Power-Tech .1 Series
Power Amplifiers
page 13
Operation Manual
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.
5.1.2 Ultrasonic 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.
5.1.4 Transformer 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.
5 Advanced Features
and Options
