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2-8
INSTALLATION
Orban Model
464A
Grounding
(continued)
Audio
Input:
•
Input connections
are the
same
whether
the the driving source
is
balanced
or
imbalanced.
•
Do
not connect
the cable shield
—
it
should
be connected
at
the source
end
only.
Connect
the red (or
white)
wire
to
the appropriate
m
input
terminal,
and
the
black wire
to
the
corresponding
LO
input terminal.
• If
the
output
of
another
unit
is
unbalanced and does
not
have
separate
^
and
LO
(or -)
output
terminals,
connect both
the
shield
and
the
black wire
to the
common
(-)
or
ground
terminal.
It is
rarely
necessary
to
balance an
imbalanced
output with a transformer.
As
long
as
it
is
feeding a balanced
input,
the
system
will
work
correctly.
(The only
situation
where
the addition
of an
input transformer
is
war-
ranted
is
one
in
which
the source
equipment
is
powered
from a
separate
mains
transformer
and
power
ground. Terminate
the transformer's sec-
ondary
with a
20K
resistor.)
Difficult
Situations:
Because
it
is
not always
possible
to
determine
if
the
equipment
driving or being
driven
by
the
Co-Operator has
its
circuit
ground
internally
connected
to
its
chassis
ground (which
is
always connected
to
the
ground prong of
the
AC
power
cord,
if
present),
and because
the
use of
the
AC
power
ground
often introduces noise or
other
imperfections
such
as
RFI,
hum,
clicks,
and
buzzes, the
wiring techniques
in Fig. 2-3
are
not
universally applicable.
If
you
follow
Fig.
2-3
and
hum
or noise
appears, don't
be
afraid to
experiment.
If
the
noise
sounds
like
a low-level crackling buzz, then
probably
there
isn't
enough
grounding.
Try
connecting
the
LO
input
of
the
Co-Operator
to
a
chassis
ground
terminal
on
the barrier
strip
and
see
if
the
buzz
goes away.
You
can
also
try
strapping
the
Co-Operator's
chassis
and
circuit
grounds
together,
and
see
if this
helps.
A
ground
loop usually causes a smooth, steady
hum
rather
than a crackly buzz.
If
you have
a
ground
loop,
you can
often
break
it
by
disconnecting
the
jumper
between
circuit
and
chassis
grounds
on
the
Co-Operator's
rear-panel barrier
strip.
In
either
case,
think
carefully
about
what
is
going
on,
and keep
in
mind
the
general
principle:
one and
only
one
circuit
ground
path should
exist
between each
piece
of equipment!
(Bear
in
mind
that the
circuit
grounds of
the
two
channels of
die
Co-Operator
are
connected
together
internally,
and
could conceivably introduce
a
ground loop
if
you
do
not take
this
connection
into
account
in
planning
your
wiring.)
When
a single-conductor
shielded cable
is
used
for
audio
connections, the
shield
will
ordinarily receive chassis
ground from
the external
equipment which
it
is
connecting
to
the
output of the Co-Operator.
The
chassis ground/circuit
ground
jumper on
the
rear barrier
strip
of
the
Co-Operator should be
left
in
whichever
configuration gives
minimum
hum
or
buzz.
To
minimize
hum
or buzz,
it
may
be
necessary
to
jumper
one
or
more
shields to chassis
ground, and/or
to
jumper
the
Co-Operator's
LO
output
to
chassis
ground.
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