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SCI Pro1

Analogue Monosynth (Retro) By Paul Ward
Published March 1994

SCI's Pro 1 is one of the classiest little monosynths on the second‑hand market, as Paul Ward explains.

Before anyone starts thinking "here's a starry‑eyed dude who's just done a bit of retro‑buying," I'll point out that I bought my SCl Pro 1 when they were still rolling off the production line. Rather than being in the honeymoon period, my synth and I are a well‑established partnership — we know each other's faults, but we stay together anyway! If you want some 'star quality' assurance for the Pro 1, look no further than Mark Kelly of Marillion or Vince Clarke of Erasure. In fact, Vince made nearly all the backing for Yazoo's 'Only You' on the Pro 1, including the bass drum (I used to have a copy of some of Vince's patch sheets, which made fascinating reading!)

Having already taken the world by storm with the Prophet 5, Sequential Circuits introduced the Pro 1 in the early '80s. On its launch, they had the bold effrontery to ask "Why would anyone make another monosynth?" And, indeed, very few companies from that time onwards did make another monosynth. Ironically, this probably had more to do with the success of SCI's excellent Prophet 5 than the Pro 1. Having been confined to chord work on electric pianos, organs and weedy string synths for what seemed an eternity, keyboard players were demanding affordable polyphonic synthesizers. The Prophet 5 went a long way towards making that ideal a reality, and other manufacturers were keen to follow the success of the Prophet 5 with their own programmable polysynths. To introduce a monosynth with no memories in 1981 might have been seen as a step backwards. But the demand for monosynths was still alive, and we of a fiscally‑challenged persuasion could now afford a piece of the 'Prophet sound' without selling the drummer's car.

The Pro 1 was essentially one voice of a Prophet 5, with near‑identical sound creation abilities. It was seen very much as a poor man's MiniMoog, and undoubtedly owed much of its architecture to the Moog — hardly surprising, since the brief for the Prophet 5 had apparently been to produce a polyphonic MiniMoog.

But SCI's little monosynth is very much its own man. To expect to hear the exact tones of a Minimoog or a TB303 from anything other than the actual machines themselves is to miss the point entirely. The Pro 1 is capable of earth‑shaking bass and ear‑splitting shrieks with the best of them, but throughout it retains its own identity.

Sonic Arsenal

Let's run through the Pro 1's arsenal of features to see what makes it beep.

Both oscillators produce sawtooth and square/pulse waveshapes, with the pulse‑width ratio continuously variable between square (50%) and inaudible (approaching 100%). Perhaps more importantly, these waves can be switched in together to provide some interesting composite waveshapes. Additionally, Oscillator B sports a triangle wave option, which is excellent for fattening up the bass end of things. Both oscillators are independently switchable between four‑octave ranges and have an independent tuning knob to provide musical (or non‑musical) intervals up or down from their (non‑detented) centre point. Oscillator sync is possible, which produces some gut‑wrenching sync‑sweeps and aggressive lead sounds. Oscillator B can also provide a second LFO; I find myself with oscillator B nearly always switched to this setting to provide a sub‑octave to oscillator A, usually with triangle wave switched in. To assist in its role as an LFO, oscillator B can be removed from the control of the keyboard to provide a fixed frequency source.

Portamento is a tweak of a knob away and has a nice little variation in a switch that allows you to trigger the effect by playing with a legato style (keeping one note pressed as you play the next); a small touch, but one that adds a little more value for your money. Additionally, you can alter the trigger mode of the keyboard to suit your playing style by flicking the normal/retrig switch — I recall being bowled over by this small feature when I first switched on my Pro 1. Most early monosynths worked on the principle of a single keyboard trigger; if you played legato the envelopes would not retrigger. This was fine at times, allowing an extra degree of expression to be added, but during faster passages, where low sustain values were in use, you had to make very sure that your fingers left the keys between individual notes or you would lose some of them as the decay faded. With the normal/retrig switch set to 'retrig', the Pro 1 will re‑fire the envelopes each time a new key is pressed, regardless of whether you are still holding another down. This was possible due to the microprocessor‑controlled keyboard scanning pioneered on the Prophet 5.

The dedicated LFO has a choice of sawtooth, triangle and square waveshapes with speed control. Just like the audio oscillators, these waves can be switched in simultaneously to generate a series of composite waveshapes. An LFO speed indicator would have been helpful — anyone care to do a modification for me? The method used to assign the LFO is a little more involved than some synths, but infinitely more flexible, as we shall see later.

A mixer section allows control of the levels of oscillators A and B, plus a white noise source. Pink noise would have been a nice option, but let's not get too picky. The noise volume control also doubles as the external input level to the Pro 1's filter and envelope sections, so feed in that sampler and freak out on the filter cut‑off control! The external input also doubles as a gate threshold level control to allow external sounds to fire the Pro 1's envelope generators. This is both a blessing and a curse, as the correct level to reliably trigger the gate is usually far lower than the ideal audio level to feed the envelope and filter! I can live with it...

The filter is a simple low‑pass affair with resonance that goes into self‑oscillation, and continuously variable controls for keyboard tracking and envelope control. The character of an analogue synth's filter goes a long way towards defining the character of the instrument as a whole. The Pro 1's filter isn't as aggressive as its Moog or ARP cousins, nor is it as polite as the old Yamaha CS‑Series. It is best described as bright and distortion‑free, unlike the Moog's, which could be overdriven from the mixer section. Where the Moogs and ARPs run out of treble, the Pro 1 opens up just that touch more to a truly glorious rasp of pin‑sharp sawteeth! A slightly less endearing trait is the tendency for the bass end of the synth's sound to die away quite dramatically as the resonance is turned up. To be fair, most synths (including the Minimoog) can be accused of this to some extent, but the Prophet filter seems more prone to it than any other I have come across. On the plus side, it does mean that a sound achieves more 'presence' with resonance judiciously introduced. Merely turning the volume up is enough to cover the shortfall of lower frequencies.

Both filter and amplifier envelope generators are provided, with full control of attack, decay, sustain and release (ADSR). The filter envelope can be fed to other destinations, such as oscillator pitch or pulse width. The attack, decay and release times at their minimum settings are viciously fast, unlike many digital synths I could mention, allowing very percussive sounds to be generated with ease. Wood blocks, snares and bass drums are a doddle to find on a Pro 1, as are chunky sequence lines and bass pulses.

Magical Modulation

Now comes the Pro 1's real piece of magic — the modulation section. In days of yore it was the norm to patch synth modules, such as LFOs and ADSRs, together by plugging leads into what looked like a telephone exchange. This gave the operator total freedom to plug any output to any input which, like all flexible systems, allowed for some wonderful creative abuse, but also produced an infinite number of possibilities for total confusion, usually accompanied by total silence. When the Minimoog came along, this flexibility was sacrificed in favour of ease of operation by hardwiring the modules together in a practical and logical manner. For instance, the LFO would modulate pitch and filter only and the envelope generators were dedicated to amplifier and filter. Where SCI scored was in providing a halfway house of relative flexibility while still maintaining the simplicity of a hard‑wired architecture.

The modulation sources that enter the modulation matrix are the outputs from the LFO, the filter envelope and oscillator B. The destinations from the matrix are oscillator A pitch, oscillator B pitch, oscillator A pulse width, oscillator B pulse width, and filter cutoff. Each modulator can be routed either directly to its destination(s), or can be passed via the modulation wheel. The incoming modulation amount from any source is continuously variable with a dedicated knob. To put this into practical terms, you could have, say, the LFO passing through the mod wheel set to produce vibrato on oscillator 1, while oscillator 2 directly sweeps the filter cutoff, while the filter envelope introduces speed fluctuations in oscillator 2 and modulates the pulse width of oscillator 1. Welcome to the wonderful world of analogue synthesis — and not a patch cord in sight! Many weird 'off the wall' sound effects are possible through the use of the modulation routings. Once mastered, the modulation capabilities hold the key to some of the most exciting analogue synth sounds to be found.

Superb Sounds

Put this all together and the Pro 1 is capable of some superb sounds. It is my first port of call for bass tones, being less 'woolly' than my Minimoog. For chunky sequenced riffs it is amongst the best in its class, particularly with judicious use of oscillator sync and envelope modulation of filter and pulse width (the lightning‑fast envelopes are invaluable in this kind of territory). The lead sounds on offer are searingly fat and creamy and, with the oscillator sync switched in, are capable of shredding silk!

I suppose some mention should be made of the arpeggiator, itself a desirable feature to many players, and the 40‑note sequencer. Both of these features rely on the LFO for their internal clock source, so the LFO is less flexible as a modulation source, unless you don't mind it sweeping along in time with the sequence! If you use an external clock source, then the LFO is back in service. The arpeggiator can be set to scan the keyboard up or up/down. A 'latching' function allows you to leave the Pro 1 playing the last notes you assigned. Whilst latched, pressing extra notes adds them to the arpeggio for as long as they are held. Clever, but I have to confess to never having found much use for this feature.

The sequencer is as basic as they come, but a great source of inspiration if you jab a few notes and insert some random gaps. There are two sequence memories available, but they share the 40‑note pool. Go over your 40‑note limit and you're overwriting previously entered data! Where the sequencer really scores is that you can transpose it as it is running by hitting notes on the keyboard. This way lies fun a‑plenty. You can't save your sequences, not even to tape, but you could always fall back on good old analogue pen and paper (OK, type it into the Cubase Info page if you must...). After all you'll only be taking note of 40 notes/gaps at most!

Undoubtedly the most joy you can have with the Pro 1 is by using it with a MIDI to CV converter. Plug in the CV and gate leads, switch the trigger mode to external and away you go. The trigger input doubles as the clock source for the arpeggiator and sequencer, so you can even set up a sequence that runs in sync with the rest of the MIDI system while still allowing you to transpose it in real time. A filter control input even allows you to modulate the Pro 1's filter by velocity or mod wheel. Why not feed a guitar through the external input for instant Shamen‑ish triggered gating, or just use the Pro 1 as a MIDI‑controlled noise gate at mixdown. And all the time those lovely knobs and switches are at your every command. Aah! Order me another dozen please...

So, when you've managed to save the exorbitant price of that cheesy little synth that everyone seems to be raving about, just have another think before you part with your hard/easy‑earned cash. Today's flavour of the month could prove to be a bit of joke in a couple of years' time. A Pro 1 can still be picked up for less than £200 at the moment, though that could change if everyone begins to realise what they are missing. At least you can't say you weren't warned!

The Bad News

o what are the down sides? Surely the Pro 1 has a few nasty surprises up its sleeve? Well, I have to say that reliability is somewhat questionable. To its credit, my own machine has never broken down, but I know of others that have — with sickening regularity. The most notorious fault seems to be the double triggering keyboard. Every Pro 1 I have encountered has eventually exhibited this anomaly as it gets older. It is caused by the keyboard mounting gradually bending with age. Happily, five minutes with a screwdriver and a folded‑up piece of cardboard soon fixes it! More seriously, the knobs and switches are prone to become crackly with age or lack of use. Some Pro 1s seem to be better than others in this respect, possibly due to the components that were available to SCI at the time of manufacture. My synth has the worst switches in the history of electronic engineering and I now have to click them two or three times and hope for a good contact; not the best of situations when playing live! Happily, most of the internals can still be bought from any half‑decent electronic component supplier — I've promised my Pro 1 a major overhaul soon. The only other criticism I can really make is the amount of acoustic hum from the transformer. Again, this seems to depend on the individual machine. But fear not, the hum does not find its way to the Pro 1's audio circuits — the output is as clean as a referee's orally‑operated signalling device.

Another point to watch out for is the output level. This synth is HOT! While every other synth in my studio spends its life at output level 10, the Pro 1 rarely creeps over 3 — with zero gain on the desk! While this is not really a problem (would that all synths put out this kind of level!), it does need to be handled with care.