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Crumar Stratus

Crumar's all-purpose keyboard, and its larger brother the Trilogy, have been available for a couple of years now, but are still being pushed hard as the sort of instrument which can take the place of two or three others in the standard electromusician's line-up. The Trilogy offers organ, strings and preset polysynth, while the Stratus has organ and variable polysynth only, but is of course a good deal cheaper.

In a sense the Stratus is a hybrid keyboard, like Roland's SA-09 Saturn, and has a battery of sounds of its own which belong neither to the world of the conventional organ nor to that of an expensive and complex polyphonic synth. The hybridisation has been achieved in an imaginative if unusual fashion, described below.

Basic Design

The Stratus is very smartly styled in grey, white and black, and is reminiscent of the Oberheim polyphonics. It's a little more compact than these, however, with a four octave C-C keyboard and wooden end cheeks. The control panel is light grey with 17 rotary controls in black, 9 rotary switches in grey and four horizontal sliders for the mixable organ footages.

The very thorough familiarisation/instruction book begins with the organ section, as this is the simplest to control. Its audio output can be taken separately from a ¼inch jack socket on the back panel, or from the socket marked 'Polysynth' which in fact gives a mix of synth and organ if used alone.

If the latter socket is used, the relative volumes of the sections are balanced by two rotary controls to the left of the control panel. Above these are the organ footage sliders, marked 16', 8', 4' and 2'. These work from left to right, and each has a slightly different tone; in each case the tone becomes slightly sharper as the slider is opened up. The sliders can give a wide range of tones, although these concentrate mainly on powerful church organ effects; there are no 5⅓ or other intermediate harmonics, and no simple way of introducing a key-click or Leslie effect, so Hammond-type sounds are out.

On the other hand, the Stratus organ section can produce many sounds of which a more conventional instrument would not be capable. Its tone oscillators are also those of the polysynth section, and as such come under a limited form of voltage control which makes several useful effects available. There are two banks of oscillators, which can be tuned apart or synchronised together; in the former mode, any effects apply only to the upper oscillator bank.

Effects available include vibrato or trill, with a variable delay, depth, speed and slope (rapidity of onset of vibrato). There are also two forms of glide — not a true polyphonic portamento, but a bend up to or down to the notes played from a variable interval and at a variable speed. This is intended to act as a substitute for pitchbending if you don't have a spare hand while playing.

Stratus opened up.


All these effects also apply to the polysynth, which again has a left-hand volume mix control, and additionally there are three main sections which apply only to the polysynth. These are the Voltage Controlled Filters, Envelope Generators, and Waveform Selection. The polysynth uses the same oscillator bank tuning and sync controls, and additionally there are two Octave pushbuttons with integral LED's, and an Octave Modulation button. The former lower the pitch of each bank by an octave, and the latter produces alternation between the lower and higher octave settings (accompanied by flashing LED's) at a rate determined by the modulation section speed control.

The VCF section has low pass cutoff, resonance and envelope depth/polarity rotaries, and a pedal on/off switch which activates the filter foot pedal. The filter gives a reasonable 'twang' and the quick selection of the reverse configuration is very useful; full resonance can almost be achieved, giving a good selection of abstract sound effects over the synth chords.

Rear connections.

The VCA section is perfectly conventional, with a good slow attack and reasonable decay and release. The Waveform Selection section gives Sawtooth or Square wave on the polysynth, with a mix position which also enables the Alternate switch. This automatically switches between sawtooth and square in Mono or Multi mode — that is, on every key depression, or only after all the keys have been released and one is depressed again.

This choice of reset modes also applies to the slow oscillator in delay mode, allowing some quite expressive playing through the use of different fingering techniques. Crumar take pride in the fact that most of the expression of the instrument comes from playing technique rather than from panel controls, and so although it isn't touch-sensitive as such, the Stratus can produce quite expressive effects without too much difficulty.

If you do have a spare hand, there's a joystick to the left of the keyboard which produces a tone of pitchbend up or down on organ and polysynth, and VCF or VCA modulation on the polysynth alone. This is pleasant to use and lightly sprung, rather like the keyboard itself.

There are one or two features missing from the Stratus — pulse width modulation would have been more useful than the Sawtooth/Square Alternate facility, and a chorus unit would do a lot to make softer and more mobile tones available. On the other hand, there are a couple of unique features, such as the facility for connecting a wind controller to the rear panel.

Voice and VCA-VCF boards.

Master Touch

Steiner's Master Touch unit uses two air tubes to control VCF and VCA, which are fed from a high level unprocessed Signal Out jack. There's also a modulation touch pad which can take over the Stratus' vibrato section.

In normal use, the Stratus is fully polyphonic, but with a limited number of VCF-VCA chains. In fact there are six, and every note in each octave together with its tritone (augmented fourth) shares a channel. This means that sometimes a lower note which is still held will re-articulate when a higher note is played; the handbook points out that you will discover new musical uses for this restrike capability and incorporate it into your playing technique.

The Stratus is a reasonably compact and smartly-designed keyboard hybrid capable of some very powerful clustered chords and with the useful feature of total polyphony in some form. As such, it will probably find itself being used in a wide range of studio and stage applications.

The Crumar Stratus is available from Chase Musicians, (Contact Details)

Also featuring gear in this article

Previous Article in this issue

Shure PE Series

Next article in this issue

Talking Shop

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


Electronics & Music Maker - Dec 1982


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Gear in this article:

Synthesizer > Crumar > Stratus

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Analog Synth


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> Shure PE Series

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