Leslie Tremolo Unit

A Hammond Aurora Organ, Circa 1975

My friend got a Hammond Aurora organ about 10 years ago and gave me the Leslie unit as well as the bass pedals from it. I used the pedals for another project but had the Leslie sitting around until I was inspired by a video on YouTube recently. So it was time to wire it up.

This Leslie Tremolo Unit has two speeds, a slow “Chorale” and a fast “Tremolo” effect. Each motor has its own power cables, so they can be powered independently. The original wiring had a switch, with Chorale on one side, Stop in the middle and Tremolo on the other side of stop. I don’t have that switch so I wired them independently. It also has speaker wires for the internal speaker. The heart of this unit is a cheese wheel shaped styrofoam baffle with a cut out that spins in the speeds mentioned, and the speaker is facing the cheese wheel so any sound is sprayed around the room, giving the warble sound Hammond organs are famous for. It’s a great, stereo Doppler effect that can be appreciated in person or with a set of stereo headphones if you’re listening to a recording.

Part of the label affixed to the side of the unit.

I tested it on slow speed playing the appropriate Cars tune “Let The Good Times Roll” and was excited to hear the cool effect. Next was soldering the AC wires, shrink tube and electrical tape was used so none of the leads shorted out and wiring up a 1/4” phono input jack so I could plug my guitar amp into it and bypass the amp’s built in speaker.

All this on the 4th of July, America’s Independence Day, so it was only fitting to do a rendition of “The Star Spangled Banner” a la Jimi Hendrix, but with me playing bass.