Korg PS3100

It may not be well known, but it is sought‑after. Simon Lowther relates the history and mystery of an early 48‑note polyphonic analogue synth and its well‑connected family.

Korg had yet to make their mark on the synthesizer big league when they launched the high‑end, sophisticated 'PS'‑series of polysynths in 1977. Though conceptually similar to the MS family of monosynths which followed, the PS‑series is probably less well known today, but is seen by some analogue synth devotees in an almost mystical light.

When the PS‑series synths were introduced, manufacturers were struggling to make polyphonic synthesis possible, let alone affordable, and polysynths were still few and far between. The most prominent were probably Moog's much‑derided Polymoog, the well–respected Yamaha CS80, and Oberheim's SEM‑based four‑ and eight‑voice machines, though all of these machines were compromised in some way — the Polymoog wasn't even truly polyphonic. Synthesizers were laboriously put together from costly discrete components, rather than off–the–shelf oscillator and filter chips, so polyphonic instruments were not only expensive but also often short of desirable features. Unsurprisingly, then, there was much contemporary interest in the apparently feature‑packed Korg PS‑series.

Indeed, I was looking to buy my first synth when I first saw an advert for the PS3100. I had not heard of Korg, but the synth immediately grabbed my attention, looking like a modular Moog with a steeply rising control panel, walnut–effect trim, a 48‑note keyboard with a nice action, and lots of knobs and jack sockets. The performance controls comprised an expensive–feeling metal non‑sprung pitch‑bend wheel (with the faintest ever centre detent) and a trigger button usually used for triggering such things as the onboard EGs. In total there were three synthesizers in the PS series (see 'Family Plans' box), along with some accessories, but since the PS3100 is what I have in front of me right now, that's the one I'll be focusing on.

Voice Architecture

If you can afford it, the 3300 is arguably the most desirable of the PS synth family.

The PS3100 and 3300 have built a fan base because they are intriguing and wonderfully quirky, but still highly usable, synthesizers. This is due in no small measure to their unusual architecture and some interesting variations Korg introduced on the normally accepted ways of doing things. (Korg also confused matters by using unorthodox terminology, which I'll try to clarify where possible, to describe familiar functions.)

Perhaps the most remarkable feature of the PS3100 is that each note on the keyboard has its own filter, envelope and share of a divide‑down oscillator, making it a fully 48‑note polyphonic synthesizer. There are also temperament controls at the left‑hand side of the fascia, allowing you to tune all the C‑sharps (or whatever) independently of the other notes, to make alternative scales. The manual explains the creation of mean‑tone and just‑intonation scales, as well as a heptatonal scale consisting of seven equal intervals.

Triangle, fixed pulse and square, PWM and saw waveforms are offered by the VCO, and pitch modulation is generated by the hardwired LFO1 (or Modulation Generator 1, in Korg‑speak). However, the patch panel has a socket that allows you to access pitch from the envelopes or any other voltage source you can harness.

There's only one oscillator per note on the 3100, and no supporting sub‑oscillator — which Korg must have considered a problem, as they added a switchable 'Ensemble' chorus circuit to beef up the sound. The larger PS3300, being effectively three PS3100s in one box, offers three oscillators per note, which means that there are three sets of tuning knobs (3x12) for modifying scales. Fortunately, the oscillators don't really drift in pitch — just as well, because tuning them all together can take quite a lot of fiddling. Since the pitches in a scale are linked, if one C‑sharp goes AWOL, all the C‑sharps go the same way!

The PS‑series VCF is a low‑pass design with Cutoff Frequency and Peak controls, amongst others. The latter is known as resonance, or Q, to you and me (although Peak is actually not a bad name for a circuit that emphasises — or peaks up — the harmonics at the cutoff point!). Korg's literature claims it to be a 12dB/octave, two‑pole design, but it sounds even weaker than that to my ears. This filter has to be the biggest disappointment on the PS‑series synths, making it very difficult to produce classic big filter sweeps. On the plus side, however, modulation control of the filter is good. Both LFO and envelope modulation can be applied to filter cutoff (called 'Expand', for some unfathomable reason), and keyboard tracking of the VCF frequency and VCA gain are independently fully variable, both negatively and positively, across the keyboard. This facility is handy in the absence of touch response, as it can be used to emphasise either end of the keyboard. On the PS3300 it could also be used to create positional crossfades between layers.

There are two envelopes. The main Envelope Modifier has knobs for the attack, decay and sustain phases, with release time switchable between damped (no release), half‑damped (half a second or so) and 'Release', which, as on a Minimoog, makes the release time equal the decay knob setting. The other envelope is called the 'General' envelope generator. All three PS‑family members had only one of these — and I mean one only, not one per note. It's a DAR (delay/attack/release) envelope, with auto‑trigger and invert polarity switches, and is hardwired to VCF cutoff by default. However, it could just as easily be connected to some other destination with a patch cord.

If you do use the General envelope rather than envelope 1 to control filter cutoff, some nifty playing is required to avoid held notes re–articulating each time you press a key. One nice feature of the General envelope, though, is that it can be triggered once a certain number of notes have been pressed. So you can, if you wish, introduce a filter swell on four‑note chords but not on melody lines or triads, or bring in delayed vibrato on chords only. Used sparingly, this is a very effective performance technique.

Resonators

The PS3200 with "optional" (actually pretty essential) PS3010 keyboard.

A module you don't come across very often outside esoteric modular systems is the three‑peak voltage‑controllable resonator, which greatly increases the PS‑series synths' flexibility in creating timbres. This resonator boosts bands of frequencies over the range 100Hz‑10kHz and features controls for bandwidth and frequency. It's a great tool for creating more realistic synthesized 'acoustic' instruments, and produces great electronic noises when you sweep the frequencies either manually or with an LFO, envelope or other modulation source. In fact, one could say that the sound of multiple‑resonator sweeps is the PS‑series' signature tone. If you haven't heard a multiple resonator before, think of it as a bit like a focused flanger or powerful EQ, but crisper and clearer. It's a shame you can't route external audio through the resonator, as this would surely make the 3100 very popular with modern dance producers.

Modulation Generators

The PS3040 dual control pedal and 3050 junction box for connecting several PS synths together.

The first of the 3100's two LFOs is called Modulation Generator 1 and offers a choice of four waveforms plus white or pink noise. It's a proper voltage‑controlled LFO, with two associated jack sockets: one controls LFO speed and the other controls output amount via a dedicated VCA. MG2 is simpler, offering only a sine wave, and although it is hard‑wired to the resonator frequency and PWM, it also has an output, so you can connect it elsewhere. Overall, the PS3100's modulation facilities are rather well developed for its time.

Characteristically for a 1970s instrument, the PS3100 features a sample and hold generator, which has its own separate clock generator. You can use it to sample envelope outputs for staircase glissando effects, or perhaps noise for random chaos — if you must!

As with any modular synth, the 3100 also boasts various 'utility' modules. These include two voltage processors, which can be used to modify input voltages — so that, for example, a signal that varies from +5 to –5V is restricted to the range +2 to +3V. The voltage processors can also be used to invert the input. Finally, there's an amplitude modulator which is useful for pseudo ring‑modulation and tremolo sounds.

Patch Panel

The PS‑series synths have an internal, hard‑wired signal path, but — as you will have noticed by now — there are also a lot of jack sockets on the front panel. (These are conveniently kept away from the knobs as much as possible, so that you can get to the knobs without reaching through a mess of cables.) The patching options offered by these sockets increase the instrument's flexibility by allowing the default connections to be overridden with patch cords, allowing more unusual control and modulation routings to be used. For instance, it can be very useful to have voltage control of envelope attack and release or LFO1 frequency, as well as the more normal PWM, LFO amount, filter cutoff and so on. If there's a limitation to the system, it is that there are not as many controllers as some would like, and that you cannot change or break into the audio signal flow.

Sound Stuff?

One could be forgiven for thinking that a synth with divide‑down tone‑generator circuits and only one VCO per note might not sound very impressive. But actually the PS3100's VCOs sound rather good, boosted by the extra programming options provided by multiple LFOs, resonators and patchability — and, of course, no‑one could complain about the 3300's complement of oscillators! The PS‑series synths don't leap out with hard‑edged, contemporary sounds, but rather excel at warmer, richer, more organic patches. In the hands of a skilled operator they have a distinctive character, especially when creating animated pads and washes using the filters, resonators and amplitude modulation. Nice woofy analogue basses are also possible. In spite of their complex appearance, the PS synths are pretty straightforward to use, but though the 3100 has the ability to generate some good sounds it's not as sonically versatile as you might think. Soaring Prophet‑ or Moog‑style lead sounds do not easily fall out of a PS‑series instrument.

Fashion Victim

I don't think the PS series was ever very fashionable in its production lifetime. The 3100 didn't even look trendy at its launch, with its sharply sloping panel and patch sockets. And its popularity was arguably hindered as much as it was helped by endorsements from prog‑rock giants such as Keith Emerson, who were falling out of favour in the wake of new wave and electro–pop. The PS synths were soon eclipsed in the eyes of many buyers by Sequential's Prophet 5 which, although comparing poorly on polyphony and routing flexibility, offered the significant innovation of digital patch storage. The PS series was as different then as it is unique now, and I am sure this did not help its case. The family was quietly dropped in 1980‑81, and Korg settled into a more mainstream groove with the subsequent Poly 6/61 and DW synthesizers.

Today the place of the PS instruments is difficult to assess. They are undoubtedly quite unwieldy, and with the limited exception of the PS3200 (which features a 16–memory patch storage facility) they lack memories for the user's carefully crafted sounds. On the other hand, they do offer a lot of sound‑mangling potential, the keyboard is very playable and you get lots of knobs to twiddle. If you want to incorporate one into a modern studio, Kenton Electronics provide a retrofit which gives MIDI In for note on/off messages and a discreet external box that sprouts patch socket outputs for velocity, pitch‑bend, modulation, aftertouch, volume, and a couple of assignable controllers. All these can be connected by patch cords to whatever you want to control.

If you're thinking of buying a PS‑series instrument today, the PS3300 must be the one to go for — a big, complex, multi‑layered instrument with multiple VCFs and six LFOs. Its capabilities were unprecedented in 1978, and even Bob Moog reportedly rated it very highly at the time. By comparison, the PS3200 has a traditional analogue synth configuration that would be considered relatively mainstream these days, and the PS3100 suffers from not having two VCO banks to put through its resonators.

Korg have recently returned to the world of 'analogue' polysynths with their MS2000. Although this new instrument clearly owes a visual debt to the PS‑series synths, it has different features and a different sonic character. There is no doubt that today's technology and design has caught up with what, at the time of the PS‑series, were advanced modulation routings on a mass‑produced instrument, and what would have been pretty unique when the series was in production is probably today regarded as normal. Nevertheless, these grand old instruments do things in a different way, are creative and fun, and can certainly produce the goods.