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HARMONIC DRAWBARS
The left group
of
eight
(8)
harmonic drawbars
(Figure
19) is
associated with
the
lower manual, and the right group
of
nine
(9)
drawbars controls
the
upper manual.
By
sliding these drawbars in and
out, the
organist
is
able
to
mix
the
fundamen^
tal and
harmonics
(or
overtones)
in
various porportions.
The distance
a
bar
is
pulled
out
determines the strength
of
the corresponding harmonic; and
if a
draw-
bar
is
set all the way
in,
the
harmonic
it
represents
is
not
present
in the
mixture.
Neither manual will play unless
at
least one
of
its
drawbars
is
pulled
out at least part of the
way in
the case
of
the M, M-2, M-3, or
with
the "Draw-
bars^'
tab
pressed
or
preset
tab
pressed
in the M-100.
The drawbars slide over nine
(9)
busbars
,
representing intensity
levels, and
each drawbar has two contacts connected together by
a
one ohm resistor.
As the
drawbar moves,
at
least one
of
the
contacts
is
touching some busbar
at
all times,
and therefore there
is no
"dead spot"
in
the
drawbar motion.
The one ohm re-
sistor avoids an actual short circuit between adjacent busbars.
These busbars
extend the length
of the
drawbar assembly but are split
in the
middle
to
form
two groups
of
nine
(9)-
Those
in the left group,
under the lower manual draw*
bars, are
connected
to low
impedance primary
taps
on the lower manual matching
transformer.
Similarly, those
in the
right group, under the upper manual
drawbars, are connected
to
taps on the
upper manual matching transformer-
Sig-
nals from the high impedance secondaries
of
these
two
transformers
go
through
the
lower manual "Vibrato Cancel" and upper
manual "Vibrato Cancel"
tabs
to
the
apraplif
ier input terminals
-
PEDAL DRAWBAR
The
12
(M,
M-2, M-3) or
13
(M-100)
playing pedals are operated
by the left foot
and are connected
to
the
lowest
12
or 13
frequencies
of
the
generator.
The
center drawbar adjusts
the
volume
of the
pedals.
It
operates
a
variable con-
denser (shown
in
Figures
3,
5,
and
7)
which
is
connected
to the
pedal section
of the
amplifier.
For
operation
of
the
circuit see description
of
"amplifier,"
PEDAL KEYBOARD
The
13
playing pedals
are
operated by the left foot
and are
connected
to the
lowest
13
frequencies
of
the
generator.
Like the manuals, they have light
and
dark keys arranged
in the
standard octave pattern.
Figures
20
and
21
identifies
the
pedals and shows the generator frequency number associated with each.
A "pedal contact"
on each pedal opens
when
the
pedal
is
pressed, thereby allow-
ing the
correct generator frequency
to
reach
the
amplifier.
In
addition there
is
a
"pedal keying
contact''
for all pedals,
which closes when
any
pedal
is
operated.
It
serves
to
key the pedal amplifier,
causing
the
note
to
sound
at the
desired
rate-
When
a
pedal
is
pressed
its "pedal
contact" opens
first,
selecting
the
correct
note.
Immediately
the
"pedal keying contact" closes, causing
the note to sound.
When
the
pedal
is
released
a
mechanical latch keeps
the
"pedal contact"
open,
so
that the
last-played pedal note continues
to
sound
for
a
length
of time
de-
termined by
the
position
of
the
pedal "Fast Decay" and "Pedal Legato"
tabs in
the M-100.
In the M, M-2, and M-3; the
time
which
the
pedal sound
is
heard
is
determined
by the setting
of
the
"Pedal Decay" tablet and
a
"Pedal sustaining
control" attached
to the
expression control.
The electrical operation
of
these
circuits
is
described under "amplifier"-
9
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