So end of march last year I started building a rather big digital poly synth with a couple of analog effects. Nobody asked so sorry for the endless novel, but with the twelvemonth coming closer I figured it would be a good time to start documenting my build a little bit, for others to possibly learn something (if only how to not do it) and also for me as a reminder and motivation to finish it. Because out of those last 10 months the project has been dormant for at least half of the time. And we all know how easy it is to just add something to the big pile of unfinished ideas…
So here we go, I guess I’ll start with a basic description of what my synth currently is:
- 6 voice polyphony, 3 osc per voice, with:
- various VA waveforms with basic FM and sync possibilities
- unique-per-oscillator extra synthesis models, mostly based on mutable instruments algorithms (extra FM, basic wavetable, physical modeling etc). OSC1 will have 2, OSC2 two others, and OSC3 a third set of 2 unique models.
- Most importantly, a bunch of my own lofi one shot ableton samples for quick convenient vintage sample vibes and character, including noise and drum samples for transients.
- All synthesis engines are macro-ed down to 2 main parameters.
- Overdrive/waveshaper per oscillator
- Going back and forth whether I wanna add a dedicated sub and/or noise osc. Prolly not.
- VCF & VCA with adsr envelope, plus extra mod adsr.
- 2 LFOs, one global, one per voice, including several chaotic entropy detuning “waveforms"
- Additional global detune/chaos modulators for vco pitch and filter drift.
- Fixed Modulation matrix, roughly 10x10 sources x destinations. Dedicated “map” button for each mod source which lets you dial in the amount on each destination encoder.
- All parameters (>300 inclusive mod matrix) communicated and stored in NRPN for higher resolution over 7bit CC.
- Digital overdrive/saturation on the sum of each 2-voice board
- Several analog saturation circuits, currently based on black market modulars color palette module
- 1-2 FV1 multi effect units w analog routing/mixing
- In review: Spring reverb with driver and recovery circuit, analog Juno chorus
- Around 40 ALPS rotary encoders and a 61 key fatar semi weighted TP8/S with aftertouch
- Several small OLED displays for visual feedback, ie. OSC/LFO waveforms.
Here’s a very basic and somewhat old signal flow diagram:
The planned modulation matrix:
A screenshot of the patch for one synth voice in Axoloti. A lot of these objects are custom coded or heavily altered so it’s kind of hard to understand what it does from looking at it. As I mentioned before most parameters are controlled by a big global NRPN lookup table that gets updated via midi. Also this is a rather old screenshot, quite some changes since then.
Here are some pictures of the last iteration of my prototype enclosure and frontplate:
The design is and arbitrary and old random sketch so ignore alignments and style, but this is roughly what my final parameter/knob arrangement will look like:
Current prototype front plates were done on a laser cutter at the local makers pace, but I now have a proper CNC machine incoming which will do the final aluminum front plate. Design and enclosure shape are still under heavy review. The shape will remain roughly the same but materials and front plate design will be much different, I was recently dabbling in some much more color intensive, “artistic” designs because I think color is such an important cognitive grouping/orientation dimension that shouldn’t be left out. At least some coloured engraving like this:
“Inside” everything is still wired up only with cables. Midibox with 10pin IDC, all other 2-3pin connections have recently been moved from Dupont to slightly better JST XH/EH connectors, will start making some basic routing PCBs these days. I tried to avoid DIN midi and go direct serial or USB MIDI for a while but couldn’t get it to play nice. In retrospect I am happy about the optocouplers because probably less EMI/ground loops.
Long term I plan to get rid of any commercial eurorack modules of course, this was just very convenient for development. I really dislike patch cables… For that I have to finalize my analog signal chain and then make a big PCB with all buffering/summing and VCA circuits soldered in, reducing cable length. And change all remaining cables to well shielded ones instead of tiny 22awg Dupont madness.
And a diagram of my power supply situation - LEDs and their controller are currently on their own PSU which helped a lot with EMI. I had a local synth repair pro over this week for some consultation on my power/analog signal situation and i am also in touch with MWs own PSU god Mr. Hinton...
I spent a lot of time last summer to develop these RGB LED rings with the help of another actual electronics guy. They came out really great I think and are one of the greatest features to me. There’s sooo many nice and intuitive ways to display information, I am only starting to explore that dimension. Here’s a video that shows some of the first display functions I wrote, have more and much nicer ones by now:
Here’s my current most-important-to-do list, not in any particular order:
- Fix the power distribution/supplies: currently I have one +/-12V/+5v meanwell for all analog stuff and most of the MCU boards, and a 5v wall wart for the LED rings and their controller MCU. I have to add another linear power supply and better/new busboards/power PCBs. Figure out a general grounding and power supply scheme cause there’s quite some EMI and other noise currently, especially when digital data lines like SPI are being used actively.
- Update the frontplate, I want to take the mixer section out of the oscillators 4xring set into a dedicated mixer section
- Along the first two points I have to learn more about isolation and shielding within a complex digital/analog system like this. And then:
- Add Pitchbend/Modwheels, more (illuminated?) prototyping buttons & status LEDs.
- Re-arrange the MCU modules within available space and start finalizing internal mounting options.
- Update the encoder mapping on midibox side, only recently scaled up form 24 encoders to 40.
- Update global nrpn mapping to new order of encoders/parameters
- Extend modulation matrix on Axoloti side - currently only implemented for osc1 and lfo1/2 as proof of concept
- Re-implement analog signal chain, I significantly cut this down after the most recent system breakdown...
- Detailed planning of the final enclosure in fusion360
- Finally decide on a goddamn pushbutton model and find some appropriate encoder knobs.
My main motivation for this synth was not really one of the two reasons I think most people go DIY: to either make something better, that hasn’t been there before, or to make something cheaper than what’s commercially available. My mission was rather only to build my perfect personal device. I spend a lot of thought the last few years about insipration, technical limitations and their benefits, interface design etc and studied a lot of old synthesizers and just want to build the machine that inspires me the most to write great music. It’s not supposed to be a sound design mega monster like a Quantum, neither a basic rompler without any editing like the mellotron 4000d. Just something very inspiring and immediate that doesn’t overwhelm me with too many possibilities but also doesn’t limit me completely. In a way it also resembles my personal ableton production workflow a lot, where i layer several totally different sounds and glue them together with destructive plugins and then map everything to a couple fun macros.
Also duh I wanted it to look good, so, fancy LED rings.
I hope to keep this thread updated with progress pics and info, but for detailed technical questions like my power situation I will soon make a couple related threads so others can find those questions easier. If anybody has any questions, shoot. There’s very few things I enjoy more these days than talking about my synth.
To wrap it up and waste a final bit of your bandwidth, here's a link to the imgurl album with all pics in high res, plus a couple extras: