Macro-Tech 3600VZ Power Amplifier
Page 22
Reference Manual
Its name describes what it does: Output Device Emula-
tion Protection or ODEP. It not only simulates the opera-
tion 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 proportional 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 out-
put transistor utilization while greatly increasing ampli-
fier reliability.
Finally, this onboard 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 PIP connector at the back of the amplifier so ad-
vanced PIP modules like the IQ-PIP-SMT can use it to
make decisions and control the amplifier.
With ODEP you get the maximum power with the maxi-
mum protection—the show goes on!
4.3.2 Standby Mode
An important part of a Macro-Tech amplifier’s protection
systems is standby mode. Standby protects the ampli-
fier during potentially catastrophic conditions. It tempo-
rarily removes power from the high-voltage supplies to
protect the amplifier and its loads. 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 which
reduces the system’s current demand during start-up.
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 ampli-
fier 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 com-
mon-mode current unless its circuitry is damaged in
some way, and putting the channel in standby mode
helps to prevent further damage.
The amplifier’s transformer thermal protection circuitry
is activated where the unit’s transformer temperature
rises to unsafe levels. 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 trans-
former cools to a safe temperature. (For more informa-
tion on transformer thermal protection, refer to the
section that follows.)
4.3.3 Transformer Thermal Protection
All Macro-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 each channel’s power transformer removes
power to that channel’s high-voltage power supply if it
detects excessive heat. The switch automatically resets
itself as soon as the transformer cools to a safe tem-
perature.
If your amplifier is operated within rated conditions, it is
unlikely that you will ever see it activate transformer ther-
mal protection. One reason is that ODEP keeps the am-
plifier working under severe conditions. Even so, higher
than rated output levels, excessively low-impedance
loads and unreasonably high input signals can gener-
ate excessive heat in the output devices. This can over-
heat the transformer and activate its protection system.
Macro-Tech amplifiers are designed to keep working
under conditions where other amplifiers would fail. But
even when the limits of a Macro-Tech are exceeded, it
protects itself—and your investment—from damage.
4.3.4 Circuit Breaker
A circuit breaker is provided to prevent excessive cur-
rent draw by the high-voltage power supplies. A reset
button for the circuit breaker is provided on the back
panel. The rating of the circuit breaker for each amplifier
model and each AC mains voltage is provided with the
specifications in Section 6. When operating with rated
loads and output levels, this breaker should only trip in
the incredibly rare instance of a catastrophic amplifier
failure. Other protection systems such as ODEP keep
the amplifier safe and operational under most other se-
vere conditions. The breaker can also trip in situa-
