There's a lot more to Moog's Subsequent 25 than meets the eye...

Back in November 2014, Gordon Reid reviewed the Moog Sub 37. He was impressed by its combination of hands-on, uncompromising design and, of course, the classic Moog sound. At the time it represented a return to form for Moog. Gordon was suitably impressed. In the intervening years the analogue monosynth market has become ever more crowded and Moog's own Grandmother and Matriarch synths have set a new company standard for '70s analogue allure. So can the diminutive Subsequent 25 carve its own place?

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The Subsequent 25 is a Subsequent 37 at heart, carefully whittled. But if you read the marketing copy, you'll notice it's presented as an update, or successor, to the Sub Phatty. The visual similarities between the two are undeniable. The Sub Phatty is a two octave monosynth with almost the exact same front–panel layout. It was also reviewed by Gordon, back in June 2013. The Sub Phatty ultimately fathered the Sub 37, which gave way to the Subsequent 37 (see the 'Sub Vs Subsequent' box), which has now sired the Subsequent 25. To put it another way, Moog have taken many of the improvements made in the Subsequent 37 and put them, largely, back into the Sub Phatty. Confused? I'm not surprised, it's a confusing product line, but I'll attempt to clarify it as we go along.

For the purposes of this review I think it easier to see the Subsequent 25 as a trimmer, leaner Subsequent 37. If you want a quick reference of exactly what has changed, again see the 'Sub Vs Subsequent' box. For the most part, they share the same synthesis engine. The obvious differences are a shorter, 25-key keyboard and a dramatic reduction in physical controls to better match the Sub Phatty layout.

Despite the much simpler front panel, more features have been retained than you might think. A lot of lesser used functions remain as what Moog call 'hidden parameters', accessed via a Shift mode. There are two types of hidden parameter. The first can generally be turned on or off, or selected from a small number of options — things like enabling duo mode, pitch-bend ranges, MIDI sync, LFO re-triggering, etc — many of which had dedicated buttons on the Subsequent 37. These require the use of Shift mode and the keybed to select specific options. The second are variable parameters, which are accessed by entering Shift mode and using the front–panel knobs — things like extra envelope parameters, external input level and oscillator beat frequency, which don't have their own dedicated controls anymore. By hiding away a lot of the lesser used functions, Moog have managed to keep a great deal of the Subsequent 37's synthesis engine, whilst reducing the complexity, size and cost.

The Subsequent 37 and 25 are two-note paraphonic analogue monosynths. They both share the same core architecture with dual variable waveform oscillators, a sub-oscillator, mixer section with feedback control, and the classic Moog ladder filter. Both wield dual DAHDSR envelopes and LFO sections, although there is only a single LFO on the Subsequent 25, instead of the dual LFOs on the Subsequent 37. The sequencer and arpeggiator from the Subsequent 37 also didn't make the cut. The paraphonic mode, which Moog call 'Duo mode', allows for the two oscillators to be played independently on the keyboard. Oscillator 2 will track either the highest or lowest note, depending on what preference you have set.

The sloped design, which originated with the Moog Little Phatty and continued through the Sub Phatty and Subsequent 37, is retained. The steel chassis, wooden end cheeks and aluminium curved back panel look as beautiful as ever. Knobs feel sturdy and butter-smooth. In short, no compromises have been made to the build quality. The Subsequent 25 feels every bit as premium as the Subsequent 37.

The exact same connectivity side panel offers MIDI in and out via 5-pin DIN or USB, CV inputs for gate, pitch, volume and filter, audio in and out, and an IEC mains socket for internal 100-240 V, 50/60 Hz AC power supply. The keyboard retains its modulation and pitch-bend wheels and its velocity sensitivity, but sadly loses aftertouch.

The Subsequent 25's front panel sports 31 knobs and 13 buttons. The vast majority of these are direct synthesis controls, with the exception of nine buttons on the left which are grouped under the label of 'Presets'. As you might expect, these buttons allow you direct access to the Subsequent 25's presets — just 16 — which are grouped into four banks of four. This grid of buttons doubles up as a way to access many of the hidden parameters too. Unfortunately there are no labels on the panel to guide you in this endeavour, so unless you use a certain function a lot, you'll have to dive into the manual to find the exact combination of buttons needed. To mitigate this, the manual does offer a handy tear-out A4 reference card which shows all the hidden parameter button combinations. It slips easily underneath the synth, ready to be pulled out at a moment's notice. Alternatively, if you plan to use the Subsequent 25 with a computer, the free editor will give you access to all the hidden functions and much more (see the 'Software Editor' box).

Into The Detail

Enough of the comparisons for now, let's focus on the synth at hand. The Subsequent 25's dual oscillators offer four octave transpose switches and a variable waveform control which sweeps from triangle through sawtooth, square and pulse. The second oscillator has an additional ±7 semitone detune control, and there's also a Hard Sync option which locks the second oscillator's phase reset to the first.

The oscillator section is where we find our first hidden parameters. Enabling Shift mode allows the Oscillator 2 frequency control to be used as a 'beat frequency'. This offsets Oscillator 2's frequency by a fixed amount, plus or minus 3.5Hz. The creates a linear constant detuning so that the beating of both oscillators against each other is constant, regardless of the note being played. Another hidden parameter, tucked behind the Hard Sync button, will enable oscillator phase reset.

Both oscillators feed into the mixer section, along with noise and the sub-oscillator, which is fixed as a square wave one octave below Oscillator 1. The mixer section is classic Moog. Turn any knob past around 12 o'clock and the signal will begin to overdrive the filter in a very pleasing manner. The external input can be mixed in by using the Shift mode and Noise control. With nothing plugged into the input, the synth's output will feed back into the mixer section for the classic Minimoog feedback trick, which is a great way of adding some grunge and further saturation.

From the mixer, the signal somewhat predictably heads to the filter. There really isn't much one can say about the classic Moog ladder filter that hasn't already been said. It sounds fantastic, let's leave it at that. The huge filter cutoff knob feels as smooth as Michael Jackson's criminal. It's joined by resonance, envelope and keyboard amount, and the Multidrive control, which adds anything from gentle tube-like warmth to aggressive clipping. One very nice feature, retained from the Subsequent 37, is the ability to change the filter slope. By default, it is set to the classic Moog 24dB per octave but you can change this to 6dB, 12dB or 18dB via one of the hidden parameter settings.

Moving over to the envelope section we find the two DAHDSRs, one each for the filter and amplifier. Despite being six–stage envelopes, there are only four knobs per envelope. Very sensibly, the attack, decay, sustain and release are all available on the front panel, whereas the lesser used delay and hold are accessed using Shift mode plus the Attack and Decay controls respectively. Velocity to filter amount is available using Shift plus Sustain, and velocity to decay/release via Shift plus Release. I find myself wishing that Moog had printed these Shift mode assignments on the front panel. There is easily enough room and it would have helped with the overwhelming number of hidden parameters.

Most of the time, the Subsequent 25 feels like one giant sound-design sweet spot. You'd be hard pushed to get a bad sound from it.

The modulation section houses the Subsequent 25's single LFO. It can produce triangle, square, sawtooth, inverse sawtooth and Sample & Hold waveforms. The waveform selector also has a setting for filter envelope, which allows the envelope to reach parameters that the LFO is meant for. The LFO range is around 0.1Hz to 100Hz, but it can be shifted to either a slower 0.01-10 Hz or a faster 1-1000 Hz via a hidden parameter. This means you can focus on a range that's right for the patch at hand, and even do some basic audio-rate frequency modulation with the faster setting. The range settings are saved per patch.

If MIDI Clock sync is more your style, the LFO can do that too. Once enabled, the Rate knob lets you select a clock division ranging from four whole notes to 1/64th note. The LFO can be routed to either pitch (either both oscillators, or Osc 2 only), filter frequency or oscillator waveform (both oscillators, or either one in isolation). There's a also hidden parameter to allow the LFO to reset on each Note On.

The modulation wheel always acts as the modulation amount source. One nice touch is that the modulation wheel position is saved in a patch, so if you want a precise level of LFO in your patch whenever it is recalled, you can have it. This can be disabled if you prefer your mod wheel to be consistent.

The remaining front–panel controls are more utilitarian. The output section provides two controls, one for master volume and one for headphone volume. The headphone jack is also conveniently located on the front panel. The Pitch section offers a Fine Tune control, which affects all oscillators, and a Glide Rate control. You can change the Glide type between constant rate, constant time and exponential, as well as toggling legato via Shift functions. Also in the Pitch section are the Octave Up and Down buttons, which transpose the keyboard by ±2 octaves.

The final control to point out is the Activate Panel button. As well as being used, in combination with the Bank 4 button, to enable Shift, Activate Panel will relinquish digital control of the front panel and set all parameters to be exactly the values you see in front of you. Of course, when switching presets, it's common to end up with knobs which don't reflect the values you're hearing. The Activate Panel button makes sure that you're hearing exactly what you're looking at. For any old school purists who don't believe in presets, this is the mode for you.

Conclusion

I must confess, I was initially worried by the seemingly drastic cut–down of controls on the Subsequent 25's front panel when compared to the Subsequent 37. The Subsequent 25 looks, on the face of it, like a much simpler synthesizer. In reality, though, Moog have done an excellent job of transplanting the beating heart of the Subsequent 37 into its new body. Not everything survived the surgery of course, with the big casualties being aftertouch, the second LFO, the arpeggiator and the sequencer.

A good portion of what was previously found on the front panel of the Subsequent 37 is now hidden behind esoteric button combinations and keyboard presses. This could be a problem for some. On the other hand, it's clear that Moog have thought carefully about which parameters are important and which might be used less. The Subsequent 25 could easily have felt like a crippled Subsequent 37, but mostly it feels like a very focused design which offers extra power under the hood for those that wish to find it. You could, in fact, use the Subsequent 25 only from its front panel, never accessing any of the hidden parameters, and you would still have a superb synth. With the Subsequent 37, I always felt I might be paying for features which I wouldn't use often. The two-note paraphonic mode, for example, whilst great to have, is not something I'm likely to use in every session. With the Subsequent 25, it feels more like a freebie, a bonus to be used when the time is right.

Sonically, the Subsequent 25 is exactly what you'd expect. I love the smooth analogue basses and Boards Of Canada-style '70s leads which fall effortlessly out. This synth is at its best when doing classic sounds, and the smaller front–panel design reflects this perfectly. Most of the time, the Subsequent 25 feels like one giant sound-design sweet spot. You'd be hard pushed to get a bad sound from it.

In the end, it's about options. Both the Sub Phatty and the Subsequent 37 are still sold by Moog, although I have a feeling the Sub Phatty's days are numbered. The Subsequent 25 is clearly a replacement. The choice, therefore, is between Subsequent 25 and Subsequent 37. That will boil down to finances, size, those few extra features and whether you can live with the hidden parameters system, which really isn't as bad as it might seem. I would gladly recommend the Subsequent 25 to beginners and experienced synthesists alike. In fact, I'm highly tempted to buy one myself. Or do I go for the bigger brother? Decisions, decisions...