Crown ma-1200 Guía De Referencia

the loads and prevent oscillations. The unit resumes
normal operation as soon as the amplifier no longer
detects dangerous low frequency or DC output. Al-
though 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 in standby mode in rare situations where
heavy common-mode current is detected in the
channel’s output. The amplifier should never output
heavy common-mode current unless its circuitry is
damaged in some way, and putting a channel in
standby mode helps to prevent further damage.

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 the channel of the affected transformer in standby
mode. The amplifier will return to normal operation after
the transformer cools to a safe temperature. (For more
information on transformer thermal protection, refer to
the following section.)

4.3.3 Transformer Thermal Protection
All Macro-Tech amplifiers have transformer thermal pro-
tection. It protects the power supplies from damage un-
der the rare conditions of transformer temperatures
rising too high. A thermal switch embedded in each
transformer removes power to the channel if there is
excessive heat. The switch automatically resets when
the transformer cools to a safe temperature.

It is extremely unlikely that you will ever see a
Macro-Tech amplifier activate transformer thermal pro-
tection as long as it is operated within rated conditions
(see Section 6, 

Specifications). One reason is that

ODEP keeps the amplifier working under very severe
conditions. Even so, higher than rated output levels,
excessively low impedance loads and unreasonably
high input signals can generate more heat in the trans-
former than in the output devices. These conditions can
overheat the transformer and activate its protection sys-
tem.

Macro-Tech amplifiers are designed to keep working
under conditions where other amplifiers would fail. But
even when the limits of a Macro-Tech amplifier are ex-
ceeded, it will still protect itself—and your investment—
from damage.

Macro-Tech amplifiers provide extensive protection and
diagnostics capabilities. Protection systems include
ODEP, “standby” mode, fuses (or breakers), and spe-
cial thermal protection for the unit’s transformers.

4.3.1 ODEP
Crown invented ODEP to solve two long-standing prob-
lems in amplifier design: to prevent amplifier shutdown
during demanding operation and to increase the effi-
ciency of the output circuitry.

To do this, Crown established a rigorous program to
measure the 

safe operating area (SOA) of each output

transistor before installing it in an amplifier. Next, Crown
designed intelligent circuitry to simulate the instanta-
neous operating conditions of those output transistors.
Its name describes what it does: Output Device Emula-
tion Protection or ODEP. In addition to simulating the
operating conditions of the output transistors, it also
compares their operation to their known SOA. If it sees
that more power is about to be asked of them than they
are capable of delivering under the present conditions,
ODEP immediately limits the drive level until it falls within
the SOA. Limiting is proportional and kept to an abso-
lute minimum—only what is required to prevent output
transistor 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 back
panel PIP connector so advanced PIP modules like the
IQ-PIP can use it to monitor and control the amplifier.

With ODEP, the show keeps going because you get the
maximum power with the maximum protection.

4.3.2 Standby Mode
At the heart of the protection systems is the standby
mode which removes power from the high-voltage sup-
plies to protect the amplifier and connected loads. The
standby mode can be identified using the indicator
table in Figure 4.2.

Standby mode can be activated in several situations.
First, if dangerous subsonic frequencies or direct cur-
rent (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