Crown Audio Macro-Tech MA-5000VZ - Manual (Page 23)

Page 24
Macro-Tech 5000VZ Power Amplifier
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 Load / I Limit indicators show current
flow to the loudspeakers (“load current”) and the maxi-
mum current available from the amplifier (“limit cur-
rent”). As load current indicators, they glow green to
show that current is flowing to the loads connected to
the amplifier outputs. As current limit indicators, they
turn red to show that the amplifier is delivering its maxi-
mum output current. The indicators turn off when there
is no significant 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 to-
tal 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 output power capability will go unused.
The I
Limit
feature is designed to help you get the maxi-
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
Limit
, you have to do some lengthy cal-
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 Limit . The I Limit function
turns a channel’s I
Load
/ I
Limit
indicator red when it
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
Load
/ I
Limit
indicator turns red.
The optimum load is achieved before the I
Load
/ I
Limit
indicator turns red, so disconnecting the last added
loudspeaker gives you an optimized load.
4.3 Protection Systems
The Macro-Tech 5000VZ provides extensive protection
and diagnostics capabilities. Protection systems in-
clude
ODEP, “standby” mode, power supply fuses and
special thermal protection for the unit’s transformers.
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 intel-
ligent circuitry to simulate the instantaneous operating
conditions of those output transistors. Its name de-
scribes what it does: Output Device Emulation Protec-
tion 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 ca-
pable 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 tran-
sistor 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 re-
sult from excessive AC line voltage, voltage spikes, and
other unusual conditions.