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 moved dancefloors around the world since the late 80s. Made for producers who want exactly that sound in their DAW. No compromises, no detours, no hardware.
Read the full review → · Original at Loop Rituals
The KA-303 takes the sound of the legendary TB-303 as its starting point and goes far beyond it. A full composing engine for acid patterns, a complete modulation system, four distortion models, a unison engine with up to seven voices and the Flavor Palette with seven hardwired character engines make the KA-303 not a clone, but an instrument of its own with its own character.
The Flavor Palette: One Synth, Seven Instruments
Seven DSP engines hardwired into the voice's signal path, from the dry 303 to a screaming sync wall. The MODE selector is not an effects carousel and not a preset list. Each mode is its own engine, and they escalate: every higher mode keeps the character below it and stacks exactly one new signature engine on top. You don't pick a sound, you pick a character.
Original, the pure 303
One oscillator, the 18 dB diode ladder filter, envelope and accent. Dry squelch, growling basslines, fat sub. The foundation every other mode builds on.
Angel Fish, inspired by Robin Whittle's Devil Fish
Pre-filter overdrive, audio-rate filter FM for metallic screams on the accents, and Hi Reso, a resonance that tips over into self-oscillation. This is aggressive hardfloor acid: screaming leads, hard-hitting accents, long expressive slides.
Stonefish, saturation with teeth
An asymmetric tanh saturator, Venom as drive in front of it, Howl behind it. From warm grit to a brutal saturation wall, with fat even harmonics. Howl pushes the filter into singing, so self-oscillating screamers and inferno leads.
Sea Devil, depth and motion
Cavern opens a tuned resonant space, Abyss pulls downward with a sub-dive, and Tide lays a slowly breathing modulation on top, up to two bars long and tempo-synced. It sounds hollow, cathedral-sized and bottomless. Made for dub basses, underwater pads and evolving ambient acid textures.
Lionfish, the talking 303
Three parallel formant filters over a vowel table. Spines sets the sharpness, Vowel morphs from Ooo through Aaa to Eee, Motion moves the mouth on every note or only on the accents. Talking leads, wah sweeps, choir-like pads.
Dragonfish, the Scream Machine
A hard-synced slave oscillator that resets on every note and fires off the classic tearing sync overtones, clean via PolyBLEP and oversampling. Sweep drags the ratio across the note, Bite adds aggression. Tearing hard-sync leads and industrial stabs.
Torpedo Ray, the harmonic fan
Three pitch-tracked resonators ringing on the fifth, octave and twelfth above the fundamental. Fan blends the upper partials in, Bloom raises the resonance for a blooming ring. Harmonically rich stacked leads, organ- and choir-like tones that fill the whole mix.
Seven real instruments in one voice. Dial one in and start tweaking.
Modulation: When the Acid Line Comes Alive
The new MOD tab turns every static patch into a moving soundscape. Assign almost any source to almost any control, and the sound starts to breathe. Three LFOs handle the classic cyclic movement, from slow filter sweeps through wobble to tremolo. Two modulation envelopes shape the contour per note, including a true one-shot AD mode that shapes individual notes percussively. Two freely drawable curves let you sketch your own modulation shape by hand. A step sequencer with 1 to 16 steps adds rhythmic, pattern-locked movement on top. Four macro controls bundle whole parameter groups under a single knob. And performance sources like velocity, accent, note pitch, modwheel and random let the synth respond to how you play.
Assigning is deliberately simple: right-click any control, pick a source, done. A colored ring shows the modulation depth right on the knob, and a moving dot tracks it in real time, so you always see what is happening. Every routing is saved with your preset and your project.
And no worries about your existing library: modulation only moves what you assign to it. All existing patches sound exactly as before; the update changes nothing about your sounds.
Circuit-Modeled at Component Level, nicht emuliert
The heart of the KA-303 is no generic filter model. It is a detailed recreation 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 after 1S2473 silicon diodes, the original 150 Hz highpass in the feedback path. The result is the fat, signal-dependent squelch that transistor ladder designs simply cannot replicate.
Slide, accent and the gimmick circuit are modeled at component level too, including the capacitor-based accent sweep that accumulates across consecutive accented notes. Just like the hardware.
Waveform Morph: The Sweet Spot Between Saw and Square
Every other 303 plugin forces you to choose: saw or square. The KA-303 doesn't. With the dedicated MORPH knob you blend continuously between both waveforms. At 30 percent with high resonance you get timbres that neither saw nor square reach on their own. Automated via MIDI CC, basslines start to breathe and evolve in real time.
Pulse Bias and Analog Drift: Authentic Square Like the Hardware
The real TB-303 has no dedicated square oscillator. The sawtooth is clipped through a single transistor whose Vbe bias and component tolerances produce a systematically asymmetric square wave. The duty cycle typically sits between 46/54 and 48/52, the transitions are soft rather than sharp, and even harmonics appear that an ideal square lacks and that interact audibly differently with the filter resonance. That is exactly what gives the 303 its character, and almost every other emulation skips it.
With Pulse Bias you shift the square's switching point bipolar. To the left the pulse gets wider, the sound fatter and more hollow. To the right narrower, more nasal, thinner. Analog Drift switches between a hard-clip comparator for the clean, modern square and a BJT soft-clip with deterministic per-voice bias variation. Every unison voice gets a slightly different switching point, which comes very close to a small collection of slightly differently calibrated 303s. For the classic acid character à la Josh Wink, Higher State of Consciousness: Drift on, resonance high, tube distortion on.
Four Distortion Models with Intelligent Crossover Logic
DS-1, Tube, Rat, Fuzz. Four models, each with its own character. But the crucial part happens before that: 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, and ENV>HP links velocity to the high-pass frequency for dynamically responsive distortion. From light crunch to aggressive acid growl, without the bass collapsing.
Composing Engine: Acid Basslines in Seconds
The built-in pattern editor was made specifically for acid basslines. An intelligent note grid only allows notes that sit in the selected scale. Wrong notes are simply not possible. Slides and accents are visible right in the piano roll, no hidden menus. 98 factory patterns from Chicago Deep through Berlin Basement to Final Boss deliver instant inspiration. Plus Scramble, Mutate, Octave Jumps, Groove and Density as creative tools. A completely new pattern in a few clicks, straight into the DAW via MIDI drag and drop.
Dynamic Pattern Grid: As Flexible as the Idea
The Dynamic Pattern Grid allows pattern lengths from 1 to 32 steps, freely adjustable per pattern. The key trick: patterns with odd lengths, so 3, 5, 7 or 11 steps, run against the DAW's 4/4 grid and create natural shifts that build up over bars and resolve again. That is exactly the hypnotic effect that Hardfloor and the early acid producers turned into their sound. Classic 16-step basslines work just as well, but once you know that living, constantly realigning groove, you won't want to go without it.
Page System: More Than One Bassline
One pattern, several pages. The Page System creates and chains multiple independent step pages inside a single pattern. That builds longer structures with internal variation without needing several pattern slots. Verse, fill, chorus, all organized in one pattern.
MIDI Import: Your Material, the Power of the KA-303
Sketched a bassline in the DAW, or an old MIDI file on your drive? Just drag it into the KA-303. The notes land in the acid grid immediately, and from there the composing engine takes over. Scramble shuffles the pattern, Mutate evolves it, slides and accents go in directly, Groove brings it to life. What would mean editing note by note in the DAW becomes a squelching acid pattern in seconds in the KA-303.
Editor Workflow: Resolution, Lasso, Groove
The pattern editor works at 1/8, 1/16 or 1/32 resolution, from short staccato notes through dense triplet feels to the classic acid timing grid. You select, move, copy and delete notes with lasso selection, using the same gestures you know from any piano roll. And the Groove Engine goes far beyond simple swing: Tight, Shuffle, Funk, Push and Laid Back each shift timing and velocity in their own way, from minimal human feel to a pronounced pocket. Combined with Density and Mutate, basslines feel alive.
SLIDE Straight From the Pattern
Between BPM and LEN sits a bipolar slide knob that controls the glide character right in the composing view. The 60 ms default is TB-303 authentic, fully left 20 ms for fast, accented slides, fully right 360 ms for long, drawn-out glides. It works in both modes and mirrors the slide parameter from the Angel Fish tab, so no tab switching while composing.
Two Separate Preset Worlds
Sound presets and pattern presets are completely independent. 158 factory sounds across all seven modes, from a clean sub to an inferno lead, meet 98 pattern presets — 256 presets out of the box. Every one of the original sounds now has a “(modulated)” twin: the same foundation, but in motion. Slow filter sweeps, breathing character parameters, living spaces, each one tuned by ear, slow, smooth, never nervous. In practice that means letting a pattern run and clicking through the sounds, hearing the same bassline in completely different timbres. No rebuild, no loss. Sound and notes live in two separate worlds and combine freely.
Unison Engine: When It Needs to Be Fat
Up to seven full synthesizer voices, each with its own filter, its own envelopes and its own slide processor. Continuous detune and stereo spread. From subtle thickening with two voices to a massive wall of sound with seven voices and 30+ cents of detune. Automatic gain compensation keeps the level consistent across all voice counts.
Everything On Board
Tempo-synced stereo delay with crossfeed and a darkening filter. Reverb based on the Signalsmith algorithm with room sizes from 0.3 to 5 seconds. A master limiter as a brick-wall peak limiter on the output protects against clipping, no matter how extreme you push resonance and distortion. Up to 8x oversampling for top audio quality, full MIDI CC mapping via right-click and MIDI Learn, dark and light theme. Multi-level undo/redo in the composing view (Cmd+Z / Cmd+Shift+Z), five new modulation targets in the pre-distortion filter, tooltips on every control, and a tidied-up tab order (Sound, Modulation, Composing, Settings).
Now Also as CLAP
Alongside VST3, AU and Standalone, the KA-303 now runs as CLAP, the open plugin format. For everyone working in Bitwig, Reaper or Studio One it is on board with no detours. Same engine, same sound, one more option.
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 should squelch, scream and move the dancefloor, this is for you.
Try Before You Buy
Not sure? No problem. Download the free demo and test the KA-303 in your DAW, with all features and no time limit. The only restriction: every 30 seconds a short burst of white noise fades in, and after 30 launches audio is muted. So you can try the sound, the Flavor Palette and all distortion models in peace before you decide. Once the KA-303 wins you over, you just activate your license key and the noise is history.
Formats and Systems
Formats: VST3, AU, CLAP, Standalone
Systems:
- macOS 10.14 or newer, Intel and Apple Silicon
- Windows 10 64-bit or newer
- Linux x86_64
The macOS version is signed and notarized, the Windows installer is signed.
Demo free. Full version 69.00 EUR including 19 percent VAT.
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.