Protection Systems; Odep; Standby - Crown Macro-Tech 5002VZ Reference Manual

with a 0.1 second hold delay to show that an input sig-
nal is too large and must be compressed at the input.
The indicators will also stay on brightly for a channel
that is put in standby mode (see Section 4.3.2). Under
abnormal operating conditions, a high-voltage power
supply may be put in standby mode to prevent ampli-
fier damage. If this happens, the channel's Signal/IOC
indicator will stay on with full brightness.
The two-color I /I
Load Limit
to the loudspeakers ("load current") and the maximum
current available from the amplifier ("limit current"). As
load current indicators, they glow green to show that
current is flowing to the loads connected to the ampli-
fier outputs. As current limit indicators, they turn red to
show that the amplifier is delivering its maximum output
current. The indicators turn off when there is no signifi-
cant load current flowing. This can happen when a
channel has no input signal, the input signal is at a very
low level, there is no load connected to the output, or
the output cable is damaged.
The amount of current an amplifier can produce deter-
mines the lowest impedance it can drive. Parallel-Mono
mode can deliver the most current, so it can drive the
most loudspeakers wired in parallel with the lowest total
impedance. For maximum performance, loads should
be matched to the amplifier. If load impedance is too
low, the amplifier's protection systems will limit output. If
load impedance is too high, some of the amplifier's out-
put power capability will go unused.
The I feature is designed to help you get the maxi-
Limit
mum power out of your amplifier. In the real world, loud-
speaker impedance varies with frequency, and
loudspeaker impedance ratings are only approxima-
tions. Without I , you have to do some lengthy cal-
Limit
culations to approximate the maximum number of
loudspeakers you can drive with the amplifier—and this
does not allow for a 4 ohm loudspeaker whose imped-
ance drops below 2 ohms at 80 Hz.
This is why your amplifier has I
turns a channel's I
Load
reaches maximum current output. This makes it pos-
sible to connect real loudspeakers and conduct realis-
tic tests to find the maximum number of loudspeakers
that should be connected. To do a test like this, you can
operate under worst-case conditions and continue to
connect additional loudspeakers in parallel with each
output until the I / I
Load Limit
timum load is achieved before the I
tor turns red, so disconnecting the last added
loudspeaker gives you an optimized load.
Page 24
indicators show current flow
. The I function
Limit Limit
/ I indicator red when it
Limit
indicator turns red. The op-
/ I indica-
Load Limit
Macro-Tech 5002VZ Power Amplifier

4.3 Protection Systems

The Macro-Tech 5002VZ provides extensive protection
and diagnostics capabilities. Protection systems in-
clude ODEP , "standby" mode, special thermal protec-
tion for the unit's transformers and power supply fuses.

4.3.1 ODEP

Crown invented ODEP to prevent amplifier shutdown
during demanding operation and to increase the effi-
ciency of the output circuitry. To do this, Crown estab-
lished a rigorous program to measure the safe operating
area (SOA) of each output transistor before installing it
in an amplifier. Next, Crown designed intelligent circuitry
to simulate the instantaneous operating conditions of
those output transistors. Its name describes what it
does: Output Device Emulation Protection or ODEP . In
addition to simulating the operating conditions of the
output transistors, it also compares their operation to
their known SOA. If it sees that more power is about to
be asked of them than they are capable of delivering
under the present conditions, ODEP immediately limits
the drive level until it falls within the SOA. Limiting is
proportional and kept to an absolute minimum—only
what is required to prevent output transistor damage.
This level of protection enables Crown to increase out-
put efficiency to never-before-achieved levels while
greatly increasing amplifier reliability.
The on-board intelligence is monitored in two ways.
First, the front panel ODEP indicators show whether the
amplifier is functioning correctly or if ODEP is limiting
the drive level. Second, ODEP data is fed to the PIP
connector so advanced PIP modules like the IQ-PIP-
USP2 can monitor and control the amplifier.
With ODEP , the show keeps going because you get the
maximum power with the maximum protection.

4.3.2 Standby

At the heart of the protection systems is standby mode
which temporarily removes power from the high-volt-
age supplies to protect the amplifier and connected
loads. Several conditions can put a channel into
standby mode. Use the indicator table in Figure 4.2 to
identify an amplifier channel in standby mode.
The overvoltage protection circuitry puts both chan-
nels in standby if the AC line voltage increases to more
than 11% of the amplifier's rated AC configuration. This
circuitry prevents power supply damage that can result
from excessive AC line voltage, voltage spikes, and
other unusual conditions.
The undervoltage protection circuitry can also activate
Reference Manual