New polysynth project - now with 8 voices & bitimbrality :-)

[adamstan]

Somewhere around 2015 I started new polysynth project - analogue rackable desktop module, with multimode filter. It even had its thread here, unfortunately it got accidentally nuked during spam wars. In the meantime I still worked on it, and now I can show you hopefully final prototype

This synth has 8 voices that can be split between two layers. Each voice features two VCOs (with sync and pwm), Ring Mod, noise source, FM (OSC A or noise to OSC B and/or VCF), multimode 12dB/oct. VCF, 3 EGs and 3 LFOs.



Previous six voice version can be seen and heard here:


VCOs use heater to keep expo converters at constant temperature. Circuit is based on Moog Prodigy - third transistor from 3046 works as temperature sensor, while transistors 4 and 5 work as heaters. There is no background tuning, only standard autotune like in vintage polysynths. Filter and VCAs are built around LM13700. There are no custom synths ICs used (because they weren't available when I started ). Envelopes and LFOs are software, with simple modulation matrix - they have up to seven simultaneously switchable destinations.

[Synthabator]

Holy s**t. Nice sounding congrats!!! Now that's what I'm talking about.

[HideawayStudio]

Adam - coming from a fellow design engineer that's a pretty darned major accomplishment there!

It sounds lovely and doubly brave for going the heated expo VCO route.

I've toyed so many times now doing something similar (esp. now the Curtis reissues are out!) but I worry it runs the risk of becoming a "me too" offering.

What would you say are the unique aspects of your beast?

It sounds like it has good consistency across the voices.. Is it a pig to calibrate?

Is there a display or is it all programmed via the front panel on dedicated knobs?

I like the way the voice cards plug in - reminds me of the Jupiter 4

[adamstan]

What would you say are the unique aspects of your beast?

I'd say that ringmods are still pretty rare among vintage or modern analog polys, so that's one. I took it directly from my previous synth - it's standard MC1496 application. I'm really proud of that DX tubu;ar bells patch coming from analog poly Three envelopes and three LFOs per voice - LFOs can be synced across the voices, or free-running with random detune per-voice. Bitimbrality and 8 voices aren't exactly common in current VCO polys either And, like my old DIY keyboard - it's built with standard parts only - they call that "discrete" nowadays, don't they? I'd say it combines features that are hard to come by in single synth (like VCOs, ringmod, cross mod, multimode filter etc), and thanks to that heated VCO design with no background tuning I hope it will have somewhat "vintage" feel to it

It sounds like it has good consistency across the voices.. Is it a pig to calibrate?

No, it's very easy to calibrate I'm quite proud that it has only four trimpots per voice:
1 - Reference voltage for heater - I'm thinkig about replacing it with 1.22 reference voltage source and fixed divider, as there is approx. 610mV needed, so that would leave us with three
2 - Triangle shape calibration
3 and 4 - Ringmod input offset adjustment

Oscillators and filters are fully calibrated with software during autotune routine.

Is there a display or is it all programmed via the front panel on dedicated knobs?

There is only that 3-digit LED display, and all buttons except up/down buttons next to the display are backlit. For example - to select LFO destinations or waveform, you press relevant button in LFO section ("wave" or "destination") and then switch those using numerical patch-selector buttons. And then there is "shift" mode, where buttons select various additional parameters (like master tuning, pitch bend range or split point) to adjust using up/down buttons next to the display. There will be "cheat-sheet" with list of that parameters printed below buttons.

[madtheory]

Very nice, did I hear glissando (i.e. quantised portamento) in there as well? Love that effect.

[adamstan]

Very nice, did I hear glissando (i.e. quantised portamento) in there as well? Love that effect.

Portamento is non-quantized. That glissando was just played on keyboard

[madtheory]

Right, part 2 of the test, play it descending!

[Mooger5]

One feature I´d like to see in LFOs synced to arpeggitor/MIDI is a positive going square wave (and negative too, given the option). Do you see the usefulness?

[adamstan]

I can see the usefulness, however I'm not sure if I can handle whole MIDI clock syncing thing software-wise, as I never did that before and it looks like pretty tricky business. We'll see.

[adamstan]

New feature - drum kit mode! Selecting any program from 120-127 range switches on the drum mode. Presets 120-127 are then loaded into subsequent voices, which are triggered according to GM drum map. Additionally, currently selected preset is open for editing.

Voice 1 - preset 120 - kick (C1 - #36)
Voice 2 - preset 121 - snare (D1,E1)
Voice 3 - preset 122 - low tom (F1,G1)
Voice 4 - preset 123 - mid tom (A1,B1)
Voice 5 - preset 124 - high tom (C2,D2)
Voice 6 - preset 125 - hi-hat (F#1, G#1, Bb1)
Voice 7 - preset 126 - crash (C#2)
Voice 8 - preset 127 - clap (Eb1)

In drum mode release knobs are ignored, and release times are always equal decay times.

[adamstan]

One more video - I made it to test Behringer phaser with my string machine, however it features drum sounds from this new poly - this time properly recorded from mixer, instead of camera mic

[madtheory]

Fantastic drum sounds.

[adamstan]

Here's quick photo of prototype with enclosure - final look should be close to that

To put it into a rack one has to remove wooden sides and put on rack ears instead. The panel is 5U.


More photos, demos and hopefully webpage coming soon

[atkbg]

Great job! It's been fun to watch your project progress. Fine work indeed!

[Broadwave]

Nothing but respect to you - Brilliant.