An Ondes Martenot-Inspired Synth? | Fess' Find

This week’s Fess Find is a synth that you play by moving a ring on a string: it's the Therevox ET-4. The ET-4 is an extraordinary analog synthesizer, constructed by the Canadian company Therevox, that ingeniously fuses the rare early electronic music instrument Ondes Martenot's au ruban interface with analog circuitry for a unique playing experience.

It's a continuous pitch instrument akin to a theremin with its own unique flair: users control your pitch by moving your finger on an attached string while two pressure-sensitive intensity keys manipulate volume, the black-and-white keys are merely reference points. In 2012, this specific version was launched, and remains to be one of the more uncommon models created by Therevox.

Therevox ET-4
Therevox ET-4

Onboard are independent temperature-compensated analog oscillators that offer six different waveforms, including sine waves, white noise, and octiviants. The latter is an especially unique sound inspired by Ondes—it's a sine wave with a reinforced first harmonic, sounding as though there’s an extra octave above the original fundamental. The oscillators can also be synced or set to a consistent note, or otherwise be used as an LFO. The internal low-pass filter with variable cutoff frequency is used to shape any sound created on this synth; this can also be further sculpted via an external expression pedal or CV source.

An internal spring reverb is included, complete with a mix control to adjust from fully dry to fully wet—this allows you to play the pitch of the reverberation. You can also get creative by taking advantage of patching its inputs and outputs. For example, a player can patch the tuning output and plug it into the expression input for greater modulation on your filter cutoff. Using all these various techniques, it's possible to create a variety of sounds, from eerie ethereal tones and thumping bass lines to extraterrestrial audio scenes and symphonic harmonies.

All these features make the Therevox ET-4 a highly sought-after instrument among professional producers and musicians alike. With only a few knob stickers lacking and some minor paint bubbling on the faceplate, this synth is listed in very good condition. Not to mention that it comes from Brooklyn's Main Drag Music one of our preferred dealers who remain open to offers. There are newer versions of the ET available as well and if you're interested in the Ondes synth voice itself Therevox recently released Ondes VCO Eurorack modules as a faithful recreation of the Ondes Martenot oscillators, which are definitely worth checking out.

Check out this official demo of the ET-4, courtesy of Therevox.
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