JBL 6290 - Grounding

2.9
GROUND
I NG
For
safe
operation
the
amplifier
must
be
connected
to a
good
mechanical
ground.
This
provides
for
a
current
path
for
any
voltage
which
should
appear
on
the
chassis
due
to
a
fault
In
the
amplifier.
This
current
path
will
result
In
blowing
the
main
power
supply
fuse.
Without
this
current
path,
the
amplifier
would
present
a
shock
hazard.
In
addition,
a
good
quality
ground
on
the
chass I
s
prov I
d
es
shielding
from
external
fields
and
minimizes
radiation
of
Internal
fields
to
the
outside
world.
To
comply
with
safety
regulations
In
many
localities
and
to
protect
our
customers,
we
provide
a
ground
connection
through
the
3-wire
electrical
cord.
There
are a
few
Instances
where a
hum or
buzz
will
be
noticed
In
the
amplifier
output.
This
Is
caused
by
a
voltage
potential
between
the
audio
ground
from
the
previous
piece
of
equipment
and
the
mechanical
ground
to
which
the
amplifier
has
been
connected,
and is
called a
"ground
loop."
If
this Is
the case,
the
first
attempt
at a
solution
should
be
to
remove
the
strap
on
the
rear
panel
barrier
strip
which
connects
audio
ground
and
chassis.
Audio
ground
will
then
be
referenced
from
the
signal
source
and
not
the
chassis
of
the
amplifier.
The
next
thing
to
try Is
a
3
prong
to
2
prong AC
adaptor
between
the
power
cord
and
the
power
outlet,
to
temporarily
unground
the
amplifier.
Try
the
amplifier
with
and
without
the
ground
strap
on
the
barrier
strip
to
determine
which
connection
works
best.
Remember
,
however,
that for
safety
you
must
still
have a
connection
to
chassljs
ground.
This
is
normally
made
through
a
properly
grounded
third
pin
connec-
tion, or
can be
accomplished
by
tying
all
chassis’
within
a
rack
together
with a
heavy
(#10
or
larger)
wire,
then
connecting
this
wire
to the
cold
water
pipe
ground.
2.10
SECURITY
COVERS
In
some
Installations
It
may
be
necessary
to
safeguard
the
amplifier
gain
control
settings.
The
Model
6200SC
Security
Cover
Is
available
and
contains
enough
covers
for
six
amplifiers.
Installa-
tion
i
nstr
uct
Ions:
1)
Remove
the
two
Level
control
knobs.
If
they
are
on
too
tight
to
be
removed
by
fingers,
use
a
pair
of
long
nose
pliers
to
grasp
the bar
on
the
knob
and
pull
outwards.
Wrap
the
jaws
of
the
pliers
with
masking
tape
to
prevent
scratching
of
the
knob.
2)
If
necessary,
adjust
the
gain
controls
using
a
small
screwdriver.
3)
Press
each
of
the
security
covers
Into
the
hole
until
It
snaps
firmly
into
place.
To
remove
the
cover,
slip
your
fingernail
under
the
edge
of
the
cover
and
pry
it up
and
off.
Alternately,
a
small
screwdriver
or
knife
blade
may
be
used,
taking
care
not to
scratch
the
front
panel.
I
1-10