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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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