The first model in a series of three produced by Korg in the late 1970s. They were early attempts at designing polyphonic synths; they were fully polyphonic -- every note on the keyboard could be played at once and all would sound.
The PS-3100 Edit
Unlike most other attempts at fully polyphonic synths of the 1970s, the PS-3100 was not paraphonic; each note had a voice consisting of its own signal source, voltage controlled filter, voltage controlled amplifier, and envelope generator. The main compromise was in the signal sources. The synth had a bank of 12 voltage controlled oscillators, each set up to play a specific note of the equal tempered chromatic scale -- the first VCO played C, the second one C#, the third one D, and so on. These 12 VCOs were connected to the 12 keys of the top octave on the keyboard; top-octave division was used to produce the notes of the lower octaves. (This led to the keyboard having an unusual span of F to E; it was necessary for the number of notes to be a multiple of 12; hence, the typical "extra" top note of the keyboard had to be omitted.) A unique feature was the set of 12 trim controls for the VCOs, one for each note; among other things, this allowed the user to execute alternate tunings.
In addition to the 48 voice circuits, the synth provided several additional processing blocks which came after the mixer which combined the 48 voices. An "ensemble" circuit, essentially a chorus effect, could be used to give the sound (which could be rather static due to the top-octave division architecture) more of a sense of space. The "resonator" was a bank of three bandpass VCFs with fixed resonance, but coupled together so that the cutoff frequencies of all three could be swept with a single control voltage. Two low frequency oscillators and a "general envelope" were available as control voltage sources; one of the LFOs, which was capable of running into the audio range, could also be used as a modulation source for a built-in amplitude modulation unit, which allowed the user to dial in any amount of modulation up to full ring modulation.
With respect to the control signals, the synth was semi-modular. Patch jacks built into the panel allowed the user to use patch cords to route control signals, in addition to a few hard-wired or switchable routings. A few inputs jacks conveyed control signals to the voice circuits; in this case, the control effected all voices equally. An oddity was that the keyboard's pitch wheel had no normalled connection; in order for it to serve its conventional function, the user had to patch its output to the VCO frequency input.
Released chronologically after the PS-3100, the 3300 is often described as "three 3100s in one box", which is not too far from the truth. The synth had three banks of voice circuits, each equivalent to the 3100's voice complement, and each note on the keyboard commanded one voice circuit from each bank. And, each bank included the two LFOs, the resonator, and the amplitude modulation processor from the 3100. There was also a set of tuning controls for each bank. Altogether the PS-3300 voices included 36 VCO, 144 VCFs, and 144 VCAs. Each bank also had its 12 tuning trim knobs. The ensemble effect, however, was omitted.
The ancillary circuits were somewhat different from the PS-3100. There was one general envelope for the whole synths, plus one sample and hold circuit, and several control voltage processing circuits. A mixer controlled the relative levels of each bank of voices, and a foot switch could be connected to switch any bank on and off.
Unlike the PS-3100, the PS-3300's keyboard was detached and had to be purchased separately. Designated the PS-3010, this had the same 48-note span as the 3100's built-in keyboard. It replaced the pitch wheel with a two-axis joystick, plus a manual gate button and three on-off switches. An interesting trigger generator could be set to generate a trigger signal only when a certain minimum number of keys was pressed, from 1 to 6. The keyboard connected to the synth with a stiff cable having bulky 60-pin conductors at each end, which provided power to the keyboard and conveyed the key signals back to the synth. What it did not do was convey any signals back from the keyboard's performance controls; in order to use these, the performer had to string patch cables between the keyboard and the synth.
The last of the three models in chronological order, the PS-3200 is often incorrectly though of as, analogous to the PS-3300, two 3100s in a box. It does have two sets of the top-octave divided VCOs (each with its set of tuning trim knobs); however, there is only one VCF and one VCA per voice. The 3200 omits the resonator circuit of the other models, substituting a 7-band graphic equalizer which was not as well liked by performers. Its outstanding virtue was something the other models lacked -- patch memory, of which it had 16 locations. (It lacked any mechanism to transfer patches to or from external storage.) A set of pushbuttons allowed for patch selection and storing; patches 1-8 could also be selected via a foot switch connected to the appropriate jack.
It employed the same PS-3010 keyboard as the PS-3300.
In addition to the PS-3010 keyboard required by the 3300 and 3200, Korg offered several accessories. The PS-3040 dual foot pedal connected to the synth via a pair of DIN jacks, and the patch panel broke out the signals and made them available as patchable control voltages. The PS-3060 was a remote patch selection box (referred to as a programmer, although it did not have the ability to edit patches) for the PS-3200; it also duplicated the foot switch selection jacks for patches 1-8. The PS-3050 junction box allowed one keyboard to control up to three 3200s or 3300s. A planned PS-3030 sequencer did not make it past the prototype stage.
The Korg PS series were among the earliest polyphonic synths. The approach taken of full polyphony made them expensive, and not many of any of the three models were sold. However, they are now highly regarded and quite valuable in the collector's market. The main problems encountered are the wood veneer peeling off the case, contact problems with the 60-pin connectors on the 3200 and 3300, and the difficulty of getting one serviced; many parts are no longer available.
All three models were dropped by 1981. That year, Korg turned its polyphonic-synth focus towards designs using voice allocation (as did other manufacturers), eventually resulting in the Polysix. MIDI was never available, since it had not been invented at the time, but retrofits are available for the 3200 and 3300.