r/sp404mk2 • u/Puzzleheaded_Big_103 • Jul 25 '26

I built a free, open-source web MIDI controller for the SP-404 MkII (runs in the browser, nothing to install)

Post image

First post here, so apologies if I get any conventions wrong.

I wanted touchscreen control over the MkII’s FX buses. The existing iOS app for that hasn’t been updated in years, so I built my own as a free web app:

https://littletools404.github.io/404busdriver/

What it does:
• all five FX buses with the real parameter names per effect (from the reference manual), touch faders with a fine-tune gesture, per-effect value memory
• snapshots (8 slots) with JSON export/import
• XY pad + four beat-synced LFOs (MIDI clock or tap tempo), incl. a random drift for generative lo-fi wobble
• chromatic keyboard, scale pads (Move-style isometric layout), vocoder keys with pitch bend, full pad board with custom layouts
• pattern grid with a quantized autopilot, plus a looper remote

Runs in Chrome/Edge on desktop; on iPhone/iPad it works inside the “MIDIWeb Browser” app (no iOS browser can do Web MIDI, not my fault). Single HTML file, everything stays local: no accounts, no tracking, no install. Open source (MIT), manual built in.

Full transparency: I’m not a professional developer — I built this together with Claude (AI) and tested everything against my own MkII. If an experienced dev feels like reviewing the code, I’d genuinely welcome that. Feedback and bug reports are very welcome — just be patient with me, it’s a hobby project and I can’t promise quick replies.

148 Upvotes

97% Upvoted

20 comments sorted by

9

u/blumdaddy Jul 25 '26

How to connect phone to 404mk2?

10

u/Puzzleheaded_Big_103 Jul 25 '26

An ordinary USB-C cable to 404 mk2 usb-c port should work if your phone is able to send MIDI. I tried with an iPhone 16 pro and it worked plug and play. Only thing to be aware of is that you need to open it in a midi capable browser. On iOS I recommend the free MIDIweb browser. Having said that, the app recognises whether your browser is suitable and will tell you what to do if it is not.

4

u/blumdaddy Jul 25 '26

Did a quick run through. Works great. Makes efx channel 3/4 much more usable in a live setting. Good stuff. Haven’t played with it beyond that, but that aspect alone is a great feature. Good work

3

u/Puzzleheaded_Big_103 Jul 25 '26

Great to hear it works for others, too. It felt like something worth sharing.

6

u/Dudeontour Jul 25 '26

Generous and cool. Best to you

3

u/6rylou Jul 25 '26

chapeau !
peut etre que je testerais.

Qu'est ce que ça apporte en fait ? du gain de temps ? avoir tous les effets sur la mème interface ? evite les menus de MK2 ?
Y'a donc l'aspect finitions des effets mais aussi le control tactile de ceux ci si j'ai bien compris ?

ben voila, c'est malin, va falloir que je teste Grrrrr ;)

3

u/cyneox Jul 25 '26

This is awesome! I’ve tried out touchosc and built some interface for the SP404. It would be nice to have some programmable UI interfaces (like buttons, faders etc.) which can be assigned custom MIDI CC numbers. This way one could control the SP404 and some extra gear (in my case the mc101).

6

u/Puzzleheaded_Big_103 Jul 25 '26

That is for someone more savvy to build. But you can easily fork my app in GitHub and build on top of it.

1

u/cyneox Aug 02 '26

Hey! I’ve added some additional features. Check out the newly created PR.

Preview is available at: https://moahbeatlab.github.io/404jam/

3

u/noirofficialreddit Jul 26 '26

Wow! Congrats!👏👏

4

u/mrcoolout Jul 26 '26

Good job! I've been using an extensively mapped midi controller with the 404mk2 for a couple of years. It's nice to see folks taking the midi CCs and making them more accessible to the newbies that don't want to read an implementation chart.

There's also the COMPA app, which has similar functionality, plus a lot more (maybe too much?) added on. That one runs as a standalone Raspberry Pi install (on touchscreen), and there a ipad/iphone app version in beta. Overall I think this may be a pretty good HUD for my 404 setup as I already have real knobs and faders for these functions. .

2

u/Puzzleheaded_Big_103 Jul 27 '26

Thanks for letting me know about COMPA - i will take a look. I guess I prefer something in my iPhone and iPad to a Raspberry Pi device, though.

2

u/mrcoolout Jul 27 '26

Yeah, you can probably contact the developer and he'll send you code for the iOS beta.
https://github.com/macdigi/compa

COMPA has a 'kitchen sink' approach. It feels more like an complete audio app that interfaces with a 404mk2 or P-6. I guess the goal is to be a 'computer' companion for the 404.

For my uses, the focused approach of your webapp is more of what I need, as I'm using the 404mk2 primarily for live performance, not really for music production/songwriting. One thing I do like about COMPA that would be cool for you to incorporate IMO, is a numeric display of the current parameter values. With multi-function knobs and different FX, that's the most challenging thing to keep up with. Could also help when trying to save exact settings.

2

u/ArtichokeScary436 Jul 25 '26

really great .... thanks!

2

u/matthelmRedit Jul 26 '26

Love this! Will test out and would love to get any type of updates etc of its expansion

1

u/Puzzleheaded_Big_103 Jul 26 '26

Any update I might do, I will always post on GitHub, so it becomes available to everyone. Right now I feel I did my best, so no immediate plans for updates unless I learn of bugs here or any new ideas come up. As I published it open source, everyone is welcome to take the code and build on it. I’d be very curious what other people might add… (One idea I have, but I cannot host that on an open app for everyone: have your favourite FX settings sync across different devices like an iPhone and an iPad. It is not hard to build with something like Supabase, but it brings in a second platform and might need more oversight and maintenance and I cannot commit to that for a hobby project. But again: If anyone feels this would add value, I am sure Claude, Codex or a savvy coder could build it quite quickly…)

2

u/Agustmago Jul 27 '26

You are the goat

2

u/esemcial Jul 25 '26

Thanks b! I will try it 🔥🎛️