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Reference Manual
Macro-Tech
®
24x6 & 36x12 Power Amplifiers
4.3 Protection Systems
Macro-Tech amplifiers provide extensive protection and
diagnostics capabilities. Protection systems include
ODEP, “standby” mode, fuses (or breakers), and spe-
cial thermal protection for the unit’s transformers.
4.3.1 ODEP
Crown invented ODEP to solve two long-standing prob-
lems in amplifier design: to prevent amplifier shutdown
during demanding operation and to increase the effi-
ciency of the output circuitry.
To do this, Crown established 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 instanta-
neous operating conditions of those output transistors.
Its name describes what it does: Output Device Emula-
tion 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 abso-
lute 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
Fig. 4.2 ODEP and Signal/IOC Indicator States
ODEP
SIGNAL / IOC
OFF
OFF
There is no power to the amplifier and all indicators are off, including the Enable light.
Possible reasons: (1) The amplifier’s Enable switch is off. (2) The amplifier is not plugged into the power
receptacle. (3) The AC circuit breaker has been tripped. (4) The amplifier’s low-voltage power supply
fuse has blown.
Indicator Status
Amplifier Condition
ODEP
SIGNAL / IOC
ON
OFF
Normal operation for a channel with NO audio output. Possible reasons: (1) There is no input signal.
(2) The input signal level is very low. (3) The channel’s level control is turned down.
ODEP
SIGNAL / IOC
ON
Normal
Normal operation for a channel with audio output. The ODEP indicator will remain at full intensity
to show that there is reserve thermodynamic energy, and the Signal/IOC indicator will flash with normal
intensity to show that the channel has audio output.
ODEP
SIGNAL / IOC
ON
Bright
The channel’s output is exceeding 0.05% distortion. The input signal level is too high and IOC is
reporting either an input overload or output clipping.
ODEP
SIGNAL / IOC
OFF
Bright
The amplifier channel is in standby mode. Possible reasons: (1) A PIP
module like an
IQ–P.I.P.–SMT
has turned off the channel’s high-voltage power supply. (2) The amplifier has just been
turned on and is still in the four second turn-on delay. (3) The DC / low-frequency protection circuitry
has been activated. (4) The fault protection circuitry has been activated. (5) The transformer thermal
protection circuitry has been activated.
ODEP limiting has been activated. Possible reasons: (1) The amplifier’s air filters are blocked and
need to be cleaned. (2) There is insufficient cooling because of inadequate air flow or air that is too hot.
(3) The load impedance for the channel is too low because the output is shorted or the amplifier is
driving too many loudspeakers for the selected stereo/mono mode. (4) The amplifier channel is
continuously being driven to very high output levels.
ODEP
SIGNAL / IOC
OFF
Normal
ODEP limiting is about to begin. Possible reasons: (1) The amplifier’s air filters are blocked and need
to be cleaned. (2) There is insufficient cooling because of inadequate air flow or air that is too hot.
(3) The load impedance for the channel is too low because the output is shorted or the amplifier is
driving too many loudspeakers for the selected stereo/mono mode. (4) The amplifier channel is
continuously being driven to very high output levels.
OR
OR
OR
Channel 2 only: The amplifier is in Parallel-Mono mode. The channel 2 Signal/IOC indicator always
turns on to full brightness whenever the amplifier's stereo/mono switch is set to Parallel-Mono mode.
A channel’s circuit breaker has tripped. Transformer overload can cause a channel’s circuit
breaker to trip.
