Don Leslie, RIP

Donald J. Leslie, the man who invented the organ amplifier that bears his name, passed away last week at the age of 93.

If you like classic rock, gospel, or jazz, some of your favorite songs were most likely enhanced by a Leslie amplifier, which gave the Hammond organ its most recognized voice.

Leslie's invention was ingenious.

His amps typically contain a crossover that splits the audio signal, directing bass frequencies to a 15" speaker aimed down and the treble frequencies to a small driver facing up. Positioned below the bass speaker is a rotating drum (originally made out of plywood) and above the treble driver is a counterweighted horn. The drum and horn deflect the audio signal out through the louvres in the cabinet.

When set at slow speed (Chorale), the lower drum would rotate slowly and the horn not at all. But when switched to high speed (Tremolo), the top horn would rotate at up to 400 RPM. This produced the distinctive doppler-shifting vibrato that many associate with the classic Hammond sound.

I didn't know that Don Leslie was still alive as of last week, as he was not a major public figure. But as the proud owner of a Leslie 147 amp, I am thankful for his invention. You can read some of his obituaries here, here, and here. (Use Bugmenot for the registration-required sites).