Macro-Tech 24x6 Reference Manual - 5 Technical Information
Page 21
Macro-Tech 24x6 & 36x12 Power Amplifiers
5 Technical Information
5.1 Overview
Your amplifier incorporates several new technological
advancements including low stress output stages, real-
time computer simulation of output transistor stress,
an advanced heat diffuser embodiment and a modular
system for signal input and processing. In addition,
Macro-Tech 36x12 models also have an articulated VZ
power supply in Channel 1.
Custom protection circuitry limits temperature and cur-
rent to safe levels while making the amplifier highly re-
liable and tolerant of faults. Unlike many lesser
amplifiers, it can operate at its voltage and current lim-
its without self-destructing.
Real-time computer simulation is used to create an
analogue of the junction temperature of the output tran-
sistors (hereafter referred to as the “output devices”).
Current is limited only when the device temperature
becomes excessive—and just by the minimum amount
necessary. This patented approach is called
ODEP or
Output Device Emulation Protection. It maximizes the
available output power and eliminates overheating, the
major cause of output device failure.
The amplifier is protected from all common hazards
that plague high-power amplifiers, including shorted,
open or mismatched loads; overloaded power sup-
plies, excessive temperature, chain-destruction phe-
nomena, input
overload damage and high frequency
blowups. The unit protects loudspeakers from DC in
the input signal, turn-on and turn-off transients, and it
detects and prevents unwanted DC in the output. The
amplifier is also protected from internal faults.
The patented four-quadrant topology used in the
grounded output stages is called the
grounded bridge.
The
grounded bridge topology takes full advantage of
the power supplies delivering peak-to-peak voltages
to the load that are twice the voltage seen by the out-
put devices and twice the voltage generated by the
power supplies.
The
grounded bridge topology is ground-referenced.
Because the required current exceeds the limits of
presently available components, composite output
devices are constructed to function as gigantic NPN
and PNP devices. Each output stage has two compos-
ite NPN devices and two composite PNP devices.
The devices connected to the load are referred to as
“high-side NPN and PNP” and the devices connected
to ground are referred to as “low-side NPN and PNP.”
Positive current is delivered to the load by increasing
conductance simultaneously in the high-side NPN and
low-side PNP stage, while decreasing conductance of
the high-side PNP and low-side NPN in synchrony.
A wide bandwidth, multiloop design is used for state-
of-the-art compensation. This produces ideal behavior
and results in ultra-low distortion values.
Aluminum extrusions have been widely used for
heatsinks in power amplifiers due to their low cost and
reasonable performance. However, measured on a
watts per pound or watts per volume basis, the extru-
sion technology doesn’t perform nearly as well as the
thermal diffuser technology developed for
Macro-Tech
power amplifiers.
Our thermal diffusers are fabricated from custom con-
voluted fin stock that provides an extremely high ratio
of area to volume, or area to weight. All power devices
are mounted directly to massive heat spreaders that
are electrically alive. Electrifying the heat spreaders
improves thermal performance by eliminating the insu-
lating interface underneath the power devices. The
chassis itself is used as part of the thermal circuit, and
this maximizes utilization of the available resources.
5.2 VZ Power (
Macro-Tech 36x12
only)
VZ means Variable Impedance and is the name of
Crown’s patented articulated power supply technology.
This technology is what makes it possible to pack such
tremendous power into Crown’s
Macro-Tech 3600VZ
and
Macro-Tech 5000VZ amplifiers. The high-power
channel of the
Macro-Tech 36x12 uses this articulated
power supply technology.
5.2.1 Background
A power supply must be large enough to handle the
maximum voltage and current needed by the amplifier
to drive its maximum rated power into a specified load.
To fulfill this require-
ment, conventional
power supply de-
signs produce lots of
heat, are heavy, and
take up precious real
estate. And it’s no se-
cret that heat is one
of a power amplifiers
worst enemies. Con-
sider the circuit that
follows in Figure 5.1.
According to Ohm’s
Law, as your power
Fig. 5.1 A Typical
Power Supply
POWER
TRANSISTOR
POWER
TRANSISTOR
SPEAKER
LOAD
POWER
SUPPLY
+
–