Hammond Organ L-100 Series, Service Manual

Page: 7 / 87

Page 7
SECTION I
HOW THE ORGAN OPERATES
1–1 GENERAL
This section contains a description of the operating principles
of L–100 Series organs.
Figure 1–1 and Figure 1–2 depict the
locations of the various subassemblies. Figure 1–4 is a block
diagram.
1–2 TONE SOURCE
Most tone sources, such as strings, reeds, or pipes, produce
complex tones. The Hammond tone-producing mechanism,
however, generates individual frequencies which can be
combined by means of harmonic drawbars to produce any desired
tone quality. The block diagram,
Figure 1–4 , shows the chief
components of the instrument.
Electrical impulses of various frequencies are produced in the
“tone generator assembly” which contains a number of “tone
wheels” driven at predetermined speeds by a motor and gear
arrangement. Each tone wheel is a steel disc similar to a gear, with
high and low spots, or teeth, on its edge (see
Figure 1–5 ). As the
wheel rotates, these teeth pass near a permanent magnet, and the
resulting variations in the magnetic field induce a voltage in a coil
wound on the magnet. This small voltage, when suitably filtered,
produces one note of the musical scale, its pitch or frequency
depending on the number of teeth passing the magnet each
second.
A note played on either manual of the organ consists of a
fundamental pitch and a number of harmonics, or multiples of the
fundamental frequency. The fundamental and harmonics available
on each playing key are controllable by means of drawbars. By
suitable adjustment of these controls the player may vary the tone
colors at will. Several pre-selected tones are also available by use
of the preset tabs.
Figure 1–1: L–100 Console, Front View