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GENERAL
I)
424A
chassis
should
always be earth-grounded
(i.e.
through
third
wire
in
power cord
or
through
rack.) for
maximum
protection
from
shock.
Floaf
this
ground
only
as
last
resort.
Because
it
is
not
always
possible
to
determine
if
the
equipment
driving or
being
driven by
the
424A
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 fhe
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
probably there
isn't
enough
grounding.
Try connecting
the
input
of
the
424A
to
a
chassis
ground
terminal on the
barrier
strip
and
see
if
the
buzz
goes
away.
You
can
also
try
strapping
the 424A'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 424A'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
424A
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
424A
With
Single-Conductor Shielded Cable:
Sometimes,
particularly
if
you
are using the
424A
with musical instruments
or
home-type
equipment,
single-
conductor
shielded cable
may
be
the only
type immediately
available,
making
it
impractical
to
use
the
preferred
two-conductor
cable.
In
this
case,
connect
the
inner conductors
of
the shielded cables
to
the
"+" sides of
the
424A
inputs
and
outputs.
Connect
the
shield of the
424A
input
cable
to
the
input,
and connect
the
shield
of
the
424A
output cable
to
the
424A
circuit
ground terminal 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
424A.
The
chassis
ground/circuit
ground
jumper
on
the
rear
barrier
strip
of
the
424A
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.
10
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