Notes
Q507, Q508,
and
Q509
are the
-LVA's
and are
arranged
¡n
mirror
image
to
the
+LVA's,
¡ncluding
D513.
On
the
positive side D514, D515,
and
C506
vía
the
+LVA's
act to
limit
slew
rate.
D514
and
D515
also
prevent dangerously excessive current
through
the
LVA's.
D516,
D517,
and
C507
are the
negative
HS
mirror
image.
Q534
and
Q540
provide
two-speed current limiting
¡n the
output stage.
Sense
lines
are
arranged such that excessive current through
any
single
HS
output device
will
result
in
current limit protection. Q535
and
Q541
are
the
negative side mirror image.
Q503
on the
positive output module works
in
tándem with Q505
on the
negative output module
as a Vbe
multiplier
circuit.
They produce and,
with great
stabilily,
control
biasforthe
High Side
NPN
and
PNP
devices.
Potentiometer R505
is
used precisely
set
bias voltage. Bias voltage
is
easily measured
from
pin 2
(hot)
to pin 4 of ATE
ports
TP1 and
TP2.
Refer
to
section
2 for
appropriate test procedures.
Q504¡stheHSNPNpre-driverandQ511
istheHSNPNdriver.
These
devices
are
biased
class
AB for
ultra
low
distortion
in the
zero-crossing
región.
Q513, Q515,
Q517,
and
Q536
are the HS NPN
output devices. These
devices
are
biased
class
B, in
soft
cut-off,
Together
with
driver
and
pre-
driver, they function
as a
three-deep Darlington.
The
output devices
work
¡n
parallel
as a
giant composite.
The
over-all
bias topology
is
referred
to as
AB+B,
originally conceived
and
patented
by
Crown
engineers
in
1966.
This
¡s
still
the
most
efficient,
stable,
and
distortion
free
method used today.
Positive
LVA,
Portion
of HS
Bias,
&
Positive
Current
Limit
Section
VCC1
High Side
+LVA's,
Current
Limit,
and the
portion
of the
Bias
Servo
Network
on the
Positive Output
Module.
D51O
R595
3
82K
C536
O.O01
r-
R5O5
HIGH)
500
SIDE
';
BIAS
U
Emitter
Sense
Output
Audio
4 -
MA-5000VZ
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