A new instrument: Moog's Polymoog #54

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opened 2026-10-12 23:32:36 +00:00 by bcox · 0 comments

bcox commented

2026-10-12 23:32:36 +00:00

Owner

Everything below is from recollection and a quick look at encyclopedia and shop pages, with no manual read; issue #20's list was wrong in several places for the same reason. Find and read Moog's owner's and service manuals before designing anything, put them in docs/references.md, and correct this.

What it covers

Polymoog Synthesizer (model 203A, 1975). Every one of its 71 keys at once. Two ranks of tone from divide-down generators, a sawtooth and a pulse, each rank able to be detuned and modulated; and for each key a card of its own with shaping, a filter and an envelope. After the keys are summed: a three-band resonator section, fixed "mode" filters, and one ladder low-pass with its own envelope for the whole instrument. The keyboard feels velocity and splits into three ranges with a level each. Eight presets and one sound that can be set freely.
Polymoog Keyboard (model 280A, 1978). The same voice with more presets and almost no way to change them.

One instrument. With memory and presets set aside, the Keyboard is the Synthesizer by name only.

In kind it sits with the ARP Omni and Korg's PS family (#24): full polyphony from dividers, and here articulation for every key, which is what sets it apart from a string machine and from the Opus 3, #55.

To find out

What a key's card really does: whether its filter is resonant, what its envelope's stages are, and how velocity reaches it.
How to give every key its own filter and envelope on a Pi 3B. 71 keys is more than the 32 voices any instrument here goes to, though a card is far less than a voice. Measure before designing.
The resonators and the mode filters: their bands, ranges and slopes. Nothing here has a resonator bank.
How the two ranks are tuned and modulated, and what the hardware's one or two master oscillators mean for detune and vibrato. engine/divide_down.h was written for the Omni; whether it gives two ranks, a sawtooth, and a pulse of variable width wants looking at.
Whether a "polyphonic" switch per quirk applies: the hardware's dividers are free-running, so a key's phase does not restart. That is a quirk, and by Ben's rule a switch.

What it does not cover

The pedal unit as hardware; its controls come as MIDI.

What is already here to build on

engine/divide_down.h, and what the Omni's instrument learned about voicing filters.
engine/four_pole_filter.h for the one ladder filter; engine/state_variable_filter.h may serve the resonators.
engine/zones.h for the three ranges of the keyboard.
The shared arpeggiator and effects.

Provenance

No processor and no stored patches.
Its presets are wired in, as resistors. Ben decided on 2026-10-12, on #26: what is wired into a circuit, such as resistor values, and can be seen on a published schematic is fair game; what needs a ROM, stored factory patches included, is another matter and stays under rules 3 and 4. So they may be had, read from the published schematic and from nowhere else, with a comment naming it (rule 5). That wants checking for the Polymoog Keyboard, whose presets are recalled as wired too but were not looked up.
Rule 2: nothing from an emulator's code.
The names. "Moog" and the model names are trademarks that are actively used and defended. Ben said on 2026-10-12 to use Moog's own names for now, so that he can tell what each is, the repository being private; nearly every instrument's name here will have to change before anything is sold, and these with them. So, say, instruments/polymoog/ and programs named minipolymoog.

Ben decided on 2026-10-12, on #26, that the Moogs up to the Memorymoog are wanted, with variants combined where that fits, and asked for an issue for each instrument that makes. This is one of five; the others are linked from #26. Not started. **Everything below is from recollection and a quick look at encyclopedia and shop pages, with no manual read**; issue #20's list was wrong in several places for the same reason. Find and read Moog's owner's and service manuals before designing anything, put them in `docs/references.md`, and correct this. ## What it covers - **Polymoog Synthesizer** (model 203A, 1975). Every one of its 71 keys at once. Two ranks of tone from divide-down generators, a sawtooth and a pulse, each rank able to be detuned and modulated; and for each key a card of its own with shaping, a filter and an envelope. After the keys are summed: a three-band resonator section, fixed "mode" filters, and one ladder low-pass with its own envelope for the whole instrument. The keyboard feels velocity and splits into three ranges with a level each. Eight presets and one sound that can be set freely. - **Polymoog Keyboard** (model 280A, 1978). The same voice with more presets and almost no way to change them. One instrument. With memory and presets set aside, the Keyboard is the Synthesizer by name only. In kind it sits with the ARP Omni and Korg's PS family (#24): full polyphony from dividers, and here articulation for every key, which is what sets it apart from a string machine and from the Opus 3, #55. ## To find out - **What a key's card really does**: whether its filter is resonant, what its envelope's stages are, and how velocity reaches it. - **How to give every key its own filter and envelope on a Pi 3B.** 71 keys is more than the 32 voices any instrument here goes to, though a card is far less than a voice. Measure before designing. - **The resonators and the mode filters**: their bands, ranges and slopes. Nothing here has a resonator bank. - **How the two ranks are tuned and modulated**, and what the hardware's one or two master oscillators mean for detune and vibrato. `engine/divide_down.h` was written for the Omni; whether it gives two ranks, a sawtooth, and a pulse of variable width wants looking at. - **Whether a "polyphonic" switch per quirk applies**: the hardware's dividers are free-running, so a key's phase does not restart. That is a quirk, and by Ben's rule a switch. ## What it does not cover The pedal unit as hardware; its controls come as MIDI. ## What is already here to build on - `engine/divide_down.h`, and what the Omni's instrument learned about voicing filters. - `engine/four_pole_filter.h` for the one ladder filter; `engine/state_variable_filter.h` may serve the resonators. - `engine/zones.h` for the three ranges of the keyboard. - The shared arpeggiator and effects. ## Provenance - No processor and no stored patches. - **Its presets are wired in**, as resistors. Ben decided on 2026-10-12, on #26: what is wired into a circuit, such as resistor values, and can be seen on a published schematic is fair game; what needs a ROM, stored factory patches included, is another matter and stays under rules 3 and 4. So they may be had, read from the published schematic and from nowhere else, with a comment naming it (rule 5). That wants checking for the Polymoog Keyboard, whose presets are recalled as wired too but were not looked up. - Rule 2: nothing from an emulator's code. - **The names.** "Moog" and the model names are trademarks that are actively used and defended. Ben said on 2026-10-12 to use Moog's own names for now, so that he can tell what each is, the repository being private; nearly every instrument's name here will have to change before anything is sold, and these with them. So, say, `instruments/polymoog/` and programs named `minipolymoog`.

bcox referenced this issue

2026-10-12 23:33:02 +00:00

Do we want any Moogs? (Yes: up to the Memorymoog, as #51 to #55) #26

~~bcox referenced this issue 2026-10-12 23:39:16 +00:00~~

Do we want any Moogs? (Yes: up to the Memorymoog, as #51 to #55) #26

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