JBL 6290 Manual page 4

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