Korg Monotron Delay and Monotron Duo

IT’S BEEN A YEAR AND A HALF SINCE WE REVIEWED THE ORIGINAL Monotron, and I still marvel at the fact that Korg—makers of highly sophisticated instruments—created an inexpensive, toy-size analog synth that streets for $60.
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Two oscillators in the all-analog Monotron Duo (left) mean you can fatten up the sound or create surprisingly complex timbres. Also real analog, the Monotron Delay (right) has a gritty delay effect instead of the second oscillator. Both use Korg’s classic MS series filter.By Gino Robair

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IT’S BEEN A YEAR AND A HALF SINCE WE REVIEWED THE ORIGINAL Monotron, and I still marvel at the fact that Korg—makers of highly sophisticated instruments—created an inexpensive, toy-size analog synth that streets for $60. Did they realize how hackable it was when they designed it? Did they predict fans of the legendary MS-series lowpass filter would buy a handful to experiment with, or that some clever chap would put the synth’s guts behind a Euro-rack panel? The pocket-size synth may be the catalyst that reintroduces the i-generation to fat hardware sounds and the joys of circuit bending.

Thankfully, Korg didn’t make the mistake of replacing the original model with a “Mk. II” that has more bells and whistles. Instead, they added two more instruments that complement the original: the Monotron Delay and Monotron Duo. Packaged in blister packs and accompanied by a one-page manual covering all three synths, the new Monotrons have the same form factor as the original—a threeposition switch, five knobs, a ribbon keyboard, a built-in speaker, an audio input, and a headphone jack—and are powered by a pair of included AAA batteries. From there, the new models are as sonically different as they are physically similar.

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Monotron Delay

More an effect than a synthesizer, the Delay adds a simulated tape-style echo effect at the end of the oscillator/LFO/lowpass filter configuration. With controls for Time and Feedback, it can easily go into grainy self-modulation, complete with the pitch changes you’d expect as you adjust the Time control—instant ’50s sci-fi and King Tubby dub effects.

If that were all the Delay had up its sleeve, I’d still drop $50 for it. But it also includes a synth voice, though with only five knobs (and two of them dedicated to the delay), some compromises were made. The main oscillator offers a sawtooth wave and goes from subsonic to about 4kHz.

The LFO modulates the oscillator and has selectable triangle and square waveforms. A recessed trim control on the rear panel changes the duty cycle/shape of the selected LFO waveform. The Rate knob controls the pitch of the LFO—from one cycle every 50 seconds to the audio range. The “Int” knob controls both the pitch of the main oscillator and the modulation depth, but inversely: Turning “Int” clockwise increases the LFO speed while lowering the overall pitch range of the keyboard. The remaining control is for filter cutoff . Although the synth might at first seem like the least interesting part of the Monotron Delay, it’s capable of creating sounds that other Monotrons can’t, specifically beepy, modular synth-like tones, which go very well with the old-school echo. The feedback buildup of the echo effect has an organic quality that’s hard to resist.

The Delay is also the noisiest of the Monotrons. It’s seriously low-fi , particularly through the internal speaker, but that’s perfect for adding grit.

Monotron Duo

What’s special about the Duo is that it offers two square wave oscillators, though that doesn’t mean it’s duophonic. VCO2 can be used to create an interval you can play up and down the keyboard in parallel to VCO1, to fatten up the overall sound, or as a modulator.

VCO1’s pitch ranges from D1 to just shy of A6 (two octaves above middle C). VCO2 has a wider pitch range, going from LFO territory up to the edge of audibility, making it perfect for modulation. In VCO1-only mode, VCO2 is used to frequency modulate oscillator 1 using oscillator 2’s Pitch and Intensity controls. In VCO1+2 mode, you can set VCO2’s pitch to whatever interval you want. Then, as you turn VCO1’s Pitch knob, the interval between the two oscillators remains constant.

The filter on the Duo, unlike the one on the Delay, has a peak control and a cutoff frequency knob. Consequently, the filter can be driven into resonance, giving your patches extra bite. The Duo also has a Scale button that makes it easier to play melodic parts on the tiny ribbon keyboard—you get chromatic, major, and natural minor scales, plus a continuous pitch mode.

Pocket Prog

Although the internal speaker enhances the portability of these instruments, both synths are capable of creating sounds that rattle their plastic housing. To fully experience their potential, plug the Duo and Delay into external speakers. You’ll need 3.5mm TRS cables as two-conductor TS cables won’t give you a stable connection.

One of the best features is the audio input, which lets you run any monaural signal through the lowpass filter, and with the Delay, the effect as well. The filter sounds particularly interesting on percussion, whether it’s from an iOS drum machine, an MP3 file, or some other source. If you have more than one Monotron, interconnect them! I own a pair of the original model, so I chained the four units together with the Monotron Delay at the end—I felt like a miniature Rick Wakeman positioned next to my tiny Stonehenge. With three Monotrons ahead of it, the Delay’s noise floor increased substantially, so I dialed back its filter cutoff to mitigate some of the hash. That gave the overall sound a vintage vibe.


It’s hard not to like the Monotron Delay and Duo. They’re fun to play, they sound great when plugged into speakers or a DAW, and they even provide an inexpensive way to introduce kids to the joys of analog synthesis. With its scale settings and second VCO, the Duo appeals to musicians interested in the melodic capabilities of these synths. The additional oscillator and filter resonance enrich the timbral palette. Fans of vintage and lo-fi effects will get more out of the Delay. Besides the fun that it offers as an echo, I enjoyed the sounds it makes on its own. At this price, though, why not get both?

Snap Judgment

PROS Inexpensive. Classic synth and filter sounds. External audio input. Ultraportable. Easy to circuit-bend.

CONS Noisy output on Monotron Delay.

Bottom Line

Unless you’re a pianist who avoids any instrument that uses electricity, we can’t think of any reason not to own every flavor of Monotron.

$70 list each | $50 street each korg.com

***Check out original audio from the winners of Korg's Monomania sound contest.

***Video clip of daisy-chained Monotrons in action.