3rd Party Unofficial Sequential Prophet‑5 / Prophet‑10 Rev4 Firmware Mods

via GitHub

prophet-rev4-mods

version 2.3.0

An arpeggiator and a polyphonic step sequencer for the Sequential Prophet‑5 / Prophet‑10 Rev4, added to Sequential's own Main OS 2.1.0 as a firmware patch. You apply the patch to your copy of the official OS in your browser and install the result over USB like any OS update. Everything is controlled from the front panel.

Built on someone else's idea. The notion of patching the Rev4's firmware, and the proof that it works, belong to another person: an arpeggiator mod that circulated privately showed the way and set the control conventions this project keeps (A440 as the arp button, Bank/Group for modes, Glide Rate for tempo). This project began as additions chained in front of that mod and makes several additions — the polyphonic sequencer with rests and ties, the keyboard octave shift, tap tempo, patch memory, tempo divisions, and more.

New here? The walkthrough takes you through every feature at the instrument, step by step; the manual below is the reference.

Not affiliated with Sequential. This is a hobby project that modifies the instrument's firmware. Installing a modified OS is at your own risk and may void your warranty. Only the project's own code, tooling and notes are published here; Sequential's OS files are not redistributed, which is why you supply your own copy.

What it adds

Arpeggiator — Up, Down, Up/Down, Random and Assign (the notes in the order you played them), 1–4 octaves, HOLD latch with re‑latch, tempo 40–300 BPM by knob or tap, MIDI clock sync, thirteen note values from four bars to 32nds including triplets and Prophet‑6‑style swing.

Polyphonic step sequencer — a second generator beside the arp: up to 512 steps of chords (up to 10 notes each, each note with the velocity you played it at), rests and ties, recorded from the keyboard or MIDI with undo. Start it and play over it; transpose it from a key; run it forward, backward or pendulum — or arpeggiated: the sequence becomes a chord progression the arpeggiator plays through, a quarter note to four bars per chord.

Keyboard octave shift — ±2 octaves from the panel, applied to the keys, the arp and MIDI Out.

Patch memory — the arp's on/off, mode, octaves, note value and gate are saved with each program, and so is the sequence: a Record on a user program stores the recording with its style, order, note value, gate, chord length, transposition and generator selection in a block of the synth's own flash, and loading the program brings it all back — on the instrument, no computer involved. Changing programs never stops a running sequence; a program with a saved sequence takes over at the next step.

Nothing else changes: with the arp off the synth is stock, and the whole patch can be bypassed at power‑on.

Verified on a Prophet‑10 Rev4 (October 2026), including the 2.0 sequencer from the panel; the spec marks the few paths not yet tried on hardware (the sequencer under MIDI clock, recording from MIDI‑in, the pedal as rest/tie). Sequential's A440 tuning‑reference tone is still there — on A440 + HOLD, since A440 itself is now the arp button.