Metasonix TX-2 Butt Probe Puts Tubes Where They Were Not Meant to Be

Metasonix TX-2 Butt ProbeNAMM 2005: Metasonix introduced the latest tube-based sonic violation from Eric Barbour, the TX-2 Butt Probe. Possibly the most offensive product released at this year’s NAMM, the TX-2 promises to be “far more extreme than the famed Sherman Filterbank, and far more tube-freaky than your mother’s enema kit.”

The Metasonix TX-2 is made with three type 4BN6 beam modulator devices. They were originally intended for use in low-cost radio receivers as FM detectors, and were not meant for audio applications. That didn’t stop Metasonix, though. The company has extensive experience with using tubes in innappropriate ways.

By using the inherent non-linearity of the 4BN6 tubes, the TX-2 Butt Probe offers a broad range of distortion effects. The TX-2 can accept guitar, mic or line-level signals, but it works best with line-levels. Adjusting the Fist and Ream controls let the user vary the screen-grid voltages of the first two tubes. Fist controls the first (input) tube, and Ream the second tube in the string.

This changes each tube’s gain and distortion behavior in a drastic fashion. It can be adjusted for mild tube-ish warmth all the way to horrid screaming broken-amp ultra-distortion from hell.

Barbour notes that the range of overdrive effects possible is far vaster and more musically useful than what is available with overdrive pedals based on Mullard germanium transistors. “Instead of simulating tube overdrive with a rare unavailable snob-value antique transistor, we simulate it with tubes.”

Instability is inherent in a circuit with as much gain as the TX-2, and the third tube provides an extra way of modulating the distortion. According to Barbour, “Basically, it is wired as a very bad bandpass filter.”

The filter’s center frequency is controlled with a Vactrol optical resistor and swept continuosly with an LFO built into the TX-2. The sweep can be disabled by turning down the Screw knob, or by plugging an unnassigned 1/4″ plug into the CV IN jack. If this is done, the Screw knob can be used to tune the filter manually, providing a wide range of tonal effects.

Barbour notes, “Face it, butt-probing is a worldwide everyday amusement. And clearly, Americans love to have their butts probed. Look at the freaks they vote into political power.”

The Butt Probe will be available starting in April 2002, and will retail for $499. For more information, check the Metasonix site.


  • Power consumption: 12 volts AC
  • Frequency response: Plenty
  • Distortion: Damn skippy
  • Size: 8 x 4.5 x 2.5 inches
  • Weight: approx 4 pounds
  • Inputs: One audio, one control-voltage via 1/4″ jacks
  • Output: One audio out via 1/4″ jack. Output is typically >20 dB hotter than input.
  • Not recommended for use with guitar amp input, suggest line level.
  • Anal lubricant not included.

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