Metasonix TS-21 Hellfire ModulatorThe TS-21 Hellfire Modulator harks back to electronic music's roots. This handcrafted, fully analog tube effects processor uses wave-shaping techniques to distort audio signals. It was designed to use with modular analog synthesizers, and you can set the TS-21 into self-oscillation and use it as a sound generator. The tubes run at a conservative level, which keeps the noise floor to a minimum and the operating temperature down, even after hours of use.

The first stage in the signal path is a pentode tube preamp with an externally controlled VCA for modifying the audio signal's volume contour. Next, the signal travels through a pulse-width modulator and a sheet-beam modulator, both adding considerable nonlinear distortion as they make the signal fold over on itself. An LFO at the end of the signal path gives you stereo panning at the output, with independent control over each channel's pan rate.

The TS-21 is so volatile that you must take great care when adjusting the front-panel controls; even the slightest movement can cause substantial signal changes: turn a knob too quickly, and you may miss something interesting.

It's refreshing to find a tube distortion device designed with audiophile sensibilities. If you're looking unlimited guitar sustain, you'll have to go elsewhere. The TS-21 was designed with more unusual goals in mind.