By virtue of their electrical properties, tubes generate a special waveform when they're saturated, which is why tube engineering has tremendous tonal advantages over solid state or DSP solutions, particularly for crunch and lead sounds. Tubes enter the saturation zone gradually or softly, which lends tube-driven tone its trademark yet totally unique character.
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Yeah i have one. They have some good effects. They are basically like a zoom pedal but smaller and hand held. Only problem is that its awkward to change effects when playing. A good thing is once you are used to it , it is easy to use and change effects.