Two Speed Leslie Conversion

Excerpted from the OriginalHammondLeslieFaq:

Early model Leslies were equipped with motors which provided only the fast speed. This gave you a choice of tremolo or off. One of the first things often asked by someone that acquires one of these is whether they can be converted to provide the chorale speed as well as tremolo. This modification can be done by either using an electronic speed control, or by modification or replacement of the motors.

The simplest, and probably least expensive way is to use an electronic LeslieMotorSpeedControl designed specifically for the purpose. There are at least three such kits on the market.

1. One such device (the Hamptone motor control) gates the power to the horn and drum motors providing one

  or two full cycles of AC out of every eight cycles.
  These devices are available from at least two suppliers: GoffProfessional, and KeyboardEngineeringInc.

1. Another device, manufactured by RTCLogic, claims to generate true variable-frequecy AC via PWM modulation.

  Prices are estimated to be $250-$300, installed.

Update: Benton Electronics Inc. has re-developed this product. Using the same circuit but with our own re-written code. Check our site http://www.bentonelectronics.com/MTCLogic.html for more info.

A more complete list of the speed controls currently available (compiled by MikeCasino) can be found here.

The single speed motors can be modified with the addition of the chorale motor and associated hardware. CAESound performs this conversion.

And finally, the motors can be replaced with the dual-motor style motor assembly but the cabinet may have to be modified to accept different motor mounting location.

George Benton recommends suspending the lower two-speed stack in the same manner as the single speed motor being replaced. This requires that the amplifier chassis be moved away from the motor (to the left as seen from the back of the cabinet) to reduce the possibility of the slow motor hitting the 12AU7 tube. The big advantage with this method is no modifications to the lower shelf are needed.

TopicModification