Therevox ET-5

Visually a blend of unusual and familiar synth elements, with some decidedly retro styling, the ET‑5 measures 812 x 266 x 88mm and weighs about 5.5kg. Using it in icy wastelands is not compulsory, nor recommended in fact.

The ET‑5 may have its roots deep in electronic musical history, but it’s very much a modern instrument.

Continuous‑pitch electronic instruments like the Theremin and Ondes Martenot have traditionally been horribly difficult to master, repellently expensive, or both. And yet they have a certain exotic appeal, and an evocative musical quality that’s hard to recreate by other means. Not to mention a huge potential for experimental use, and a formidable cultural provenance inextricably tied up with sci‑fi soundtracks and psychedelia.

The ET series of instruments by Canadian company Therevox might be less well known, but they offer a distinctive take in this field. In a nutshell, a Therevox combines aspects of the Theremin (analogue tone production, continuous pitch) and the Ondes Martenot (pitch control via a mechanical finger ring, pressure‑sensitive buttons), and adds additional, interesting features all of its own.

Phone Home

The ET‑5 may be an unusual, mould‑breaking instrument, but essentially it’s not hard to describe. The synth signal path, which is fully analogue, is quite conventional: two oscillators into a single low‑pass filter. The oscillators have minor differences in footage ranges, and osc 2 has a white‑noise option in lieu of osc 1’s narrow pulse, but otherwise can sound identical. Osc 2 can be offset by ±7 semitones, the square and pulse wave widths of both can be adjusted via patching (of which much more in just a moment), and there’s a switch to sync osc 2 to 1.

Next in the signal path is a mono send‑return loop intended for effects pedals, with quarter‑inch sockets on the rear panel. A nice touch is that standard 9V pedals can also be powered by the ET‑5, as long as they don’t exceed 200mA current draw, and conveniently placed on the nearby blank area of the control panel. A front‑panel knob applies gain to the return, and with no pedal connected it behaves as an overdrive/saturation stage, rather fine‑sounding it turns out, with a red LED showing the intensity of the effect.

The ET‑5’s filter is an 18dB/octave low‑pass with resonance, and as you might expect its character is mid way between squelchy 24dB and silky 12dB. The output feeds a vintage‑character internal spring reverb (with maximum decay an opulent 10 seconds or so) that gets its own Blend/mix knob. Finally there’s a volume knob for the single line‑level 6.35mm TRS/TS output socket. The power supply, incidentally, is a substantial in‑line brick with a 16V 2A AC output, and available in 110V and 230V versions.

From here on, things are much less conventional. Let’s start with everything happening on and around what looks like a keyboard, but is what Therevox call a fingerboard.

To the left of it, two large wooden blocks are ‘intensity keys’, controlling the amplitude of oscillators 1 and 2 respectively, and essentially acting as real‑time, manual envelope generators. The equivalent of what on an Ondes Martenot is called a ‘touche d’intensité’ or a ‘lozenge’, they’re spring‑loaded vertically and can be depressed into the casework about 10mm. Initial resistance is light, increasing with depth, and the action is both smooth and quick: they allow for long swells, but striking or tapping gives very fast, almost instantaneous, attacks and decays.

Shown here in profile, the wooden intensity keys and nearby hold faders are at the heart of the ET‑5’s expressivity. The left hand end panel duplicates some CV connectivity on 6.35mm sockets.

The 30mm faders either side of the keys are ‘holds’. They’re not sprung, will stay put where you leave them, and have no predetermined function of their own. They’re variable voltage sources, and do various things when you patch them in the ET‑5’s patchbay. With a standard 3.5mm TS Eurorack patch lead patched from Hold 1 to Vol 1, for example, the left hold will take over the role of its adjacent intensity key, breaking an internal normalled connection. Great for setting up drones, but you could just as easily patch the hold to PWM for static control of pulse width, or FX Mix to create a variable send level for the effects loop, which otherwise has no physical control of its own.

More about the fingerboard itself now. Conspicuously, it’s marked with a black and white semitone layout reminiscent of a normal keyboard, spanning nearly four octaves. But these aren’t keys, and instead a rigid transparent plastic strip forms the surface, into which evenly spaced dimples have been drilled. So there’s both a visual and tactile guide to where in‑tune semitone centres lie. About 2cm above runs a wire, emerging from the casework each side, supporting a metal ring with a rubber tensioner. The idea then is that you play the Therevox with a right hand finger inserted into the ring, moving left and right across the pitch range to define pitch, and your left hand operating oscillator intensity and the holds. It’s quite like a Theremin in this respect, with the hands performing essentially the same roles, but with the addition of tactile feedback for both aspects of control.

Finally, the patchbay, which operates on a 0‑5 V standard and with 3.5mm sockets typical of Eurorack. Five short patch cables are included with the ET‑5 and they’ll get you quite a long way. I’ve mentioned a few internal patching examples already, but many more are possible. A further infinity of possibility awaits if you have outboard modular gear of course.

CV outputs include the intensity keys, holds, ring position (tracking at 1V/octave), the position of a connected expression pedal, and the audio output of oscillator 2 (5V bipolar). There are also ‘gate’ outputs that send a full voltage signal any time an intensity key is operated: they’re ideal for firing external envelope generators.

As for CV inputs, most aspects of the architecture can be modulated, and the ET‑5 oscillators track at...