Today, applying modular gear and concepts to the realm of guitar isn’t exactly commonplace, but it’s absolutely present in the minds of makers, players, and vendors. From articles about unlocking the true potential of expression pedals to the wide array of CV-capable effects currently on the market, the ability to wrangle some voltage control in a standalone box is an attractive option in which more guitarists and synthesists alike find immense creative possibility.

But from whence did this lovely concept emerge? Like many innovations in the world of musical equipment, we achieved the fun heights of today by standing on the circuits of giants, in this case Dr. Robert Moog and his game-changing Moogerfoogers. If you’re reading an article on Perfect Circuit, you probably recognize these icons: boxy build, esoteric names, big wooden cheeks, and those signature silvery Moog knobs. What you may not know is that these unassuming pedals carried the name and ideas of a Father of Synthesis through fallow years, preserving elements of a foundational system and providing inspiration to new engineers, simultaneously, for decades.

A quick note before diving further: I will frequently refer to Bob Moog as the inventor of modern synthesis and his creations as the foundation of modern synthesis. While this is certainly true in part, many concepts including the voltage-controlled oscillator, envelope generator, and modularity in the context of synthesis itself, were conceived in parallel with Don Buchla, another electronic musical instrument pioneer whose first work emerged independently from and contemporaneously with Moog's. And of course, their work had predecessors—Harald Bode, Hugh le Caine, and countless others.

All this is to say: West Coast Synth friends, plz don’t come for my head.

Road to the Moogerfooger

The story of the Moogerfooger really begins with the first Moog synthesizer system. Referred to as “The Abominatron” in early communiqués between Bob Moog and composer/co-inventor Herbert Deutsch, the prototype debuted at the 1964 Audio Engineering Society convention. Much smaller and much more affordable than the hulking RCA MkII Sound Synthesizer, which ran on hundreds of vacuum tubes, took up an entire room, and cost an absolutely astonishing amount of money, the first Moog synthesizer was immediately more enticing to musicians and aspiring designers alike.

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[Above: a Moog Model 12 modular synthesizer system; image via Perfect Circuit's archives.]

In addition to its new-fangled silicon transistors for better size/sound and ability to operate with a keyboard, the first Moog system drew crowds for its modular design. All the classic components of a synthesizer—now easily recognizable to modern audiences—were laid out in neat little boxes that could interact with one another via patch cables, all contained in a single housing. The VCO, the famous Moog Ladder VCF, LFO, envelope generator, mixer: all these elements solidified in the aural primordial soup of ‘60s synthesis to emerge as a shining, fearsome EVA of amazing sounds which would fascinate and entice for decades to come.

Fast forward: Robert Moog sold his titular company in 1971 due to poor sales (more on this towards the end), continued on as a designer for the new company, split with said company in 1977, and made a new company in 1978: Big Briar. Until Moog regained the rights to his own name in 2002, Big Briar effectively was Moog Music by another name. Primarily a producer of theremins and other controllers, Big Briar was also the banner under which Bob Moog recreated the original concepts and components of his lauded synth system in tough-as-nails “stompboxes” that bridged the look and feel of a guitar pedal with the CV functionality and modulation possibilities of synthesis.

Enter the Moogerfooger.

The Big Moogerfoogin’ Deal

Come with me to a distant time, the far-far away of 1998. I was nine years old and went to my first concert: Ben Folds Five, Foo Fighters, and The Crystal Method. But more salient to this story, the world of 1998 hadn’t seen Bob Moog’s original designs out in the wild for years. Today we have an embarrassment of riches in our analog and digital options, but the ‘90s and early 2000s saw a market saturated with the latter. In an era already nostalgic for the warmth and uniquely physical presence of analog, synth fans were primed for a marvel like the Moogerfooger to come along.

[Original Moog Moogerfooger training DVD, uploaded to YouTube by The Industrial Retrospective]

The Moogerfoogers' appeal is kind of twofold: they offered a high degree of control/modulation/connectivity with CV and plenty of ins/outs, and they were new renditions of Bob Moog’s original analog circuit designs. That last part was particularly important, as your options in 1998 were either vintage Minimoogs (rapidly climbing in value) or the company’s dinkier ‘80s offerings (did you know they made a synth for Radio Shack?). With the Moogerfoogers, a central pillar of synthesis was once again available to musicians of all keys and strings at an attainable price. They worked with guitars—they worked with synths—they worked with studio gear—and they were primed to become a cult classic.

Now let’s start foogin’.

Moogerfooger Series Breakdown

MF-101 Lowpass Filter

The series started on one of Moog’s strongest notes: its filter. The MF-101 Lowpass Filter was released in 1998, based on Moog's original and widely-celebrated -24dB/Oct transistor ladder design, still used in modules and hardware synths to this day. Gooey and lush, the MF-101 immediately drew praise from fans and institutions like Sound on Sound alike for its great sound and ease of use.

Enveloping (pun intended) that great sound was a simple, intuitive layout that was clearly the byproduct of years thinking about design. The pedal’s interface consisted of Filter and Envelope sections, with a central Drive knob and the I/Os situated up top. While already a great filter, the MF-101 Envelope function which gave the player control over the Filter Cutoff via their playing dynamics for some pretty sweet sweeps. This super well-considered functionality became another hallmark of the Moogerfooger series: each pedal combines an audio processor with a built-in modulation source especially designed to complement the audio effect in question. Additionally, each pedal features both audio and control voltage I/O—making it possible to connect them together with other pedals or modular gear for supreme levels of nuanced control.

On the Filter side, you got control over cutoff and resonance with a rocker switch between 2-Pole and 4-Pole operation. On the Envelope side, you got controls for the Amount of Envelope, a Mix knob, and another rocker switch with options between Fast and Slow tracking. The I/O featured standard audio ins and outs and CV-capable jacks for Cutoff, Mix, Resonance, and Amount.

Being a Moog filter, there are few places where this beefcake wouldn’t fit well. If you stick this after an Intellijel Dixie 2+ or ALM MCO, even the most dire cases of a sickness for the thickness will be sated. It’s been a favorite effect everyone from living instructional video Joe Satriani to bass wizard Thundercat to *gasp* The Crystal Method! My first concert tied in!

MF-102 Ring Modulator

Released the same year as the MF-101, the Moog Moogerfooger MF-102 Ring Modulator captured the creepy, experimental, awesome sound of ring modulation in stompbox form with a suite of new tricks. In order to produce that sound, the MF-102 multiplies an incoming mono signal by an internal voltage-controlled oscillator (the carrier) to produce tremolos, swooshes, gongs, and flat-out ripping robotic inharmonic distortion.

The pedal was divided in sections for the Modulator (carrier), LFO to modulate the carrier, a central Drive knob much like the MF-101, and the I/O arrangement located up top. The Modulator section featured knobs for Frequency and Mix and the familiar two-way rocker switch for switching between Lo and Hi frequency modes for the carrier signal. The LFO section knobs for Amount and Rate and its rocker switch kicked you back and forth between Square and Sine wave shapes, great for all manner of sonic debauchery from smooth sweeps to jarring, repetitive transitions in frequency.

For the I/O, the MF-102 offered even more control and versatility than the MF-101. Standard quarter-inch jacks were on tap for Audio I/O, Carrier I/O, and LFO out as well as CV control for Rate, Amount, Mix, and Frequency. The MF-103 was a particular favorite amongst guitarists and bassists of the era looking for more extreme and distinct sounds: John Frusciante, Omar Rodríguez-López, and Lee Ranaldo all had the Moogerfooger Ring Mod on their boards. At at least one point in time, bassist Juan Alderete had no fewer than three Moog MF-102s on his touring board for the Mars Volta (whoa).

MF-103 12-Stage Phaser

Two’s a pretty good number to start out on, so Moog introduced the third member of the Moogerfooger series in the following year of 1999: the MF-103 12-Stage Phaser. Another personal design of Bob Moog, the MF-103 delivers classic analog phasing in a pleasantly undulating package with plenty of connectivity, but its ace in the hole is its namesake: the 12-stage phasing. Whereas the classic six-stage phasing only has three notches in its filter, the 12-stage doubles it to six, allowing for especially deep and flavorful phasing tones.

The MF-103 is laid out with Phaser and LFO sections along with a central Drive knob for juice and a new contender in the arena: an Output Level knob just below the Drive for output gain compensation adjustments. The Phaser section features knobs for Sweep frequency and Resonance along with a rocker switch to toggle 6-stage and 12-stage phasing modes. The section for the internal LFO gives you Amount and Rate knobs along with a LO/HI rocker switch that kicks the LFO between a .01Hz-2.5Hz operation range and a 1Hz and 250Hz range.

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The I/O section of the MF-103 is another arena where it stands out from its Moogerfooger brethren. In addition to standard jacks for Audio, Aux, Sweep, and LFO, you get CV control on the phase Sweep and Resonance and the LFO Rate and Amount. The point to note is that the Aux out can be panned hard right and the Audio out hard left and get some swirling stereo sound for your trouble.

The 12-stage functionality gets you added depth, but at the end of the day, the MF-103 is a tried-and-true phaser. That’s also what makes it one of the best-loved members of the Moogerfooger roster. I personally would love to get my mitts on one of these guys, as much to have a really cool piece of history as a warm and fantastic-sounding phaser. Some fellow fans of the MF-103 12-Stage Phaser include Daft Punk, Tycho, and Lou Reed.

MF-104 Analog Delay

The undisputed marquee act of the Moogerfooger series, the MF-104 Analog Delay continues to earn the adoration of collectors the synth land throughout for its rarity and delicious bucket brigade sound. Limited to 1000 units in its original run and introduced in 2000 at a time when the fanfare for digital delay had lessened, the MF-104 immediately made waves.

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A decided contrast to the pristine-yet-thin digital repeats, the MF-104 typifies the dark, organic sound of analog delays. Utilizing NOS bucket brigade integrated chips, it achieves a wonderfully umbrous tone. The MF-104 reminded the world that analog delays did a stellar job of thickening parts and adding mood and atmosphere to music that previously felt inert or thin.

The MF-104 was laid out with sections for Feedback and Delay Time, with dedicated knobs for Drive, Output Level, and Loop Gain (more on that in a bit). Delay Times ranged from 40 milliseconds to 800 milliseconds, or 0.8 seconds, so not a crazy amount, but more than enough to work with. The time ranges were divided into Short and Long, selectable via rocker switch, and the Mix knob, well, mixed the affected signal back into the clean one. The Feedback section gave you control over not just the feedback amount, but whether you affected the Internal or External effects loop.

Now back to that nifty Loop Gain knob. The MF-104 sports an I/O for its effects loop to run the affected signal to an external audio processor and then mix it back in. With the right touch on the Loop Gain knob and a solid knowledge of the outboard effect, you can cook up sounds that keep your clean signal and surround it with echoes warped by an external effect. Pronounced effects tend to work the best, so think, oh I dunno, maybe a phaser like the Moogerfooger MF-103 12-Stage Phaser? Or hey, how about the MF-102 Ring Modulator?

In addition to the effects loop routing, the I/O section also features a standard Audio in with both Mix and Delay outs, and a CV section comprising control for Feedback, Time, and Mix.

MF-104 Bonus Section: MF-104 Variants

There are a few Moogerfoogers that synth enthusiasts went so rabid for that Moog made special editions and one-off runs whenever they had the requisite materials.

The MF-104Z Analog Delay was released in 2005 after Moog secured some more of those holy bucket brigade chips and even went under the hood a bit. The MF-104Z is identical to the original MF-104 with the addition of a longer delay time that went over a second. Concurrently, Moog released another batch of 250 units dubbed the MF-104SD (short for “Super Delay”) that stretched the delay time out to 1.4 seconds.

The MF-104M was the most update-intensive version to date during its release in 2012. The MF-104M incorporated user-requested features like a six-shape LFO wave selector, tap tempo, MIDI functionality, additional ports, and Spillover mode, which allowed echoes to continue after hitting the footswitch, even when the footswitch is hit again and new echoes are created.

Finally, following the discontinuation of the MF-104M in 2018, Moog made a limited run of models called the MF-104MSD (is this starting to feel like Dragon Ball?) which combined the new functionality of the 104M with the added delay time of the 104SD. These later variants remain especially desirable today.

MF-105 MuRF

Now we traipse into the further reaches of the Moogerfoogerverse, the more ambitious and experimental entries in the series. But with a name like “MuRF”, how could it not get weird (but also really fun)?

Introduced in 2004, the Moogerfooger MF-105 MuRF is part graphic EQ, part band pass filter, part sequencer, and all awesome Moog interconnectivity. Short for “Multiple Resonance Filter Array,” the MuRF gave you eight bands of resonant filtering between 200Hz and 3.4kHz with an onboard control for the gain of each filter, but the real star of the show was the animation possibilities. The MuRF featured a Pattern selector which would provide automated animation sequencing patterns.

The beefy I/O section featured multiple outs as well as a Tap/Step function for further rhythmic manipulation, which CV controls for Rate, Mix, Envelope, and LFO Sweep absolutely stacked the MuRF with modulation potential.

MF-105 Bonus Section: MF-105M + Bass MuRF Variants

To accommodate engineers using the MuRF in a clocked studio setting, Moog released the MF-104M MIDI MuRF. Similarly, the MF-104B Bass MuRF offered a distinct set of filter frequencies, with the four-stringed and left-handed crowd in mind.

MF-107 FreqBox

Ok, the hits are in: let’s get really weird. Released in 2007, the MF-107 FreqBox is, on paper, an analog VCO with an internal envelope follower, frequency modulation (FM), and hard sync. In practice, the results can be a little unwieldy, but the overall experience lends itself well to those interested in exploring radical sonic territory rather than pinning down traditional song ideas. The idea is that the internal oscillator can be synced to external sound sources—giving you a crude flavor of frequency tracking that turns your instrument's sound into a synth sound. Combine with the MF-101 filter and you've got wacky synth sounds for days.

The knobs for FM Amount, Envelope Amount, and Mix all have corresponding CV jacks at the top. This also goes for the Frequency and Wave knobs under the VCO section. The first Moogerfooger produced after Bob Moog’s death in August of 2005, the FreqBox was a proud exclamation that the pioneering spirit that began the company continued through a desire to make new things that made musicians go “OoooOOoooOOo.”

MF-108M Cluster Flux

Let’s go out on a bang, a big Cluster Fluxy bang. Released much later—in 2011—the Cluster Flux combined LFO and Delay sections with a muscular array of CV options and more modern perks like MIDI connectivity and LFO tap tempo. Ultimately, it looks quite similar to an MF-104M…but instead of offering long delays, it is focused on extremely short delay times…bringing it into the realm of comb filtering, chorus, and flanging.

The internal LFO offered six waveforms with dedicated knobs for Rate and Amount, while the Delay section gave you Time and Feedback knobs along with a Ranger rocker switch that alternated between Chorus and Flange modes. As always, Drive and Output Level knobs were at the center along with the Mix knob.

Equally of note in the Cluster Flux is the inclusion of Bucket Brigade Delay (BBD) chips, the same ones that were used in the MF-104Z Analog Delay. The resulting chorus and flange were both described as lush and full, and animating the LFO Rate and Amount provided huge swells and sweeps that recalled the glory of the MF-103 12-Stage Phaser.

Bonus Round: CP-251 Control Processor

We’ve covered all the “stompbox” entries of the Moogerfooger series, but what’s a world of effects without a little control? The Moogerfooger CP-251 Control Processor acts as the jack-happy brain of not only the Moogerfooger series, but of any analog system requiring a well-considered and elegantly-designed control surface.

Comprising essential utilities familiar to anyone in Eurorack, the CP-251 sports sections for a Four-Input Mixer, Lag, an LFO, dual Attenuators, a four-spot Multiple, Noise generator, and even a Sample & Hold section in the corner. Totaling a whopping 24 jacks across its surface, the CP-251 was tailor-made to efficiently and effectively navigate the many functions of the Moogerfoogers, but again, this is a fantastic concept that’s been repeated in a number of utility/CV modulation units.

It's worth remembering, though, that the Moogerfooger series and the CP-251 came out before Eurorack had reached its current heights: for a time, this series was the ultimate tool for exploring modular synthesis, albeit in a slightly different form.

What Did the Moogerfoogers Give Us?

[Moog official video demonstrating limited edition white Moogerfooger pedals with a Fender Telecaster]

In the 25 years since the Moogerfoogers were first introduced to the public, the concept of CV-capable guitar pedals has evolved from a far-fetched idea to an essential function for discerning effects sommeliers the land throughout. The evidence is everywhere, including all across this website: Asheville Music Tools, Meris, Strymon, EarthQuaker Devices, and most recently, in Gamechanger Audio's MOD Series effect pedals. And of course, the modern-day Moog Music has recreated all of these pedals (and more) as affordable plugins, giving you easy digital access to the sound of all of these iconic effects. All of these companies incorporate design concepts and technology that follow in the footsteps of Bob Moog and his original dreams for a more accessible synthesizer.

Which brings us to a point I touched on earlier in the article: Bob Moog’s original designs and his odyssey of a career. It’s often said that Bob Moog was a great engineer but a bad businessman, but I prefer to think of him as a great engineer who (kind of haphazardly) became a great humanitarian. While it’s true that had Moog patented his designs and kept them under a strict umbrella, he would have greatly benefited financially. But without those designs out in the public domain for hungry minds to discover and pore over, synthesis as we know it, as an incredible community of curious people who love to make and talk about sound, probably wouldn’t look the way it does today.

So in a way, the Moogerfoogers were these little capsules of that spirit which pioneered the world of synthesis. Thank you, Moogerfoogers. Thank you, Bob. :’)