The Dual Footswitch can be used with the TA 501, TA 503, MoMark LMK and Studio Pre. The Single Footswitch is designed for the Classic 300 and R 500. For the TA 501 and TA 503 heads, one button on the Dual Footswitch controls the mute function (allowing you to tune silently), and the other activates EQ bypass. The same pedal, used with an LMK, gives you an on/off switch for each channel of the amp. On the Studio Pre one bypasses the Amp Channel, the other switches the Pure Parametric Filter in the Clean Channel on and off. The Single Footswitch gives you mute-to-tune control for the Classic 300 and R 500.