JBL 6260 User Manual

The
internal
gain-match
adjustment
allows
the
level of
the
signal
at the output
of
Channel
B
to
be
adjusted
to
the
same
level
as the
output of
Channel
A. This is
done
by
making
the
loss
through
IC2D exactly equal
to the
gain
through
Channel
A.
Channel
B,
therefore,
produces a
mirror-image
signal
of
Channel
A:
i.e.
equal
voltage but
opposite
polarity.
Bridging
the load
across
outputs A
and B results
in twice
the
voltage
across
the
load and
four
times the power
of
one
channel
alone
into
the
same
load.
The minimum
load impedance in
this
configuration
is
8
ohms.
4.3 POWER
AMPLIFIER
The
JBL
6230/6260
power
amplifier
employs
discrete
trans-
istor
circuitry after
the
input gain control.
A perfectly
symmetrical topology
is chosen
in order
to
take
advantage
of
distortion
cancellation
effects
inherent in
such
arrangements
and
the equal group
delay
for each
half of an
amplified
signal.
This
configuration
allows
simple
compensation,
exceedingly
wide
open
loop
frequency
response
and
excellent
transient
intermodulation
performance.
Examination
of the
accompanying
schematic
will aid
in
under-
standing the
following
circuit
description:
Q26, Q27,
Q28
and Q29 are
configured
in
matching
differen-
tial
amplifiers
loaded by
the
emitters of Q30
and Q19.
Note
that
no
inverting
voltage
amplifiers are
used.
All
transistors
are
used in
current
mode,
non-inverting
connections.
This
eliminates
bandwidth
limiting due to
Miller
effect
(the
effective
multipli-
cation of
collector
base
capacitance by
voltage
gain) and
result-
ant
reductions of
high frequency
response.
Looking
at
the "top
half" of
Channel
A,
Q26
functions as an
emitter
follower
driving
Q27
in the
common base
mode. The
feedback
signal at
R67 is
sub-
tracted
from the input
at this
point.
Collector
current
from
Q27
is cascode
connected to
the
emitter of
Q30,
which is
also
common
base
connected. Q30
functions as a
non-inverting
current
to
voltage
converter
with
exceedinglv
high low
frequency
voltage
gain
and
a
dominant pole
at
24 kHz with
an
8 ohm load and
nominal
beta
output
transistors.
Closed loop
gain
rolls at
6
dB/octave
to the
unity gain
crossover
(somewhere
beyond
2 M"z).
A conventional
bias
transistor
with
delta Vbe
multiplication
spreads
the
collectors
of
the upper
and lower
transconductance
amplifiers
to
compensate
for the
Vbe
drop of the
output
devices.
The bias
transistor is,
of course,
fastened to the
heatsink
assembly
in order to
temperature
track
the output
devices.
The
output stage
is a
conventional full
complementary
Darl-
ington
configuration.
Again, full
complementary is
chosen
to
assure
most
symmetrical
amplification of
signals.
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JBL 6260 Specifications

General

Brand	JBL
Model	6260
Category	Amplifier
Language	English