Electro-Harmonix Mono Synth

The Electro-Harmonix Mono Synth is a digital guitar synthesizer pedal that transforms a guitar into eleven monophonic synth sounds, from vintage synth emulations to fat, stacked voices to soaring lead sounds¹. It was designed to work on guitar without any modifications, special pickups or MIDI implementation: you plug straight into the 1/4 inch input jack and play¹. Released in 2019, it followed the Bass Mono Synth, the bass version Electro-Harmonix announced earlier that year².

The "Mono" in the name is the key thing to understand before buying. As a multi-oscillator monophonic device, only one note can be played at a time, and it cannot cope with chords³. Play single-note lines and it tracks them; play a chord and the voices collapse into one pitch.

The synth voices

The TYPE knob selects from the eleven synthesis voices¹. Electro-Harmonix describes the range as running "from vintage synth emulations to fat, stacked voices to soaring lead sounds and more"¹. In his review for guitar.com, Michael Watts walked through several of the voices:

The CTRL knob controls a specific parameter for each synth type, so what it does changes as you move between voices¹.

The controls and footswitches

The control set is shared with the Bass Mono Synth: DRY, SYNTH, SENS, CTRL and TYPE knobs, plus BYPASS and PRESET footswitches⁵.

The two footswitches divide the work:

• BYPASS: Toggles the SYNTH OUTPUT jack between buffered bypass and effect modes; the status LED lights in effect mode¹.
• PRESET: Toggles between Preset and live What You See Is What You Get (WYSIWYG) modes, and is also used to save a preset to the current synth type set by the TYPE knob¹.

The preset system is one of the pedal's distinguishing features. You can create, save and recall eleven user presets, one for each of the eleven synth sounds, and factory presets can be restored¹. Delicious Audio noted that a user customizable preset for each of the eleven synth sounds can be created, saved and recalled using the built-in Preset footswitch².

The separate DRY and SYNTH volume controls let you set the blend. As Michael Watts put it in his review¹⁴:

Outputs and expression control

The Mono Synth has separate synth and dry outputs⁴:

• SYNTH OUTPUT jack: Produces the mix set by the DRY and SYNTH volume controls¹.
• DRY OUTPUT jack: Produces the signal present at the INPUT jack¹.

The EXP jack accepts a TRS cable from a standard passive expression pedal, or control voltage (CV) on a TS cable¹. Each synth type has a specific parameter the expression pedal controls, so the pedal becomes a live performance instrument rather than a set-and-forget effect⁷. Delicious Audio highlighted this as a feature that lets you control an entirely different parameter in real time with an expression pedal².

The Mono Synth and the Bass Mono Synth

The Mono Synth was announced after the Bass Mono Synth², and the two pedals share the same architecture: eleven synth types, the same five knobs and two footswitches, buffered bypass, digital design, and a 9.6VDC-200mA adapter included¹⁷. The Bass Mono Synth is described by its maker as a Bass Synthesizer that transforms a bass into eleven great sounding synthesizers, "from vintage synth emulations to thick, stacked voices to deep pulsing sounds and more"⁷, where the guitar version's range runs toward stacked voices and lead sounds¹.

Both pedals carry the preset system. Delicious Audio called the Preset footswitch "the biggest addition to the Bass Mono Synth," noting it was something not featured on any of EHX's 9-series pedals at the time⁸. The Bass Mono Synth's I/O matches the guitar version: a 1/4 inch input, a 1/4 inch expression input and a PSU in⁵.

What reviewers said

Michael Watts reviewed the Mono Synth for guitar.com in June 2019, rating it 7. His verdict⁴:

He also found the eleven types varied and lots of fun, and that an expression pedal brings out the best in the pedal⁴. At the time of his review the UK price was £115 GBP⁴.

At gearnews.com, Jef saw a practical use case: the pedal "could be well suited for use playing with a band that has no keyboard player but needs the odd synth tone for a song"⁶.

Reviews of the Bass Mono Synth point the same way. MusicRadar called it a "High-value unit for synth fans to treasure," citing great value, fast tracking and a wide effects range, with no reasons to avoid listed³. The same review praised its rugged metal chassis and well-sized, clearly labeled and intuitive controls³, and noted that with separate outputs for the dry and synth signals, bassists no longer have to suffer a fixed blend whether recording or playing live³.

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