Hammond Sk PRO, Reference Manual

Page: 349 / 624

CUSTOM SETS - Tone Wheel
331
u CUSTOM TONE WHEEL FUNCTION Mode Page
This FUNCTION Mode allows you to select from among a library of different Tone Wheel settings so that each
of the Hammond ORGAN Types will have the sound you want, as well as create your own Custom Tone Wheels.
t
What Are “Tone Wheels?”
Tone Wheels (or “phonic wheels”) are the method by which vintage Hammond Organs generate tone. Each
individual frequency is generated by a steel disk 1 7/8" in diameter and containing a number of high and low
points called teeth on its outer edge. (See the illustration below.) These disks are the Tone Wheels. The most
common tone-wheel generator has a total of 96 tone wheels. In order to generate all the different frequencies,
the tone wheels have different numbers of teeth - some wheels have 2 teeth, others have 4 teeth, others have 8,
16, 32, 64, 128, up to 192 teeth. On a B-3-type organ, only 91 of the 96 wheels generate musical notes - five of
the wheels are blanks, or wheels having no teeth, to maintain balance. On later Hammond models such as the
H-100 and X-77-series, the last 5 tone wheels are cut with 256 teeth, allowing them to play frequencies 92
through 96.
Notice in the drawing above that the tone wheels are placed so that they rotate next to magnetized rods. Each
rod has a small coil of wire wrapped around one end. The tip of the magnet at the coil end is ground to a sharp
edge and mounted near the edge of the tone wheel. Every tone wheel that produces a note has a magnet
associated with it.
Notice also that the tone wheels are geared together. A constant-speed motor drives the gears which in turn
cause the tone wheels to rotate. As the wheels rotate they do not touch the magnets, but pass very close to them.
Each time a high spot passes the magnet, it generates a very small electrical current in the coil.
The number of high spots or teeth passing the magnet each second determines the musical note produced. If,
for example, 440 teeth pass the magnet each second, 440 electrical impulses will be generated which, when
converted into sound with a speaker, will sound the note, “A-440.”
After going through a number of other processes, the electrical impulses finally reach the amplifier, which
strengthens them enough to drive a speaker system, which in turn converts the electrical signal into audible tone.
It is this audible tone which is heard as the “Hammond Sound.”
HA<O>
SK PRO Reference Guide