Crown Audio MA-36X12 - Manual (Page 14)

Operation Manual
Macro-Tech MA-24X6 & 36X12 Power Amplifiers
page 14
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
4.1 Protection Systems
Your Crown amplifier provides extensive pro-
tection and diagnostic capabilities, including
ODEP, IOC., “standby” mode, fuses (or break-
ers), and special thermal protection for the
unit’s transformers.
4.1.1 Output Device Emulation
Protection (ODEP)
Crown invented ODEP to solve two long stand-
ing problems in amplifier design: To prevent
amplifier shutdown during demanding opera-
tion and to increase the efficiency of output cir-
cuitry.
To do this, Crown established a rigorous pro-
gram to measure the safe operating area (SOA)
of each output transistor before installing it in
an amplifier. Crown also designed intelligent
circuitry to simulate the instantaneous operat-
ing conditions of those output transistors. Its
name describes what it does: Output Device
Emulation Protection or ODEP. It not only simu-
lates the operation of the output transistors but
it also compares their operation to their known
SOA. If ODEP sees that more power is about to
be asked of the output devices than they are
capable of delivering under the present condi-
tions, ODEP immediately limits the drive level
until it falls within the SOA. Limiting is propor-
tional and kept to an absolute minimum—only
what is required to prevent the possibility of
output transistor damage.
This level of protection enables Crown to
increase output transistor utilization while
greatly increasing amplifier reliability.
Finally, this onboard intelligence is monitored
in two ways. First, the front panel ODEP indica-
tors show whether the amplifier is functioning
correctly or if ODEP is limiting the drive level.
Second, ODEP data is fed to the PIP connector
at the back of the amplifier so advanced PIP
modules like the IQ-PIP-USP2 can use it to
make decisions and control the amplifier.
With ODEP you get the maximum power with
the maximum protection—the show goes on!
4.1.2 IOC (Input Output Compara-
tor)
The IOC circuit compares the output signal of
the amplifier with the input signal. If there is
any difference other than gain, then it is consid-
ered distortion and the indicator comes on. The
LED indicator will come on whenever there is
distortion of 0.05% or more. An IOC condition
may also be sensed by an IQ PIP module
installed in PIP-compatible amplifiers.
IOC is designed to report any form of distor-
tion. IOC not only checks the waveform for dis-
tortion, but also reports input overload and
even a protective action that mutes or shuts
down an amplifier. With all of these features,
IOC monitors the entire amplifier. When the IOC
indicator is off the amplifier is definitely opera-
tional and undistorted. IOC provides an on-line
proof of performance.
4.1.3 Standby Mode
At the heart of the protection systems is the
standby mode which removes power from the
high-voltage supplies to protect the amplifier
and connected loads. The standby mode can be
identified using the indicator table in Figure
5.2.
Standby mode can be activated in several situa-
tions. First, if dangerous subsonic frequencies
or direct current (DC) is detected in the ampli-
fier’s output, the unit will activate its DC/low-
frequency protection circuitry and put the
affected channels in standby. This protects the
loads and prevent oscillations. The unit
resumes normal operation as soon as the
amplifier no longer detects dangerous low fre-
quency or DC output. Although it is extremely
unlikely that you will ever activate the ampli-
fier’s DC/low-frequency protection system,
improper 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 amplifier channel in standby mode in rare
situations where heavy common-mode current
is detected in the channel’s output. The ampli-
fier 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
circuitry is activated in very unusual circum-
stances where the unit’s transformer tempera-
ture rises to unsafe levels. Under these
abnormal conditions, the amplifier will put the
channel of the affected transformer in standby
mode. The amplifier will return to normal oper-
ation after the transformer cools to a safe tem-
perature. (For more information on transformer
thermal protection, refer to the following sec-
tion.)
4 Advanced Features
and Options