I'm building a synth.

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weasel79
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I'm building a synth.

Post by weasel79 » Fri Jan 31, 2020 8:04 pm

Hey guys
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.
The digital part is mostly based on the axoloti platform which supplies a graphic patching environment like max4life or puredata, but also allows low level c coding at any point. Incredible system, if you don’t know it yet go check it out. Due to CPU limits I had to split up the whole synth on 4 boards, one for voice handling, CV control of the analog devices, OLED displays, and then 3 voice boards that do 2 voices each. The control inputs in form of currently 40 endless rotary encoders, some buttons and a fatar keybed are being handled by two midibox systems. And finally there is a teensy in there to control the RGB LED rings around the rotary encoders and some extra OLEDs. Everything is wired up via good old DIN MIDI, mostly one way only. Presets are stored on the midi box side.

Here’s a very basic and somewhat old signal flow diagram:
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The planned modulation matrix:
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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.
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Here are some pictures of the last iteration of my prototype enclosure and frontplate:
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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:
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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:
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“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.
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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...
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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.
There’s a bunch of lower priority features I wanted to add at some point, like a smart arp thing, a simple sequencer/looper maybe, also a joystick and ribbon controller. Maybe a super simple organ-like drum machine. And I have a bunch of leftover CV I/o from my digital controlled analog chain, would be nice to route these out as external CV patch points, just to show off. But I will attack these as bonuses once I approach completion. Also super long term I am aware that I have really inefficient MCU CPU use and could probably squeeze this on half the boards. Like, midibox could control the LEDs directly and I could save the teensy. I just went the path of lowest resistance for now.

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:

:rastanana:

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revtor
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Re: I'm building a synth.

Post by revtor » Fri Jan 31, 2020 8:46 pm

Woah!! Awesome work!! Bravo, keep it going!!!
Fellow North Jersey Synthaholic

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Red Electric Rainbow
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Re: I'm building a synth.

Post by Red Electric Rainbow » Fri Jan 31, 2020 8:50 pm

major props
TOO FAR GONE

Lemmy
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Re: I'm building a synth.

Post by Lemmy » Sat Feb 01, 2020 6:02 am

Great stuff. Post some sounds too if you get a chance. Or share your axoloti patch!

Did you hand-solder the leds for the encoder displays, or get them fabbed for you? Any problems with bleed through from neighbouring leds, or is that not a priority?

You are clearly a good project manager to get it to this stage, so I have no doubt you will finish - hope you will document the rest of the build and share it with us...

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guest
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Re: I'm building a synth.

Post by guest » Sat Feb 01, 2020 9:08 am

thats intense! im looking forward to seeing the progress.
openmusiclabs.com

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devinw1
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Re: I'm building a synth.

Post by devinw1 » Sat Feb 01, 2020 2:37 pm

Fuck, dude. Hellofa project! :tu: :tu:

Looking forward to updates!

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Flareless
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Re: I'm building a synth.

Post by Flareless » Sat Feb 01, 2020 2:46 pm

Outstanding work :yay:

Thank you for taking the time to document it for us in such detail!
Rich

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What can this strange device be? When I touch it, it gives forth a sound - Neil Peart

ashleym
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Re: I'm building a synth.

Post by ashleym » Sat Feb 01, 2020 6:34 pm

Pretty all round incredible.

I love the different LED ring set ups. I had never thought about the options these give and you appear to be working through. The red LED at midnight for panning type of controls, a single point or an arc that fills up to show a value or position. That solves a lot of ergonomic problems.

Colour coordinating the panel will be a real winner. To be honest, the wooden temporary one works for me.

i am very glad to see you are using nice switches. I like toggles as much as you like patch cables.

040B
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Re: I'm building a synth.

Post by 040B » Sun Feb 02, 2020 6:37 am

Awesome project.

weasel79
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Re: I'm building a synth.

Post by weasel79 » Mon Feb 03, 2020 9:25 am

Thanks for the kind words,

@lemmy i had the LEDs assembled by elecrow. i once soldered a single SMD IC and i'm pretty sure that was my one and only lifetime experience. also the sheer amount would have taken me months to manufacture without a pick and place machine etc.
regarding bleed through, i was trying to figure out a shielding mask for a while on the 36-led prototypes, see here
viewtopic.php?f=17&t=218357
but after trying those tiny light pipe stubs from aliexpress i am totally happy the way it looks. very slight bleed to the directy neighbouring ones, but the contrast to "actually on" is so obvious i don't bother. will get pictures soon.

@ashleyism i am also just starting to grasp the possibilities of these high-res rgb rings. sequencers, fades, decay times, all coming up one of these days.

weasel79
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Re: I'm building a synth.

Post by weasel79 » Mon Feb 24, 2020 8:01 am

ok so here's a little update of what i did these past days:

- enhanced the frontplate w more encoders, buttons and displays:
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the empty slots top left and top right are probably gonna be removed. i think i'm at the somewhat final amount of encoders now. need to add some more pusbuttons here and there, and settle on a better pushbutton model. the c&k are way too wobbly. right size OLEDs also arrived today so i'll make an updated verison of the OSC segment frontplate later today. and some single 5mm-led shapedd ws2812 for the button stati.

- swapped the old PSUs for two linear +/-12V ones (clicks&clocks) - final model will most likely get a perfectly matching hinton PSU
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and with that, redid most of my power/ground distribution:
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- added a fifth axoloti board to supply two OLED with accurate OSC waveforms. third osc and lfo waveform OLEDs are being supplied from the poly control axoloti, i2c and the cheap ssd1306 limit me to 2 screen per board. don't wanna hook up OLED to the voice board axolotis, for CPU/RAM and diggital noise reasons.

- 2.4" OLED and supplying teensy 4 for the main menu screen - might add another one of these for a scope/spetrum OLED (currently sitting outside the case, top left on first pic)
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this uses one of the super neat because tiny midi boards from elektor that i just discovered, saves so much space and clumsy DIN connectors...

- received the pedalpcb eproms for FV1 chip, program select works via axoloti, CV control currently being worked on...
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- made a new module frontplate for the max11300 codec device, used to remote-control my analog chain from the digital realm.
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- made a diy octoled adapter to split up the adressing of 1000+ ws2812 LEDs on 8 serial lines, controlled by a teensy
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- added new diy MCP3208 board to the midibox for wheels, aftertouch and stick.
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- on the software side, i implemented the modulation matrix to about 80%, 8 sources and around 15-16 destinations so far. control is a breeze with the coloured buttons on the left side acting as a selector, if you press LFO2, all the available desitnation knob LED rings light up in yellow and can be set directly.
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the scaling of some of the sources is still off here and there, i soon have to spend a day or two really finetuning all the software ranges. of everything.

- settled on oscillator models: multi-VA on each osc, then 6 different MI algorithms spread amongst the 3 oscillators (2x wavetable, csaw, fm, fluted, blown) plus of course the all-important sample player.

- started on the gfx system for the main teensy OLED, drawing envelopes and stuff

- learning fusion360, coming from sketchup, so i can directly make the CAM files for my CNC router (which itself is still stuck in production/delivery...) and then start figuring out the internal mounting of all this crap..


my biggest issue currently is still the power/noise situation. overall noise levels improved dramatically after installing the aluminum busbars and thicker gaguge wires as recommended by Mr. Hinton. So, in normal use, while not perfect i'd be at acceptable noise levels by now. But as soon as i connect any of the CV inputs of my max11300 module to any of the analog gear, i get substantial new digital noise. clearly audbile when the CV is set to 0 or 10v, even worse anywhere in between (worst in the first third of the CV range). i randomly experimented with changing the power and/or ground supply for both the max module as well as its controlling axoloti, but no success so far. the idea is to keep the fully analog and the digital PCBs on seperate power circuits, but obvisouly that leaves me with all the mixed mode modules that do a bunch of digital communication but also are in the analog chain.
i'm gonna take another couple days to try and trouble shoot this noise, and otherwise try and get some commercial standalone midi/cv converters that i can decouple from my digital system via DIN midi. even though i am totally not sure that the max board actually is where the noise gets inserted. might come form the axoloti boards, just something gets worse when i connect the CVs. electronics still remain a mystery to me. fwiw, a similar axoloti/max11300 combination works just fine in a much smaller build in my studio...

also, i am looking for better wheel mechanics, and some debouncing/scaling/filtering of the wheel pots & aftertouch. currently aftertouch and pitchbend are easy to overflow my system with too many midi messages.

thats it for now, if anybody has some more ideas regarding the CV-added noise, i'd be very thankful to hear them. do i need those fast galvanic i2c/spi isolators?

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BadPixel
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Re: I'm building a synth.

Post by BadPixel » Mon Feb 24, 2020 10:56 am

Massive jawdrop!! :jawdrop: Thank you for sharing :tu:

ashleym
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Re: I'm building a synth.

Post by ashleym » Mon Feb 24, 2020 6:13 pm

:tu:

“Empty slots” - no. Space for some tweeters and/or some sort of funnelled output for the main speaker drive units if you’re using full range units.

Fantastic work and progress.

Dave.ID
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Re: I'm building a synth.

Post by Dave.ID » Mon Feb 24, 2020 6:22 pm

Woah, I've no idea how a full size synth project takes shape but at what point do you think you'll be able to post sound demos? Not necessarily of a finish synth but at a prototyping level.

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plushterry
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Re: I'm building a synth.

Post by plushterry » Mon Feb 24, 2020 6:24 pm

This is great. What a beast of a synth, makes me feel a bit better about some of my monster projects.

weasel79
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Re: I'm building a synth.

Post by weasel79 » Tue Feb 25, 2020 6:09 pm

ashleym wrote:
Mon Feb 24, 2020 6:13 pm
“Empty slots” - no. Space for some tweeters and/or some sort of funnelled output for the main speaker drive units if you’re using full range units.
hah the little tangband fullrange you can seee in some of the pictures was originally meant to go in the synth enclosure, but given how much noise i have already i don't think i want a big amp, moving parts and magnets in there...
Dave.ID wrote:
Mon Feb 24, 2020 6:22 pm
Woah, I've no idea how a full size synth project takes shape but at what point do you think you'll be able to post sound demos? Not necessarily of a finish synth but at a prototyping level.
yeah i meant to do a video with sound but keep pushing it back "until i added this one feature". soon™.
that being said though, the actualy synthesis part has been basically done for a while now, just tweaking. and of course it sounds ridiculously good, bestest synth in the worldddddd.

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sebiiksbcs
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Re: I'm building a synth.

Post by sebiiksbcs » Fri Mar 27, 2020 9:00 am

I like the SAVE LOAD WHAT NO labeling. All this won't be worth it if you don't keep that.

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