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Yamaha CS70M

Programmable Dual Channel Polyphonic Synthesiser

The CS70M is a mixture of an update of the CS60 and the CS80. Keyboard-wise it doesn't supercede the CS80; it's more like the CS60 version but electronically it's better. It's two channel stereo with 12 oscillators, playing 6 notes on each separate channel output (or mixed mono if desired). Thirty different sounds can be programmed and stored via 30 buttons arranged in two rows of 15 on the main panel above the 61 note keyboard. Any sound from the top or bottom row can be selected, so Channel 1 button 2 can play with Channel 2 button 9 and so on.

In addition, there is a special magnetic data card system that extends the sound storage to the number of cards you possess. These fit conveniently into the small wallet supplied and hold two voices, one at each end of the card. The voice card selected is fed into the small slit just below the right hand end of the keyboard. The whole transfer operation takes just about a second and allows all the sounds in the CS70M's memory to be changed using 15 cards. Yamaha hope to Supply around 30 cards with programmed sounds already on them, but you can also 'store' your own sounds on blank data cards or re-use cards included in the wallet.

The idea of this system is to eliminate the use of a cassette recorder and extra interfacing and it does make it possible to enter one or two new sounds between numbers (although the 30 memories should be sufficient for most performances and could be programmed by a set of cards beforehand). The same card system is employed on the new GS1 and GS2 instruments.

The CS70M is something of a departure from their norm for Yamaha. The heart of this particular beast is not one of their own in-house three thousand leg LSIs, but a very standard Z80 CPU!

Three EPROMs, each 2K x 8 bit, provides instructions for key assignment, programming and sequence modes. The machine has 5K x 8 bits of static RAM with battery back-up to facilitate storage of sound patches. A-nice spin-off from using a micro is the 'auto-tune' button which fractionally adjusts the key voltages of the 12 VCOs to maintain highly accurate pitching. This is achieved by digital comparison between the master clock and the tone oscillators. Polyphonic sequencing is achieved by digital recording and playback of keyboard data.

The synthesiser has 12 VCO, 12 VCF, 12 VCA, 24 EG and 2 LFO functions. The individual tone generator blocks are essentially similar to the earlier CS range. However, the CS70M oscillators are a new design with far better tuning stability.

Each channel has a grey 'manual' button which makes available all the controls for one single VCO, VCF, VCA synthesiser, with extensive LFO modulation facilities. Using these 39 controls, a new sound can be programmed (or an existing sound edited) and stored in one of the 30 memories. The built-in memory has battery back-up for storage when the synthesiser is switched off. Alternatively programs can be loaded on to a magnetic data card for future use.

Another versatile feature is that any one of the programmed sounds can be put into 'edit' mode (even in keyboard split mode), so that its parameters can be altered using the manual controls. No information stored is changed until you actually move a yellow slider or touch a grey button in the programmable section and no change to the original sound will be made unless you 'write' the information in. A clear indication of edit mode is given by the flashing LED on the program button selected.

Programmable Parameters

The synthesiser section is almost completely digital in its control. You can hear this as you adjust e.g. volume by its stepped changes.

The sliders and specially designed touch buttons (with LED indication of their selection), can all be used to make the polyphonic synthesiser sound. The VCO section offers sine wave plus square wave, with up to 50% pulse width adjustment (manually or through modulation), or sawtooth wave, and noise is provided as the third mixable sound source. Oscillator basic pitch is chosen from 16, 8, 5⅓, 4, 2⅔, and 2 foot for both Channel 1 and 2 so that useful pitch mixtures can be obtained. These are selected using special sliders that have 'click-stop' positions.

Next we have Yamaha's very smooth filters which can be in low pass, band pass or high pass mode. The usual filter controls are available for setting attack, decay, release times and sustain level (ADSR) with variable EG depth, cut-off frequency and resonance sliders. The resonance in conjunction with cut-off frequency will give a very useful harmonic sweep without actually going into oscillation. ADSR times can be multiplied by 5 and the envelope generator shape it produces can be inverted to give maximum tone variation. I missed the CS50/60/80 layout of high and low pass filters here — they gave some superb tonal changes which are not possible with this new more usual arrangement.

The VCA has its own ADSR controls (with x5 option) plus a volume slider, positioned correctly at the far right as the final setting for the programmed sound. There have been some 'programmables' without this, yet it is essential for quick matching of the 30 presets to the desired levels in performance.

The LFO section is most comprehensive and gives a great many modulation possibilities, probably derived from the CS30 synthesiser. There are six basic treatments that can produce modulation and these can be sent to one or more of the four main 'destinations' — to change VCO pitch, to give pulse width modulation, to change VCF tone and to modulate the VCA.

LFO speed can be adjusted to give a steady modulation between one cycle every 10 seconds and 100Hz — a range that's wide enough for most performance purposes. In addition, the LFO speed can be made to speed up and slow down by use of the attack and decay time sliders respectively. Increasing the EG depth will give progressively wider variation of the basic 'speed' setting of the LFO.

The amount of modulation that takes place can be programmed and the six modulation effects are sine wave, sawtooth wave, sample and hold, ring modulation and upwards or downwards glide to the notes played.

Non-Programmable Controls

In the sections so far mentioned, all the controls are programmable and will be remembered on the chosen preset button. Other non programmable controls provided includes a fine tune rotary control for LFO speed, a 1 or 1 + 2 select button for the LFO modulation, and a pitch modulation 'wheel' select button that overrides an extra LFO section (mentioned later) and sends the main LFO to vary the pitch of channels 1 or 2 or both. A 'hold' button keeps the VCA open for continuous playing of the synthesiser sound.

The balance between channels 1 and 2 can be adjusted and the overall filter tone brightness can be increased or decreased using the 'brilliance' slider. 'Sustain' can also be further extended from the programmed setting and the superb polyphonic 'glissando' effect is featured in addition to portamento, with variable jump time from one chord to the next. There is a further 'Master Volume' with a sound on/off switch for setting output levels to your mixer or amplifier.

In the Pitch Modulation section, to the left of the keyboard, a second wheel lets you 'play' the pitch between octave, fifth and third limits.

In Use

During setting up, the synthesiser outputs two voices, so if you're programming a new sound (or editing an old one) it's best to put the balance slider to the channel you're working on.

This dual system, operating from 15 presets and the panel, really stretches the sound creating possibilities. For example, a whistle can have its 'chiff' accurately set on Channel 2 without altering the basic whistle envelope and tone shaping parameters, which are obviously different, on Channel 1. Not only can dual pitch and tone combinations be used but, because of the 'stereo' output facility (Channel 1 = Left, Channel 2 = Right) you can create exciting panning and spatial changes, and complex sounds such as strings can be really exploited.

Programmable Split Keyboard System

The keyboard itself offers further scope for expressing the player's music. In 'Split' mode the CS70M's keyboard divides between the second and third octaves so that channels play separately for left and right hands. You can also choose another split point by simply pressing the 'split' key as you select the split mode switch. Since only 6 notes maximum are obtainable in the synthesiser, a choice of 2 or 4 notes for upper or lower split (and vice versa) is given. A 'unison' mode puts all the 6 notes on one for a very big sound — although in practice the normal dual channel mode over the whole keyboard is sufficient to give the same kind of effect.

Yet another important aspect of the keyboard is its touch control. Once you've played with touch/pressure sensitive keyboards (or indeed, learnt to play on the piano as most of us do) then this becomes an essential facility. Surprisingly on a sophisticated machine as this certainly is, the areas of control which come from pressing the key harder — the VCO, VCF and VCA — using the 'After Touch', are mixable but all at the same sensitivity. Although the overall pressure sensitivity is adjustable, using a rather out of place miniature rotary pot, it is quite a disadvantage not to be able to give e.g. a little pitch vibrato and tonal 'wah' whilst achieving a big dynamic change (back to the CS80!).

The after touch controls form part of a second LFO section, in other words, you're not just opening the VCF, VCA or VCO pitch — you are of course modulating it by the amount of pressure you apply to the note. There's a metal bar under the keyboard which operates a photo cell to give a varying control voltage (so pressing one note hard modulates all the others being played). This simple mechanism does work well and gives precise depth control once you've improved your playing technique!

LFO modulation 'speed' and waveshape (sine, sawtooth and square) can be chosen and routed at the same time or separately to the pitch modulation wheel and/or a foot pedal. This is a nice extra in that 2 LFOs effects such as slow PW modulation and fast vibrato can be used.

The usual tone control for overall pitch setting over a few semitones is provided, plus a Channel 2 'detune' that makes brass, strings and piano sounds much richer. I am surprised that Detune cannot be programmed — it's vital on many sounds. Incidentally, retuning with the autotune button takes merely a second without affecting the mode, program etc that you're using at the time. It's certainly the quickest tune-up in the business!

One more effect to go before we reach the sequencer. It's called 'Chorus' and is taken directly from the SK20/50 series to give 'Ensemble' (3-stage phased delay) that's essential for strings, and slow/fast tremolo for chorale and Leslie effects especially useful with an organ type of program. It has limited use with bright synthesiser sounds in ensemble mode as it reduces the upper bandwidth and definitely adds extra hiss to the signal.

4-bank Polyphonic Sequencer

Sequencer and additional control facilities.

Where there's a micro there's usually RAM and Yamaha makes use of both these items with the sequencer. Becoming more and more part of the 'high class' family of polysynths, the sequencer can memorise up to four different extracts played in real time on the keyboard — all with up to 6-note polyphonic playback if desired. What is innovative, is that if less than 6 note 'events' are used in a sequence, then the remaining voices can be played manually. In the split mode, you can play different pairs of voices with the sequencer and your hands.

No battery back-up means you approach this sequencer as a live performance facility — play a sequence once and after that just have fun playing your solo (or bass and lead) with it! It opens up new ideas in playing technique especially using the tempo control (and x2 button) to speed up 'events' faster than you can normally manage.

A sequence can be repeated for as long as you want and if set to CV only mode, it triggers presumably from the keyboard, or via the clock speed (tempo) set. 'Record' and 'Play' buttons operate the system and sequences A, B, C, D when recorded will play back in that order automatically. Hitting the play button at the right time at the end of the sequence is essential to keep the basic tempo correct when repeating.

There are 180 events (holding note pitch and on/off times) possible for each sequence. When you're reaching the end of the memory, the LED on the sequence button flashes. A busy 4-6 note chord sequence lasts only a few bars, so middle 8's and longer sequences have to be shared out, but a stored melody or bass line can be quite long. It's not really any problem on stage as the short sequence is all you need with the 'repeat' button in use, but its application in the studio situation would be more for repeating polyphonic sequences rather than recording a complete piece (especially as you can't take the instrument into a session with stored sequences).

If you're doing a single riff it's nice to do it in different keys on each sequence button so you can change keys during an improvisation just when you want. Or you could use the pitch wheel to do the same thing using one sequence only! Of course, the sequence can be replayed on any of the programmed voices. Doubling up with the 'x2' button is interesting too!

Rear connections.

Rear Connections

Some interesting developments here. Besides the usual outputs jacks (including balanced XLR mixed output), there's foot control sockets for modulation depth, brilliance and volume, and foot switch sockets for sequencer start, portamento and sustain. But more important is the provision of solo output control voltage (operating from highest note played) plus trigger, so that any Yamaha (or Korg) synth with external CV and trigger inputs can be played at the same time.

This extra control of 'mono from poly' is a feature on the new Yamahas and certainly emphasises their concept of 'one keyboard plays many instruments'. Yamaha take this a step further with a multiway 'keycode' input socket that allows you to play the CS70M from another Yamaha that has a mating output socket. To date, this means the SK30 and SK50D. I had visions of linking up my micro to control the synth but no circuitry, cable link or advice is available as yet.

Finally, as with most programmables, a lock/unlock switch is tucked away on the rear to protect all those precious programmes you've forgotten to store on magnetic card.

Magnetic card and storage wallet.

To sum up, the CS70M is exactly what it is meant to be — a first class performance instrument that has all the quality expected of Yamaha.

With 30 presets on board and a wallet of sounds in your pocket you should be ready for the charts! Touch sensitivity and sequencer are great facilities although other extras such as case (or lid), stand (music or legs) are not available. Its recommended price is £3,479 inc. VAT and foot pedals and switches are optional extras which can turn out to be expensive if you want to have as many as Rick Wakeman! Don't miss the chance of hearing it played by Dave Bristow on E&MM Cassette No. 5.

The CS70M is distributed in the UK by Kemble Organ Sales Ltd, (Contact Details).

Also featuring gear in this article

Previous Article in this issue

Bio Music

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Vox Custom Bass and Custom 25 Guitar

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


Electronics & Music Maker - Dec 1981

Gear in this article:

Synthesizer > Yamaha > CS70M

Gear Tags:

Analog Synth

Review by Mike Beecher

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