike.

Price: £299 incl. VAT

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

TEL: 0117 9561885

FAX: 0117 9561885



Copyright © 1997 Chris Carter / SOS Publications.