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Com-Tech Power Amplifiers
Reference Manual
conditions, ODEP immediately limits the drive level until
it falls within the SOA. Limiting is proportional and kept
to an absolute minimum—only what is required to pre-
vent output device damage.
This level of protection enables Crown to increase out-
put efficiency to never-before-achieved levels while
greatly increasing amplifier reliability.
The on-board intelligence is monitored in two ways.
First, the front panel ODEP indicators show whether the
amplifier is functioning correctly or if ODEP
is limiting
the drive level. Second, ODEP data is fed to the con-
nector inside the amplifier’s back panel PIP compart-
ment so advanced PIP modules like the IQ-PIP-USP2
can use it to monitor and control the amplifier.
This is how ODEP keeps the show going with maximum
power and maximum protection at all times.
4.3.2 Standby Mode
An important part of a Com-Tech amplifier’s protection
systems is standby mode. Standby protects the ampli-
fier during potentially catastrophic conditions. It tempo-
rarily removes bias in all four output stages, protecting
the amplifier and its loads. This advanced protection
implementation, called
“Quad-Mute,”
is new to the
Com-Tech series amplifiers. Standby mode can be
identified using the indicator table in Figure 4.2.
When you turn on the Enable switch, standby mode is
activated to provide
turn-on protection
.
This power-up
delay lets other system components settle before any
signals are amplified, and it provides some “random-
ness” to the power-up sequence of multiple units re-
ducing the system’s current demand during start-up.
For further protection, Com-Tech “10” series amplifiers
are equipped with a
“Soft-Start”
line current limiter
which also reduces turn on inrush.
If dangerous subsonic frequencies or direct current
(DC) is detected in the amplifier’s output, the unit will
activate its
DC/low-frequency protection
circuitry and
put the affected channels in standby. This protects the
loads and prevents oscillations. The unit resumes nor-
mal operation as soon as the amplifier no longer de-
tects dangerous low-frequency or DC output. Although
it is extremely unlikely that you will ever activate the
amplifier’s DC/low-frequency protection system, im-
proper source materials such as subsonic square
waves or input overloads that result in excessively
clipped input signals can activate this system.
The amplifier’s
fault protection
system will put an am-
plifier channel into standby mode in rare situations
where heavy common-mode current is detected in a
channel’s output. The amplifier should never output
heavy DC current unless its circuitry is damaged in
some way, and putting the channel in standby mode
helps to prevent further damage.
4.3.3 Transformer Thermal Protection
All Com-Tech amplifiers have transformer thermal pro-
tection which protects the power supplies from dam-
age under rare conditions where the transformer
temperature rises too high. A thermal switch embed-
ded in the power transformer puts both channels into
standby if it detects excessive heat. The switch auto-
matically resets itself as soon as the transformer cools
to a safe temperature.
The amplifier’s
transformer thermal protection
cir-
cuitry is activated in very unusual circumstances where
the unit’s transformer temperature rises to unsafe lev-
els. Under these abnormal conditions, the amplifier will
put both channels into standby mode. In addition, the
cooling fan will run at full speed. The amplifier will return
to normal operation after the transformer cools to a safe
temperature.
If your amplifier is operated within rated conditions, it is
extremely unlikely that you will ever see it activate trans-
former thermal protection. One reason is that ODEP
keeps the amplifier working under severe conditions.
Even so, higher than rated output levels, excessively
low-impedance loads and unreasonably high input sig-
nals can generate more heat in the transformer than in
the output devices. This can overheat the transformer
and activate its protection system.
Com-Tech amplifiers are designed to keep working un-
der conditions where other amplifiers fail. Yet, even
when the limits of a Com-Tech are exceeded, it still pro-
tects itself—and your investment—from damage.
4.3.4 Circuit Breaker
A circuit breaker is provided to prevent the high-voltage
power supplies from drawing excessive current. A re-
set switch for the circuit breaker is provided on the back
panel. The rating of the circuit breaker for each ampli-
fier model and each AC operating voltage is provided
with the specifications in Section 6. When operating with
rated loads and output levels, this breaker should trip
only in the unlikely event of a catastrophic amplifier fail-
ure. Other protection systems such as ODEP keep the
amplifier safe and operational under most other severe
conditions. The breaker can also trip in situations where
extremely low-impedance loads and high output levels
result in current draw that exceeds the breaker’s rating.
