Advanced Features And Options; Protection Systems; Odep; Ultrasonic And Radio Frequency Protection - Crown Micro-Tech 1200 Operation Manual

Micro-Tech Series Power Amplifiers
5 Advanced Features
and Options
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 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.
5.1.4 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 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.
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