No other synthesizer manufacturer exploits the limits of tube technology the way Metasonix does. The company's founder, Eric Barbour, revels in finding
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No other synthesizer manufacturer exploits the limits of tube technology the way Metasonix does. The company's founder, Eric Barbour, revels in finding untapped tube resources that challenge the musician in ways few products do these days. The TM-3 Gas-Tube Dual VCO with Suboctave ($399; $549 with MIDI) is no exception.

The TM-3 uses two parallel-wired 2D21 (or 5727) thyratron tubes as oscillators. The resulting waveform is a warped sawtooth that sounds beefy, especially when filtering and shaping are added. In addition, the oscillator 2 signal is fed into a bistable multivibrator, which yields a suboctave square wave at half the input frequency. An artifact of this scheme is a pulsing sound, pitched two octaves above the input frequency, that can be used to add LFO-like modulation in the oscillator's midrange. Together, these features add up to a big, albeit unusual, sound.


The TM-3's front panel has a tuning control for each of the oscillators, a suboctave level control, the Suboctave Stability control, and an output level control. The basic version of the module has three ¼-inch jacks: an audio output and a pair of CV inputs. You can run audio-rate signals into the CV inputs to get a range of distorted timbres.

The TM-3 includes a soft-sync switch, which helps oscillator 2 track a little closer to oscillator 1. A pilot lamp, visible through the top-panel window, offers visual feedback by flickering in time with the superoctave pulses.

An optional MIDI input port — a Synhouse MIDIJack II — is available; it includes a sidemounted Channel/reset switch and a ¼-inch gate output. I highly recommend adding the MIDI option, because the TM-3 uses the V/Hz (linear) voltage-control system rather than the typical V/octave (logarithmic) system. Unless you plan to interface the TM-3 with one of the few classic synths that adhere to the V/Hz standard — the Korg MS-series and Yamaha CS-series synths come to mind — spring for the MIDIfied TM-3.

Using the CV input, the TM-3 has a three-octave frequency range — roughly 66 to 528 Hz — making it suitable for use as a bass synth, for midrange lead work, or for effects. MIDI control gives the synth a range of about two octaves and a major sixth.

Ghosts in the Machine

When controlling the TM-3 with MIDI, you can use the signal from the Gate output to drive other analog modules, such as an envelope generator. To get a sense of how the TM-3 sounds and behaves in a conventional setting, I ran its audio output in to the filters of a Moog Music Minimoog Voyager. Using the Voyager's filter EGs and onboard mixer, I was able to shape and blend the TM-3, adding extra warmth and punch to the Voyager's presets. I had to retune the TM-3's VCOs for each octave I planned to play in, though, because the tube oscillators track unevenly, even with the sync switch engaged.

However, it's this unpredictability that makes the TM-3 interesting. When you set the Suboctave Stability control to maximum and play the TM-3 with a MIDI controller, for example, you may get FM-like timbres or perhaps a bit of added clicking on one or two notes. Play a note above or below, and the strangeness disappears.

I found a host of other artifacts as well. As you tune one oscillator up about a major third, the other oscillator lowers incrementally in pitch — a usable effect when the TM-3 is part of a complex, evolving patch. Flip the Sync switch, and the oscillators will go up a half step in pitch. And, when you use MIDI to control the TM-3, an expression pedal plugged into one of the CV inputs can change the pitch of the oscillators up a minor third.

Like all Metasonix products, the TM-3 integrates well with analog modules from other manufacturers. Mounting hardware ($40) is available for installing it in 3U Eurorack (Analogue Solutions, Analogue Systems, Blacet, and Doepfer) and 5U (MOTM and systems.

Bold Buy

The TM-3 is a useful addition to the Metasonix line, although its price puts it at the upper end of analog VCO modules. However, no other company makes a tube-based VCO, let alone a dual-tube VCO with an added suboctave.

Used with the TM-1 Vacuum-Tube Waveshaper and Ring Modulator and the TM-2 Vacuum-Tube Bandpass Filter and VCA, the TM-3 can create sounds that are downright dangerous. No matter how it is used, the TM-3 is not for the timid.

Overall EM Rating (1 through 5): 3.5

Metasonix; tel. (707) 263-5343; e-mail; Web