Advertisement
TECHNICAL DATA
Orban Model
464A
Component-level
description:
C101,
C102
shunt
RF
from
the input leads
to the chassis.
Since
these
capac-
itors
are not effective
at
VHF
and
higher
frequencies,
ferrite
beads have been
placed around
the
input
and
output
leads
to
suppress
such high-frequency
RF.
Although
this
RF
suppression
is
modest,
it
should be adequate
for the vast
majority of
installations.
The
filtered
signal
is
applied
to
opamp
IC108a.
3.
Voltage-Controlled Amplifiers
The
current-controlled
gain block
used
in
the
Co-Operator
is
a proprietary
class-A
voltage-controlled amplifier
(VCA).
It
operates
as
a
two-quadrant analog
divider
with gain
inversely proportional
to
a current
injected into
a
first
gain-control
port,
and
is
cascaded with
a
two-quadrant analog
multiplier
with gain
directly
proportional
to
a current
injected into a
second
gain-control
port
For most
gains,
levels,
and
frequencies,
total
harmonic
distortion
(THD)
is
well
under 0.1%.
Overload-to-noise
ratio
(noise
measured
in
a
20-20,
000Hz
band)
is
typically
90dB, and
is
constant with
respect
to
gain
and
level.
A
specially-graded
Orban IC
contains
two
matched,
non-linear gain-control blocks
with
differential
inputs
and
current outputs.
Used
alone,
one such
gain-control
block
would
introduce considerable
distortion.
Therefore, the
first
of
the
two matched
blocks
is
used
as the
feedback element
for
a separate
opamp,
and
the
second
is
driven
by
the
pre-distorted
output
of
that
opamp.
The
gain
of
the
VCA
is
therefore
inversely proportional
to
the
gain of
the non-linear gain-control blocks.
This enables
the
VCA
to
function
as
a
two-quadrant analog
divider.
If
the
VCA
is
not
perfectly
balanced,
"thumps"
due
to
control current
feedthrough
can
appear
at
the output.
These
are
eliminated
by
applying
DC
offset to the
VCA's
input.
The
basic current-controlled gain
in
the
leveler/compressor
is
inversely proportional
to the
control
current
generated
by
the leveler/compressor control
circuitry.
The
gain
is
made
proportional
to
a control voltage
in
dB
by
an exponential current
converter.
Component-level
description:
The
first
gain-control port
is
pin
6 of IC105b;
the
second
gain-control port
is
pin 3 of
IClOSa.
1005
is
the specially-graded
Orban IC
containing
two matched
non-linear
gain-control blocks with
differential
inputs
and
current outputs.
The
separate
opamp
in
the
feedback loop
is
IC106.
The
output of
IC106
is
first
attenuated
by R120, R121
,
C109, and
then applied
to the
input
of
the
feedback element
IC105b
at
pin
9.
The
output
of
IC106
is
pre-distorted
as
necessary
to
force the current
output of
IC105b
to
precisely
and
linearly
cancel
the
audio
input
into the "virtual
ground"
summing
junction
of
1006.
This
same
pre-distorted
voltage
is
also
connected
to the input
of
IC105a
at
pin
16.
Thus
the
output of
IC105a
at
pin 13
is
an
undistorted
Advertisement
