EHX9MIDI - midi control of EHX 9-series pedals

[pruttelherrie]

Hi guys,

I managed to modify an Electro Harmonix C9 pedal to be controlled over MIDI. Actually I finished that over a year ago, but never got around to document that. So here it is!

The pedal in action:


More build pics can be found here:
https://imgur.com/gallery/W1GQnxx

And I made a small demo video here:
https://youtu.be/IeoBxncWoLM
Since I can't play decent guitar even if my life depended on it, it's a dry guitar soundfont played by Reaper, and also some automation (Program Changes and Control Changes) by Reaper.

I'm planning to add more information here later this week, since I'll be staying at home anyway with this COVID-19 thing doing the rounds.

One thing I've been thinking of adding to the Bluepill firmware: LFO's to control the parameters. There's actually CC's reserved for that kind of functionality.
Actually, the firmware needs a big overhaul since it's more or less a Quick'n'Dirty amalgamation of testfunctions and it needs some real structure, but for now it works so I'll leave it at that ~~~

[bluebunny]

Wow. 

[Firesledge]

Impressive

[micromegas]

Hey! This looks super cool (and your photo tutorial is really nice). I always thought these pedals would definitely benefit from some kind of MIDI compatibility.

I just noticed that a company from the Czech Republic commercialises a similar solution (they even tried to fund it through an Indiegogo campaign). Here is the link, just for reference: https://www.microdesignum.cz/EN/Products/MIDI-Modules/MIDI-Control-for-Electro-Harmonix-x9

I wonder if something similar could easily be done with other EHX pedals, like the Superego...

[pruttelherrie]

Thanks all!

I always thought these pedals would definitely benefit from some kind of MIDI compatibility.

Indeed. That was the whole purpose of this exercise: when you use more than one setting per set of even per song, it sucks to have to bend over and change settings or to have to buy extra pedals.

I just noticed that a company from the Czech Republic commercialises a similar solution (they even tried to fund it through an Indiegogo campaign). Here is the link, just for reference: https://www.microdesignum.cz/EN/Products/MIDI-Modules/MIDI-Control-for-Electro-Harmonix-x9

Nice! I didn't know of that solution. They offer more MIDI control solutions I see. From what I saw of their photo-manuals, they basically do the same as what I do (see below).

I wonder if something similar could easily be done with other EHX pedals, like the Superego...

From what I can see how the Superego is controlled: "I think so" but we would need to see some gutshots and/or measurements to be sure. It looks like there's 4 pots and 1 switch, and EHX's modus operandi is to have platforms from which they build lots of different pedals so I expect the Superego to share a lot with the 9's.

I started with probing the controls, to see if I could substitute them from an MCU. The pots turned out to be 0-3.3V control signals, but the switch was more difficult. As you can see from the photo below, there's lines with pull-ups going to the DSP. But the switch was placed on the wrong side of the board so the common of the switch was not connected to GND but to one of the pulled-up lines, and another setting was tied to GND. Simple reading of the lines was out of the question, so they did a rewrite of the DSP code that sort of "polls" the lines to detect which one is selected.
After a bit of experimentation it turned out that pulling the lines low and high in the right order can tell the DSP what program to run.



The photo below shows the sandwiched PCB partly installed. There's a small mistake in the VCC wiring so there's a small patch wire.



Last year I bought a Synth9, I'm planning to convert that one as well and make a walkthrough for people who want to do the same. Modifying the Mono Synth is also on the program later this year. Then I'll have a couple of boards left, if anyone wants one drop me a PM.

pruttel.

[pruttelherrie]

And here's the schematic of the sandwich board, pretty straightforward. My first project with KiCAD
Should have added the MIDI opto, oh well.

[pruttelherrie]

And the opto. I used a Sharp PC900, but others can be used as well, like 6N138.

[micromegas]

But the switch was placed on the wrong side of the board so the common of the switch was not connected to GND but to one of the pulled-up lines, and another setting was tied to GND. Simple reading of the lines was out of the question, so they did a rewrite of the DSP code that sort of "polls" the lines to detect which one is selected.
After a bit of experimentation it turned out that pulling the lines low and high in the right order can tell the DSP what program to run.

That's interesting, I guess that's maybe their way of detecting a tri-state? 3.3v, GND and floating?

And here's the schematic of the sandwich board, pretty straightforward. My first project with KiCAD
Should have added the MIDI opto, oh well.

Thanks for the photos and the detail explanation (Kicad is GREAT btw).

I have a 2nd hand superego arriving in the mail in the next few days. I'll open it up and take some pictures, I imagine their approach wasn't too different to the X9 series,