Before Bob Moog passed away in 2005, he and his engineering team were working on a relatively affordable analog synth called the Little Phatty. The instrument was completed the following year and has since been a big seller for Moog Music. More recently, Moog began shipping a smaller version without a keyboard called the Slim Phatty ($795 street), affectionately known as simply the Slim. Like their more powerful sibling, the Minimoog Voyager, the Phatty instruments have an entirely analog, monophonic signal path. Its vital stats include 100 internal presets, two voltage-controlled audio oscillators, a voltage-controlled lowpass filter, one LFO, two ADSR generators, an onboard arpeggiator, an external audio input, and a monophonic output.

The Slim has a look all its own. Designed to be either mounted in a rack or resting on four rubber feet, it comes with neither side panels nor rack ears, but you’ll likely want one or the other. Rack ears cost a rather steep $25, and Moog’s wood side panels (which also include a strip for the unit’s lower front edge) don’t come cheap at $89. If you mount the Slim in a rack, you’ll need to leave enough clearance above it to reach the rear-mounted power switch—an obvious design flaw. On the plus side, it has a standard 3-conductor IEC power connector instead of a wall wart.

The front panel sports four potentiometers with multiple functions, three knobs with dedicated functions, 34 buttons, 18 LEDs to indicate selections, and a 2-line-by-16-character, monochrome, backlit LCD. The rubberized buttons are slightly smaller than the Little Phatty’s buttons, and almost all of them are LED-backlit.

In addition to MIDI In, Out, and Thru jacks and MIDI over USB, the Slim has a 1/4-inch headphone jack and control-voltage inputs for gate, pitch, filter cutoff, and volume (see Fig.1). For previewing patch changes on headphones, you can disable the main output using the Output On/Off button.However, the headphone jack is on the back panel rather than on the front (unlike the keyboard version), making it challenging to connect headphones to a rack-mounted unit. The Slim is class-compliant; Audio MIDI Setup recognized it as soon as I connected its USB to my Mac.

FIG. 1: The Slim Phatty’s USB is class compliant and transmits MIDI.

Front and Center
The Slim Phatty’s user interface is a hybrid, combining the immediacy of front-panel knobs with the economy of hierarchical pages displayed on the LCD. Four main sections—Modulation, Oscillators, Filter, and Envelope Generators—each have a single knob with buttons to select its function. A circle of 15 red LEDs indicates each knob’s current value. The Envelope Generators section, for example, has four buttons for volume and four more for the filter, and pressing the A button gives the knob control over the Attack parameter. In practice, this scheme works quite well because you can always see which parameter the knob controls as well as its value.

The Slim Phatty has two identical oscillators that generate continuously variable waveforms, letting you smoothly transition from triangle to sawtooth to pulse waves by either turning the knob or applying modulation. Each can be transposed over a 4-octave range by simply pressing its corresponding Octave button. Other buttons let you use the potentiometer to change each oscillator’s output level, adjust the second oscillator’s frequency, and change the portamento (glide) rate. If you press the button that hard-syncs the second oscillator to the first, you can produce classic swept-sync timbres by applying modulation to the second oscillator’s pitch.

The filter is one area where the Slim Phatty differs considerably from the Minimoog Voyager. Whereas the Voyager’s filter is stereo, the Slim Phatty’s is mono, and whereas the Voyager’s is multimode—combining lowpass and highpass responses—the Slim Phatty’s is strictly lowpass. Neither is a serious limitation, and the Slim Phatty’s filter still has that famously fat Moog sound. The filter can self-resonate, if you wish, and you can adjust its overload level to achieve warm and ballsy distortion.

The Modulation section’s knob controls either the LFO rate or the mod depth. You can set up a single routing by sending any of eight mod sources (if you consider each LFO waveform to be a separate source) to one of four destinations—the pitch or waveform of both oscillators, the filter cutoff, or oscillator 2’s pitch. A button on the front panel toggles between six sources—four LFO waveforms, the filter envelope, and oscillator 2—but you can also dive into the menu pages (more about those soon) if you want to assign noise or sample-and-hold as a source. The ability to use oscillator 2 as a mod source lets you cross-modulate the oscillators—a real plus. Another menu selection allows you to specify a second mod routing, but its depth is identical to the primary mod routing, limiting its flexibility.

Dig Deeper
On the far left is the interface panel, where you’ll find the main display and buttons to access the Slim Phatty’s menu pages, as well as a knob to adjust the tuning and buttons to enable portamento and shift octaves. When you shift one octave up or down, the corresponding octave button glows red, and when you shift two octaves, it glows orange, making it easy to determine your transposition at a glance. The interface panel has two modes, Preset and Master, which you select with corresponding buttons. You change pages and parameter values in the LCD by turning the Value knob, and change selections within the menus by pressing the Cursor button.

In Preset mode, turning the Value knob scrolls through the 100 rewritable patches stored in the synth’s internal preset bank. If you change any parameter, the Preset button changes from red to orange and allows you to toggle between the saved preset and your unsaved edit. Master mode lets you change global settings, perform system utilities (self-calibration, restoring defaults, etc.), edit Advanced Preset parameters (more on these in a moment), and set up performance presets. Global settings include MIDI parameters, program-change reception status, keyboard priority, LFO sync (internal or external clock and note value), and the like.

The Slim Phatty’s Performance Sets allow you to arrange four banks, each containing up to eight presets that you can load one after the other by turning the Value knob. This allows you to create banks containing all the patches you’ll need for your live-performance set list, for example. Performance Sets ease the problem of not being able to jump directly to any preset stored in the synth’s memory, as you can with many synths.

The Advanced Preset menu is where things get interesting, because its parameters apply to individual presets and not just global settings. You can, for example, change the filter slope from the typically Moog 4-pole response to 1-, 2-, or 3-pole. You can set up alternate tunings for each preset, as long as they have 12 notes per octave. (A free downloadable intonation editor is available, too.) Pot mapping allows you to send any MIDI CC you specify whenever you turn one of the four knobs and route the data to control internal destinations, external destinations, or both. Advanced Preset menus are also where you adjust the filter’s Velocity sensitivity—something I’d expect to see controlled by a knob rather than buried in a menu page.

Especially notable in the Advanced Presets is the Gate menu, which gives you three choices. Legato On doesn’t retrigger the envelope until you fully release a key, and EGR Reset retriggers the envelope with every note you play, regardless of whether you’ve released the previous key. Legato Off, however, lets you retrigger successive notes beginning at their current envelope value rather than at zero—a capability I wish all synths offered.

The Hidden Arpeggiator
Glancing at the front panel, there’s no evidence that the Slim Phatty has an arpeggiator, but you can access it from seven pages within the Advanced Preset menu. Each preset has settings that allow you to enable the arpeggiator, determine its pattern (up, down, or in the order played), specify each step’s duration and octave range, determine its clock source, and so on. Enabling Latch ensures that the arpeggio will continue repeating when you lift your fingers from the keyboard.

In Preset mode, you activate the arpeggiator by pressing down on the Value knob, and latch it by pressing the Enter button. You can adjust the internal tempo on the fly, if you like, by turning the Modulation control, or for finer adjustments, the Value knob. In addition, you can set the arpeggiator to transmit clock and note data to external MIDI devices, which I found useful for syncing my Moogerfooger MIDI MuRF.

Jack Sprat’s Ax
The Slim Phatty is Moog’s entry-level synth, and in many ways, its feature set reflects that. Its design is an odd mix of surprisingly thoughtful touches and even more surprising limitations. For example, although its two oscillators generate continuously variable waveforms, noise is not available as a sound source. Though you can easily access a few esoteric functions using front-panel knobs and buttons, several more-common functions require a trip to the interface panel.

Perhaps most perplexing is that you can set up keyboard Velocity to affect filter cutoff, but not amplitude, which is considerably more useful and more customary. Considering Bob Moog’s devotion to making synthesizers as expressive as possible, I find it somewhat ironic that the Slim Phatty doesn’t support Aftertouch and Velocity doesn’t modulate amplitude. However, the addition of control-voltage inputs for external CV sources mitigates these issues somewhat for anyone with modular capabilities.

". . . the Slim’s greatest advantage is its sound. . . It sounds exactly like a Moog

Nonetheless, the Slim’s greatest advantage is its sound. Its factory patches supply all the piercing solo timbres, deep basses, and over-the-top sound effects you’d expect. Thanks to a versatile pair of analog oscillators and the lowpass filter’s 24dB-per-octave ladder mode, it sounds exactly like a Moog. For even fatter sounds or the ability to play polyphonically, you can layer three Slim Phattys for about the price of a single rackmount Minimoog Voyager RME.

If you want the genuine Moog sound with modern conveniences at a rock-bottom price, the Slim Phatty is the only way to go.

Pros: Fat analog sound. Very good factory presets. USB connectivity. Control-voltage inputs. Performance preset banks. Unique Legato Off mode.
Cons: Velocity has no effect on amplitude. No Aftertouch response. Noise isn’t available as a sound source. Rear-mounted power switch. Pricey options.

Former Electronic Musician senior editor Geary Yelton has been playing and programming electronic instruments for nearly 40 years. He is author of The Rock Synthesizer Manual.