JBL 6290 - Introduction

SECTION
I
INTRODUCTION
The
JBL
Model 6290
power
amplifier
has
been
designed
to
meet
the
most
critical
professional
sound
requirements.
It
Is
rugged
and
road-worthy,
conservatively
rated,
and
can
handle
reactive
loads
with
ease.
The
engineering
design
approach
stresses
the
optimization
of
each
stage,
allowing
high
slew
rate
and
relatively
low
loop
gain.
Overall
feedback
has
been
held
to
a
minimum
and
Is
employed
only
to
stabilize
the
gain
and
the
operating
point.
This
design
approach
results
In
an
amplifier
with
excellent
performance
under
the
most
demanding
dynamic
Input
and
load
conditions.
As
evidence
of
the
stress
on
dynamic
rather
than
static
or
steady-state
distortion
mechanisms,
transient
I
ntermod
u I
at I on
distortion
measures
less
than
0.03$
by
the
DIM
100
test.
(Lelnonen,
Otala,
and Curl,
"A
Method
for
Measuring
Transient
Intermodulation
Distortion
(TIM)",
J
o u
r n
aj^
of
the
Audio
Engineering
Society
,
Vol.
25,
No.
4,
April,
1977,
pp.
170-177.)
This JBL
amplifier
uses
multiple
200-watt
output
devices
In
complementary
configuration
for
high
reliability
and
low
distortion.
At
rated
power
Into
8
ohms,
these
output
devices
are
operated
at
less
than
25$
of
their
rated
power
dissipation.
The
benefit
Is
high
reliability
and long
component
life.
Reliable
operation
Is
ensured
through
the
following
protection
modes:
current
Is
limited
under
Improper
load
or
drive
conditions;
output
relays
with
front
panel
Indicators
protect
the
loudspeaker
under
conditions
of DC
offset
or
excessive
low-frequency
transients.
The
relays
also
provide
power-up,
power-down,
and
"brown
out"
muting
to
protect
loudspeakers
from
AC
power
transients.
Clip
Indicators
allow
for
system
optimization.
The JBL
amplifier
may
be
operated
In
the
normal
stereo
mode,
dual
mono
mode, or
bridged
mono
mode.
These
modes
are
switch
selectable
on the
rear
panel.
Active
differential
Input
circuitry
offers
the
benefits
of
balanced
operation
without
the
use
of
Input
transf
ormers.
Input
connections
may
be
made
via
3-pIn
XL-type
connector,
three-cond
uctor
(TRS)
6.3
mm (1/4
In.)
phone
Jack,
or
barrier
strip.
The
barrier
strip
has
separate
terminals
for
audio
ground
and
chassis
ground.
The
rack
ears
and
heatsink
of
the
amplifier
are
made
of
high
grade
aluminum
extrusions;
the
chassis
Is
fabricated
of
heavy
gauge
steel.
All
Internal
components
are
easily
accessible
through
removal
of
top
and
bottom
panels.
Front
panel
graphic
details
are
Incorporated
on the
rear-side
of
a
polycarbonate
laminate
which
Is
virtually
Indestructible.
1-1