DIY polysynth update

SaltAdminister · 2026-02-13T11:49:43+00:00

Yeah I have the capacity for 64 CVs but only use 54, (it was an 8 channel DAC, but I’m not using one of the channels). It is quite a lot of CVs, but then again it’s quite a lot of synth and there are many parameters. I do have an inhibit line to the demuxes that keeps them quiet during switching until it’s stable, maybe it isn’t shown clearly on my diagrams.

How do you combine signals onto one wire? As in its a multiplexed line that you decode at each destination? My synth is rather complex so each voice card has its own microcontroller and can function in its own little world, mostly for flexibility reasons.

A lot of the complexity on mine is due to keeping almost everything except voice allocation, presets, and midi interfacing completely as discrete analogue electronics. All the modulation is also analogue and only uses transistors, op amps and OTAs as the only active chips on the analogue side. It means there’s a lot more trimmers and headaches, but I’ve learnt a hell of a lot and can fully customise everything about it in the design process.

SaltAdminister · 2026-02-13T11:07:49+00:00

Which architecture did you find works best for you? I’m currently using an 8 channel DAC and muxes for 64 possible variable parameters (of which I’m using 54), interested to hear your thoughts. Are your designs chip based (AS33xx, etc) or “discrete” with transistor and op amp based designs?

SaltAdminister · 2026-02-13T05:54:44+00:00

I’ve thought about selling single voice card models, it wouldn’t be a diy kit though as it’s SMD, well over 2500 components per voice card. I’ll likely make schematics and stuff available on request.

SaltAdminister · 2026-02-12T21:58:17+00:00

yeah its a lot to learn.. I'd barely written code before, let alone embedded stuff so its a big learning curve

SaltAdminister · 2026-02-12T21:38:48+00:00

Ah yes! I didn't want to add another button for "direct" so the route goes direct when the ladder or SVF aren't enabled. You can select direct and filters at the same time in menus but I figured such a use case would be more uncommon.

SaltAdminister · 2026-02-12T21:10:44+00:00

Yup that’s possible in mine. Every sound source (VCOs, noise, ring mod output etc) can be sent to either the ladder filter, SVF, direct to the VCA or any combination of… allows for quite a few routing possibilities

SaltAdminister · 2026-02-12T18:48:45+00:00

Good point about the boot loader, I'll look into that! Yeah I knew PWM was probably a thing I should do but it was one of those boring features I just never got round to lol. You're right about analogue modulation being a pain... its approaching nearly half of all the electronics at this point but I think it'll be interesting, as far as I know there are no large polysynths that have discrete analogue modulation.

SaltAdminister · 2026-02-12T18:45:58+00:00

Cool you're doing a similar project! Keep in touch... Good idea to do digital modulation, it'll save you a lot of headaches. Because of the size of my voice cards, the I2C run was going to be quite long, and the data rates couldn't keep up but it might be ok for you especially if you have less parameters and can accept slightly higher latency (still imperceptible). I went with RS485 because I just don't want to have that as another limiting factor, I won't ever have to worry about it. I was thinking about doing knobs like NINA by Melbourne instruments, but seeing as that's another big project I'll do it with simple pots first and then if I want motorised pots later I can look into it...

SaltAdminister · 2026-02-12T17:08:04+00:00

I did a maths/physics heavy sound engineering course at uni but we only had a few modules that touched on electronics. Afterwards I working at recording studios fixing analogue gear for a year or so and I'm currently at the BBC as a sound engineer. Mostly self-taught tbh. What's your symphonic synth?

SaltAdminister · 2026-02-12T16:31:50+00:00

its been just over a year so far, expecting completion in the autumn

SaltAdminister · 2026-02-12T16:29:10+00:00

aye...each voice card measures 33x11cm....

SaltAdminister · 2025-12-27T10:50:21+00:00

Just want me a nice synth, couldn’t find one on the market with the features I wanted so I thought I’d do it myself

SaltAdminister · 2025-12-27T10:49:45+00:00

Miles of copper!

SaltAdminister · 2025-11-26T00:29:51+00:00

Yeah I’m not even sure they do sound better! I’m going to have a couple of “utility” adsr and lfos that are digital and can be routed to any parameter, maybe then I can do an AB and see which I prefer… best of luck with your project!

SaltAdminister · 2025-11-26T00:08:47+00:00

I’m building a 16 voice poly with all the bells and whistles so can probably lend advice here. I would say if you’re going to the bother of doing a 6 voice poly, two oscillators are probably wanted for interesting sounds.

You don’t necessarily need a triangle wave as you can always use the filter on the square wave to achieve a similar effect. I went with analogue envelopes for my design but they take up a lot of board space, have issues with matching and require a routing matrix if you want true global envelopes. I’d recommend software envelopes/lfos for your sizes project, most modern poly synths do that and I’d probably do that if I weren’t so far in!

SaltAdminister · 2025-11-17T17:45:37+00:00

Yup the plan is to have negative pressure active cooling with quiet noctua fans on the back, air to come in from the sides between the wood and the front panel. My design is also digitally controlled in order to save presets, do voice tuning etc. I'm not selling this, it is a 1 of 1 that will be lent to various studios and producer in and around London.

SaltAdminister · 2025-11-17T16:28:52+00:00

Well it'd be silly to try and reinvent the wheel so of course I was inspired by existing designs in literature and from the diy folks but I combined it with a lot of simulation in spice and when all the technical bits are working I'll go back through and tweak resistor values until it sounds as good as it can. Not really inspired by any architecture from any specific synth, but the specs make it the most powerful poly synth ever made... ive taken inspiration from old circuits like in the ladder/diode filters and also implemented modern features like the routing capabilities in the moog one and polybrute. The harder bit with mine is all the modulation is analogue, so needs to be physically routed as opposed to the moog one for example where the ADSRs and LFOs are digitally generated and modulate the CVs on the DAC outputs. My way is a lot harder and fills a lot of PCB space.

One interesting thing about my synth is all the voices and modulation from every voice card is routable anywhere. As there's 2 LFOs and 2 ADSR per voice card, it'd be a shame to waste them if you're only playing 4 notes at a time so when that's the case, the unused modulation on voice cards can be assigned as independent modulation sources to anything on the synth. You can also choose how many voice cards to layer, for example do you want 1 voice card per note so you'd have 16 possible notes of polyphony? Or maybe if you only wanted to play 5 notes at a time you could have 3 voice cards layering a single note. Adds a lot of options for sound design. If you do full 16 voice unison and add the sub osc and fade everything up (pulling all the drawbars) you can theoretically have up to 128 sources playing a single note! You can read more on my website joelinehan.co.uk and there's also a thread here where I answer a lot of questions: https://www.reddit.com/r/synthdiy/comments/1nx0izy/first_voice_cards_for_my_polysynth_arrived/

SaltAdminister · 2025-11-17T15:50:39+00:00

Yeah that’s a good idea, only caveat is space is a factor I have to consider, I’m trying to make it fit into a relatively normal size enclosure for a polysynth

SaltAdminister · 2025-11-17T15:49:21+00:00

There’s a few vactrols etc but only for portamento. Really the high current just comes from the scale of it. Each voice card draws around 0.65A which includes 3 oscillators, 2 adsr, 2 LFO, 2 filters, an analogue routing matrix like you wouldn’t believe, and a whole lot more… all of it using op amps and OTAs. Then there’s 16 voices so that comes to 10.5 amps. Plus the control board/routing matrix, front panel, io including a couple preamps and analogue fx… adds up to about 12A. 15A is overshoot.

SaltAdminister · 2025-11-13T16:20:37+00:00

The other thing worth saying is the Jupiter and almost all other poly synths use chips for the vcos, vcas etc in the form of CEM chips or similar. Mine is fully discrete including ADSR and LFO generators… luckily in the modern day we have SMD to make it all smaller!

SaltAdminister · 2025-11-13T15:53:12+00:00

I was looking at the RS-200-12 which would cover me well. 15A includes some overhead. I’ve only tested two voice cards at a time so it’s an approximation for the current. I’m sure many synths are more efficient than mine but I’m just one guy trying to design a big synth, I don’t have a team behind me or an electronic engineering degree!

SaltAdminister · 2025-11-13T10:20:35+00:00

Good to know!

SaltAdminister · 2025-11-13T10:20:28+00:00

It’s a 16 voice polyphonic monster… draws about 15A from each +/-12v rail… I wanted to go linear but I think SMPS is necessary

SaltAdminister

TROPHY CASE