Boss RT-20

The Boss RT-20 is a Leslie speaker emulator based upon the Leslie 122. Its four modes offer two choices of mic position, a Leslie emulation fronted by a Marshall 1959 emulation (John Lord fans take note), and a Univibe emulation. A variable drive control is supposed to emulate an overdriven Leslie power amp, but falls short of the real thing by being dark and muffled-sounding. Fast and slow speeds as well as ramp time are all adjustable. A bicolored rotating display which indicates rotor and drum speeds is not as distracting at it appears it might be. One foot pedal turns the effect on and off while the other toggles speed. Pressing both pedals simultaneously sets or releases the brake.

Aside from the issues with the drive sound (which can be disabled) the RT-20's Leslie emulation can be fairly convincing. The trick (counter-intuitively) is to mix the direct and effect sound using the individual controls on the panel.