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GENERAL
1)
The
414A
chassis
should
always be earth-grounded
(through the
third
wire
in
the
power
cord
or
through the
rack) for
maximum
protection
from
shock. Float
this
ground
(to
reduce
hum)
only
as a last resort.
Because
it
is
not
always
possible to
determine
if
the
equipment
driving
or
being
driven
by the
414A
has
its
circuit
ground
internally
connected
to
its
chassis
ground
(which
is
always connected
to
the
ground prong
of
the
AC
line
cord,
if
present),
and because
the use
of
the
AC
power
line
ground often
introduces noise
or
other
imperfections such
as
RFI,
hum,
clicks,
and buzzes,
the wiring techniques
in
the
diagram
are not universally applicable.
If
you
follow
the
diagram
and
hum
or
noise
appears,
don't
be
afraid
to
experiment.
If
the noise
sounds
like
a
low-level crackling buzz, then there probably
isn't
enough
grounding.
Try connecting
the
(-)
input
of
the
414A
to
a chassis
ground
terminal
on
the barrier
strip
and see
if
the
buzz goes away.
You
can
also
try
strapping the
414A's
chassis
and
circuit
grounds together
(on
the
barrier
strip)
to
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
414A'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
the
414A
dual-channel
unit
are
connected
together
internally,
and
could conceivably introduce
a
ground
loop
if
you do
not
take
this
connection
into
account
in
planning
your
wiring.)
Wiring
The 414A
With
Single-Conductor Shielded Cable: Sometimes,
particularly
if
you
are
using
the
414A
with musical instruments
or
home-type
equipment,
single-
conductor
shielded cable
may
be the only type
immediately
available
(as
opposed
to
the preferred two-conductor
cable).
In
this
case,
connect
the inner
conductors
of
the
shielded cables
to
the
(+)
sides of
the
414A
inputs
and
outputs.
Connect
the
shield
of the
414A
input
cable
to
the
(-)
input,
and connect
the
shield of the
414A
output cable
to
the
(-)
output on the rear-panel
barrier
strip.
The
shield
will
ordinarily
receive
chassis
ground
from
the
external
equipment
which
it
is
connecting
to
the output
of
the
414A. The
chassis
ground/circuit
ground
jumper
on
the
rear
barrier
strip
of
the
414A
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.
Because
use
of single-
conductor
cables
virtually
eliminates
any
possibility
of
carefully
controlling
the
system
grounding
scheme,
it
is
NOT RECOMMENDED!
Even
so,
it
often does
work
adequately.
9
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