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This function may also be controlled from a footswitch. For the footswitch to operate, this button must be in its OUT position. VALVE DRIVE (ABM/RPM-1 only) This routes the signal either through a clean Solid State amplification section (control on zero) or through a Dual Triode Tube amplification/overdrive section to add either tonal character, i.e. warmth with the control set at 9 o’clock, a slight edge in the sound at 12 o’clock, through to an increasing degree of Tube distortion/overdrive as