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Voyager By Bob Moog

Version 2 OS Updates • Anniversary Edition • VX351 • CP251
Published November 2004
By Gordon Reid

Voyager By Bob MoogPhoto: Mark Ewing

Since the release of the Voyager analogue monosynth last year, Bob Moog's company have been busy producing OS updates, special-edition versions, and accessories. We bring you up to date with a look at the lot.

It has been nearly two years since Bob Moog's Voyager first hit these shores, and it has been developing ever since. The operating system has now reached version 2.3, with the last four updates addressing almost all of the points that I raised when I originally reviewed the instrument in SOS June 2003. There have also been two hardware additions to the family. The VX351 CV Expander is specifically a Voyager expander, while the other, the Moogerfooger CP251 Control Processor, has wider application, but is nonetheless happy to act as a member of the clan.

In addition to all of these, there's also a new version of the Voyager — the Anniversary Edition (pictured above), which is a limited edition that celebrates Bob Moog's 50 years in the music business. In fact, although it's cosmetically different, the Anniversary's internals are no different from the latest standard Voyagers being produced, so we can treat it like the latest version of the instrument. Given that the original review is now hopelessly out of date, I reckon that it's high time that we returned to the Voyager to see what the latest hardware, the changes in the operating system, and the add-on boxes mean for both new and existing users.

Finishing The Voyager

You may recognise the table on the right — it's the list of future updates that were promised for the Voyager at the time of my original review. Happily, these have now all been carried out, although some of them didn't happen until the version 2 OS arrived, as you can see.

Over the course of the past year, I've acquired my own Signature Edition, so I've followed the Voyager through its various upgrades, even before the Anniversary Edition arrived for review at SOS. So let's see what's changed...

One of the most annoying things about the original Voyager operating system was the way the cursor buttons worked. When you pressed Up, the selection moved Down, and vice versa. I was delighted when this was corrected in OS v1.5. What's more, OS v1.5 introduced numbering of each mode's menu items, which helped users to navigate the system. More significantly, it introduced scrolling of the '+' and '-' buttons, with acceleration if you held either button for a few seconds. Other small but welcome improvements included the Voyager powering up in Panel Mode, and it remembering and returning to the sound you were using before you switched off.


Hold -1/+1 buttons to scroll through values — Done (OS v1.5)

Upgrade touch surface destinations — Done (OS v1.5)

Add filter pole selection (12dB-per-octave) — Done (OS v1.5)

Local control On/Off  — Done (OS v1.5)

MIDI In On/Off & MIDI Out On/Off — Done (OS v2)

Receive MIDI CCs, Note On, velocity and aftertouch — Done (OS v1.5)

Transmit MIDI CCs, aftertouch and pitch-bend — Done (OS v2)

Receive MIDI Clock for LFO sync — Done (OS v1.5)

Send and receive single memory via SysEx — Done (OS v1.5)

Transpose MIDI output — Done (OS v2)

Add filter envelope gate sources — Done (OS v2)

Add amplitude envelope gate sources — Done (OS v2)

Updates to modulation buss PGM shaping — Done (OS v2)

System Reset — Done (OS v2)

OS version 1.5 also saw the arrival of MIDI Sync for the Voyager's internal LFO. Of course, this is not MIDI Clock control of the LFO rate, which would be tricky to implement using an analogue oscillator. Instead, it is 'hard sync' of the start point of the LFO cycle, with seven options ranging from one 'sync' every two MIDI Clock beats to one sync every quarter of a MIDI Clock beat.

Other upgrades in OS v1.5 included Local On/Off, Program Change On/Off, and Merge, which merges incoming MIDI messages with those generated within the synth, and then transmits the resulting stream from the MIDI Out. This revision also received velocity and aftertouch over MIDI. But just as important as this was the ability to Dump and Load single patches via SysEx. This made it possible for the first time to save and restore individual sounds, and to build banks from disparate combinations of existing sounds.

One of the biggest problems with the original Voyager was the hard-wiring of the touch-screen to the filters' cutoff frequencies, spacing and resonance, and the fact that the position memory applied only to the values sent to the modulation busses, not to the filter destinations. Things improved in OS v1.5; the fixed destinations were disconnected, and three of the touch-screen's degrees of freedom (X-axis, Y-axis and Area) appeared to offer four independently assignable parameters: Destination, MIDI CC transmitted, Direction (the 'polarity' of the parameter) and Amount (the MIDI CC transmission didn't work under OS v1.5, but this has now been attended to — more on this in a moment).

No fewer than 32 touch-screen destinations were added (see the table below), but the Amount parameter was less flexible than you might think. This offered just three options — 0 percent, 50 percent, and 100 percent — meaning that the maximum amount of control exerted by X, Y or A was zero, half of the destination's total variability, or 100 percent of the destination's total variability.

This improvement introduced a problem of its own, although it only affected owners who used patches created on earlier OS revisions. When loaded into an upgraded Voyager, pre-OS v1.5 patches lost their fixed touch-screen destinations and ended up with random settings. These patches sounded correct until you touched the screen, at which point strange things could happen. Not a fundamental flaw, this nonetheless required a frustrating hour or two spent reassigning the touch-screen parameters to get back to where you started.

Another problem concerned the new global touch-screen memory and modulation buss touch-screen memory functions. These were supposed to remember where your finger was the last time you touched the screen, and to continue to apply the appropriate 'X' and 'Y' CVs to their destinations after you removed it. I found it extremely difficult to remove my finger without shifting the position of final contact slightly, so that the magnitude of the remembered CV was always slightly more or less than I wanted it to be. But after a while, I began to think that the fault was not mine alone, and a couple of tests showed that the screen does not hold extreme values correctly; it substitutes values that are closer to the 'centre' of the screen. This means that, in almost all cases, sounds glitch slightly when you remove your finger from the screen, and glitch again when you next touch it. If anything is going to be done about this, it still hadn't happened following the OS v2.3 upgrade.



  • Oscillator 1 level.
  • Oscillator 1 octave.
  • Oscillator 1 waveform.
  • Oscillator 2 frequency.
  • Oscillator 2 level.
  • Oscillator 2 octave.
  • Oscillator 2 waveform.
  • Oscillator 3 frequency.
  • Oscillator 3 level.
  • Oscillator 3 octave.
  • Oscillator 3 waveform.
  • Noise level.
  • External audio input level.


  • VCA attack.
  • VCA decay.
  • VCA release.
  • VCA sustain.
  • Volume.


  • Filter cutoff.
  • Filter keyboard amount.
  • Filter resonance.
  • Filter spacing.
  • Filter envelope amount.
  • Filter attack.
  • Filter decay.
  • Filter sustain.
  • Filter release.


  • Glide rate.
  • Keyboard pitch CV.
  • LFO rate.
  • Mod wheel modulation buss amount.
  • Pedal/On modulation buss amount.

One OS v1.5 upgrade significantly expanded the sonic character of the instrument. This was the long-awaited inclusion of 12dB-per-octave filters. Indeed, the Voyager's manufacturers went two steps beyond their original promise; the Voyager now offers 6, 12, 18 and 24dB-per-octave slopes independently for both the high-pass and low-pass filters. This is no trivial upgrade, and it allows you to sculpt sounds with characters reminiscent of many other synthesizer manufacturers. I noted in last June's review how the Voyager's high-pass/low-pass option lent itself to the creation of Korg-y and ARP-ish timbres, but the new slopes take things further, making the Voyager a true sonic chameleon.

The touch-screen in the centre of the Voyager was previously hard-wired to fixed parameters, but is now freely assignable, and transmits MIDI continuous controllers.The touch-screen in the centre of the Voyager was previously hard-wired to fixed parameters, but is now freely assignable, and transmits MIDI continuous controllers.Photo: Mark Ewing

Regrettably, the filters still lacked some features in OS v1.5, and these have not yet been added in the current revision. Firstly, despite many users' requests, it remains impossible to control and modulate the filters independently; you can't sweep one and leave the other unaffected, or have one on the edge of self-oscillation while the other exhibits zero resonance. Secondly, there's still no option to place the filters in series in dual low-pass mode. And thirdly, there is still the on-going problem, mentioned in my previous review, that Glide cannot be made to affect the filter cutoff frequency.

One of the most interesting facilities promised by the Voyager's original sales blurb was MIDI control over all the Voyager's programming parameters. This appeared in OS v1.5, with the synth responding to no fewer than 53 messages that control almost all aspects of its sound. Transmission of continuous controller information did not become possible until the version 2 OS arrived, but now that it has, the Voyager has become a feast of MIDIness. You can transmit CCs from the left-hand controller panel (pitch-bend and modulation), you can transmit aftertouch, and you can send a CC from every front-panel control with the exception of the fine-tune and headphone volume knobs. Even more excitingly, you can now program the touch-screen to transmit the CCs of your choice on all four degrees of freedom (X-position, Y-position, Area and Gate). This is no small benefit, and opens up all manner of possibilities for innovative control of instruments such as digital workstations that suffer from more limited control capabilities.

Although more subtle, other MIDI updates in OS2.x are just as useful. These include MIDI In On/Off, MIDI Out On/Off, programmable SysEx ID (which allows you to control more than one Voyager over MIDI simultaneously), the ability to dump any patch via SysEx, and three velocity curves for the output MIDI velocity. Another improvement that I've been requesting since the Voyager appeared involves MIDI Key Transpose. To their credit, the Voyager's programmers have surpassed themselves here, implementing not one, but two Transpose functions: keyboard transpose (which affects the note emitted by the Voyager itself when you play it from its own keyboard) and MIDI Key Transpose (which affects the MIDI Note Numbers transmitted when you play the Voyager keyboard). Among other things, this means that you can now use the Voyager to program or play rhythm parts on standard MIDI note numbers.

The most recent upgrades also include many tweaks to the menus in Edit Mode and, for me, this is where the most significant improvements reside. Let's start with a couple of minor ones. 'Compare to Preset' allows you to decide whether to overwrite the sound being edited, or find a sound that you don't mind losing. There's also the addition of a factory setup (reset) menu, which allows you to reload the factory patches and reset various performance parameters to their default values.

Next, we come to a new method of naming patches, in which you can use the keyboard as an alphanumeric keypad. More significant is the 'User Definable Pitch-bend Amount', which allows you to define the amount of pitch-bend, rather than being limited to a handful of well-tempered options. As we shall see later, this helps (in part) to sidestep an extremely annoying fault in the hardware of early Voyagers.

Another important addition is the introduction of alternative Gate sources for the filter and amplifier envelopes. In addition to the standard sources, these now include the Gate signal from the touch-screen, the LFO square wave, and MIDI Clock. Provided that you remember to switch the Env Gate switch to On/External, these sources should be enough for all but the most arcane requirements. The touch-screen Gate signal now has many other uses, too. You can use it to switch the Glide and Release switches on and off, as well as every switch on the front panel. I'm not immediately sure how I might use this, but I can think of numerous ways in which it could be useful.

Moving relentlessly up the scale of significance, we now come to the addition of two more 'Shaper' sources, one for each of the modulators. There's a huge list of sources for these (43 in all) that includes many of the front-panel controls as well as conventional sources such as velocity and aftertouch. Having four Shaper sources makes possible a huge number of complex modulation options that, in many ways, echo those of a modular synthesizer. However, these still don't allow you to use the Shapers to introduce modulation where none existed before... they only allow you to modulate the amount of an existing modulation, as explained in my original Voyager review.

Last on my list, but most significant among the upgrades for me, are the oddly named 'Pot Mapping Source/Destination' parameters. These provide four new modulation paths that are completely independent of the modulation busses. This is quite something... it allows you to send (for example) aftertouch directly to mod-wheel amount, keyboard CV directly to LFO rate, velocity directly to filter cutoff frequency, or choose from hundreds of other Source/Destination combinations, without being subject to the complexities and limitations of the mod wheel and Pedal/On busses.

There are 40 sources and 40 destinations in the Pot Mapping system, and four modulation maps available at any given time, which means that there are, umm... 1600 to the fourth power combinations, which is... over six and a half trillion source/destination combinations. I'm suitably impressed, especially since each of the four modulation paths can have positive or negative polarity and an 'amount' of 0, 25, 50 or 100 percent. Silly numbers aside, the great thing about these paths is that they're simple to understand and use. What's more, by allowing you to direct a single modulation controller (aftertouch, say) to four destinations simultaneously (for example filter cutoff, amplifier gain, LFO depth and LFO rate), pot mapping makes the Voyager extremely responsive and musical.

The Anniversary Edition

Following in the footsteps of the Signature Edition, the Anniversary Edition is another limited-edition Voyager. It comes in a stunning black finish, but the most noticeable thing about it is the illuminated front panel on which all the controls' annotations glow at you in an almost actinic blue. The intensity of illumination is controlled by a small knob set into the small wooden strip immediately to the right of the keyboard. Turning this knob anticlockwise to its minimum switches off the backlight, and turning it progressively clockwise increases the intensity until the illumination of the panel legends becomes visible even in daylight, which equates to being dazzling in a darkened studio. Unfortunately, at anything higher than minimal intensity, the system emits an annoying whine. This is not going to be of concern at a gig, but in my studio it renders the backlight almost unusable. I also wish that the designers had sited the intensity knob more sensibly — I kept catching it with my fingers when playing at the top end of the keyboard.

Moving back to musical matters, the Anniversary Voyagers — and, I assume, others of this vintage — have been cured of two of the hardware faults exhibited by earlier versions. The most obvious of these concerns the quiet but annoying noise emitted by some Performers and Signatures when you turn the Master Volume knob past '5' in either direction. This has been eliminated.

A more significant fault on early models concerned pitch-bend. No matter how you programmed the values in the menus, the pitch-bend interval was far from what was promised. What's more, the whole instrument went flat when you increased the pitch-bend range.

Happily, the upward bend on the Anniversary is exactly what the menu promises, even over large bends of two octaves or more. The downward bend is not quite right — a two-octave bend is sharp by a few cents — but the error isn't noticeable when using musical intervals of a handful of semitones. Furthermore, I found that when programming the pitch-bend using the new Pitch-bend Amount parameter, the upward and downward intervals were identical.

The previous hardware fault with the Voyager's pitch-bend wheel has been attended to on the Anniversary Edition. The attractive blue backlighting of the Anniversary is also visible emanating from under the wheels in this shot.The previous hardware fault with the Voyager's pitch-bend wheel has been attended to on the Anniversary Edition. The attractive blue backlighting of the Anniversary is also visible emanating from under the wheels in this shot.Photo: Mark Ewing

But there's bad news for owners of older Voyagers. The errors in the pitch-bend intervals in early models were not a function of dodgy software; they were the result of a hardware fault. This means that, even if you upgrade the OS of a Signature (as I have done) or one of the earlier Performers, you still cannot obtain the correct pitch-bend intervals without returning your pride and joy to a workshop for a hardware modification. How is that a very expensive synth can suffer from a hardware fault as easily spotted as this?

This is where the 'User Definable Pitch-bend Amount' parameter can help. Take, for example, the '1 Octave' pitch-bend setting on my Signature. Pushing the wheel fully away from me sharpens the pitch by 13 semitones, but pulling it fully toward me flattens it by just 11 semitones. A user-defined pitch-bend value of 104 sharpens the pitch by exactly an octave (12 semitones). Having said that, the same value flattens the pitch by ten-and-a-bit semitones, which is useless. So you can now make your older Voyager more useable than before, but it's still a sorry state of affairs.

Fortunately, it is now possible to correct all Voyagers of their tendency to go flat when you increase the pitch-bend range. You need to remove the controller panel to the immediate left of the keyboard (it's not as hard as it sounds) and adjust a trim pot while watching a parameter value on screen. I set up my Signature according to the method described in the documentation, and it was cured of this problem.

Another fault with all Voyagers concerns the Envelope Gate switch. When set to On/External, this should hold the VCA permanently 'open' at the Volume Envelope Sustain Level, but it doesn't. What actually happens is that the Level starts at the correct point, but immediately enters a very slow decay.

Next, I would like to point out another slight deficiency that has become apparent on all Voyagers. The synth's manufacturers claim that the 12-bit A-D converters used to translate the positions of the front-panel knobs into digital values, the interpolation of those values when the CVs are generated, and the scanning speed of the front panel are all sufficient to ensure that the Voyager is indistinguishable from a pure analogue synthesizer. However, this is not the case. To discover this for yourself, just sweep two knobs simultaneously while listening to a patch. If one of the parameters you're adjusting makes obvious changes to the sound — say, the filter cutoff frequency — you will hear audible stepping. To be fair, the amount of 'zippering' is very small, and will bother almost no-one, but it's there nonetheless.

A final fault that is cured neither in the Anniversary Edition nor by upgrading my Signature Edition concerns the nature of the aftertouch response. This was always like on on/off switch, and so it remains, making it extremely hard to introduce modulation progressively without using a VX351 and a CP251 to smooth and attenuate the response. This is very unmusical behaviour for an instrument of this value. However, it provides the perfect excuse to move on to discuss... the aforementioned VX351 and the CP251. For the background and basic functionality of these two add-ons, see the boxes below and over the page respectively. For more on using them with the Voyager, read on.

The VX351 CV Expander

As I stated last June, the Voyager's numerous control inputs are not complemented by equivalent outputs so, while you can control an unadorned Voyager from external sources, you cannot use it to control other non-MIDI synths and modules. Nor can you patch CV routings that are not provided by the internal busses (although this is now far less of an issue thanks to the pot-mapping facilities added in the version 2 OS). Both of these functions can be added using the VX351 CV Expander.

The VX351 control-voltage breakout box.The VX351 control-voltage breakout box.Photo: Mark Ewing

Now, you might think that the 25-way 'D' connector marked 'Accessory Port' on the back of the synth would tap the Voyager's control voltages, and in this you would be partly right. Unfortunately, it seems that matters are not straightforward, because the VX351 comes with a small piggy-back board that you must insert inside the Voyager before the port will work as specified. I'm not sure why this is necessary, because I tested some of the CVs without it and they seemed to be correct. Nonetheless, I had no wish to risk faulty operation (I seem to remember that one user reported that the LFO failed without the board) so I installed it before proceeding further. At this point you might ask, "If it is necessary to have a piggy-back board to use the expansion port, why does this come only with the VX351?" Since the piggy-back comprises just four resistor networks, it should have been simple to build its functionality onto the Voyager's main board, or at least to ship it with the piggy-back board already installed. The unattractive thought has occurred to me that the board might be a way to compel you to buy the VX351 rather than build your own CV breakout box, but this is just speculation on my part, and — I hope — untrue.

With the piggy-back board installed, the VX351 provides outputs for 18 CV sources, two Gates, and the noise generator, and adds two attenuators and two four-way multis to the Voyager. Together, these transform the instrument from a powerful integrated monosynth into a powerful semi-modular monosynth. Strangely, all of the VX351's facilities appear to be passive. This is a non-trivial point... even the sockets in the multiples are soldered together without buffering, which means that when you use the multiple as a signal splitter, you may experience voltage 'droop'. More seriously, if you try to use either of the multiples as a cheapo mixer (as many people do) you may — at best — obtain unexpected results. At worst, you will sum voltages in excess of the Voyager's ability to handle them. Beware!

Hang on a moment, let's step back half a paragraph... semi-modular? I'm afraid so. Neither the synth nor the CV Expander offer individual patch points for the audio generated by the oscillators, so the combination of the Voyager and the VX351 is architecturally closer to a Korg MS20 than an ARP 2600.

Some users have complained that the VX351's 21 CV and Gate sockets do not drive other synths correctly, so I measured voltages for those outputs that I could determine using a digital multimeter. After two to three hours 'on' at room temperature, most voltages fell a fraction short of specification, although a number were well over five percent off (by the way, I think that the quoted 'A' range for the touch-screen should be 0V to +5V, not ±5V as specified in the VX351's literature). Nevertheless, the measurements do not fall too far outside the expected ranges... this is an analogue synth, after all!

The measurements I took allayed one significant fear I had: that the VX351 would be incapable of driving my 1V-per-octave modular synths correctly. This is because the voltage-to-pitch scaling within the Voyager itself is 0.935V-per-octave, which is not just non-standard — it's unique to the Voyager. Apparently, the earliest VX351s did indeed output this strange scale, but it seems that this has now been fixed; the review unit produces almost precisely 1V-per-octave, and a trimmer allows you to calibrate the pitch CV if it becomes necessary to do so.

Putting Everything Together

I received the VX351 and CP251 some months before OS v2 existed, so my first experiences of them were with my Signature Edition Voyager running OS v1.5. I installed the required piggy-back board (see box below), connected the VX351 and CP251, and was ready to start experimenting. This was when I noticed how useful the optional £50 CP/VX rackmount kit would be. The kit converts the two boxes into a shallow, 3U rackmount assembly, and allows the Voyager to power the CP251 through the VX351.

My first use for the VX351 was to route control voltages back into the Voyager in otherwise unavailable ways, and this allowed me to overcome a number of limitations in the synth itself. For example, it was obvious how to patch the VX so that the Voyager could trigger its envelopes using its own LFO. This is now no longer necessary thanks to the new facilities in the version 2 OS, but the principle remains valid. Likewise, I eventually worked out how to use the VX and CP to overcome the Voyager's maddening Modulation Buss problems...

To recap this problem briefly, which is described in more detail in my original review; the Shaping options in the modulation busses do not allow you to introduce an effect from zero, which is a remarkable limitation in so expensive an instrument. But if you add the VX and CP to the equation, it becomes relatively simple. Let's hypothesise that you want to use aftertouch to introduce and control vibrato. The solution works like this... You patch the Pressure output on the VX through the CP251's slew generator to slow the almost instantaneous 10V sweep from -5V to +5V that occurs whenever you lean on a key, and then route the modified aftertouch CV back to the Voyager's Mod1 buss input, whereupon it acts as a multiplying factor for the Amount control in the Pedal/On buss.

Having patched the devices, you must now set the Voyager's Pedal/On source as the LFO triangle wave (which generates the vibrato) and set the destination to Pitch. The position of the Shaping control is irrelevant (although I suspect that it's best set to 'On'), but the Amount must have a non-zero value, or no modulation is produced by the buss. You can now set the mod wheel to zero (ie. fully towards you) and use aftertouch alone to introduce pitch modulation into an otherwise unmodulated signal. This certainly works, but why does it need to be so convoluted?

Now, you might say that the pot-mapping facilities introduced by the Voyager's version 2 OS render all of this unnecessary, and for the most part you would be right. However, leaning even gently on the Voyager's keys causes the aftertouch value to jump from zero to 'lots', so that the pot-mapping destination jumps almost instantaneously from one state to another. Patching pressure sensitivity through the VX and CP produces a more pleasing effect, because of the slew you can introduce into what is otherwise an almost on/off response.

Once I'd got used to the low-budget feel of the VX and CP's connectors and sockets, and had used both units to overcome two of my biggest complaints regarding the Voyager, I started to feel rather more enthusiastic about them, and used them to cure the Voyager's inability to apply portamento to the filter cutoff frequency (which still exists, even in OS v2.3). I did this by directing the VX351's keyboard CV output to the CP251's slew generator and returning the resulting signal to the synth's filter CV input (remember to set keyboard tracking in the Voyager to zero, or you'll get 200-percent tracking when you try this). It wasn't possible to match the filter portamento precisely to the keyboard Glide, but I found that all manner of interesting sounds were now available, primarily by forcing the self-oscillating filter to track the VCOs, with different amounts of glide on each. I also created some interesting effects by setting the amount of slew differently for playing up the keyboard than for playing down. Unfortunately, you can't apply this trick to the oscillators themselves, because you can't disconnect the internal keyboard CV, so the patch always generates 200-percent tracking, which is — for melodic work — useless. Even setting Oscillator 3's tracking to 'Off' does not work, because this also disconnects it from the CV input.

I found that, with the 'aftertouch patch' permanently in place, it was no mean trick to keep track of the 'virtual' patching within the busses themselves, as well as the physical patching between the three boxes. But once I had got the hang of things, creating traditional modular synth effects became straightforward. For example, I used the CP251's LFO and sample-and-hold facilities to trigger the Voyager's envelopes and modulate its filters, while at the same time producing slow pitch sweeps and pulse-width modulation effects using the Voyager's internal LFO. This took me deep into sound effects territory, but the combination of the three units was equally at home creating musically interesting patches that are often the preserve of modular synths and their software equivalents.

While experimenting, I found that the Inverter in the CP251's Mixer proved to be an unexpected bonus, and I ended up wishing that there were more of these. It's useful to be able to modulate one parameter upwards while another is sweeping downward 180 degrees out of phase. Likewise, I became accustomed to having the CP's and VX's attenuators at my disposal, finding that these tamed the Voyager's performance CVs, thus making it possible to create patches that were more subtle than those available on the synth alone.

Once I had upgraded to OS v2.3, it was immediately obvious that I needed the VX and CP far less frequently to overcome restrictions in the Voyager itself. This then released them for more esoteric duties. I placed the Voyager, CP251 and VX351 alongside my Analogue Systems Integrator RS8000 modular, and started cross-patching between the two systems. Suddenly, the Voyager leapt into life as the (almost) modular system it had always promised to be. Using the VX351 to direct pitch CVs and Gates to the Integrator, I found that the RS oscillators tracked perfectly, and that its envelopes and VCAs responded exactly as one would wish. Remembering to use the VX's and CP's attenuators to protect the Voyager from the Integrator's meaty ±10V signals, cross-patching was a doddle, and I finally realised why I — and all other Voyager owners — will eventually have to cough up for the VX. Why? Because it makes experimental synthesis with the Voyager fun. Imagine playing both synths simultaneously, directing the Integrator's output to the Voyager's external signal input so that you can filter and re-filter it using the Moog's filters as well as its own comb filters, EMS Synthi filters and on. The resulting sounds are big. Really big.

The CP251 Control Processor

Although part of the Moogerfooger range, the CP251 can also be used as part of a Voyager system, although it requires a separate power supply when used as a stand-alone unit. The module offers seven distinct sections: a four-channel CV mixer, a slew or lag generator, a dual-waveform LFO, dual attenuators, a four-way multiple, a noise source, and a sample-and-hold section. Five of these offer TRS sockets that allow you to use expression pedals if desired. These sockets are denoted by the red, rather than black, retaining nuts. You can also use conventional tip/sleeve jack plugs in these, but they will short the power supply to ground, resulting in a tiny current flowing within the plug itself. There's no risk associated with this, nor will there be any adverse effects on the operation of the unit, but shorting any one socket in this way disables the ability of any other sockets to work with pedals.

The Mixer is in many ways the most interesting part of the CP251. It combines two inputs with attenuators (inputs 1 & 2), two direct inputs (3 & 4), an Offset control that provides a DC offset, and a Master knob that controls the amplitude of the mixed signal, up to a maximum of unity gain, subject to an absolute maximum of +5V. Oh yes, and there are positive and negative outputs available simultaneously. The Mixer has a bandwidth in excess of the upper limit of human hearing, so it's also capable of audio mixing, but there's no way to use it as a VCA, which is a shame.

Alongside the Mixer, the Slew Generator (or 'Lag Processor') has a novel twist: independent controls for slewing the rise time and fall time of a waveform. This means that if, for example, you direct the square wave output from the LFO to the Slew In, you can shape it into a trapezoid, a sawtooth, a ramp wave, or a triangle, with many subtle variations in between. I like this. The fastest and slowest slew rates are quoted as 1ms and 1s respectively and, although the slowest is still rather rapid to be considered all-encompassing, it will be adequate for many synthesis tasks.

This brings us to the LFO itself which, as on the Voyager, offers just two cyclic waveforms; triangle and square, with a nominal frequency range of 0.2Hz to 50Hz. However, you can apply control voltages to the Pedal In socket to extend this down to 0.03Hz at the low end (which can produce the languorous sweeps I like) and up to 100Hz or more at the top end, which suggests a number of FM possibilities.

The CP251 control-voltage processor.The CP251 control-voltage processor.Photo: Mark Ewing

The dual attenuators do their job well, with a measured output of 0 percent at the minimum setting, and very nearly 100 percent at the maximum. Likewise, the four-way Multiple does what it says on the tin, although — as on the VX351 — its sockets are merely soldered together without buffering.

The CP251's noise generator is different from the noise source provided on the Voyager, being altogether smoother and 'bluer'. If you heard either in isolation you would think it typical, but an A/B comparison demonstrates how different they are from one another. Bear in mind, however, that the output is low. At well under 1V, this restricts the CP251's use as a noise modulation source.

Finally, as with the Mixer and Slew Generator, the S&H section offers somewhat more than is immediately apparent, with the stepped signal presented at Output 1, and a smoothed (low-pass filtered) version presented at Output 2. The low-pass filter frequency is determined by the LFO Rate knob, which is a bit strange, but this ensures that a consistent response is obtained if the LFO is used as the S&H Trigger. Regrettably, the maximum sample voltage is of the order ±3V, which means that you must take care when you use the CP251 with other modular synths. What's more, the sample is triggered by a falling transient, not a rising one, so you will obtain unexpected results unless you take this into account.

The seven sections on offer seem to be reasonable choices, although the CP251 is let down by the lack of a VCA. Notwithstanding this, if you tried to purchase all of these modules in modular synth form, they would almost certainly cost more, so I'll sum up by saying that the CP251 is good value for money, if you want the exact combination of facilities it offers.

A word of warning, however... When I first used the CP251, inputs 1 and 2 on the Mixer were unusable, refusing to allow a quarter-inch jack plug all the way in, so no connection was made. Having first satisfied myself that there was no internal obstruction, I managed to get a jack into each with a bit of 'encouragement'. After this, the plugs worked as normal, but it didn't leave me with a good feeling about the CP251's build quality.


We've covered a vast amount of ground in this review, with two major revisions of the Voyager's operating system, a new hardware model, and two add-on boxes that you can use in all manner of ways to enhance your synthesis.

Starting with the operating system upgrades, there's only one conclusion to be drawn: you would be certifiably insane if you did not upgrade to the current OS. It doesn't cure all the bugs in the Voyager, and even ignoring the hardware faults, there should be at least one further software revision to iron out the remaining problems with the touch-screen. However, minor faults aside, the version 2 OS has fulfilled the promises made nearly two years ago. The Voyager is now a much better instrument. In fact, it's excellent.

Moving on to the Voyager hardware, you may think that I've been rather uncompromising, poring over all manner of minor defects and quibbles. This may be true, but, at this price, you have the right to expect something that is finished and works correctly. Thankfully, we are now much closer to that ideal than ever before, with the Voyager performing as specified, and with fewer faults than previously.

As for the Anniversary Edition, it's very nice, and seems slightly better built than the Signature model that I own. The switches are a tad more positive, the LEDs are brighter, and there's that all-important fix to the pitch-bend wheel. However, you'll have to decide whether you can live with the whine that the backlight emits. If you can, this is the Voyager for you. If you can't, you can always leave the backlight permanently off.

Next... I was initially a little disappointed with the VX351. It promised much, but seemed a bit clumsy, and didn't add quite as much as I had hoped. It wasn't until I stopped using it to overcome limitations within the Voyager itself and placed it next to another patchable synth that the VX proved its worth... which then proved to be considerable. I still have reservations about paying extra for outputs that should — in my opinion — be built into the synth itself, but if you are truly serious about synthesis and own a Voyager, the VX is almost a necessity.

I'm less convinced by the CP251, but that's because — in keeping with most players interested in modular synthesis — I already have access to its functions elsewhere. But here's the acid test... If I were today offered my walnut Signature for its original price of approximately £3000, or an Anniversary for under £2000, there is no contest which I would choose... the Anniversary Edition. It looks great, works better and, with the money I had saved, I could buy the VX351 and CP251, and still have enough cash left over for a cheap holiday in the sun.

Published November 2004