Crown Audio Power-Tech 1.1 Protection Systems, Odep, Ultrasonic and Radio Fre- quency Protection

Power-Tech .1 Series Power Amplifiers

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 pro- tection systems, including ODEP, ultrasonic/RF protection, drive protection, transformer ther- mal protection and fuses or circuit breakers to protect the power supplies.

5.1.1 ODEP

Crown invented ODEP to prevent amplifier shutdown during demanding operation, and to increase the efficiency of the output circuitry.

To do this, Crown measured 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 output transis- tor operating conditions, it compares their operation to their known SOA. If ODEP sees that more power will be asked of the output devices than they can deliver, ODEP immedi- ately 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. Under nor- mal conditions, no limiting is required and ODEP is transparent to the audio signal.

5.1.2Ultrasonic and Radio Fre- quency Protection

An amplifier's slew rate only needs to be large enough to deliver the maximum voltage at the highest required frequency. Higher slew rates actually let the amplifier reproduce undesirable frequencies. By design, Power-Tech .1 Series amplifiers have a controlled slew rate to put a frequency limit on the highest frequencies that they reproduce. This limit occurs well above 20 kHz, so there is no audible effect on perfor- mance. This approach protects the amplifier from radio frequencies and can even protect some sensitive loads (including some tweet- ers).

5.1.3 Drive Protection

This system temporarily removes output drive to protect the amplifier and its loads. Drive pro- tection can be activated in two situations. First, if dangerous subsonic frequencies or direct current (DC) is detected in the amplifier's out- put, drive protection will activate. The amplifier resumes normal operation when it no longer detects dangerous output. Activating this pro- tection is very unlikely, but improper source signals like infrasonic square waves or a severely clipped input signal can activate this system.

Second, the amplifier's fault protection system puts the affected channel into drive protection mode in rare situations where heavy common- mode current is detected in its output. The amplifier should never output heavy common- mode current unless its circuitry is damaged. Activating drive protection helps prevent further damage.

5.1.4Transformer Thermal Protection

This activates in the rare case where the unit's transformer temperature rises to unsafe levels. Then the amplifier will remove power to the high-voltage transformer. The fan will continue to run in all units except those with 220/240 VAC transformers. The amplifier will return to normal after it cools to a safe temperature.

Your amplifier is designed to keep working under conditions where other amplifiers would fail. But even when you exceed the limits of a Power-Tech .1 Series amplifier, it still protects itself — and your investment — from damage.

5.1.5 Fuses and Circuit Breakers

Your amplifier's low-voltage power supply is protected by an internal fuse, and its high-volt- age power supplies are protected by a circuit breaker. The circuit breaker is built into the power switch for all Power-Tech 1.1, Power- Tech 2.1 and 220/240 VAC Power-Tech 3.1 amplifiers. The circuit breaker is located on the back panel of 100/120 VAC Power-Tech 3.1 amplifiers.

With rated loads and output levels, the circuit breaker will shut down the amplifier only in the rare instance of a catastrophic amplifier failure. Other protection systems such as ODEP keep the amplifier operational under most other severe conditions. The breaker can also shut down the amplifier if extremely low-impedance loads and high output levels result in current draw that exceeds the breaker rating.

Operation Manual page 13