Open500
Firmware for MPC500 (Akai Professional)
Loader injected into the stock MPC500 OS 1.31 that runs add-ons from WAV files: master FX, grid sequencer, auto chop, sample FX, pad tools and input thru.
by M45K
- Distribution
- Browser installer (WebMIDI / WebUSB)
- Requires stock
- 1.31
- License notes
- The project site calls Open500 free and open source, but the repository has no LICENSE file and does not include the add-on source.
- Source
- github.com https://github.com/M45K/open500
- Homepage
- m45k.github.io https://m45k.github.io/open500/
- fx
- sequencer
- sampler
- loader
Description
A 1.3 KB loader is written into an unused area of OS 1.31 and hooked into the main loop. It reserves 896 KB of sample memory for add-ons and effect buffers. Add-ons are WAV files with a signed relocatable payload, managed by a HUB add-on that holds up to eight at once. The bootloader is never touched and flashing the original OS removes everything. The repository contains no Akai code. Tested on one MPC500 with OS 1.31 according to the README.
Install notes
Drop the official OS 1.31 file into the web page to add the loader locally in your browser, flash the result, then load add-on WAVs from the sample list.
Version history
| Version | Date | Notes |
|---|---|---|
| v11 (loader v10) | 2026-09-29 | Adds Master FX, Grid Seq and Input Thru. |
| v9 | 2026-09-26 | Loader with 8 add-on slots and autoload, Pad Tools, Sample FX chain. |
| v8 loader | 2026-09-24 | First site, in-browser patcher, HUB and Auto Chop. |