Metasonix continues to reach into new areas of noise with the TX-2 Butt Probe ($549), a tube distortion effect that works standalone or mounted in an
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Metasonix continues to reach into new areas of noise with the TX-2 Butt Probe ($549), a tube distortion effect that works standalone or mounted in an analog modular synth rack. The TX-2 uses three 4BN6 tubes, which are related to the BN6 tubes used in the TM-5 guitar preamp. According to Metasonix-mastermind Eric Barbour, the 4BN6 was originally used as an FM detector in inexpensive radios and televisions and is appropriately nonlinear for extreme audio waveshaping.

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The Metasonix TX-2 Butt Probe uses three tubes in series to create highly unstable distortion. The built-in bandpass filter gives you control over timbre.

The tubes in the TX-2 are visible through the top window, and a small light illuminates them when the device is switched on. All three tubes are used in series as preamps, with the Fist and Ream knobs controlling the screen grids of the first two tubes, respectively.

The third tube has a fixed screen voltage, but it is part of a feedback circuit involving a “crude” bandpass filter with a range of roughly 1 to 5 kHz. (Barbour wouldn't speculate on the filter's roll-off characteristics.) An internal LFO, with a set rate, sweeps the filter frequency. You also can use a 10V peak-to-peak CV to do the job. To interrupt the LFO, insert a ¼-inch plug into the CV input and use the Screw control to set the filter frequency manually. The behavior of the Screw control is shaped like an inverted bell, while the Fist and Ream controls behave — and interact — unpredictably. The Level knob sets the audio input amount. The TX-2 has a power switch and a bypass button.

The Butt Probe's I/O is basic: ¼-inch jacks for audio input and output, and a CV input. Surprisingly, the TX-2 offers dual outputs if you use a ¼-inch insert cable (a Y-cable with a TRS plug on one end and two ¼-inch TS plugs on the other). The tip of the TRS plug provides the main output signal that comes after the third tube and filter.

The ring of the TRS plug captures the signal after the second tube. There's noticeable bleed through on that output, but for the most part, the ring channel is less distorted than the tip channel, and it's 10 to 12 dB lower in signal level. The bypass switch doesn't affect the sound of the ring channel, so it's always on, and a hint of distortion is always present. I found this “stereo” option to be most useful when the signals are panned apart slightly, and a hint of the unprocessed sound comes through.

Because of its high output, the TX-2 is intended for use with devices accepting line-level inputs, such as mixers and keyboard amps rather than guitar amps. And according to Metasonix, the output of the TX-2 is divided down and more compatible with solid-state devices than the TX-1 Agonizer was.

Ring of Fire

Operationally, the TX-2 is similar to other Metasonix tube effects: it loves a strong input signal with lots of edges, (particularly synth sounds), and to hear the full sonic potential of the device, you have to turn the knobs slowly and allow the tubes to catch up. You can create fill-like glitches by subtly adjusting the Fist and Ream controls near their lowest settings (see Web Clip 1).

On drum sounds, certain settings cause the distortion to ride the envelopes of sustained sounds such as booming bass drums or open hi-hats (see Web Clip 2). Overall, the TX-2 responded best to electronic percussion.

The TX-2 easily achieves the characteristic chirpy squeal of other Metasonix effects, but it also hums like crazy when the knob levels are set at low levels and no input is present. But that's to be expected when you have three distortion circuits in a row.

The one disappointing aspect of the TX-2 was the sound of the filter. Although I found it most useful in its static mode, a wider frequency range would be a welcome addition. Because a Vactrol is used to control the filter frequency, sweeping it with an external LFO or EG with a fast rate doesn't allow you to get into extreme FM sounds.

In the End

The TX-2 Butt Probe has a broad noise palette and is particularly useful on percussive and sharply defined line-level sources. Its chunky, crunchy sound is both musical and extremely useful, and anyone seriously into noise will enjoy it.

Three-tube satisfaction doesn't come cheap: The TX-2 is a hand-made, limited-edition item accompanied by a serious price tag. Nonetheless, if its predecessor, the TX-1 Agonizer, is any indication, the Butt Probe will be a hot item that moves quickly.

Overall Rating (1 through 5): 3.5