Axoloti interfaced with a Moog-style modular synth

modular
#1

I was asked to re-post the following to 'your projects' in hopes of sharing with more users. I have a large modular synth and became intrigued by the potential of the Axoloti being part of that system. Catch is, the modular runs audio at typically -5v to +5v, or more, which appears hazardous to the Axo. Also, most control voltages run 0 to +5 which also gets into trouble with the gpio inputs. So I needed to build an interface board to protect and level shift the various ins and outs to the Axo. Luckily, my modular is based on Moog units so the Axo board easily fits in a module space...

re-post:
Some progress made. The audio in (at the stereo jack) will take -1.65v to +1.65v before clipping which is consistent with the gpio inputs of 0 to +3.3v. For the gpio inputs I found some low voltage, rail-to-rail opamps and am amazed how well they work... never used them before. They're powered directly off the Axo board's gnd and +3.3v so any excess signal into the opamps clip perfectly at 0 and +3.3v. The bipolar audio input was trickier so I just ran them into 'normal' opamps powered at +-15v and set the gain such that they clip just after my desired, useful levels. Then let a pot take the signal down to safely enter the Axo's inputs. The dual Schottky diodes are probably not needed but they were cheap and might provide a little safety? At least now I'm comfortable plugging anything into the Axo. Which reminds me, I need to quit building stuff and start playing with it. :wink: Thanks again!

Schematic Design_ Axoloti Interface.jpg937x1280 198 KB

Front.jpg630x1024 161 KB

Side-Axoloti.jpg682x1024 206 KB

Side-Interface.jpg695x1024 227 KB

#2

Update: the schematic on the previous post had the twelve Schottky diodes mislabeled. They are now corrected to: 1N5818. Sorry for any inconvenience!

#3

Wow, very impressive!

What kind of patches are you using with this?
And can we get an audio example? :slight_smile:

#4

Thank you dreamer! To answer your questions, I'll use one of my primary skills: making short stories long. :wink:

For the last 30+ years, I've been an aerospace robotics engineer specializing in software design and basic electronic design. Before that, I lived the life of a pro rock musician... guitars, keys, and synths. Where this is going is I'm now 67 years young and am trying to retire from my tech work and get back into my love of music. After all this time, that's harder than I would have expected. I find myself having more fun building these things than actually using them!

As to patches, I'm new to this and still wandering through the factory and community samples just to get a feel for what can be done. But as a C and assembly programmer, this all looks like way too much fun. It just takes time and focus.

As to an audio sample, I stumbled across a patch by Mr. Matthew Tyas (mtyas) that has a stunning chime-like sound that should work well in conjunction with a standard synth tone to sound like a music box. The melody will be panned through the stereo field on a note by note basis using a hardware sequencer with a delayed copy of the notes also panned differently by another sequencer. This plays out through the ending of an older song I want to remix... someday. If I can get happy with just the 'panned music box sequence', I'll post it. I'm also so new here I don't really know where to post such a thing!

#5

It looks very nice indeed!

#6

Fantastic.

I can imagine a nice collection of vintage and other (diy) gear that you can use to influence, or get influenced by, the axoloti.

#7

Yes! I come from the old-school analog world but my days in tech work makes me appreciate what the digital domain can offer. They are both different but each has it's own value. Merging them seems the best of both worlds. And as a result of my early tests and hearing a couple of community patches, I've already ordered another Axoloti board.

This could become addicting! :wink: