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Oberheim Poly

Article from Sound International, May 1978

Dave Crombie checks out the Oberheim 4-voice polyphonic synth.

Oberheim synthesisers may be a new name to many, but with musicians and bands such as Chick Corea, Herbie Hancock, Patrick Moraz, Pink Floyd, Tangerine Dream, Weather Report, and many others all having used Oberheim synthesisers, we felt a deeper look into the Oberheim catalogue was in order.

Tom Oberheim, head of the comparatively small Santa Monica company, is not unknown to the rock fraternity; it was he who designed the Maestro phaser. The first product he put out under the name of Oberheim Electronics was the reasonably successful digital sequencer, but the problem with connecting a sequencer to an ARP 2600 or a Minimoog was that you could not play your synthesiser and use the sequencer simultaneously: the sequencer took over. To overcome this problem the Oberheim synthesiser expander module was born. This was a small, compact unit with similar facilities to an ARP Odyssey without the keyboard. It was, in fact, this synthesiser expander module that was to become the basis of the 2, 4, and 8-Voice synthesisers. At present, the most popular of the Oberheim range is the 4-Voice with optional programmer, on which we will concentrate for the remainder of this article.

When first confronted with this machine the immediate reaction is one of awe. Does it really need all those knobs? The answer, in fact, is no! On closer examination, however, it can be seen that the instrument consists of 4 main sections: (a) the four synthesiser expander modules (SEMs); (b) the keyboard and polyphonic keyboard controller; (c) the programmer; (d) the output module. The instrument's capabilities will become a lot clearer by taking each section in turn.

The basic Synthesiser Expander Module

(a) The Synthesiser Expander Modules (SEMs)
Each SEM is a synthesiser in itself, containing two voltage controlled oscillators, each providing sawtooth and pulse (width adjustable) waveforms; a four mode, two pole voltage controlled filter; a voltage controlled amplifier; a low frequency oscillator; and two ADS envelope generators, one of which can sweep the filter either up or down (a useful facility, not often encountered). This is a most impressive little unit with signal routing controlled by slide switches and centre-stop rotary controls which allow patches to be quickly and easily generated. There are four identical SEMs incorporated in the standard 4-Voice instrument.

(b) The keyboard and polyphonic keyboard controller (positioned just to the left of the keyboard) This module is not quite so simple. When a note is pressed on the 49-note keyboard (C-C), control signals are directed to an SEM as determined by the settings of the keyboard switches. The 'reset-continuous' switch is used to select whether successive notes are always assigned to the SEMs in ascending numerical order (1, 2, 3, 4) or whether a note is assigned to the SEM following in sequence the last one assigned, hence a four note chord can be played in several different ways. The keyboard may be split into two equal parts and the '1-3, 2-2, 3-1' switch directs control signals from the lower and upper halves of the keyboard to different, independent, combinations of SEMs. The 'unison' switch, with the 'split' off, puts the instrument into monophonic mode, each note triggering all SEMs; with the 'split' on, the instrument becomes duophonic, grouping SEMs as designated by the '1-3, 2-2, 3-1' switch. There is a portamento control assignable to either top, bottom, or all the keyboard. To complete the keyboard controller module, there is a master VCF tune control which will change the filter frequency on all the SEMs, and a master VCO tune control with centre-stop for pitchbend applications, coupled with an 'up one octave, down one octave' switch to increase the range of the keyboard. This complete module sounds a bit complicated, but after ten minutes with the instrument one can see how straightforward and versatile it is.

(c) The Programmer
When purchasing the instrument this comes as an option, so you can still play the instrument without it, but in my opinion it is this module that makes the instrument a world beater. The programmer is basically a memory, and looks a bit similar to an SEM. With it you can remember the most important settings of the SEMs, namely oscillator pitch, filter frequency and modulation, vibrato rate and depth, and envelope generator parameters. These can all be set and stored separately for each SEM. All the normal polyphonic keyboard functions such as pitchbend, portamento, master filter tune, and keyboard split are unaffected by the programmer.

When using the programmer it is best to tune up all the SEMs, setting the filters, and then work exclusively with the programmer controls to get the sound you want, programming each SEM individually. With this system you can program sixteen complete sounds, i.e. 16 sets of four SEM settings. And that is not all — with a cassette interface, groups of sixteen programmes can be dumped on to a standard cassette tape, so that you can store any number of patches. If you do not want to use the cassette system, the programmer will not forget your sixteen programs, unless told to do so, even when the power is turned off!

(d) The output module
This consists of a four-input mixer with a level control and a pan control on each channel, a master gain control, left and right channel 600-ohm line outputs and a pair of stereo headphone amplifier outputs. The pan controls allow you to obtain a stereo spread of the four SEM outputs producing a most effective live sound. There is also a master filter pedal socket and connections for upgrading the 4-Voice to an 8-Voice.

These then are the basic modules that make up the instrument.

The actual construction of the instrument is excellent, consisting of a wooden case with removable hinged lid. Into this case is fastened a metal frame to take the modules. Each module is beautifully made and designed using a 'piggy-back' printed circuit board technique, which cuts down the wiring inside considerably. Installing or removing modules is very simple, requiring only four screws and the making (or breaking) of a handful of push connectors. The components used are of high quality, and overall the physical design is one of the best I have come across. This contributes to both the reliability and to the stability of the instrument, the voltage controlled oscillators being very stable indeed.

With an instrument of this nature the variety of sounds obtainable is infinite. Having eight independent oscillators gives you the capability of obtaining realistic copies of most instruments - I even managed to get a brass sound that impressed a sax player! Almost the only real limitation to the sounds available lies with the imagination of the user. Having said that, there are a couple of areas for complaint. One is that the instrument has no noise source built into it as standard. This can be added via another module, but I feel it would be useful to have one built into each SEM. The other small fault is the portamento, which in my opinion does not give a wide enough range. However, there are many pluses to cancel out these two minuses.

Being a modular system, this instrument can be bought with any number of SEMs, and more purchased at a later date. Blank panels are supplied for those who want to start with less than 4-voices or without the programmer, or alternatively Oberheim manufacture a complete 2-Voice system with a small analogue sequencer built in.

The 4-Voice with programmer is not a cheap instrument, but it is a musicians' instrument and as such is exceptionally good value for money. Having worked with it for some time, I have found the range of sounds obtainable, the quality, and the value this machine offers, far superior to that of the nearest competition, and I think this will continue to be the case for some time. Words cannot adequately describe sounds, so if you get a chance, do go and have a listen.

rrp (without Programmer) £2638.89/$4295.OO

Dave Crombie is resident electronic design engineer at Rod Argent's professional keyboard store in Central London.

Also featuring gear in this article

Previous Article in this issue

Sonor - Phonic Sound Machine XK9409

Next article in this issue

Elvis Costello

Publisher: Sound International - Link House Publications

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Sound International - May 1978

Donated & scanned by: Mike Gorman

Gear in this article:

Synthesizer > Oberheim > 4 Voice

Gear Tags:

Analog Synth

Review by Dave Crombie

Previous article in this issue:

> Sonor - Phonic Sound Machine...

Next article in this issue:

> Elvis Costello

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