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Doepfer MS404

MIDI Analogue Synthesizer By Chris Carter
Published December 1997

Doepfer MS404

Apart from a few MIDI‑supported commands, the Doepfer MS404 is completely analogue — so there are no patch memories, no SysEx, and no storable front‑panel settings. Chris Carter explains why you'd nevertheless be mad to overlook it...

German synth manufacturers Doepfer Musikelektronik have been producing excellent analogue synth gear for about four years now, including MIDI keyboards, hybrid analogue/MIDI sequencers, MIDI‑CV interfaces, and a open‑ended, expandable modular synth system, the A100, with more than 40 individual, affordable — and some quite esoteric — synth modules available, and more on the way. Until recently, the UK hasn't really been one of Doepfer's target markets; however, Bristol‑based EMIS have now been appointed official UK distributors, and are re‑launching the entire range, with a revamped pricing structure and a new mouth‑watering catalogue, so watch this space.

Craft Work

The MS404 being reviewed here is a MIDI‑controllable, one‑oscillator, monophonic analogue synth module, and is the baby of the Doepfer range — though it still holds a few surprises considering its price. Apart from a built‑in MIDI‑CV interface, the audio and CV side of the MS404 is pure analogue — there are no patch memories or SysEx to bother with for owners of this instrument.

This synth is small. The fact that it's presented in a sturdy, pressed‑steel, 1U rackmount case only 80mm 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 (real‑time analogue pots, and not scanned digital controllers, remember — so no zipper noise here), six small toggle switches, a couple of LEDs to indicate LFO speeds, and a couple more to show MIDI input activity and Glide status. 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 ‑10dB line level, plus a small audio input level control and two jack sockets labelled CV and Gate (see the 'CV In Or Out?' box). There's also a neat combined IEC mains input socket/fuse holder/power switch. Nice!

The MS404 rear panel features MIDI In and Thru DIN sockets, Gate and CV jacks, plus Audio In and Out.The MS404 rear panel features MIDI In and Thru DIN sockets, Gate and CV jacks, plus Audio In and Out.

Bundle Of Fun

The front panel is divided into five sections: MIDI, VCO, VCF, VCA and Envelope, which gives you a pretty good idea of what to expect. Running through these in order, left to right:

  • The minimalist MIDI section has just one small rubber push‑button, labelled Learn, and two LEDs, with one labelled Glide, and the other unlabelled (more on this section later).
  • The first analogue section contains the controls relating to the MS404's single VCO (Voltage Controlled Oscillator). The first knob is marked Glide and is for setting Portamento amount (from zero to four seconds), then come Tune (plus or minus a couple of tones) and Pulse Width (for varying the width of the Pulse waveform, but naturally, only when the Pulse wave is selected). There are then three 3‑way switches: the first for selecting the VCO waveform (offering a choice of Sawtooth/Off/Pulse), and the second for choosing the VCO output signal (here the selection is VCO (on), Off (no signal) or Noise (the white variety). Unfortunately, you can't have the noise signal and oscillator on simultaneously, which is a shame. The third of the 3‑way switches is a modulation selector, which works in tandem with the next two knobs and another switch; together all four of these control the first of the MS404's two LFOs.

LFO 1 produces a fixed triangular control waveform (though this can be altered to a square wave with a factory modification, if you really are desperate) and can only be used to modulate the VCO. Three types of modulation are available, via the aforementioned 3‑position modulation selector switch: 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 width of the Pulse waveform in a cyclic manner, so that it changes from a short pulse to a square wave over time. 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. Aside from the modulation selector switch, the other three controls relating to LFO 1 are the Level knob, which adjusts the intensity of the modulation that will be applied to the LFO, the Freq control for adjusting the LFO speed, and, rightmost in the VCO section, a 3‑way frequency‑Range switch, which defies convention by using a Low/High/Med configuration instead of the usual Low/Med/High. Despite this, the LFO's range is impressive for an LFO, stretching from 0.01Hz, where one cycle takes a few minutes, to 5kHz, and way up into the audio range, which allows for some useful intermodulations, drones and generally weird effects across the whole frequency spectrum.

  • The third section on the front panel contains the controls relating to the VCF (Voltage Controlled Filter). Here you find the Freq knob (for adjusting the filter cutoff frequency), the 3‑way Tracking switch (for selecting how much of the keyboard control voltage affects the filter frequency), and the Envelope knob (for adjusting the extent to which the filter is affected by the ADSR envelope). Next come the three controls relating to LFO 2, which is solely for modulating the VCF frequency, and is identical to LFO 1, except that it lacks the modulation selector switch. Last in this section is the Emphasis control (also known as 'Q', or Resonance), which emphasises harmonics at the filter cutoff 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. Once oscillating, the filter becomes, in effect, a second VCO, to be played by the MIDI or CV In, and modulated by LFO 2 if required.
  • The MS404's Voltage Controlled Amplifier (VCA) merits a section to itself, but is only represented by 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. This knob, in reality, acts as a master volume control, because decreasing the Accent control also reduces the envelope generator signal and the effect of any MIDI volume changes.
  • The final front‑panel section contains the controls for the MS404's Envelope generator, which uses a standard Attack, Decay, Sustain and Release (ADSR) configuration, with a knob for each stage. The Envelope outputs a control voltage directly to the VCA and VCF (to the latter via the VCF Envelope Depth control, so if you don't want the same envelope settings to affect the oscillator and filter, you can at least set this control to zero; the filter will then be completely unaffected by the envelope). The Attack, Decay, Sustain and Release 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.

The M Word

Because this is a monophonic instrument with no programmable analogue functions, Doepfer have only included a few basic MIDI features, providing a single (but selectable) MIDI channel via which MIDI information may be transmitted into the MS404 from an attached MIDI keyboard or sequencer. Once in the unit, various MIDI commands are converted into CV/Gate signals (see the table in the 'MIDI‑Supported MS404 Functions' box). 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 Retrigger on/off mode (for example, Program Change 2 turns VCF velocity response off, while Program Change 3 turns it on, and so on).

Setting any MIDI function couldn't be easier; you press the MS404's Learn button, whereupon the MIDI LED above it flashes until the MS404 receives a MIDI signal on a given channel from your attached MIDI keyboard or sequencer. When you perform this 'learning' process, the MS404 registers the MIDI channel you're transmitting on and stores this and any MIDI functions you have set (such as velocity, retrigger mode, and so on) in non‑volatile memory; however, if you forget yourself and send other MIDI functions on a different MIDI channel when the MS404 is in Learn mode, the synth will switch to receiving further data on the new MIDI channel automatically. I also couldn't get the MS404 to respond to more than one program change message at once; I had to send them individually.

Although the MS404 will respond to the full MIDI Note range (0‑127), the VCO only has a range of five octaves (with an audio upper limit of 5kHz, the same as the LFO's). This five‑octave 'window' can be anywhere on your keyboard and is best set each time you turn on the unit. Setting this simply involves pressing the Learn button (as above) and playing your lowest C note; from then on you won't hear any notes below this bottom C, or above the five‑octave ceiling.

Hooked up to a MIDI keyboard controller, you could consider this as a serious alternative to a lot of second‑hand monosynths 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.

In Use

Because the MS404 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 five 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 be 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'other.

The VCF is generally considered to be one of the most important ingredients of the overall character of a synth, and the filter in the MS404 is no exception. Of the 24dB/octave low‑pass type, it uses a 'transistor ladder' design, the same kind used in Moog synths. It sounds particularly sweet, with a nice musical quality in the mid frequencies, and, with the emphasis control whacked up to about three‑quarters of its maximum setting, it's almost crystalline in the upper regions. In the lower octaves, the filter loses a little of its character, 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 Minimoog‑style basslines and Roland TB303‑style, peaky, resonant type bass sequences.

The inclusion of an external audio input is welcome, particularly when you can then mangle your sounds with such a fine‑sounding filter. I tried out a number of sources, including a sampler, drum machine and several keyboards, to see how accommodating the input level was. Generally, most source material came out sounding great; digital synths, in particular, benefited from a touch of analogue warmth. When I deliberately pushed the input into distortion (which can sometimes happen if you're just playing big chords on a keyboard) it sounded more like an overdrive effect. This could prove quite usable, in the right situation.


I like the MS404; it's small, it's solid, and it sounds superb. It may look a little bland (if anything, it resembles 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 monosynths 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. But without two VCOs, the MS404 is never going to sound as fat as a Minimoog, 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, others may bemoan the lack of programmability, patch memories and MIDI SysEx, but that would be missing the point. The MS404 is, and is meant to be little more than, an analogue monosynth (complete with 20 minute warm‑up); one that has the option of controllability 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 voltage‑controlled filter. If this is a sign of what's to come from Doepfer, I can't wait to see more.


Unfortunately, Doepfer haven't published any technical specifications for the MS404 in its manual (which is a good read, by the way). However, after discussing this with EMIS, I came up with the following:

  • 1 x VCO Sawtooth and variable pulse waveforms, range approximately 1Hz to 5kHz
  • 1 x VCF 24dB/octave low‑pass with resonance (no further spec available)
  • 1 x VCA Logarithmic response, ‑10dB 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 0.01Hz to 5kHz
  • 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
  • Dimensions 1U rackmount module, depth 80mm, weight 3lbs

CV In Or Out?

The two rear‑panel sockets labelled CV and Gate need a little further explanation. As supplied from Doepfer's 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 In are converted in the MS404 and retransmitted out 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 also quite capable of acting as a totally analogue, non‑MIDI, voltage‑controlled monosynth module. But for your MS404 to receive and act on external CV/Gate signals, you currently have to either order the unit pre‑configured to CV/Gate input, or return it to EMIS for a small modification. Not a very satisfactory arrangement, as 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 I voiced my frustration to EMIS, they informed 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.

MIDI‑Supported MS404 Functions

The following MIDI events are recognised by the MS404's internal MIDI/CV converter and turned into CV/Gate signals.


  • MIDI Note VCO Pitch and VCF Frequency
  • MIDI Note length Gate
  • MIDI Velocity VCF Frequency and VCA Level
  • MIDI Pitch‑bend VCO Pitch
  • MIDI Volume controller (#7) VCA Level
  • MIDI Sustain controller (#64) Gate
  • MIDI Portamento controller (#65) Glide on/off
  • User‑definable MIDI Controller (usually mod wheel) VCF or VCA Modulation


  • 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 converter.
  • 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.


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


£299 including VAT.

Published December 1997