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In
stereo
installations,
it
is
important
that
both
left
and
right
audio inputs
be
in
phase.
This
is
ordinarily
assured
simply
by
connecting
the
red
and
black
wires
within
all
shielded cables
symmetrically and
consistently
when
wiring the
two
stereo
channels.
If
a phasing error occurs,
it
will
be indicated
in
on-air
testing
by the
stereo
monitor's
indicating
more L-R
than
L+R
level.
Accessory
Chassis
Output Connections:
In
the
dual-chassis
configuration
of
OPTIMOD-TV,
the
output
of
the
Accessory
Chassis
presents
a
600
ohm
pure-resistive source
impedance, balanced
to
ground, with
a
nominal output
level of
+
10dBm
when
loaded by 600 ohms.
It
is
thus suited
for driving
a land-line
directly,
or for driving
the balanced
input of a
microwave STL
transmitter.
If
you
wish
to
drive
an
unbalanced
input,
connect such
an
input
between
the
Accessory
Chassis
"+"
output
and
circuit
ground.
Do
not
ground the
output;
while no
damage
will
occur,
it
will
short the output
of
the
line
amplifier to
ground through
a
300
ohm
resistor,
unnecessarily
stressing
the
opamp.
Main
Chassis
Output
Connections:
The
outputs
of
OPTIMOD-TV
are
balanced
to
ground from
an
active
source.
They
are
designed
to
be loaded
by an essentially
resistive
load
of
600
ohms +10%
to assure correct
frequency and
transient
response.
Some
high-quality
transformers
are
suitable.
However, most
transformers
will
degrade
the
pulse
response
of
the system,
and
use of active input stages at
the
aural exciter
or
stereo generator
is
advised, as discussed
in
Part 2 under
Exciters.
(The
output
RFI
suppression
network
was
designed
to
have
no overshoot
or
ringing
when
properly terminated).
The
output
should be run
in
100%
foil-shielded
cable
(like
Belden
8451).
See
the
comments
on grounding
in
Input Signal
Connections
above.
If
bypassing
the exciter's
input
transformer, preemphasis network, and any
filtering
(as
recommended
above
for
best
peak
level
control) requires that
the exciter
be
driven unbalanced,
this
driving signal
should be taken
between
the
(+)
output
and
circuit
ground
on the rear-panel
barrier
strip.
Total load
impedance
should be
300
ohms,
+10%.
Usually,
the
exciter
presents
a reasonably
high
impedance
when
operated
in
this
configuration,
and
the load
must
be provided by
an external
300
ohm
resistor (not supplied).
IMPORTANT
Do
not
ground
the
(-)
output
in
an
attempt
to
get
an
unbalanced
output; you
will
short the
output
of
the
(-)
amplifier to
ground through
the
RFI
suppression
filter.
Just leave the
(-)
output
floating.
If
the
exciter
modification
results
in
very
high
input
sensitivity,
then the
input
may
have
a
tendency
to
pick
up
noise
due
to
RFI.
If
this
occurs,
operate the
OPTIMOD-TV
output
at
a
higher
level,
and
build
an "L" pad
at
the exciter
.
This
"L" pad can
be designed
to
have
an
input
impedance
of
300 ohms,
correctly loading
the
OPTIMOD-TV
output.
3-7
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