Macro-Tech
®
602/1202/2402
Power Amplifiers
Page 22
Reference Manual
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
the loads and prevent 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 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 dam-
aged 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.)
An
IQ-PIP module
may also temporarily place the
amplfier in standby mode, typically for power conser-
vation. The standby mode status can be triggered ei-
ther manually or through IQ's “auto standby” feature. If
triggered via the IQ auto standby feature, the standby
status will be automatically cancelled when the defined
level of input signal is detected. However, if the standby
status has been triggered manually, this status must be
manually cancelled using IQ.
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, ex-
4.3 Protection Systems
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-USP2 can use it to monitor and control the am-
plifier.
With ODEP, the show keeps going because you get the
maximum power with the maximum protection.
4.3.2 Standby Mode
An important part of a Macro-Tech amplifier's protec-
tion systems is standby mode. Standby protects the
amplifier during potentially catastrophic conditions. It
temporarily removes bias in all four output stages, pro-
tecting the amplifier and its loads. This advanced pro-
tection implementation, called
"Quad-Mute,"
is new to
the Macro-Tech series amplifiers. 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-
