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DSTEC OS1 Original Syn

Analogue Monosynth By Chris Carter
Published July 1999

DSTEC OS1 Original Syn

dsTEC's eye‑catching new analogue mono is bad — but in a good way. Chris Carter reaps the wages of Syn...

The closer the 21st century looms, the more we hark back to the '70s and '80s — or so it seems. New and repackaged analogue and wannabe‑analogue gear, from theremins to drum machines, is being announced on an almost weekly basis, and one of the latest old‑style instruments to appear is the eye‑catching new synth from UK company dsTEC. The OS1 Original Syn is a rackmounting, digitally controlled, monophonic analogue synthesizer conforming to the now classic VCO‑VCF‑VCA‑ADSR‑LFO subtractive synthesis configuration.

As you can see from the photo, the OS1 is exceedingly yellow. Maybe its appearance won't be to everyone'staste, but it's certainly striking. Personally, I quite like the colour, which is an identical shade to the vintage EDP Wasp monosynth — sheer coincidence, I'm sure! One benefit of the bright colour scheme is that the smallish legending is quite easy to read even on a darkened stage. Being constructed of welded steel, the synth feels solid, built to last and prepared for a hard life on the road. Unsurprisingly, it's very heavy for its size.

It's obvious that a lot of thought has gone into the design of the OS1, and that it hasn't just been cobbled together overnight to jump on the retro bandwagon. Indeed, it has apparently been four years in development, is the fir st in a planned series of instruments, and has been created by the same team that dreamed up the Control Synthesis Deep Bass Nine monosynth — see SOS December '94. Accordingly (and refreshingly), it's entirely UK‑designed and built.


DSTEC OS1 Original Syn

Despite its relatively minimalist outward appearance, the OS1's internal synth and MIDI specification is very comprehensive. The unit has three independent VCOs, a VCF, a VCA, two envelope generators, an LFO, an arpeggiator and a MIDI interface, and while the discrete audio circuitry is pure analogue, the user interface is decidedly digital. All editing and programming is performed using the increasingly common 'parameter grid' method — in this case a combination of buttons and LEDs arranged as a 4x11 matrix to represent the editable parameters, with a single data knob and two increment buttons for entering parameter values. The only other visual feedback is from a staggered row of three rather neat circular single‑digit LED displays. There are no LCDs or menus (like I said — minimalist!) but it's easy to operate and get to grips with. In addition to the parameter grid, there are three Mode buttons and a 'Write' button for saving edited programs into one of the 128 user patch memory locations.

The sparse feel continues at the rear of the case, with the usual MIDI trio of In/Out/Thru connections and a standard 3‑pin AC socket. There's a single mono output jack and a mono input jack for processing external audio signals (more on this later), but unfortunately no CV in/out connectors for those wishing to hook up to existing analogue CV kit.

The Synth Inside

There are three modes of operation, accessed by buttons labelled Program, System and Edit. The OS1 default mode is Program; user patch locations are instantly accessible in this mode using either the data knob, increment buttons or MIDI program changes. The System button changes MIDI channel, turns patch memory protection off or on (on is the default state) and sets the various ADSR trigger modes, which I'll explain shortly. The Edit button activates the parameter grid mentioned earlier.

As might be expected with the comparatively basic user interface I've described, the OS1's internal architecture is pre‑configured — that is to say, the VCOs feed into the VCF which, in turn, feeds into the VCA. Envelope Generator 1 triggers the VCF, and Envelope Generator 2 triggers the VCA. The downside of thistype of arrangement is that you can't re‑patch the internal modules to come up with unusual custom combinations; the benefits are that what you see is what you get, and that there are no unnecessary multi‑page menus to wade through. The front panel is clearly and logically laid out and, assuming they know the basic principles of analogue synthesis, most users will find the going straightforward enough. I managed to get into some serious editing within minutes, before I'd even glanced at the instruction manual.

Using the front‑panel parameter grid as a guide, let's take a look at the OS1 from an analogue perspective:

  • LFO: This is first in line and has four editable parameters — Rate (the rate of the LFO is always indicated by a flashing dot in the left LED), waveform Shape (Triangular, Square, Saw‑Up, Saw‑Down, Random), Sync (off, key down, MIDI clock and MIDI clock + key down), and Delay. As you'd hope, when the LFO is synchronised to an external MIDI clock nine different MIDI sync ratios, ranging from one cycle every two bars at one extreme to three cycles per quarter note at the other, are available.
  • VCOs: There are three independent VCOs, which are well specified and cover approximately six octaves — not bad for analogue VCOs! To find three of these in any kind of analogue synth would be a bonus, but to find so many in a compact unit such as this is pretty amazing.
Don't be fooled by the day‑glo colour scheme: the OS1 is definitely a professional instrument.

Each VCO has Coarse Frequency, Fine Frequency, VCO Shape (see below), LFO Depth, Env 1 Depth and Output Level parameters. VCOs 2 and 3 have an additional X‑Mod feature which allows variable cross‑modulation and waveform sync with the other VCOs, while VCOs 1 and 2 can output saw, inverted saw,variable pulse (including square) and modulated pulse (dubbed 'Chorus') waveforms. It's worth noting that the pulse waveforms are modulated by an additional, uneditable 16‑speed LFO that that doesn't tie up the main LFO and allows for some animated, full‑bodied effects when all three VCOs are in action. VCO3 offers all the above waveforms but also provides white noise and can be set to enable the external audio input. This external signal is then available, alongside output from the other VCOs, for processing by the VCF and VCA. All the VCOs will respond to MIDI pitch‑bend and modulation.

Something that certainly inspires confidence in the OS1 is the stability of the VCOs, which require no warm‑up period. On the review model they also showed no signs of tuning drift at the extreme ends of the keyboard, a common problem with many analogue VCOs. Apparently this stability is down to the very clever '90s‑style oscillator circuit design. Well done, team!

  • VCF: The voltage‑controlled filter is a 24dB low‑pass type which can be pushed into self‑oscillation to act as a fourth (sine wave) VCO. Half a dozen editable parameters are available, namely Frequency, Resonance, LFO depth, Envelope 1 depth, Keyboard tracking and Keyboard Velocity. The frequency of the VCF can also be controlled from a MIDI modulation wheel.

Filters are an important part of the sound of a synth, but trying to make comparisons of the sound of one VCF against another is asking for trouble — people take this stuff far too seriously! I'll just say that to my ears it sounds perfectly fine; better than some I've come across but maybe not as 'sweet' as a few I've used. And I'm not naming names!

EGs: The OS1 has two envelope generators — Env 1, for control of the VCOs and VCF, and Env 2dedicated to the VCA. These are standard ADSR‑type envelopes with attack, decay and release times variable from 0‑10 seconds (calibrated in 127 steps) and a 0‑100 percent Sustain parameter. The minimum ADR settings aren't the shortest I've come across, and I found trying to adjust the lower values frustrating: for example, with Attack time, instead of a smooth change between zero and the first digit in the display, as would be the case if this parameter was changed with a normal analogue control pot, there's a noticeable step as the speed of the attack changes. The resolution of the control system doesn't seem to be quite good enough for really precise changing of these parameters — a side‑effect of digital control. Four different keyboard trigger and re‑trigger modes are available for the envelopes, and these settings are saved with each patch.

  • ARPEGGIATOR: Love them or hate them, there's no denying that, used sparingly, arpeggiators can be a useful and creative tool. The OS1's arpeggiator allows you to arpeggiate between one and eight notes. The basic modes are: Off, Up, Down, Up/Down, Down/Up and Random, with a further 40 or so variations covering eighth‑ and 16th‑note triggering over a three‑octave range. The arpeggiator has its own Rate (displayed by a flashing dot in the middle LED display), and can also be sync'ed to MIDI clock. As both the arpeggiator and LFO can be sync'ed to MIDI, some fun rhythmic effects can be programmed using different timebase sub‑divisions for each.

Praise and Blame

I'd like to have seen a more adventurous implementation of the VCA on the OS1 (as there's no amplitude modulation available from the LFO waveform), and a choice between logarithmic and linear ADSR control would be useful, as would an LFO‑controlled panning stereo output. The fact that the OS1 doesn't feature a ring modulator is a disappointment, too. Although similar effects can be achieved using the VCO X‑Mod feature, nothing beats the real thing for really extreme modulations and FM‑style effects.

As I've already observed, a side‑effect of using digital editing control with an analogue system, as in this synth, is the relatively coarse resolution of the controllers: occasionally you can hear a stepping effect when adjusting or sweeping some parameters. I also wasn't entirely happy with the data knob and would have preferred a continuous 180‑degree rotary controller included, rather than the standard end‑stop type — though I could live with it.

Having said all that, there's an awful lot to like about the OS1. Not least, it's a breeze to use, with no hidden menus or arcane operating systems to hinder you. Using the parameter grid and a display which basically amounts to three digits isn't as restrictive as you might imagine. This is partly due to the (relatively) limited number of parameters available, but that's the nature of monophonic subtractive analogue synthesis. To a large extent you can ignore the displays during programming and simply let your ears be the judge.

This synth is going to be an investment and is destined to become much sought‑after in years to come.

The instruction manual is informative and well laid out, which is a refreshing change. The factory preset sounds are, on the whole, very good, and they showcase the abilities of the OS1 very well. There are some genuinely cone‑busting basses, screaming lead sounds, zany effects, perky arpeggiator patches and plenty of contemporary (and over‑used) TB303‑type resonant basses. But I must say I had the most fun programming my own sounds.

Audio quality is top‑notch and, for an analogue instrument, the noise floor is relatively low. As is the case with many analogue synths, the OS1's upper and lower audio ranges can produce some frighteningly extreme frequencies approaching subsonic and ultrasonic, so beware!

Breeding Hybrids

Funnily enough, even in an increasingly crowded analogue market, there aren't many truly analogue synths which are digitally controlled — not that I'm aware of, anyway. The closest relative to the OS1 is probably the very non‑programmable (but infinitely tweakable) Doepfer MS404 Synth, which includes a built‑in MIDI‑CV interface but has only one VCO. While it's a fine synth, it's frankly not in the OS1's league.

Don't be fooled by the day‑glo colour scheme: the OS1 is definitely a professional instrument. It's well specified, easy to program, very stable in use and capable of some outstanding analogue sounds. Admittedly the single‑knob approach is unusual for an instrument proclaiming its analogue heritage, and analogue die‑hards may find this a bridge too far. But the OS1 has been designed as a hybrid programmable analogue MIDI performance synth and is happy to leave the dirty work of CVs, gates and patch cords to the modular big boys. The price may appear to be slightly on the high side but this synth is going to be an investment and is destined to become much sought‑after in years to come.

Maybe the Original Syn doesn't break any new ground in synthesizer design, using, as it does, proven analogue and MIDI technologies, but nevertheless dsTEC have succeeded in breeding an excellent and professional hybrid instrument.

Analogue Acronyms

  • ADSR: Attack‑Decay‑Sustain‑Release.
  • CV: Control Voltage.
  • EG: Envelope Generator.
  • LFO: Low‑Frequency Oscillator.
  • VCA: Voltage‑Controlled Amplifier.
  • VCO: Voltage‑Controlled Oscillator.
  • VCF: Voltage‑Controlled Filter.

If you're not familiar with analogue synthesis theory, its mysteries are explained in parts 1 and 2 of the 'Synth School' series which ran in the June and August 1997 issues of SOS, and in the very understandable 'Sound Foundation: A Synthesis Primer', in SOS February and March 1994.

MIDI Mischief

The OS1's MIDI specification is impressive, with all editable parameters controllable over MIDI (a controller number chart is included). This allows for extraordinary and, some may say, over‑the‑top manipulation of sounds via a MIDI sequencer, or in real time using something like the Doepfer Drehbank (see review on page 136 of this issue), Kenton Control Freak or Keyfax Phat Boy MIDI controllers. Other MIDI parameters recognised are MIDI clock start/stop, hold, portamento, pitch‑bend and volume.

The 128 user patch memories can be saved and reloaded as individual MIDI SysEx dumps. This involves the truly unpleasant process of writing raw SysEx code into your sequencer to instruct the OS1 to start dumping or loading, something not all sequencers can do (particularly non‑computer types) and something I feel a lot of users won't bother with. In addition, there's no way to perform a bulk dump or load of all the patches in one procedure. This aspect of the OS1 is not very user‑friendly, considering how approachable the rest of the synth is.

I voiced my concerns to dsTEC and was told that an editor/librarian program is being written that will handle the day‑to‑day process of saving patches to a computer and re‑loading them into the OS1. The program should be available to download from the company's web site by the time you read this review. An on‑line user group is also being set up so that Original Synners can exchange custom patches and tips — assuming, of course, that they all have a computer and access to the web!


  • Analogue, yet programmable.
  • Powerful, three‑VCO sound and impressive VCF.
  • Easy to use and program.
  • Comprehensive MIDI specification.
  • External audio input.
  • Solid, heavy‑duty construction.


  • No ring modulator.
  • No CV in/out.
  • Basic VCA control.
  • Awkward MIDI patch dump/load implementation.
  • Not quite as 'hands on' as a regular analogue synth.


The Original Syn benefits both from the eminently programmable analogue powerhouse under its bonnet and its user interface, which is slightly spartan but allows you to get jobs done with the minimum of fuss. In short, the OS1 is ideal for anyone who wants a great‑sounding pro analogue instrument but doesn't fancy dirtying their hands with control voltages and patch cords.