When Doepfer released the MS-404 in 1994, they weren't trying to build a perfect 303 clone—they were building something better. By adding two LFOs capable of reaching audio rates, they created a monophonic analog synth that could do everything the classic could do, plus a whole lot more in the realm of modulation and FM synthesis.
The MS-404 is built around a single voltage-controlled oscillator with sawtooth and pulse waveforms, paired with a 24dB-per-octave resonant lowpass filter that can self-oscillate for classic acid-style sweeps. The filter responds to MIDI velocity and controller data, letting you shape dynamics in real time. A full ADSR envelope handles amplitude and filter modulation, while the two LFOs—each with three frequency ranges stretching from sub-audio to 5kHz—can modulate either the oscillator pitch or pulse width, or the filter frequency. The external audio input means you can process external sources through the filter, expanding the synth's palette beyond its internal sound generation.
All parameters are MIDI controllable, and the MS-404 also functions as a MIDI-to-CV interface for controlling other analog gear. Glide, accent, and legato are all available via MIDI, recreating the tactile feel of playing the original while adding modern sequencer integration. The whole thing fits in a single-space 19-inch rack unit, making it compact enough to integrate into larger setups without taking up much real estate.
The MS-404 earned respect in the acid and techno communities—artists like Hardfloor and Josh Wink put it to work—and it remains a solid choice for anyone wanting authentic analog bass and lead sounds with surprising modulation depth. The fast LFOs and FM capabilities give it character that goes beyond simple 303 emulation, and the price point made it accessible when vintage originals were climbing in cost.
