JBL 6230 - 2.7 APPROPRIATELY RATED LOADS

Where
audio must be
transmitted
through
cables
or wire pairs
of
more
than
several
hundred
feet in
length,
however,
transmiss-
ion line
termination
practices
should
still
be
observed.
This
amplifier has
input
impedances
of
40,000
ohms when used
in a
balanced,
differential
input
configuration,
and
20,000
ohms
when used
unbalanced
(one
side
grounded).
This
makes
the
amp-
lifier
suitable for
use with any
normally
encountered
source
impedance,
low or
high. Therefore,
there
are
only
two
situations
which
will
require an
input load at
the
amplifier:
1)
when the source
requires
a
600 ohm
load,
such
as
a
passive
equalizer,
older vacuum
tube
equipment,
etc,
2)
when
the source
is
a
transmission
line such
as a
tele-
phone line.
In some
instances
it may
prove
beneficial
to
treat the
input feed to
the power
amplifier as a
transmission
line
to
lower its
impedance
and its
susceptibility
to
noise
pickup.
Input load
resistors, if
required,
may
most
conveniently
be
attached to
the
barrier
strip connector
of
the
amplifier,
2,7
APPROPRIATELY
RATED LOADS
2,7,1
IT IS THE
USER’S
RESPONSIBILITY
TO
AVOID
OVERPOWERING
It
is
essential
that
the
amplifier be
used
with
loudspeakers
of
suitable
impedance
that can
handle
the
amplifier's
power
out-
put, We
realize
this is not
always
easy to
determine,
especially
since
speaker
power ratings
have not
been
standardized.
Nonethe-
less,
JBL
IS NOT
RESPONSIBLE
FOR
DAMAGE TO
LOUDSPEAKERS
RESULT-
ING FROM
OVERPOWERING,
Fuses may be
inserted
in
series
with the
loudspeaker
to
protect against
overpowering.
The fuse
value
must be
chosen
with
some care.
Ideally,
the
value will
be
high enough
that
the
fuse
does
not excessively
reduce
the
capability of
the
loudspeaker
to
handle peak
transients
which are
above
its
continuous
power
rating.
On the
other
hand, the
fuse
value must be
low
enough
that
the fuse
can actually
do its
job.
It takes
some
period
of
time to
heat
the fuse
element
enough to
cause it to
melt
and
break the
circuit.
If it
takes
too
long, the
loudspeaker may
go
first.
Obviously,
delayed
action
(slo-blo)
fuses are
not
accept-
able
for
use here.
Also, if
fuses are
used,
consideration
must
be
given
to their
location.
Put
them where they are
accessible
for
ease of
replacement
and provide
clear
labelling
of the
replacement
fuse value.
Place
spare
fuses nearby for
ease
of
replacement
with the
correct
type.
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