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Nicholas Michalek edited this page May 14, 2026 · 8 revisions

OS-303 Firmware - User Manual v0.7

Most of the standard 303 sequencer functions work the same as the original or other clones, so you should be able to get started with any existing 303 sequencer tutorial.

This guide provides a quick-reference of button combos and menus specific to the OS-303 firmware.

Modes

Pattern Play

In normal Pattern Play mode, the NORMAL MODE LED will be lit up solid, and the currently selected pattern LED flashes in sync with the tempo.

Switch patterns using the 8 pattern selector keys, and the A/B buttons to switch sections.

If you switch patterns while the clock is running, the sequencer will wait until the end of the current pattern to change. The next queued pattern LED will appear solid, while the current pattern LED is flashing.

Pattern Write

In Write Mode, you can modify the current pattern in several ways. The familiar 303 sequencer programming functions are here:

  • Hold FUNCTION + press the STEP button (aka DOWN) to tap in the number of steps.
    • You can also hold FUNCTION + use the pitch keys to set the length directly.
  • Press PITCH to enter PITCH MODE; use pitched keys and modifiers to enter or edit Pitch steps.
  • Press TIME to enter TIME MODE; use the Time keys (aka UP/DOWN/ACCENT/SLIDE) to enter or edit Time steps.
  • Press FUNCTION to exit either PITCH or TIME mode.
  • Press TAP or BACK to advance the sequence with the clock stopped; hold to make edits in PITCH or TIME mode.

TIME Mode

For Time steps, the 3 familiar options are here: DOWN=Note, UP=Tie, and ACCENT=Rest There is also a 4th option: SLIDE=Ratchet, which acts like a Note, but retriggered as a fast triplet.

  • Hold CLEAR + press DOWN (Note) to reset all steps to Rests.
  • Hold CLEAR + press UP (Tie) to change all Ties to Rests.
  • Hold CLEAR + press ACCENT (Rest) to change all Rests to Notes.
  • Hold CLEAR + press SLIDE (Ratchet) to change all Ratchets to Notes.

PITCH Mode

Use the 13 pitch keys to enter notes, optionally holding DOWN/UP/ACCENT/SLIDE for modifiers.

  • Hold CLEAR + press ACCENT to clear all accents in the pattern.
  • Hold CLEAR + press SLIDE to clear all slides in the pattern.

Live Edit

If the clock is running in Pattern Write mode, you can make edits while the pattern is playing. Enter either PITCH or TIME mode, and use the keys to punch in new pitches; modify octaves, accents, and slides; or change Time steps.

Track Play / Write

You can compose chains of patterns in either Track Play or Write mode. They will only be saved in Write Mode (or if you switch to Write Mode and back after making edits).

To clear the current chain, hold CLEAR + press BACK.

To sequence a chain, hold FUNCTION and press the pattern select buttons, using A and B to switch sections as needed. Pressing one pattern key multiple times automatically adds up to 16 repeats, indicated as a 4-bit binary number by the LEDs of the C#/D#/E#/F# keys.

Transpose

From any mode, hold PITCH to modify global transpose. While holding PITCH, use the 13 pitched keys to set the root note, and the UP/DOWN keys to switch octaves.

While the clock is running, transpose changes are synced to the beginning of the pattern.

Config Menus

Global Config

Hold FUNCTION + press CLEAR for the global config menu. Each of the 8 pattern select keys/LEDs represents a toggle option:

  1. MIDI Note Receive
  2. MIDI Clock Receive
  3. MIDI Note Send (not yet implemented)
  4. MIDI Clock Send
  5. MIDI Program Change Receive
  6. MIDI Program Change Send
  7. (unused)
  8. (unused)

Press FUNCTION to exit.

Quantizer Menu

In either Play Mode, Hold FUNCTION + press PITCH for the quantizer menu. The 12 pitch keys/LEDs can be used to enable/disable each semitone. (The 13th key has no effect.) Pattern steps will round down to the nearest enabled pitch.

Press FUNCTION to exit.

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