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.
View post (Which is better, V-amp or Pod?)
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I have a feeling the new v-amp is good too. Check out the forums on http://www.harmony-central.com/ i think there are quite a few sound clips that people have put up there of the new v-amp.