Advanced Features And Options; Protection Systems; Output Device Emulation Protection (Odep); Ioc (Input Output Comparator) - Crown MA-5002VZ Operation Manual

5 Advanced Features
and Options
NOTE: For detailed information about these
Crown amplifier features, please consult the
Crown Amplifier Application Guide, available on
the Crown website at www.crownaudio.com

5.1 Protection Systems

Your Crown amplifier provides extensive protection and
diagnostic capabilities, including ODEP and IOC.
5.1.1 Output Device Emulation Protection
(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 efficiency
of output circuitry.
To do this, Crown established a rigorous program to
measure the safe operating area (SOA) of each output tran-
sistor before installing it in an amplifier. Crown also
designed intelligent circuitry to simulate the instantaneous
operating conditions of those output transistors. Its name
describes what it does: Output Device Emulation Protec-
tion or ODEP. It not only simulates the operation of the
output transistors but it also compares their operation to
their known SOA. If ODEP sees that more power is about to
be asked of the output devices than they are capable of
delivering under the present conditions, ODEP immedi-
ately limits the drive level until it falls within the SOA.
Limiting is proportional and kept to an absolute mini-
mum—only what is required to prevent the possibility of
output transistor damage.
This level of protection enables Crown to increase output
transistor utilization while greatly increasing amplifier reli-
ability.
Finally, this onboard 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
at the back of the amplifier so advanced PIP modules like
the IQ-PIP-USP2 can use it to make decisions and control
the amplifier.
With ODEP you get the maximum power with the maxi-
mum protection—the show goes on!
page 14

5.1.2 IOC (Input Output Comparator)

The IOC circuit compares the output signal of the amplifier
with the input signal. If there is any difference other than
gain, then it is considered distortion and the indicator
comes on. The LED indicator will come on whenever there
is distortion of 0.05% or more. An IOC condition may also
be sensed by an IQ PIP module installed in PIP-compati-
ble amplifiers.
IOC is designed to report any form of distortion. IOC not
only checks the waveform for distortion, but also reports
input overload and even a protective action that mutes or
shuts down an amplifier. With all of these features, IOC
monitors the entire amplifier. When the IOC indicator is off
the amplifier is definitely operational and undistorted. IOC
provides an on-line proof of performance.

5.2 Circuit Designs

5.2.1 Grounded Bridge

Grounded Bridge is the name of Crown's unique four-
quadrant amplifier topology. The Grounded Bridge topol-
ogy takes full advantage of the power supplies delivering
peak-to-peak voltages to the load that are twice the voltage
seen by the output devices and twice the voltage generated
by the power supplies.
The power supply bridge rectifier is not ground referenced,
and the transformer secondary is not center-tapped. This
allows the power supply to deliver +VCC and -VCC from
the same bridge rectifier and filter as a total difference in
potential regardless of their voltages with respect to
ground.
Composite output devices are arranged to function as
gigantic NPN and PNP devices. Each output stage has two
composite NPN and two composite PNP devices. The
devices connected to the load are referred to as "high-side
NPN and PNP" and the devices connected to ground are
referred to as "low-side NPN and PNP." Positive current is
delivered to the load by increasing conductance simulta-
neously in the high-side NPN and low-side PNP stage,
while decreasing conductance of the high-side PNP and
low-side NPN in synchrony.
Crown's Grounded Bridge design delivers large voltage
swings without stressing output transistors. The results
are higher efficiency, lower distortion and superior reliab-
lility.
Macro-Tech MA-5002VZ Power Amplifier

5.2.2 Variable Impedance (VZ)

VZ is the name of Crown's patented articulated power
supply technology. This innovative technology permits us
to pack large amounts of power into a compact package
while achieving ultra-low distortion and without generat-
ing excessive heat.
An amplifier power supply must be large enough to handle
both the maximum voltage and maximum current necesary
for the amplifier to drive its rated power into a specified
load. In order to meet this requirement, most conventional
supplies are heavy, large, and produce lots of heat. In
contrast, the VZ supply gets more current AND voltage out
of a smaller, lighter, and more efficient package by dynam-
ically adapting to both signal and load requirements in
real-time. This provides the best power match to the
widest range of loads.
The VZ supply is divided into two segments. When the
output stage requires high-voltage, the segments are
arranged in series to deliver twice the voltage of a single
segment. When the output stage requires high-current, the
segments are arranged in parallel to deliver twice the
current of a single segment. Sensing circuitry "watches"
the voltage of the signal to determine when to switch VZ
modes. The switching circuitry is designed to prevent
audible switching distortion to yield the highest possible
dynamic transfer function—you hear only the music and
not the amplifier.
With VZ, you get not only maximum power and safety, but
you also get the best power matching to your load.
The VZ (Variable Impedance) mode causes the power
supplies to automatically shift between high-current and
low-current modes of operation as operating conditions
change. Normally, the power supplies operate in the high-
current (low-impedance) mode for maximum thermal effi-
ciency. When voltage demand reaches highs levels, the
supplies quickly shift into high-voltage (high-impedance)
mode. Because voltage and current requirements vary with
the output level and frequency content of the source
signals, the power supplies are designed to be able to
continually switch between the two modes as needed with
no degradation to the audio signal.
Operation Manual