Electro Harmonix Bass Mono Synth

The Electro-Harmonix Bass Mono Synth is a digital bass synthesizer pedal that transforms a bass guitar into eleven mono synth voices, which the maker describes as "from vintage synth emulations to thick, stacked voices to deep pulsing sounds and more"¹. It was announced at Winter NAMM 2019 and released that year², and it works on a plain bass signal: no modifications, special pickups or MIDI implementation are required¹. It is the bass-focused sibling of the Electro-Harmonix Mono Synth, a guitar synthesizer in the same format³.

Unlike the Electro-Harmonix Synth9, whose presets aim to emulate specific vintage synths, the Bass Mono Synth's sounds are not modeled on any particular instruments⁴. Delicious Audio noted that each of the mono synths in its library would cost several thousand dollars as real hardware, which it called the most bang for your buck in the synth pedal world⁵.

The controls

The pedal has five knobs, BYPASS and PRESET footswitches, and jacks for input, synth output, dry output and expression¹⁷. The SENS knob matters most for getting a clean trigger: it adjusts the gain of the input signal before the signal hits the trigger block, so it is how you tune the pedal to your bass and playing touch¹.

The CTRL knob is the shape-shifter of the panel. MusicRadar's review found that "the CTRL control has a different interaction with each synth setting, from decay and attack times to envelope filter resonance, sweep depth, oscillator volume and modulation rate"⁸. With eleven synth types and voicings to choose from, MusicRadar also noted that "there is inevitably some experimentation required before you find the s"ound you want⁸.

Outputs and routing

The SYNTH OUTPUT jack produces the mix set by the DRY and SYNTH volume controls, so you can blend your clean bass with the synth voice in one cable. The DRY OUTPUT jack is independent: in either EFFECT or BYPASS mode, the dry signal is always present there, which lets you run the synth to a separate amp or channel while your bass tone stays untouched¹.

Presets and the Preset footswitch

The Preset footswitch was the biggest addition over EHX's earlier 9-series pedals⁵. You can create, save and recall eleven user presets, one for each of the eleven synth sounds, and the factory presets can be restored¹. In use, MusicRadar describes the workflow simply: "the Preset switch allows you to store a preferred sound for easy recall; set the pedal as you require, press and hold th"e switch for three seconds to store, then press to recall⁸.

Bass Gear Magazine's Sean Fairchild noted a detail players might miss: "a saved preset also saves the state of a connected expression pedal, whether or not that pedal is connected later when t"he preset is called up⁷. So the expression pedal position you used when saving becomes part of the preset itself.

Expression pedal

The EXP jack accepts a TRS cable from a standard passive expression pedal, and each synth type has a specific parameter the expression pedal controls¹. Premier Guitar's launch coverage described it as an input "that lets the player control an entirely different parameter in real-time with an expression" pedal⁹. On the guitar version of the pedal, guitar.com's reviewer Michael Watts found that "adding an expression pedal brings out the best in the pedal"¹⁰, which points to how much live control the EXP jack adds.

What reviewers said

MusicRadar's review found the build typical of EHX: "the new Mono Synth is typically rugged, with a metal chassis and well-sized controls, clearly labelled and intuitive"⁸. That review's take on the range of voices, and the experimentation needed to find the right one, is quoted above.

Premier Guitar reviewed the pedal in 2021 at a $124 street price, testing it with a Sandberg T5 bass with both pickups engaged, recorded direct into an Avid Mbox and Logic X⁶. Bass Gear Magazine's Sean Fairchild covered the pedal alongside the BOSS SY-1, highlighting its PRESET mode, "which allows you to recall one previously saved preset for each of the 11 separate synth voices"⁷.

At launch, MusicRadar framed the pedal as being "all about the big vintage synth tones" while noting that, unlike the Synth9, the presets are not aiming to emulate any specific vintage synths⁴. Guitar.com reported the launch availability: "Available early February at $123.50."¹¹

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