Hammond organ

Laurens Hammond, who had previously made synchronous motors for clocks, launched the organ in 1935. A motor drives a shaft lined with tonewheels — metal discs with a wavy edge — and each wheel spinning past an electromagnetic pickup produces a nearly pure sine tone. Nine drawbars mix the fundamental and harmonics at different levels, making the instrument a mechanical take on additive synthesis. It was meant as a cheap substitute for church pipe organs.

The B-3 (1954) became the standard in jazz, gospel and rock, almost always paired with a Leslie speaker. Key click, which the engineers tried to eliminate, became part of the sound organists then demanded back. Spring reverb was developed partly to give the organ some room ambience in living rooms.