ARP 2600 - Voltage Controlled Amplifier (VCA); VCA Gain Control: Linear vs. Exponential Sensitivity

31
system
and
may
be
used
for
various
percussion
effects
depending
on its
resonant
frequency
(identical to
F
c
)
and
on the
pulse
o
r train
of
pul-
ses
exciting
it.
As
the
Q
is raised
still
higher,
beyond
about
the
halfway
point
in
the
control
slider
travel,
the
filter will
begin
to
oscillate
and will
produce a
pure
sine-wave
output
even
in the
absence
of any
signal
input.
4.1
21
There are
FIVE
SIGNAL
INPUTS
to
the VCF.
They
are fed
through
logarithmic
attenuators
to a
summing
point,
and
then to the
VCF itself.
Prewired
connections
are
from
the
Ring Modulator,
VCO-1
Square, VCO-2
Pulse, VCO-3
Sawtooth,
and
Noise Generator
outputs.
Any of
these is
automatically
disconnected by
insertion of
a patch cord
into
the
proper input
jack. Each
input has
an
impedance
of
not less
than
50Kohms.
There are
THREE CONTROL
INPUTS
to the VCF.
Two
are
fed
through
linear attenuators;
prewired to
these
are
the
ADSR
Envelope
Generator
output and
the VCO-2
Sine
output.
The
third,
unattenuated,
is
normally from
the Keyboard
Control
Voltage. Any
of
these
is auto-
matically
disconnected by
insertion
of patch
cords
into
the
proper
input
jack.
The
impedance of
the
coniroi
inputs is
not iess than
SOKohms.
4.1 22
The
output
impedance of
the VCF
is
1
Kohm and
the signal-to
noise
ratio is greater
than
60Db
referred to a
10V
P-to-P
input.
4.13 The
VOLTAGE
CONTROLLED
AMPLI-
FIER
has
a
maximum
gain
of
unity
and a
dynamic
range
of 100Db.
With the
INITIAL
GAIN control
at
maximum,
and
with no
control
input, the VCA
will
pass with
unchanged
ampli-
tude any
signal
presented to
its
signal
input.
On
the other hand,
with
the INITIAL
GAIN
control
at
minimum,
no signal
will pass
through
the
amp-
lifier
at
all
unless some
positive
voltage
is
present
at
one or
both
of
its control-voltage
inputs.
One of these
inputs has a
LINEAR
sensitivity.
Th$
gain
of the
amplifier
in
response to
a
control
voltage
presented through
this
input
will equal
V
c
/1
0,
i.e.
dividing
the
value of
the control voltage
by
1
will