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Korg Mono/Poly

Here's an interesting new synth from Korg - the Mono/Poly, and, as you can see, judging from the internal photo of the instrument, we've managed to get hold of one of the very first units to arrive in the country. I say this, with reference to the photo, because you can see that there is a fair bit of loose wiring, and also a piggybacked board has been fitted - presumably the production models will have dispensed with this board, and incorporated the circuitry onto the main PCBs. Apart from this, I'm assured that the review instrument I was given performs identically to the models that will be in the shops very shortly, and sporting a price tag of £689 (the RRP) or less.

I was told, by a none too reputable source I might hasten to add, that originally Korg wanted to call this synth the 'Monopoly', but their trade mark solicitors warned them that they would be required to go directly to jail without passing GO, and without collecting £200, if they did so. Thus Korg settled on the name of Mono/Poly.

It doesn't take a great deal of intelligence to gather that this synthesiser is going to be able to perform in two modes - monophonic and polyphonic. At £689, you aren't going to expect too much from the polyphonic operation, but you would expect quite a high performance monophonic for such money. This new Korg synth does, in fact, perform well in both modes, and it incorporates some interesting ideas, which make a genuine contribution to the instrument's performance.

You are getting quite a bit of hardware for your money here: a 44 note F to C keyboard, 41 control knobs, 14 slide switches, 6 push button momentaries with LED indicators, 2 performance control wheels, and ten jack sockets, and, of course, a mains ON/OFF rocker switch.

The keyboard isn't bad; the action is good and positive with just the right amount of key dip, but the actual construction does warrant me to use the term 'plasticky'. The casework, however, is very nicely constructed, as most Japanese products are these days. The sides and front are a dark wood veneer, with a plain wooden base board. Into this sits the keyboard, and plastic performance control mountings, and the main control panel (hinged up in the internal shot) is black anodised formed aluminium, with a blue block overlay, for identifying the separate control sections, and white graphics. The control knobs are nothing to write home about, but overall the instrument does have something of an air of quality about it.

There are four voltage controlled oscillators that perform as the main tone generators, and it is the way that the control circuitry assigns these oscillators that dictates whether the machine operates in monophonic or polyphonic mode. The signal from the oscillators, and noise source, is mixed together before proceeding to the voltage controlled filter and voltage controlled amplifier as per usual. So you can immediately see where the polyphonic compromises start, there being just one VCF and one VCA. But let's start by looking at the assignment controls.

Key Assign Modes

These are controlled by the push button momentaries that are conveniently positioned one and a half inches up from the keyboard. Five buttons do all the work here - two polyphonic options marked Poly and Unison/Share; two monophonics - Unison and Chord Memory; and lastly, there's a Hold button. The functioning of Unison and Poly should be obvious - the former assigns the control voltage from the last note played, and routes it to all four oscillators; the latter assigns the first note played to VCO 1, the second note to VCO 2, though if key 1 has been released VCO 1 is used again, and so on. If four notes are played and held, and a fifth note triggered, then VCO 1 is robbed, and gets key 5. Although this is a sensible system to use, it would have been a good idea to have provided a cyclic assignment option, whereby the first note played goes to VCO 1, the second to VCO 2 no matter what VCO 1 is doing, and so on, such that by playing just one note over and over for example, all the VCOs are used in turn. The reasons for wanting this option are rather involved, but with the system provided it is difficult to play and hold a note whilst playing triads on the rest of the keyboard without robbing the sustained note. I won't delve any deeper here, but you may appreciate my suggestion for a cyclic mode better when you've tried the Mono/Poly for yourself.

'Chord/Share' isn't anything breathtakingly new and exciting - Roland had it on their JP-4. Basically, all that happens is that the instrument operates monophonically with all the oscillators in parallel only when the keyboard is being played monophonically; if two notes are played VCOs 1 and 2 are assigned to one note, 3 and 4 to the other; when three notes are played it's a matter of one VCO per note, the fourth just idling.

Finally, we have 'Chord Memory', which again has been seen before, most notably on the Oberheim OB-X, OB-XS, and OB-Xa. Basically, what happens is that a chord is played, say a major seventh, the Chord Memory switch is activated and from then on every note played causes the oscillators to split off into a major seventh, so you now have a monophonic machine but with the oscillators set at predetermined intervals apart. Obviously, you can do this without a special button, purely and simply by tuning the oscillators to different pitches and using the synth in mono mode, but this is far faster to use.

Mono/Poly opened up.

So far so good, but with any pseudo-polyphonic synthesiser of this type, sharing all the oscillators with just one VCA and one VCF, there are going to be problems. What happens, for example, when you hold and sustain one note, and play and release another, especially if you want the voicings to sound similar, and they have relatively long release times? The first problem is the filter triggering of the envelope - this is got round by having a single or multiple trigger switch, so that in multiple mode the filter envelope retriggers every time a new note is played, thus affecting not only the new note, but also the one being held; in single mode, however, a new trigger pulse will only be generated after the keyboard has been cleared, thus the new note in our example won't affect the filter. This is a fairly good compromise, with not too drastic limitations - but what happens to the loudness envelope of our second note. In the Mono/Poly the oscillators are gated to the VCF, so when the second key is released, the sound is cut off sharply, leaving just the held note, even if the release time is set for several seconds. This isn't a good state of affairs, so Korg have come up with an 'Auto-Damp' switch, which sustains the release note until the first key is released, both notes fading with the VCA envelope release time. Again, it isn't an ideal situation, but it does come in useful for a lot of playing styles, and with these two facilities, the polyphonic performance of this pseudo-polyphonic machine is greatly enhanced. Before looking at the various voicing elements in more detail, I should point out that the Mono/Poly does offer polyphonic portamento, i.e. there's a slew limiter on the control voltage line to all oscillators.

Each oscillator is affected by the master tune control (± a semitone), and oscillators 2, 3 and 4 have separate fine tune controls (also ± a semitone); in addition, a master detune knob can be used to shift the frequencies of VCOs 2 and 4. Otherwise, the oscillators are all the same, offering 16', 8', 4' and 2' pitches with triangle, ramp, pulse (width variable) and pulse width modulated waveforms. As previously mentioned, each oscillator has its own level control and the sound generation network is completed by a noise source.

The voltage controlled filter is a 24dB/octave low pass type, that can be made to self-oscillate, and has keyboard track, positive and negative envelope modulation facilities. The filter has its own ADSR envelope, as does the voltage controlled amplifier.

The Mono/Poly has two low frequency oscillators, or modulation generators as Korg would have them; one providing sawtooth, ramp up, ramp down, and square waves, and being used to modulate, via the performance wheel, the pitch of the oscillators, or the filter, and if required, the pulse width of the oscillators and the second LFO is used again either to control the pulse width, or to act as the clock for the Arpeggiator.

The Mono/Poly is nothing if not comprehensive, and neatly arranged in the centre of the control panel, we have an array of controls that provide different forms of cross modulation and synchronisation effects. These can be preset before hand, and introduced at the touch of a momentary button when required to come into action. I won't delve too deeply here, but I will stress that this is a particularly impressive modulation/effect section.

The Arpeggiator is an increasingly popular feature of today's monophonic and polyphonic synths. Basically, all you need to do is play and hold a chord (you can use the latch feature), and the control circuitry of the synth will play each note in turn at a rate determined by the speed of the second low frequency oscillator. This arpeggio can be further expanded automatically across the width of the entire keyboard, and with the Mono/Poly three patterns are provided: Up, Up/Down and Down.

The final control that we've not yet discussed on the Mono/Poly's fascia is one of the most important yet in the case of this machine, one of the weakest. It's the pitch-bend performance control wheel, which has a centre-dente to ensure that it returns to its initial position. This is important, because if you don't get the instrument back in tune after a 'bend' then all is lost. Here the centre-dente is very weak - I suggest that it should be strengthened considerably (Korg engineers please note).

Finally we come to the rear panel, which offers us: an audio output, headphone output (good and loud), control voltage and gate ins and outs (I'm glad to see that Korg have now gone over to the volts/octave system), VCO FM in, VCF FM in (both for pedals), Portamento (footswitch), and Arpeggio TRIG in (for driving from a drum machine I guess). So a good array of interface sockets here.


Well, I don't think that the Mono/Poly can take much of a knocking - at £689 it is a very nice machine indeed. At first it looks a bit confusing with all the knobs, but it is surprisingly easy to operate. It is well built and has a good overall tone. This synth really is an all-purpose machine - its modulation facilities make it good for home recording, sound effects, imitative synthesis etc., whilst it is suitable for use live, though you'd have to be well experienced on the machine to make quick sound changes. As a polyphonic it performs as well as any other costing under £1,000, and as a monophonic it truly is a versatile beast, especially with the four independent oscillators. So, a good eight out of ten for Korg on this one... no, perhaps even nine.

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Electronics & Music Maker - Copyright: Music Maker Publications (UK), Future Publishing.


Electronics & Music Maker - Apr 1982

Scanned by: Stewart Lawler

Gear in this article:

Synthesizer > Korg > Mono/Poly

Gear Tags:

Analog Synth

Review by Dave Crombie

Previous article in this issue:

> Human League in the Studio

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