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.
5.1.1Output 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-USP3 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!
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.
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.
