The Leslie 122 is a rotating speaker unit, commonly used with the Hammond B3 organ. The speaker unit has a 40-watt power stage that drives the speaker. The rotor unit disperses the sound of the speaker to create a whirling effect. The 122 rotor has two speeds, both create a distinct tremolo sound. Guitar amp manufacturers have attempted to emulate the sound of a Leslie speaker with varying degrees of success. Fender’s Vibratone amp used a Leslie speaker. It’s possible to modify your signal chain in order to hook up your guitar to the Leslie 122.
Purchase a suitable preamp. The Leslie 122 is powered, so organ users need not add additional power. The issue is connectivity. Rather than physically modifying the Leslie 122 speaker cabinet to accept electric guitar cables, use a dedicated preamp such as the Hamptone LPRE3 preamp from BT Products. It has a 1/4-inch input and a five-pin and six-pin output that connects directly to the Leslie. The preamp is designed to process a guitar signal, while the Leslie 122 is designed to process an organ signal so the sound will be cleaner. This method makes the Leslie function as a speaker only, not an amp.
Turn off the Leslie. It’s always better to turn off a speaker before plugging in, it avoids power surges.
Plug your guitar cable into the 1/4-inch input socket. Power up the preamp and set the tone dials to neutral for now. Set the volume dial to zero, this limits the output signal going into the Leslie.
Plug the output cable from the preamp into the organ input on the Leslie. Your signal will be passed through the preamp into the organ input and out to the speaker.
Turn up the volume of the preamp and strum the guitar. Adjust the volume so you can hear what you’re playing, but keep it quiet for now as you need to tweak your tone.
Select the rotor speed on the preamp. The Hampton preamp can control the rotation speed of the speaker. The 122 has two speeds, select the one that you like the sound.
Tweak the equalization on the preamp. The two tone controls and single volume control are located on the front of the preamp. Tweak the volume to increase the gain going into the Leslie. Higher gain will drive the speaker hard and generate the characteristic warm crunch that so many guitar players desire. Then adjust the tone and bass to shape the sound.
The Dunlop Uni-Vibe pedal emulates the sound of a rotating Leslie 122 speaker.
The Leslie 122 is very heavy and not designed to be transported.