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 and diagnostic capabilities, including ODEP, ultrasonic/RF protection, drive protec- tion, and power supply fuses or breakers.
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.
This level of protection enables Crown to increase output efficiency to never-before- achieved levels while greatly increasing reli- ability. The front-panel ODEP indicators show whether the amplifier is functioning correctly or whether ODEP is limiting the drive level.
5.1.2 Ultrasonic and Radio Fre- quency Protection
Micro-Tech amplifiers have a controlled slew rate. This means that their design puts a limit on the frequencies they can reproduce. The
controlled slew rate has no effect on audio per- formance because the high-frequency limit is well above 20 kHz. This approach protects the amplifier and tweeters from radio frequencies. 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 unde- sirable frequencies.
5.1.3 Drive Protection
This system temporarily removes drive from the output stages to protect the amplifier and its loads, and prevents oscillation. Drive protec- tion can be activated in two situations. First, if dangerous subsonic frequencies or direct cur- rent (DC) is detected in the amplifier's output, drive protection will activate. The amplifier resumes normal operation when it no longer detects dangerous output. Activating this pro- tection is very unlikley, but improper source signals like subsonic square waves or a severely clipped signal can activate this sys- tem.
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 from the affected channel's high-voltage power supply, which puts the channel in drive protection mode. The channel will return to normal opera- tion after its transformer cools to a safe temper- ature.
A transformer can overheat during very severe conditions: higher than rated output levels, excessively low-impedance loads, and unreas- ionably high input signals.
Micro-Tech amplifiers keep working under con- ditions where other amplifiers would fail. But even when a Micro-Tech's limits are exceeded, it will still protect itself — and your investment
— from damage.
5.1.5 Fuses and Circuit Breakers
120 VAC, 60 Hz models and all Micro-Tech 2400s have an internal fuse that protects the low-voltage power supply and cooling fan. The high-voltage power supplies for the Micro-Tech 600 and 1200 are protected by internal fuses, while the power supplies for the Micro-Tech 2400 high-voltage supplies are protected by circuit breakers.
With rated loads and output levels, the fuses (or circuit breakers) should shut down the amplfi- ier only in the rare instance of a catastrophic failure. ODEP protection keeps the amplifier operational under most other severe condi- tions. The fuses (or circuit breakers) can also shut down the amplifier if extremely low- impedance loads and high output levels result in current draw that exceeds their rating. Again, this should be possible only when operating outside rated conditions, as when the amplifier is used to drive a 1-ohm load in Stereo mode, or when an input signal is clipped severely.
Micro-Tech amplifiers do not blow their fuses or trip their breakers unless something is wrong. In the rare event that an internal fuse blows, please refer the unit to a qualified tech- nician. If a breaker in a Micro-Tech 2400 trips, try to identify and correct the problem before resetting the breakers. If the problem persists, refer the unit to a qualified technician.
