Poly Zero synth build

Front panel of the new “Poly Zero” 8 voice RP2040 based synth is coming alive, all the mux section wired up, next the buttons and LEDs. For some reason I decided to go with 2 displays. I had the crazy idea of showing a group of parameters, say LFO on the small display whenever any LFO control was touched etc.


Teensy controller for my latest synth, 3* 16 bit DACs for 8 CVs, 8 velocity CVs and 2 control CVs for the 32 channel demux. An 8 way shift register for gates. Pretty much untested at the moment, I know the DACs work and the gates, but how stable it will be when attached to the demux board I don’t know. Putting a 40 way ribbon from this board to the motherboard with the demux and voice cards onboard. I ran out of pins on the Teensy so I connected to the 7 spare pins under the board, tricky but well worth it.


I must be getting more and more stupid as I get older, I keep finding functions and the required buttons missing from this build, I forgot the poly/mono/unison and note priority buttons, then today I realised I’d forgotten the multi trigger button for the LFO delay. Fortunately there was enough space on the front panel and spare shift register connections to accommodate them. It’s connected up to the demux board now and seems to be spitting out the correct voltages from the demux, the LFO speed is working and the led flashes. And the 16 DCOs arrived today, time to make a DCO board.

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Wow, I can’t explain why this looks so awesome; “monolothicness?”

& I appreciate you admitting you forgot critical bits, so folks like me know the goal doesn’t have to be NEVER make mistakes, but identify 'em before anything cooks & learn how to incorporate a last-minute fix!

Edit: Also, do you have any shots of the solder side? I can’t tell if I like perfboard/stripboard better, and I’m curious how you made your connections.

This is typically what it looks like under neath a board.


Brilliant! Do I want the poster or the T-shirt? I just love your point to point wiring shots. Were you one of my kids this pic would go on the fridge door!


Very nice.
Is this using two RP2040 based DCOs per voice?

Yes it is, rather wasteful, but cheap enough

Partially constructed dual DCO voice card, can produce 24 waves per DCO with modulation of the wave, frequency, tuning, octave shift, glide.


:dizzy_face:Wow, creating these connections must be a very special type of meditation… how often do you have to correct mistakes?

I make loops of cable for common connections, so for example a lot of these cables are made up of 8 sections but one piece of wire.

Very rarely make a mistake nowadays, forget things yes, mistakes not so much


Finished it off now, added the CV control circuits and the 2nd bank of DCO wiring.


Are these direct digital DCOs? How they compared to the pico-dco digitally controlled analogue ones?

These are individual DCOs, basically modified Hagiwo $9 VCOs, added midi control and glide but the functionality of the waves is still the same.


Ahh, thank you. I should have a closer look at Hagiwo’s stuff.

So here is a video update, sorry about the repetitive arpeggio.


Added the FV-1 effects processor to the build now, it’s nearing completion but still needs a lot of programming.


Sunday update, despite numerous attacks by Russia, probably 3 overnight of missiles and drones, plus at least 5 attacks today, I’ve almost completed the synth. I was just tweaking the pitchbend options as at the moment I could only bend the notes a tone, so now I’ve tweaked that and reprogrammed all 16 DCOs to respond to an octave each way. Menus are much improved and all the MIDI functions such as aftertouch, modulation. Pgm change and pitchbend all function as they should, parameters are all accessible over MIDI as CC messages and it transmits MIDI CC for all controls too. What I like about this is it is modular, the boards could in theory be swapped for some other design. There is the demux board which contains 32 CV channels, 24 shift register outputs, a noise source, two LFOs, only one used here. The next board is the DCOs, 16, for 8 voices, dual oscillator. Then 4 dual filter, adsr, VCA boards with onboard mixers for the waves, up to 8 inputs but only 4 used. Then finally there is the final VCA/effects board which has a programmable digital effects unit, stereo volume and amplitude modulation and muting circuitry to avoid the power in thump. The filters and demux boards are from the poly kit 16 synth which saved a lot of time when putting this together.

Teensy 4.1 controls the front panel and handles all the MIDI messages and outputs CVs for the pitch (only used for key tracking), velocity, bend and all control CVs from 3 * 8 channel 16 bit DACs.


another epic build. well done


Saturday update, hard to think that I started this front panel over 6 days ago, but a bad bout of food poisoning has kept me away from the workshop until today. Bad burger last Sunday and I’m still not right. So hopefully this is only temporary until my good friend Bill Wilkinson creates a lovely front panel, I mounted everything too high on this one so it’s a bit tight. But like I said, temporary. I didn’t do the LED holes for the notes yet, but it’s something that will be in the final version moved to the right.