Orban 8182A Operating Manual page 21

An
accessory
port
is
included standard
to
interface the
unit
with the Orban
8182A/SG
BTSC
Stereo Generator.
Comparison
With
OPTIMOD-FM: OPTIMOD-TV
(Model 8182A)
is
conceptually
similar
to
OPTIMOD-FM
(Model 8100A).
If
you are familiar with the
8100A,
this
comparison
may
be of
interest.
Otherwise,
skip to the
next
section.
The
following characteristics
are different:
--
The
stereo generator (Card #7)
has
been
replaced with
a
two-channel
audio
output
buffer
card
to drive
an
external
BTSC
television stereo generator.
While
the
8182A
can drive any stereo generator equipped with conventional
Left/Right
or
Sum-And-Difference
audio inputs, best results are
obtained
when
the
8182A
is
mated
with the
Orban 8185A
BTSC
Stereo Generator. This
is
because
the lowpass
filters within the 8185A
were
specifically designed to
complement
the
lowpass
filters
which
already
exist
within the 8182A.
In addition, the
8185A
interfaces
to the
8I82A
by
means
of a
special
multipin rear-panel connector, placing the
first
part of the
8185A
lowpass
filtering before the
8I82A's
preemphasis,
high
frequency
limiter,
and
Hilbert-
Transform
Clipper. This
interleaving
of stereo generator and audio processor
circuitry prevents stray
15,7
34Hz which
may
be present on the
program
line
from
spuriously
triggering the audio processor or causing
intermodulation
distortion within
its
peak
limiting circuitry.
—
The
output wiring (including the
RFI
filter card) has
been changed
to
accomodate
stereo audio.
—
Since the stereo generator
is
omitted, the
STEREO/MONO
mode
switch and
indicator
lamp
have been excluded.
The
rotary switch controlling
the
diagnostic
VU
meter
excludes positions relating to the stereo generator but
has
new
monitor points for the
system
outputs.
—
The
compressor gating circuitry has been altered to prevent the
compressor's
gain from
recovering
beyond -lOcB
in
absence
of
program. This prevents
noise
rush-up, especially
when
the audio source
is
16mm
optical film.
(The
gain of the
8100A was
permitted
to
slowly recover to
OdB since source
material used
in
FM
is
typically
much
quieter.)
To
avoid operator confusion, three of the four
Gain Reduction meters
(Total
Master G/R, Compressor Master G/R,
and Total Bass G/R) have
new
scales
where lOdB
gain
reduction
is
represented
as "OdB".
—
Both
"linear"
and "exponential" compressor release characteristics
have been
made
available.
(The
release
shape
of the
8100A
is
essentially
linear.)
In
"linear"
mode,
the
compressor
releases
at a
constant number
of
dB
per
second.
In "exponential"
mode, the release starts slowly and speeds up
as
it
progresses. This
is
useful
when
the "open" sound
of
slow release
is
desired,
yet large input level
changes must
be followed quickly.
— A
sophisticated peak
limiting circuit called
the "Hilbert-Transform Clipper"
has been developed
specifically
for
TV
applications
(where voice material
is
dominant).
This "clipper"
replaces the simpler variable-threshold diode
clipper
used
in
the
8100A's
distortion-cancelled clipper
circuit.
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