Not sure if that is the correct term, but can somebody explain the difference between a Polymoog keyboard/sound engine and that of the Opus 3 (and even the Radioshack variant).
I love my Opus 3 but having just one filter and a VCA that is rather limited is sometimes a bummer. Did the Polymoog go about it a different way?
Fold down circuits in Moog instruments
Fold down circuits in Moog instruments
'76 Minimoog, Taurus 3, Oberheim FVS + Son of 2-voice; Sequential ProOne; Juno 106; Moog Model 15; Kurzweil 250; Hammond M3; and a handful of Fender Basses Flickr!
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Kevin Lightner
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Re: Fold down circuits in Moog instruments
I think you mean divide down circuitry, not fold down.
Regardless, a good question.
On an opus, a fixed high frequency is sent to a top octave generator (TOG) chip.
The outputs, one for every note in an octave, are then sent to successive dividers.
(dividing a freq in half, lowers the pitch one octave.)
With this scheme above, the TOG simultaneously generates a full octave of notes pitches very high (ie: the top octave) and are then divided down individually to realize the same notes, but in lower octaves.
In a Polymoog, things are much the same.
However instead of using a fixed high frequency, they use a high frequency VCO.
This allows it to be voltage controlled.
All the same things happen afterward: TOG chip and dividers.
The major difference is that instead of a single VCO, TOG and dividers, the Polymoog has two of each.
This allows beating between the two oscillators and all the notes produced later.
Regardless, a good question.
On an opus, a fixed high frequency is sent to a top octave generator (TOG) chip.
The outputs, one for every note in an octave, are then sent to successive dividers.
(dividing a freq in half, lowers the pitch one octave.)
With this scheme above, the TOG simultaneously generates a full octave of notes pitches very high (ie: the top octave) and are then divided down individually to realize the same notes, but in lower octaves.
In a Polymoog, things are much the same.
However instead of using a fixed high frequency, they use a high frequency VCO.
This allows it to be voltage controlled.
All the same things happen afterward: TOG chip and dividers.
The major difference is that instead of a single VCO, TOG and dividers, the Polymoog has two of each.
This allows beating between the two oscillators and all the notes produced later.
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Re: Fold down circuits in Moog instruments
Interesting. So it uses true VCOs (but only two) and they are fixed at some high frequency, then the audio gets divided down similarly.
What about filters and VCAs? I have a JH Resonator which I believe is very much like the Polymoog circuit. It has a Low pass, Hi pass, Knotch, Bandpass modes and three frequencies with resonator and gain per. Work very well when playing mono or poly/chords, etc. through but it's fixed and no envelopes to speak of.
Did the Polymoog have any concept of filters and envelopes per x # of keys (I know there is a web site that explains all of this but a few short answers would be good to hear).
... and thanks.
What about filters and VCAs? I have a JH Resonator which I believe is very much like the Polymoog circuit. It has a Low pass, Hi pass, Knotch, Bandpass modes and three frequencies with resonator and gain per. Work very well when playing mono or poly/chords, etc. through but it's fixed and no envelopes to speak of.
Did the Polymoog have any concept of filters and envelopes per x # of keys (I know there is a web site that explains all of this but a few short answers would be good to hear).
... and thanks.
'76 Minimoog, Taurus 3, Oberheim FVS + Son of 2-voice; Sequential ProOne; Juno 106; Moog Model 15; Kurzweil 250; Hammond M3; and a handful of Fender Basses Flickr!
Re: Fold down circuits in Moog instruments
Opus 3 only has a master VCA, but Polymoog has a EG/VCF/VCA per key via the Polycom custom IC. Unfortunately the independent VCF is largely crude and ineffective (12dB/oct only and no facility for resonance or modulation), thus the Polymoog has a master VCF with resonance and modulation. During those days, custom ICs were a new market and very expensive, so there was a limit what they could squeeze on an IC.
A little known trick of the Polymoog is that the 12-tone dividers (following the TOG) are offset one semitone between the two VCO/TOG systems IE for a given note one system is divider output (n), the other system it is (n+1). This was done to produce uneven beating between the 12 notes of a scale - subtle but effective for strings and choirs. This works because the output pitches of 12-tone dividers are equal tempered IE each output is not a constant interval apart. This is described in patent #4,228,717
Vintage mono synths are actually a Pythagorean system of pure intervals between notes, due to the design of the keyboard CV system. This works for a monophonic system but not for a polyphonic system as a scale of pure intervals between notes will not work in all keys. IE a major triad in the key of C in a Pythagorean scale will sound OK, but a major triad in the key of F# won't. That's why equal tempered scales are used for polyphonic systems.
I do not know if modern mono synths under the control of a microprocessor follow the equal or Pythagorean scale...
A little known trick of the Polymoog is that the 12-tone dividers (following the TOG) are offset one semitone between the two VCO/TOG systems IE for a given note one system is divider output (n), the other system it is (n+1). This was done to produce uneven beating between the 12 notes of a scale - subtle but effective for strings and choirs. This works because the output pitches of 12-tone dividers are equal tempered IE each output is not a constant interval apart. This is described in patent #4,228,717
Vintage mono synths are actually a Pythagorean system of pure intervals between notes, due to the design of the keyboard CV system. This works for a monophonic system but not for a polyphonic system as a scale of pure intervals between notes will not work in all keys. IE a major triad in the key of C in a Pythagorean scale will sound OK, but a major triad in the key of F# won't. That's why equal tempered scales are used for polyphonic systems.
I do not know if modern mono synths under the control of a microprocessor follow the equal or Pythagorean scale...
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nicholas d. kent
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Re: Fold down circuits in Moog instruments
That last point about Pythagorean scales just doesn't sound right at all. It is true that chords in equal temperament (what everything uses with the exception of gear where you have a custom or alternate tuning option).
Equal temperament is each note in the scale is the same distance apart. Chords with any root note sound equally good or bad depending on one's opinion. Something like Pythagorean, Just or other non-equal tuning systems are just that. They go for perfect intervals or in some cases a smaller compromise from equal. The down side, which is correctly pointed out, is that a chord based on say the note of C will sound superior while the same chord on a different note, say F# since it's the worst if C is perfect, will sound pretty sour/wrong compared to Equal.
In Top Ocatve divide down gear you simply have 12 generators and divide for all the octaves. Those 12 generators are set at ET intervals on just about every instrument at the factory though could certainly be modified to different pitches. You do have hundreds of year old pipe organs, and other instruments that were tuned differently.
When modular gear came in in the 60s, you had one approach were you had a sequencer or touch pads that could be tuned to whatever you want with a knob or you had a keyboard with resistors following the keys. They were all set up in ET scaling but you did have the rare Moog Scale controller that used a trimpot after each key, almost like the just mentioned sequencer (but each key needs to be a higher value unlike a sequencer where any step can have any CV value). You have an advantage over Top Octave technology in that you could do microtuning with more than 12 notes per octave, different intervals in different octaves too, not that that is called for very often.
you do have a special situation in pythagorean that you wind up a little short if you follow it to the letter, that whole comma business
When poly gear came in, you had approaches like the polymoog and some early Korg poly gear where you had something complex going on with every key producing sound or the Yamaha and Oberheim approach of using a scanned keyboard and circuits to assign the keys being played to a smaller number of what are essentially monosynths. Nothing about this technique stops you from using an alternate tuning. The prophet 5 was an early poly and you could have the intervals in the octave altered to what you want. It's all about the capability of the circuitry that now takes an number for a key (no resistor on each key any more) and interprets that as a pitch for a voice to play. It's by no means a universal feature but something like the Marion prosynth responds to every MIDI key and you can define each in cents to any value
Nothing to do with temperament, but small amounts of detuning make patches sound richer and it seems like that would be going on in chords.
Equal temperament is each note in the scale is the same distance apart. Chords with any root note sound equally good or bad depending on one's opinion. Something like Pythagorean, Just or other non-equal tuning systems are just that. They go for perfect intervals or in some cases a smaller compromise from equal. The down side, which is correctly pointed out, is that a chord based on say the note of C will sound superior while the same chord on a different note, say F# since it's the worst if C is perfect, will sound pretty sour/wrong compared to Equal.
In Top Ocatve divide down gear you simply have 12 generators and divide for all the octaves. Those 12 generators are set at ET intervals on just about every instrument at the factory though could certainly be modified to different pitches. You do have hundreds of year old pipe organs, and other instruments that were tuned differently.
When modular gear came in in the 60s, you had one approach were you had a sequencer or touch pads that could be tuned to whatever you want with a knob or you had a keyboard with resistors following the keys. They were all set up in ET scaling but you did have the rare Moog Scale controller that used a trimpot after each key, almost like the just mentioned sequencer (but each key needs to be a higher value unlike a sequencer where any step can have any CV value). You have an advantage over Top Octave technology in that you could do microtuning with more than 12 notes per octave, different intervals in different octaves too, not that that is called for very often.
you do have a special situation in pythagorean that you wind up a little short if you follow it to the letter, that whole comma business
When poly gear came in, you had approaches like the polymoog and some early Korg poly gear where you had something complex going on with every key producing sound or the Yamaha and Oberheim approach of using a scanned keyboard and circuits to assign the keys being played to a smaller number of what are essentially monosynths. Nothing about this technique stops you from using an alternate tuning. The prophet 5 was an early poly and you could have the intervals in the octave altered to what you want. It's all about the capability of the circuitry that now takes an number for a key (no resistor on each key any more) and interprets that as a pitch for a voice to play. It's by no means a universal feature but something like the Marion prosynth responds to every MIDI key and you can define each in cents to any value
Nothing to do with temperament, but small amounts of detuning make patches sound richer and it seems like that would be going on in chords.
Re: Fold down circuits in Moog instruments
Like Nicholas said...
There were no vintage keyboards that produced a Pythagorean scale. Many of them could be tuned that way, though the standard was (as it is today, as it has been for 300 years,) 12 Tone Equal Temperament. Early synthesizer keyboards chose a scaling like 1V/Oct and sent that to an oscillator with similar scaling inputs. The keyboard would divide that voltage equally from key to key producing Equal Temperament. It's the easiest way to go, any other system would take more work to create (like individual trim pots per note). Even early transistor organs had trim pots per note with divide down circuitry. Turning a trim pot would affect all similarly named pitches, like all D#'s for instance.
BTW, a Pythagorean scale just means that all fifths (except one) are perfectly in tune. A Just Intonation scale could be any collection of notes that were tuned perfect, though there is a typical 12 note per octave Just Intonation scale that is commonly used that is mostly based around pure thirds and fifths.
Stephen
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There were no vintage keyboards that produced a Pythagorean scale. Many of them could be tuned that way, though the standard was (as it is today, as it has been for 300 years,) 12 Tone Equal Temperament. Early synthesizer keyboards chose a scaling like 1V/Oct and sent that to an oscillator with similar scaling inputs. The keyboard would divide that voltage equally from key to key producing Equal Temperament. It's the easiest way to go, any other system would take more work to create (like individual trim pots per note). Even early transistor organs had trim pots per note with divide down circuitry. Turning a trim pot would affect all similarly named pitches, like all D#'s for instance.
BTW, a Pythagorean scale just means that all fifths (except one) are perfectly in tune. A Just Intonation scale could be any collection of notes that were tuned perfect, though there is a typical 12 note per octave Just Intonation scale that is commonly used that is mostly based around pure thirds and fifths.
Stephen
.