5 Advanced Features and Options; 5.1 Protection Systems; 5.1.1 ODEP- Page 13

Micro-Tech 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 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.

5 Advanced Features
and Options