JC-303
Key Features
- Uses the community-developed Open303 engine for a focused TB-303-style bassline voice.
- Provides a GuitarML-based overdrive section for pedal- and amp-inspired drive textures.
- Includes selected Devilfish-inspired parameters for more radical bassline shaping.
- Adds a 16-step monophonic sequencer with rests, accents, slides, ties, and adjustable pattern length.
- Can send the internal sequencer's MIDI output to the host alongside its built-in 303 engine.
- Supports VST2, VST3, LV2, CLAP, and AU workflows across Windows, macOS, and Linux.
Description
JC-303 is Midilab's open-source virtual bass synthesizer based on the Roland TB-303, built for the resonant, sliding lines associated with acid house and techno. Its Open303-derived engine focuses on the original's distinctive voice while adding modern host formats across Windows, macOS, and Linux.
The instrument combines the familiar bassline controls with a GuitarML-based overdrive section and selected Devilfish-inspired modifications, letting a sequence move from rounded bass to more aggressive, driven acid tones. The current release also includes a 16-step monophonic sequencer with accent, slide, tie, rests, editable pattern length, and MIDI output to the host.
That makes JC-303 most useful when the character of the line matters as much as the notes: automate cutoff and resonance, program slides and accents, then use the internal sequencer or a DAW MIDI pattern to shape movement. It is a focused bassline instrument rather than a general-purpose polyphonic synth.
Midilab's product page currently provides direct download actions for all three desktop platforms and identifies VST2, VST3, LV2, CLAP, and AU builds. The project is published as open source, and neither the official page nor the discovery listing presents a deadline, coupon, trial conversion, or other limited-time condition.
Frequently Asked Questions
What kind of instrument is JC-303?
JC-303 is a monophonic virtual bass synthesizer modeled after the Roland TB-303 Bass Line. It is aimed at the resonant, sliding bass patterns associated with acid house and techno rather than broad polyphonic synthesis.
Does JC-303 include a sequencer?
Yes. The current Midilab page documents a 16-step monophonic sequencer with rest, accent, slide, tie, pattern-length, record, and generative controls. It can play the internal engine and send MIDI out to the host.
Which plugin formats does JC-303 support?
Midilab lists VST2, VST3, LV2, CLAP, and AU compatibility. The available formats vary by platform, so use the appropriate download action on the official product page.
How does the overdrive section work?
JC-303 includes an overdrive section based on GuitarML technology. The official documentation describes it as using pedal and amplifier emulations, providing an integrated way to add more aggressive color to a bassline.
