The KA-303 is a software synthesizer for the sound that invented Acid House, Acid Techno and Hard Acid: squelchy, resonant, driving basslines that have been moving dancefloors around the world since the late 80s. Built for producers who need that sound in their DAW, no compromises, no detours, no hardware.
The KA-303 takes the sound of the legendary TB-303 as its starting point, but goes far beyond it. With a full Composing Engine for acid patterns, four distortion models, a Unison Engine with up to 7 voices and the Angel Fish Mod as an independent sonic extension, the KA-303 is not a clone. It is a standalone instrument with its own character.
Circuit-Modeled. Not emulated.
The KA-303’s filter is not an approximation. It’s a detailed reproduction of the original Diode Ladder circuit at component level, with Zero Delay Feedback architecture. Asymmetric integrator stages, diode saturation, the original highpass in the feedback path. The fat, signal-dependent squelch that only a Diode Ladder can produce.
Waveform Morph: The sweet spot between saw and square
Every other 303 plugin forces you to choose: Saw or Square. Not the KA-303. With the dedicated MORPH knob, you can smoothly blend between the two waveforms. At 30% with high resonance, you get timbres that neither Saw nor Square alone can achieve. When controlled via MIDI CC automation, basslines suddenly start to breathe and evolve in real time. Translated with DeepL.com (free version)
Angel Fish Mod: Where the hardware stops, the KA-303 begins.
Inspired by Robin Whittle’s legendary Devil Fish mod. Overdrive, Muffler, Filter FM, extended envelopes, adjustable portamento. One click, and the 303 sound gets an entirely new dimension.
Intelligent Distortion with Crossover Logic.
Four models: DS-1, Tube, Rat, Fuzz. But the crucial part happens before: a Pre-Distortion Crossover splits sub-bass and mids. The bass stays clean, the distortion only hits where it belongs. From crunch to acid growl, no mud.
Composing Engine: No wrong notes. Literally.
The intelligent note grid only allows notes within the selected scale. Slides and accents visible directly in the piano roll. 98 factory patterns as a starting point. Scramble, Mutate, Octave Jumps as creative tools. MIDI Drag & Drop straight into your DAW.
Dynamic Pattern Grid: As Flexible as the Idea.
The KA-303 pattern editor adapts to whatever you need. The Dynamic Pattern Grid lets you set pattern lengths from 1 to 32 steps, freely adjustable per pattern. The real trick: patterns with odd lengths, say 3, 5, 7 or 11 steps, run against the DAW's 4/4 grid, creating natural phase shifts that build and resolve over bars. That is the hypnotic effect Hardfloor and the early acid producers made their signature sound. Classic 16-step basslines work just as well, but once you have heard that constantly realigning, breathing groove, you will not want to go back.
Page System: More Than One Bassline.
One pattern, multiple pages. The Page System lets you create and chain several independent step pages within a single pattern. Longer structures with internal variations, no extra pattern slots needed. Verse, fill, chorus, all organized inside one pattern.
MIDI Import: Your Material, the Power of the KA-303.
Sketched a bassline in your DAW or have an old MIDI file sitting on your drive? Just drag it into the KA-303. The notes land straight in the acid grid, and from there the Composing Engine takes over. Scramble reshuffles the pattern, Mutate develops it further, Slides and Accents can be set directly in the grid, Groove brings it to life. What would take tedious note-by-note editing in your DAW becomes a squelching acid pattern in seconds.
Grid Resolution: From Broad to Precise.
The KA-303 pattern editor works at 1/8, 1/16 or 1/32 resolution, your choice. Short staccato notes, densely packed triplet feels or classic acid timing grids, all in the same editor, no detours. The resolution follows DAW standards, which makes the interaction with MIDI Import even more direct.
Lasso Selection: Full Control in the Grid.
Notes in the pattern editor can be selected with a lasso, then moved, copied or deleted. Individual steps, entire phrases or everything at once. Drag a pattern in via MIDI Import and want to rework just the second half? Do it with the same gestures you know from any piano roll. Precise editing, no workarounds.
Groove Engine: Beyond Swing.
Tight, Shuffle, Funk, Push, Laid Back. The expanded groove types of the KA-303 go far beyond simple swing. Each groove type shifts timing and velocity in its own way, from minimal human feel to a deep, unmistakable pocket. Combined with Density and Mutate, basslines start to feel alive.
Two separate preset worlds.
Sound presets and pattern presets are completely independent. Let a pattern run, click through sounds, hear the same bassline in completely different timbres. No rebuilding, no loss.
Unison Engine: Up to 7 voices.
Each with its own filter, its own envelopes, its own slide processor. From subtle thickening to a massive wall of sound. With automatic gain compensation.
The sound that created genres. Reimagined, with its own character.
The TB-303 defined Acid House, Acid Techno and Hard Acid. That squelchy, resonant, unmistakable bassline sound is deeply embedded in the DNA of electronic music. The KA-303 takes that exact sound as its starting point and takes it where the hardware never could.
Circuit-Modeled at Component Level
The heart of the KA-303 is not a generic filter model. It’s a detailed reproduction of the original Diode Ladder Filter with Zero Delay Feedback architecture, modeled down to component level. Four cascaded integrator stages with asymmetric coefficients, soft-clipping saturation modeled after 1S2473 silicon diodes, the original 150 Hz highpass in the feedback path. The result: the fat, signal-dependent squelch that transistor ladder designs simply cannot replicate.
Slide, Accent and the Gimmick Circuit are also modeled at component level, including the capacitor-based Accent Sweep that accumulates across consecutive accented notes. Exactly like the hardware.
Angel Fish Mod: Beyond the Original
Inspired by Robin Whittle’s legendary Devil Fish mod, we developed the Angel Fish mode. One click on the MODE knob and the KA-303 becomes an extended instrument: Overdrive, Muffler, Filter FM, extended envelopes, adjustable portamento. From warm overdrive to aggressive filter FM to screaming leads with Hi Reso. This is the sound the TB-303 always wanted to have.
4 Distortion Models with Intelligent Crossover Logic
DS-1, Tube, Rat, Fuzz. Four distortion models, each with its own character. But the special part isn’t just the distortion, it’s what happens before it: a Pre-Distortion Crossover splits the signal. The sub-bass stays clean, only the mid-range runs through the distortion. HP Resonance creates the characteristic nasal growl, ENV>HP couples velocity to the highpass frequency for dynamically responsive distortion. From subtle crunch to aggressive acid growl, without the bass falling apart.
Composing Engine: Acid Basslines in Seconds
The integrated pattern editor was built specifically for acid basslines. An intelligent note grid only allows notes within the selected scale. Wrong notes? Simply not possible. Slides and accents are visible directly in the piano roll, no hidden menus. 98 factory patterns from “Chicago Deep” to “Berlin Basement” to “Final Boss” deliver instant inspiration. On top of that, Scramble, Mutate, Octave Jumps, Groove and Density serve as creative tools. A completely new pattern emerges in just a few clicks. MIDI Drag & Drop takes it straight into your DAW.
On top of that, Scramble, Mutate, Octave Jumps, Groove, and Density serve as creative tools. A completely new pattern is created in just a few clicks.
Two Separate Preset Worlds
The KA-303 keeps sound presets and pattern presets completely separate. In practice, this means: let a pattern run and click through sound presets. The same bassline, completely different sonic characteristics. No rebuilding, no loss. Sound and notes live in two separate worlds and can be freely combined.
Unison Engine: When It Needs to Be Fat
Up to 7 full synthesizer voices, each with its own filter, its own envelopes and its own slide processor. Stepless detune and stereo spread. From subtle thickening with 2 voices to a massive wall of sound with 7 voices and 30+ cent detune. Gain compensation keeps the level consistent across all voice counts.
Everything On Board
Tempo-synced stereo delay with crossfeed and darkening filter. Reverb based on the Signalsmith algorithm with room sizes from 0.3s to 5s. Master Limiter as a brick-wall peak limiter on the output, protecting against clipping no matter how extreme resonance and distortion are pushed. Up to 8x oversampling for the highest audio quality. Full MIDI CC mapping via right-click and MIDI Learn. Dark and Light theme.
Who Is the KA-303 For?
For everyone who takes acid seriously. Whether Acid House, Acid Techno, Hard Acid, Trance or Hardtechno. The KA-303 delivers the authentic sound with modern tools. If you build basslines that need to squelch, scream and move the dancefloor, you’re in the right place.
Try Before You Buy
Not sure yet? No problem. Download the free demo and test the KA-303 in your DAW with all features and no time limit. The only restriction: white noise is briefly faded in every 30 seconds, and after 30 starts audio is muted. This way you can explore the sound, the Composing Engine and all distortion models at your own pace before you decide. Once the KA-303 convinces you, just activate your license key and the noise is gone.
Formats: VST3, AU, Standalone
Systems: macOS 10.14+, Windows 10+, Linux
License Information
This product includes a professional license system with the following features:
- Online activation with hardware fingerprinting
- Up to 3 device activations included
- Automatic license delivery via email
- Customer portal for license management
After purchase, you will receive your license serial number via email within minutes.