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Moog Slim Phatty

Analogue Synthesizer
Published March 2011
By Gordon Reid

Moog Slim Phatty

Moog's Little Phatty has shed some pounds (in both senses of the word), but does this new, lightweight synth have what it takes to be a contender?

I always found Moog to be the most ambiguous of companies. My Minimoog has been a thing of joy for more than three decades, whereas my Source was unusable until the Synthesiser Service Centre fixed a design fault in its power supply. As for the likes of the Opus III, the Polymoog Keyboard and the Micromoog... none of these will be accompanying anybody to any desert islands. Nowadays, I find the same to be true of the company's reincarnation, whose price list contains sufficient curate's eggs for a large omelette. So where does the appallingly named Slim Phatty sit in the Moog pantheon? As the module derived from the equally appallingly named Little Phatty, is it a classic for a new generation, or should it be consigned to the bin of unfulfilled promises?

Philosophically, the similarity of the two Phatties to the Moog Source is striking. All three sport a 'parameter access' programming system, all three offer dual oscillators with hard sync and portamento, all have a single, self‑oscillating 24dB/oct low‑pass filter, all offer independent ADSR envelope generators for the VCF and VCA, and all have a single modulation source with two destinations. Inevitably, however, the Phatties offer more in most (although not all) departments; more waveforms for the oscillators and modulator, PWM, cross‑mod, overdrive, positive and negative filter contour tracking, an external audio input, MIDI via five‑pin DIN or USB (or both), updatable firmware, and so on. But, in essence, all three of these synths are hewn from the same lump of rock.

Physically, the Slim Phatty has eschewed the curvaceous design of its keyboard‑endowed sibling, and comes instead in an angular pressed steel case. This feels chunky and solid, as do its positive buttons, but I was less reassured by its knobs, all seven of which demonstrate an unnerving amount of wobble. Worse still is the position of its on/off switch. While I give Moog credit for incorporating a universal power supply rather than using a wall‑wart, placing the power switch on the rear of something designed to be rackmounted is silly. Talking of rackmounting, I was also disappointed to see that the rack ears cost £23.99$25 extra, while those who wish to use the Slim Phatty as a desktop module will be asked for another £99$89 for the optional Wood Kit.

Hidden Depths

The Slim Phatty's rear panel features a USB2 port, headphone socket, audio output and audio input (on quarter‑inch jack sockets), CV inputs for volume, filter, pitch and gate (again on quarter‑inch jack sockets) and MIDI In, Out and Thru ports. At the far right, we find an IEC port for the internal power supply, along with the less than conveniently placed on/off switch.The Slim Phatty's rear panel features a USB2 port, headphone socket, audio output and audio input (on quarter‑inch jack sockets), CV inputs for volume, filter, pitch and gate (again on quarter‑inch jack sockets) and MIDI In, Out and Thru ports. At the far right, we find an IEC port for the internal power supply, along with the less than conveniently placed on/off switch.

There are two ways to approach analogue synth design. On one hand, you can keep everything simple. You want to change the sound? Just twist the appropriate knob or flip the appropriate switch and something interesting will happen. On the other, you can make the instrument as complex as you like and allocate multiple functions to every knob and button using parameter access and some form of menu‑driven operating system. But what happens when you mix the two concepts? I would embrace something that combines the flexibility of a Korg OASYS with the simplicity of a Minimoog, but a basic monosynth with a menu‑driven operating system and a control panel reminiscent of the monster GEM Promega 3 is not a marriage made in heaven. "Am I affecting the waveshape, the level, or the detune?” the oscillator knob wails plaintively. Press an appropriate button and it then knows what to do, and its LED collar gives you a rough idea of the value of that parameter.

Even more arcane are the functions buried in the Phatty's menu system, all of which are accessed using multi‑function buttons and its tiny 16x2-character display. Nowhere are the problems with this more apparent than when using the arpeggiator. "What arpeggiator?” I hear you ask. The fact that it isn't mentioned anywhere on the front panel doesn't excuse you from having missed it. Or rather, it does. Completely. It's controlled by no fewer than seven pages that lie two tiers down in the menu structure, and you can only find these if you scroll through numerous Advanced Preset menus first. Then, once programmed and armed (happily, on a 'per preset' basis), you switch the arpeggiator on and off by pressing the Value encoder and you latch it by pressing the Enter/Store button! I know that adding some extra buttons would have cost a few quid and taken up some space, but the existing system is a multi‑function option too far for me.

Turning to the Phatty's sonic architecture, its ability to select filter cutoff slopes of 6dB/oct, 12dB/oct, 18dB/oct or 24dB/oct on a 'per patch' basis is an unexpected bonus. The Phatty's character remains in Moog territory — but this nonetheless widens the range of timbral options considerably. Another subtle but important bonus is its ability to retrigger envelopes from zero, or by choice, from the existing Release voltage, the latter of which eliminates the nasty sucking sound that some synths generate when played rapidly. I'm also reassured that the LFO and arpeggiator can be sync'ed to MIDI and to each other, and that adjustments to most of the control panel and menu values are transmitted as MIDI continuous controllers, thus allowing you to sequence changes to the voicing.

Further benefits include the ability to cascade Slim or Little Phatties to create a monster Moog polysynth. I bemoaned the lack of this when I reviewed the new Oberheim SEM a few months ago, so it's only right that I praise its inclusion here. Then there's the Phatty's ability to perform as a highest‑, lowest‑ or last‑note priority synth (again on a 'per preset' basis) with retrigger On or Off, as desired. However, beware... If the 'Poly' parameter has any value other than Off, the key priority and Gate menus become ineffective and, while they still allow you to change values, they do nothing. This confused me considerably until I worked out what was happening. (Or, rather, what was not.)

Other facilities worthy of mention include Performance Mode, which allows you to create four banks of eight presets that you can step though in sequence, no matter where those patches lie in the 100 memories. This will be a boon for live performers. Another is the master output on/off button which, as on the Minimoog, allows you to monitor edits through your headphones before inflicting them on your audience. A third is Precision mode, which allows you to programme and store parameter values to a higher precision than would otherwise be possible.

Bittersweet Symphony

Moog Slim Phatty

However, not all is sweetness and light in Phatty world. In particular, I was disappointed by the limited modulation facilities on offer. There's just a single source that you select from the six options presented on the control panel or from two alternatives buried in the menus. Why didn't Moog place all eight options on the control panel? There's room, so it beats me. It then appears that you can only direct the chosen source to a single destination (choose one of four options) but buried in the Advanced Preset menus there's the opportunity to direct it to a second. Unfortunately, the modulation amount is the same for both, which will rarely be what you want. Likewise, when 'Wave' is selected as the destination, the waveform of both oscillators is affected equally, which precludes a number of classic sounds, such as those that combine a sawtooth wave with a modulated pulse wave.

Another disappointment lies in the Phatty's velocity sensitivity, which affects only the filter cutoff frequency, and not the loudness of the sound. Why? As far as I can see, there's no technical reason to hobble it in this way. As for aftertouch sensitivity, forget it... It isn't implemented.

Yet more frustration lies with the EGR Release On/Off parameter. As the name suggests, this switches off the Release stages of both envelope generators. Except that it doesn't. It curtails them significantly, but the only way to end a sound abruptly remains to reduce the Release(s) to zero. I'm also going to complain about the lack of an audio noise generator, which is such an important facility that I'm always amazed when it's left off anything but the lowest‑cost synths. Finally, I was dismayed to find that the manual's suggestion that I wait 15 minutes for the Phatty to warm up before playing it was good advice. I don't think I own another synth that takes so long to settle.

But the most important thing about the Phatty is its underlying sound. As a distant descendant of the Minimoog, it still sounds like a Moog monosynth should sound and, for some potential owners, this will overcome all objections. Mind you, it's not quite as bright as my Minimoog (or even my Prodigy) and there's an easily spotted reason for this; the maximum cutoff frequency of the Phatty's filter is audibly lower than those of the vintage synths, although, interestingly, it's all but indistinguishable in this regard from my Source. On the other hand, the Phatty's hard sync is even better than the Source's, which has long been held as the standard to which other synths aspire. What's more, you can modulate Oscillator 2 using the filter envelope, to create some superb swept sync sounds, which is an omission that always left the earlier Moogs at a disadvantage.

Unfortunately, few of the 100 factory patches do the Phatty justice, and were you to walk up to one and flick through them, you might come away disappointed. It's one of those synths that rewards a bit of work, and as the review progressed, I tweaked a value here and changed something there until I had a small but growing collection of very usable patches. But did I ever head toward the 'sonic infinity' claimed by Moog's web site? No, sorry. It can sound great, but with such limited facilities, sonic infinity is definitely not on the menu.


There's a strong argument for instruments that do just a little, but do it well. There's an equally strong one for being prepared to pay for sound quality rather than lots of twiddly functions. On both these counts, the Slim Phatty scores rather well and, although I can't claim to have fallen in love with its odd control panel, I soon found I'd become accustomed to it. So if you're looking for a synth module with an analogue signal path that produces simple but classic monophonic sounds, the Phatty delivers the goods. What's more, the possibility of playing it in alternate scales opens up interesting avenues not offered by other monosynths. But there's a caveat. Although more affordable than any other current Moog, and considerably cheaper in real terms than the Source in its day, it's considerably more limited and considerably more expensive than its immediate competitor (which also sounds very good) so you may have to think carefully before splashing your cash.  


The DSI Mopho is the Slim Phatty's direct competitor. The overlap in form and function is considerable, down to its 2x16‑character screen, the four assignable knobs on its control panel, and its optional editor. As another digitally controlled synth with an analogue signal path, the nature of the sounds it produces is also similar to the Moog, but with a CEM‑derived filter instead of a Moog filter. Hey... it's 1982 and the Pro‑One versus the Source all over again! But when it comes to facilities, the Mopho is clearly superior, with two sub‑oscillators, three five‑stage contour generators, four LFOs, two modulation matrices with 13 slots to route 22 sources to 46 destinations, and even a four‑row, 16‑step sequencer. Then there are the Mopho's MIDI and performance capabilities, and it pains me to say that — particularly in important areas such as velocity and aftertouch response — the Moog isn't in the same league. At less than half the price of the Slim Phatty, the Mopho is also fabulous value and, while its parameter‑access operating system is more fiddly than the Phatty's, you should take it very seriously indeed.

The Phatty Editor

The Little Phatty editor/librarian (Mac and PC, stand‑alone and VST, $69) is compatible with the Slim Phatty and, as well as providing advanced patch management facilities, presents the synth's architecture in a more intuitive fashion than the physical control panel.

In many ways, it makes programming quicker and more intuitive. Or rather, it would, were it not for a number of bugs that presented themselves on my system. For example, when saving the sound 'GR Brassy' shown in the screen below, the Gate mode was originally set to Off, the velocity sensitivity was set to 4 and the pitch wheel was set to ±5. However, the values of these parameters were changed by the Save operation to On, zero and ±2 respectively, which changed the sound considerably. Likewise (for example), changing the arpeggiator's Clock Source in the main window caused the on‑screen arpeggiator controls to disappear, and the editor's octave switches were permanently inactive. I have no idea whether these problems were caused by my use of the Little Phatty's editor in advance of a dedicated package for the Slim Phatty but, whatever the reason, I hope that the wrinkles will be ironed out soon.

Abridged Specification

  • Polyphony One note.
  • Oscillators Two, with continuously variable waveforms.
  • Portamento Yes.
  • Sync Yes.
  • Filter Low‑pass with 6, 12, 18 and 24dB/oct options and overdrive.
  • Contour generators Two ADSR envelopes.
  • Mod Sources LFO triangle, LFO square, LFO sawtooth, LFO ramp, Filter contour, S&H, Osc2, Noise.
  • Mod Destinations Osc1 & Osc2 pitch, Osc2 pitch only, filter cut‑off frequency, wave.
  • Arpeggiator Up/Down/Ordered; synchronises to internal clock, LFO or MIDI.
  • Memories 100.
  • Audio Outs Line level and headphones.
  • External Audio In Mono.
  • CV Ins Pitch, Filter, Volume, Gate.
  • MIDI In/Out/Thru and USB2: 7‑bit and 14‑bit user‑selectable.

Alternative Scales

I was excited by the possibility of playing alternative tunings on the Slim Phatty, but while there are 31 memories for these, they were empty on the review model and the Alternative Scales Editor software was released a few days too late to be included in this review. All manner of orchestral instruments, such as pipes and horns, benefit from subtle deviations from tempered tuning, and the software also allows you to edit and load the likes of Siamese, Indian, Chinese and Turkish scales. Although untested in practice, an initial glance suggests that the editor is well laid out and simple to use and, in particular, it will be a significant bonus for electronic musicians involved in non‑Western music.

Published March 2011