(
4
44
that converts
the time
interval
between switch
contact
opening
and closing
into
a brief
output voltage
pulse.
The
faster
a key is
pressed down,
the
shorter
the
time
of switch
contact
action,
and
the
higher
the
voltage
level
of
the
pulse. The
key
timing
circuit
pulse
is used
to
create
various initial
touch
sensitivity
(velocity
sensitive)
effects,
depending
on
how
the
presets,
pro-
gramming,
and
TOUCH
RESPONSE
sections
are set.
PITCHBEND
[12]
is an
initial
touch
sensitivity
effect
whereby
the timing
circuit
pulse is
reversed
in
polarity
and
applied
to
the
VCO.
Thus,
the frequency
of the
VCO
is initially
forced
lower by
the
negative
voltage
pulse from
the Key
Timer
Circuit,
and then
comes up
to the
note's
designated
frequency
as
the
pulse
dies
out.
The
INITIAL
LEVEL
lever
[43]
in the
program-
ming
panel
applies the
key
timing
pulse
to
the
VCA,
thus
increasing
the
volume
of the
note for the
duration
of the
pulse.
The
faster
you strike
a key, the higher
the
voltage
pulse and
the
higher
the
volume.
This
effect
is
programmed
into
some
of the
preset
patches.
Similarly,
the INITIAL
BRILLIANCE
lever
[42]
applies
the
key timing
pulse
to
the VCF,
thus
raising
the
cutoff
frequency
of
both
filters.
This
increases
the
amount
of
high
frequencies
which can
pass through
the VCF
by an
amount
proportional
to
the voltage
of
the timing
pulse,
and only
for
the duration
of the
pulse.
Pressure
Sensitivity
A
sensor
beneath
the
front
of each
key
is
used
for
the AFTER
(pressure
sensitive)
effects. The
harder
you press
a
key
after
it first
touches
bottom,
the
higher
the
voltage
allowed
to get through
a variable
pad
in
the
key's
sensor.
Various
effects
are
produced
by the
voltage,
depending
on how
the
presets,
pro-
gramming,
and TOUCH
RESPONSE
sections
are
set;
the
keyboard's
after
voltage is
applied
to
the
control
input
of
the
appropriate
voltage
controlled
circuits.
Keyboard
Control
The
keyboard
control
HIGH
and
LOW
levers
affect
the
upper
and
lower
portions
of the
keyboard
separately,
with
increasing
effect
toward the
ends
of the
keyboard.
Thisis
done
for LEVEL
and
for
BRILLIANCE.
The
effect
is actually
achieved
by
a
digital
circuit
which
interprets
the
position
of
each
note
played
on
the
keyboard
and
produces
a
pro-
portional
amount
of
dc voltage.
With
the HIGH
levers,
the
higher
the
note,
the
higher
the
voltage.
With
the
LOW
levers,
the
lower the
note,
the higher
the
voltage.
If
a
BRILLIANCE
lever is
engaged,
the
extra
voltage
is
added
to the VCF,
raising
the
cutoff
point
for
a
more
brilliant
sound. If
a LEVEL
lever is
engaged,
the
extra voltage
is
added
to
the
VCA,
increasing
the
volume
of
the note. (BRILLANCE
and LEVEL
are
decreased by
reversing
the
polarity
of the
keyboard
control
voltage.)
Portamento/Glissando
The
glissando
effect
is
produced
by a digital circuit
which
"looks
at"
the
last
note played and
at
the
note
being
played. Instead
of allowing the
voltage
fed
to
the
VCO
to
jump
instantly
to
the voltage called
for by
the
note being
played,
the glissando
circuit gradually
moves
the voltage
from
that of the
previous
note
to
the
currently
played
note.
A
digital circuit
causes the
voltage
to
increase
or decrease
in
quantized
increments
that
correspond
to
half-step
increments
(a
chromatic
scale).
The
portamento
effect is actually produced by
the
same circuit
that
produces
the glissando, except
that an
additional
circuit
element
is added. This
element
"integrates" the
steps
of voltage,
smoothing
the
transi-
tion
from
one note
to
the
next.
Thus,
the change
is
continuous
rather
than
stepped.
Ribbon
Controller
The
ribbon
controller is
a felt strip beneath which
is
located
a
flat resistive
pad and
a
conductive
cord.
When
you press down
on
the
felt,
the cord contacts
the
pad and establishes
a
given
resistance.
Voltage
passes
through the
pad and
the
cord,
the
value varying
in
proportion
to
where the
strip is
pressed down. The
actual
voltage produced
when
the ribbon is
first pressed
down
is not
important;
it
serves only
as
a
reference
point. The
output
from
the ribbon
circuit
then
be-
comes
proportional
to the
difference
between the
reference
point and any
other
point touched
on the
ribbon.
A
comparator
circuit
"looks
at" the change
in
voltage
and
produces
a
positive
dc
output
when
the
second
point touched
on the
ribbon
is
to the
right
of
the
reference
point.
A
negative
dc
output
is
produced
when
the
second
point
is
to
the
left
of the reference
point.
The
further
away
the
second
point from
the
reference
point,
the higher
the
voltage
output
(positive
or negative).
No voltage
output
is produced
if only
one point is
touched.
It
is
necessary
to
move
a finger
along the
ribbon,
or to
hold
one finger
in
a
given
point
and then
touch
another finger
elsewhere
on
the
ribbon
in order
to achieve an
effect.
The
voltage
output
from
the ribbon
controller
is
fed
to
the main
VCO's,
thus
changing
the
pitch
of
any
note or
notes
being
played;
a
positive
voltage would
raise the
pitch,
and
a negative
voltage would
lower
the
pitch.
Pitch
Control & Detune CH il Control
The pitch
control adds more or
less voltage
to "bias"
the VCO
control inputs, thus raising or
lowering
the
frequency
produced when
a
given key is depressed.
The pitch
control feeds both channels
an equal
amount
of voltage.
The
coarse
pitch
control merely
produces a
greater
range of
voltage
variation
than
the fine
pitch control. The
Detune CH
II control really
does the
same thing
as the
fine pitch control, but
it
is
connected
only
to
channel
II. Thus, only
the
pitch
of
channel 1
1 changes.
Ring
Modulator
A
Ring
Modulator
blends
two
signals together
in a
special
way,
"beating"
a
sub
oscillator against whatever
input
signal is
fed to the modulator input. The
output
does not
contain
the
input
signal frequency
(or
frequencies),
but
it does contain
what
are
known
as
sum
and
difference
frequencies.
Sum and difference
simply
means
that the
sub
oscillator
frequency is
added
to
the input
frequency,
and
is also subtracted
from
the
input frequency.
(Actually,
the mathematics
that
describe the
modulation
are somewhat more
complex
because
two times
the sub
oscillator
fre-
quency is
subtracted
from
and
added
to
the input,
three times the
sub
oscillator
frequency,
etc.).
The
effect may
resemble "ringing,"
although the
term
"ring
modulator"
is believed
to be derived
from
the
configuration
of the
diodes which
comprise such
modulators; they
are wired
in
a circle.
The
sub oscillator
frequency
is set with
the
SPEED
lever, and the
amount
of sub
oscillator
voltage fed
to
the ring
modulator
is
set
with
the
MODULATION
lever. An
envelope
generator
is
provided
for the
sub
oscillator,
and
may be used
to change
the
speed when
a
note is played.
The ATTACK
TIME
lever
and DECAY
TIME
lever
respectively
speed up
and slow
down the
effect
from whatever
speed is
set
with
the
SPEED
lever
to
some
higher
value,
and
back
to the
set speed.
The
amount of change
in
speed—
the
amount
of
envelope
voltage fed
to
the
sub
oscillator-is
set with
the
DEPTH
lever.
Panels,
Memories
& Preset
Patches
The
main
programmable
panels
provide a
means for
the
player
to adjust the
many
VCO, VCF
and
VCA
characteristics,
as well as
touch
response
characteristics,
that
together comprise
a basic
"patch"
or sound. The
memories
are miniaturized
versions
of
the
program-
ming
panels, and
are used in
exactly
the same
v\/ay.
The
preset
patches (PRESET
TONES)
were
all derived
from
actual settings
of
the main
programmable
panels.
Once
a
given
patch was
derived,
the
resistance
value
or
switch
position
of each
panel
control was
measured.
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