Universal Leslie Adapter

The original source for this was from Bob Schleicher's Electronic Instrument Service website, tonewheel.com. It is gone, but has been archived on the Wayback Machine. The archive includes the Universal Leslie Adapter with its zip file, from which the following information was taken.

Universal Leslie Adapter

(From Bob Schleicher, v2. 3/27/98)

This device was built several years ago at the request of rental agencies. It allows the use of almost any Leslie cabinet with a Hammond organ equipped with an 8000 series (122 type) control kit installed. The unit we built incorporated circuitry for all the Leslie families shown, however, I?ve re-drawn the circuit in ?modular? form so you may choose the building blocks necessary for your application.

Power supply

Required in all versions. The transformer is 24 VAC center-tapped at 1 amp. This is a common part and is obtainable from Radio Shack, Mouser and most other supply houses. The diode bridge is a 200V, 1 amp device. Four 1N4001 diodes will work as well.

Input Amplifier

Converts the balanced signal from the console to an unbalanced signal with a 100 ohm source impedance. This signal is used to drive the Leslie amplifier, or the crossover circuit.

Crossover

Necessary when using Leslie models 700, 705, 710 and 720. Directs audio below 150HZ to the stationary channel, thus the 15? bass speaker and higher frequencies to the rotor channel. This provides good bass response and protects the Rotosonic drum speaker, or 10? midrange rotor speaker in the 720.

Tremolo Switching

Required in all applications. In the device we built, this was accomplished differently, but for ease of construction, the small relay does a good job. A D.P.D.T. may be used if more than one family is to be used.

Turn-on Switching

All 11-pin Leslies require a connection between pins 5 and 6 to activate them. Obviously, this circuit is needed only when 11 pin cabinets are used.

Notes

• B+ for older consoles and later tremolo kits is not provided. Current for these applications must come from the organ pre-amp, or in early consoles, a discrete power supply.
• Connections for almost all cabinets are shown. Although the 700 and 705 will operate successfully, do not expect the tonal quality of dual rotor models.
• This circuit WILL NOT WORK with brand specific models, i.e. 100, 101, 102, 103, 212 and others.
• As with all electronic construction projects, keep everything neat, leads as short as possible and use extreme caution where line voltage is present. On 9 pin sockets, pins 8 and 9 MUST be insulated with heat shrink tubing.
• I think you?ll be surprised at how good most dual rotor Leslies sound. The 720 is very convincing.

Enjoy.

ULA-1

ULA-2

ULA-3