JBL 6260 User Manual

SECTION
IV
THEORY
OF
OPERATION
IMPORTANT
NOTE
The
following
descriptions
of
the
circuitry
used
in
the
amplifier
are
presented
here
in
order
that
the
professional
user
may
have a
general
understanding
of
how the
amplifier
works.
They
are not
intended
as
a
guide
for service.
Service
on
this
product
should be
performed
only
by
qualified
technicians.
THERE
ARE
NO
USER
SERVICEABLE
PARTS
INSIDE.
In the
following
descriptions
the
component
designations
for
Channel
A are
used.
Component
designations
for
Channel
B are
included
in
the
schematic
diagram
at
the end
of
this
manual.
4.1
INPUT
DIFFERENTIAL
AMPLIFIER
The
input
differential
amplifier
is
comprised
of
IC1
A and
B
and
associated
components.
Input
signals
are
coupled to
the
amplifier
after
passing
through
one of
three
input
connector
types and
passing
across
RF
suppression
capacitors
C45-and
C46.
Two
amplifier
sections
are
used
as
unity
gain
inverters
with
the
output
of one
summed to
the
input of
the
other to
afford
common
mode
cancellation.
Thus
signals
which
appear
equally
on
both input
terminals,
such
as
common
mode
noise
and
hum,
will
be
cancelled
and
unequal
signals,
such
as
legitimate
input
signals,
will be
summed.
Use
of
the
inverting
mode
in
both
sections
assures
high speed,
good
common mode
rejection
and
equal
impedance at
both input
terminals, a
substantial
advantage
over
less
expensive
single
amplifier
topologies.
4.2
MODE SWITCH
The
rear
panel
mode
switch
allows
the
amplifier to
operate
in the
Stereo,
Dual
Mono or
Bridged
Mono
modes.
In
the
Stereo
mode, the
switch is
out
of
the
circuit
and
each
channel
input
goes to
its
respective
output.
In
the
Dual Mono
mode,
the
output
of the
Channel
A
differential
amplifier is
routed
to
both
Channel
A and B gain
controls.
The
signal to
the
Channel
B
gain
control
is
"impedance-switched",
whereby
the
extremely
low
output
impedance
of the
Channel
A
input
amplifier
becomes
the
source
for
the
potentiometer
rather
than the
higher
impedance
source
from
Channel
B input
amplifier
through
resistor
R88. In
the
Bridged
Mono
mode,
output
from
the
Channel
A
amplifier is
routed
through
IC2D configured as
an
inverting
amplifier.
The
output
of
IC2D
is
"impedance-switched"
to
the
input
of
the Channel
B voltage
amplifier.
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22
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JBL 6260 Specifications

General

Brand	JBL
Model	6260
Category	Amplifier
Language	English