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Sequential Circuits Six Trak Polysynth

This exciting six voice polyphonic synth comes under scrutiny.

With competition at the lower end of the polyphonic synthesiser market hotting-up, Sequential Circuits have entered the fray with the Six-Trak, a fully-programmable six-voice polysynth with a built-in multitrack sequencer. Dan Goldstein puts it through its paces and examines it in the context of SCI's Traks Music System.

It would seem that most keyboard manufacturers have now all but given up on the monophonic synth and are devoting their efforts instead to developing more versatile and more cost-effective polyphonic devices. Sequential Circuits' new Six-Trak polysynth is further evidence of this trend, and in fact goes one better than many of its competitors in that it also forms the basis of a complete performing, sequencing, and rhythm programming system, the like of which has only previously been seen among products of considerably greater expense.


The Six-Traks is a six-voice polyphonic synthesiser with one oscillator-per-voice, and, unlike the Korg Poly 800 reviewed in last month's E&MM, the specification also includes one 4-pole filter for each voice, so that multiple triggering is possible.

In what amounts to something of a break with tradition, the Six-Trak utilises the parameter/value method of programming popularised by Korg with the 61 and continued by the 800. For the uninitiated, this means that in place of long rows of rotary pots with one function each, the control panel is occupied instead by a control section consisting of three selector switches and a numeric keypad for selecting which parameter is to be altered.

On the Six-Trak, parameter values are selected not by a pair of increment/decrement pushbuttons, as is commonly found on synths of this type, but by a single rotary pot in the middle of the control section. This pot has no detents because some parameters are variable over a much wider range than others (the attack time has a value range of 00-15 - maximum time 11 seconds - whereas the pulse wave duty cycle has a value range of 00-63 - maximum 99%) with the result that, with the more precisely variable parameters, the merest turn of the pot sends the values shooting up or down ten units or more. Annoying.

Unlike the Korg instruments, the Six-Trak does not contain a schematic display of all the various parameters and the degrees by which they may be varied, making either a thorough knowledge of the instrument and/or the encyclopedia user's manual a prerequisite for rapid sound alteration, particularly live.

In toto, 35 different parameters make up a sound on the Six-Trak, and even if selecting their respective values isn't quite as trouble free as one would like, what matters is that put together they offer a sound-generation and modulation store of considerable versatility. Parameter 35 is 'Unison'. Value 01 selects this mode, in which the keyboard becomes monophonic, all six voices being assigned to the lowest note played.

Multitrack Sequencing

This really is the Six-Trak's nerve centre, the built-in six-channel sequencer. This has an 800-note capacity (in two memory banks, A and B) and is perhaps most remarkable for the manner in which it allows any of its channels to be recorded individually or together in groups. The closest analogy I could think of was a multitrack tape-recorder, and this is indeed exactly what SCI's designers have aimed for: a sequencer that behaves as if it were a dedicated digital multitrack recorder. To record your initial sequence (backing-track?) all you do is check that the pitch wheel (see later) and Speed knob are centred, select your program (factory preset or user-edited), select Track Record and either Bank A or B, and the sequencer will begin recording the moment your fingers touch the keys for the first time. Stopping the recording is accomplished either by switching Record off (in which case the sequence you just played is played back and looped) or by switching Seq off (in which case your sequence will not be repeated). It's possible to synchronise the first note of your sequence with the start of the sequencer's recording by using the supplied footswitch, while any track can be erased simply by holding down the Track Record button while the desired track switch is selected.

The best is yet to come, however, because on the Six-Trak, any one, two, three, and so on up to six voices can be recorded individually, so that you can build up a polyphonic sequence layer-by-layer. Once you record one voice singly, you're not confined to recording all the others the same way, since it's perfectly possible to record, say, a unison bass-line (track one), followed by a triad backing (tracks two, three, and four) and two lead synth lines (tracks five and six), so long as the overall number of tracks you're using does not exceed six, of course.

Overdubbing in this way is accomplished as follows: existing backing tracks are played back by pressing Seq, while selecting Track Record puts the sequencer into record mode for whichever track(s) you then select. While both Record and Track(s) LEDs are flashing, no notes are recorded, but as soon as this initial loop is over, the first note you play on the keyboard sends the sequencer into record mode on the track(s) selected.

Stack And Arpeggiator

The sequencer section also houses the controls for the Six-Trak's arpeggiator and Stack function. The former has two modes: Up/Down and Assign. In Up/Down the arpeggiator will play up and down all the notes being held down on the keyboard at the time, using only voice six from the oscillator bank. Assign, on the other hand, sequences keys in the order they're played, so that you can play a lead-line slowly and then replay it at a faster tempo using the sequencer section's Speed control.

It is in Stack mode however that some of the Six-Trak's brightest colours are shown to the full. A stack consists of up to six different timbres (programs) assigned to one note on the keyboard. There are two stacks (A and B) on the sequencer control section, so that two separate stacks of sounds can be stored onboard at any time. Each sound in the stack is stored by selecting the desired program on the keypad, switching Track Record on, and pressing the appropriate Track switch. Adjusting the Track Volume control up or down while holding down the relevant Track selector enables certain sounds in the stack to be brought up (or down) in level from the remainder (the same can be done with individual tracks on the sequencer itself), while setting this level to 0 for a particular voice/track deletes that sound from the stack altogether.

With the Legato switch off, the keyboard operates in unison (ie. monophonic) mode as per usual, with multiple triggering and low-note priority, but when Legato is on, single-triggering comes into operation.

Sequencer To Drumtraks

Since the Six-Trak and SCI's new digital drum-machine (see review elsewhere this issue) are intended to work together as part of a purpose-designed system, it's perhaps not surprising that the two sync together remarkably quickly and easily. A simple DIN-to-DIN cable (any old one will do) is connected so that it runs from the Drumtraks' MIDI OUT to the Six-Trak's MIDI IN. Once you've a basic track in time with the Drumtrak's rhythm pattern, turning the Six-trak's Speed control to zero automatically syncs the two devices together, so that all further overdubbing is done in sync with the drum-machine.

It is in fact possible, should you have both the inclination and sufficient capital, to connect two Six-Traks in series with one Drumtraks, while even more bizarrely, connecting Six-Trak MIDI OUT to Drumtraks MIDI IN enables the lowest Six-Trak keys to play on the Drumtraks voices.

Sound Quality

Flying in the face of Far Eastern fashion, Sequential's designers have equipped the Six-Trak with good old-fashioned VCOs as opposed to the digital sound generators now so much in favour in the Land of the Rising Sun. Each oscillator has sawtooth, triangle and pulse waveforms available, so the variety of available sounds is quite a rich one. However, there's no doubting that the Six-Trak's output - and particularly the 100 factory presets - carries a heavy bias towards big, fat analogue lead sounds of which the Americans are still so fond. There's definitely more than a hint of Prophet 5 to the sound of the Six-Trak, more so than the Pro One, I would have said. While the Six-Trak isn't really capable of producing sounds of such 'acoustic' clarity as the best digitals, the other side to the coin is that the output is blissfully free of digital noise, while tuning stability is highly commendable for an analogue design.


Due to the fact that the two machines have been released in the UK almost within days of each other, I suppose it's inevitable that comparisons will be made between Sequential's new baby and the Korg Poly 800, but in reality each has something different to offer. There are several small problem areas with the Six-Trak: the awkward positioning of its mod wheels; its dearth of interfacing sockets (only MIDI in and out provided); the limitations imposed by its four-octave keyboard (a failing it shares with the Korg); and the sponginess of some of its controls, but there are a number of other areas where it scores highly. The sequencer is supremely versatile as well as being unbelievably straightforward to use, its full complement of filters facilitates multiple triggering (once you've got it you never want to be without it), and it syncs up to what is undeniably a superb digital drum-machine in just about the easiest way possible.

If your taste in keyboard sounds leans more towards the old wave than the new - and you like the idea of buying a synth that's part of a convenient and expanding system - you shouldn't have to look much further than the SCI Six-Trak.

(Contact Details)

Also featuring gear in this article

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Music Makers Equipment Scene

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Microlink ML-1 Interface

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


Electronics & Music Maker - Mar 1984

Gear in this article:

Synthesizer > Sequential Circuits > Six Trak

Gear Tags:

Analog Synth

Review by Dan Goldstein

Previous article in this issue:

> Music Makers Equipment Scene...

Next article in this issue:

> Microlink ML-1 Interface

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