An 1U rack unit with 8 audio loops remotely controlled via MIDI messages.

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Don't love audio effect emulation and want to rely on actual hardware to build your sound? Me too. That's why a few years ago I built this unit with 8 audio loops that I can control remotely by sending MIDI Program Change messages.

I really wanted to build something that felt like a "real" product, so I went from a prototype made from eBay parts to a finished product enclosed in a custom-designed steel case.

I'm using it for years now and figured it might be a good time to set it free :)

The project started when I started to ditch my big BOSS multi-effect pedal in favor of separated units. I first built a 4 loops version with an Arduino UNO, a custom PCB and a cheap relay board on eBay.

Sadly, by the time I finished the build, the 4 loops were already used and left no room for additional hardware. I then started to build an 8 loops variant but decided to build something that I could be proud of, something that could actually look like a real product, learning as much as I could in the process.

The following months were dedicated to building a rough prototype on a breadboard, based on an Arduino Micro that time because of its additional serial port. I also knew from the start that I wanted a 7 segments display on the device because... 7 segments :D

After some trial an errors, the major components were selected :

Those components were selected because I could find them on several retailers and had good datasheets. As I wanted to learn how to drive that was an important requirement.  The external chips also all use an I2C bus, which allowed me to use only one bus to rules them all.

After the schematics were done and tested on the same breadboard, I started making the PCB. This was the most research-intensive part as I was concerned about the noise I might introduce in the audio signal with a bad designed PCB. The form factor was also an issue as I knew that I would eventually build a custom made rack to enclose the thing so I started to build the case at the same time using Solidworks just to get the dimensions right.

After a few months of sometimes intensive work on the project, I ordered the PCB from Seeed. Some stupid small mistakes were left in the PCB so I needed 3 revisions to have something I was happy with (meaning without jump wires). 

All in all, I couldn't have made this part of the project without Dave's EEVBlog YouTube channel, from which I learned so many things. Kudo Dave, and thank you so much.

I soldered everything, solve some usability problem with the code and started to use my creation for real. Without a case, I had to stick the PCB to my cabinet using some blue tack.

Fast forward a few years and a new flat later, The PCB is still glued to the cabinet. I'am seriously bored at work and need something to drive my day and get a sense of accomplishment.

Instead of starting a new project, I decided to finish what I started years before and build a 1U rack unit for my beloved loop switcher. The most complicated phase of the project was to find someone, somewhere that would be able to build my case. Lots of people told me that I should 3D print it and be done with it, but you see, I wanted a finished product, and 19" is often too large to be printed at once (well at least at the time, I don't know where we at now with that).

That's when I found Protocase. They were a blessing and a curse at the same time. A blessing because for someone who didn't know anything at building that sort of stuff, they were very comprehensive. A curse because they can build your things on demand, using self-clinching fasteners and printing them. That was too good an opportunity for someone who wanted to make (or at least try to) something with the same level of quality than an actual piece of gear that could have been bought from a shop. So I restarted the rack enclosure from scratch using the new tools at hand.

I was really pleased with the quality of the build, and I now have a not really home-made but at least fully home-designed rack unit in my cabinet that I'm using every single time I play guitar for the last...

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  • 1 × ATmega32U4 Microprocessors, Microcontrollers, DSPs / ARM, RISC-Based Microcontrollers
  • 1 × AS1115-BSST Power Management ICs / LED Drivers
  • 8 × V23079E1201B301 Switches and Relays / Electromechanical Relays
  • 8 × NSJ8HC Connectors and Accessories / 6.35mm Jack Connectors
  • 2 × NRJ4HF-1 Connectors and Accessories / 6.35mm Jack Connectors

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Dan Maloney wrote 01/22/2019 at 15:56 point

WOW! You really nailed it with form and function! And that documentation is pretty amazing too. You're right about that Protocase outfit, too - that could be a dangerous bit of information to have.

Really, really impressive project. I hope you'll be joining us for the Open-Source Synthesizers Hack Chat tomorrow. Seems like the discussion will be right up you alley.

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Bertrand Lemasle wrote 01/22/2019 at 22:07 point

Hey Dan! Thanks a lot for that comment :) I'm new at so I still have to figure out how things works and how to work with the community but I'll look into it for the chat if I can join (UTC+12 atm) !

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