Technical information

Macro-Tech 3600VZ Power Amplifier
Page 21
Its name describes what it does: Output Device Emu-
lation Protection or ODEP . It not only simulates the op-
eration 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
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 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 P.I.P. connector at the back of the amplifier so ad-
vanced P.I.P. modules like the IQ-P.I.P. 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 protec-
tion systems is standby mode. Standby protects the
amplifier during potentially catastrophic conditions. It
temporarily removes power from the high-voltage sup-
plies to protect the amplifier and its loads. Standby
mode can be identified using the indicator table in Fig-
ure 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 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 common-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 condi-
tions, 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. (For more in-
formation on transformer thermal protection, refer to
the section that follows.)
4.3.3 Transformer Thermal Protection
All Macro-Tech amplifiers have transformer thermal
protection which protects the power supplies from
damage 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 re-
sets itself as soon as the transformer cools to a safe
temperature.
If your amplifier is operated within rated conditions, it is
unlikely that you will ever see it activate transformer
thermal protection. One reason is that ODEP keeps the
amplifier working under severe conditions. Even so,
higher than rated output levels, excessively low-imped-
ance loads and unreasonably high input signals can
generate excessive heat in the output devices. This
can overheat the transformer and activate its protec-
tion 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 ampli-
fier 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