Principles Of Operation - Crown M Series Operation Manual

5 Principles of Operation

For the sake of simplicity, only channel one of
the amplifier is described.
Signal is presented to the M120 and M240
through one of three connectors when using
the standard input module. Each channel is
outfitted with a balanced XLR / phone jack, and
a barrier strip. These connectors are wired in
parallel, which allows daisy chaining when
needed. The signal is then converted from bal-
anced to unbalanced in the Balanced Input
Stage where it also receives RFI protection.
Signal then flows into the Variable Gain Stage
where the front panel level controls are allowed
to affect the gain.
Figure 5.1
M-Series Amplifier
BALANCED
Block Diagram
INPUTS
(Shown with Stan-
dard Input Module)
page 16
Following this stage, the signal is put under the
control of a full-time compressor circuit com-
prised of a symmetrical window detector, a
buffer amplifier, and the gating op amp which
uses several small components to set the com-
pressor's attack and decay characteristics. The
actual compressing is accomplished by an
opto-isolator which affects the gain in the sig-
nal path.
The signal next enters the main amplifier error
amp where it is mixed with a small portion of
the output signal in such a way as to control the
amplifier's overall output performance.
Following the error amp is the LVA stage, which
is where the low-voltage referenced signal gets
translated to the output high-voltage rails. The
COMPRESSOR
TO CLIP
CONTROL
INDICATOR
BUFFER
ERROR
VARIABLE
BALANCE
AMP
GAIN STAGE
INPUT STAGE
TO SIGNAL
PRESENCE
INDICATOR
MUTE
+ HI-VOLTAGE
BOOTSTRAP
CURRENT
SOURCE
BIAS BIAS BIAS BIAS BIAS BIAS
TRANSLATOR LVA
–VCC –VCC
DC PROTECT
LOGIC
TO
FAULT
CONNECTOR
M Series Power Amplifiers
last voltage amplifier, in conjunction with a
bootstrapped current source, drives both pre-
drivers and the bias servo. The bias servo is
mounted in such a way as to translate the out-
put heatsink temperature into a controlled bias
current to prevent thermal runaway and hold
the amplifier's notch distortion to a minimum.
The predrivers provide enough signal to acti-
vate the drivers, which together operate in the
class AB range. For the major output current
requirements, the drivers feed the various num-
bers of paralleled output transistors which
operate in a class B mode. This we call the Tri-
ple-Deep Darlington Output Stages.
HEATSINK
TRIPLE-DEEP
TEMPERATURE
DARLINGTON
NPN POSITIVE
OUTPUT STAGE
TDVI
LIMITER
TRIPLE-DEEP
DARLINGTON
NPN NEGATIVE PROTECT
OUTPUT STAGE
HEATSINK
TRANSFORMER
TEMPERATURE
TEMPERATURE
PROPORTIONAL
SPEED
POWER
FAN
CONTROL
SUPPLY
BOOTSTRAP
FAN
TURN-ON
DELAY
+
OUTPUT
CONTROL
OUTPUT
DC
TO FAULT
INDICATOR
+ VCC
+ 15V
– 15V
– VCC
+ HI-VOLTAGE
CIRCUIT
BOOTSTRAP
Operation Manual