Macro-Tech 3600VZ Power Amplifier
Page 25
Reference Manual
5 Technical Information
5.1 Overview
Your Macro-Tech VZ amplifier incorporates several new
technological advancements including low-stress out-
put stages, real-time computer simulation of output tran-
sistor conditions, advanced thermal management, a
modular system for signal input and processing, and
the articulated VZ power supplies.
Custom protection circuitry limits temperature and cur-
rent to safe levels while making the amplifier highly reli-
able and tolerant of faults. Unlike many lesser amplifiers,
it can operate at its voltage and current limits without
self-destructing.
Real-time computer simulation is used to create an ana-
logue of the junction temperature of the output transis-
tors (hereafter referred to as the “output devices”).
Current is limited only when the device temperature be-
comes 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 supplies, ex-
cessive temperature, chain-destruction phenomena,
input overload damage and high frequency blowups.
The unit protects loudspeakers from DC in the input sig-
nal, DC in the output, 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 output
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 pres-
ently available components, composite output devices
are constructed to function as gigantic NPN and PNP
devices. Each output stage has two composite NPN
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.
The two channels may be used together to double the
voltage (Bridge-Mono) or the current (Parallel-Mono)
presented to the load. This feature gives the user flex-
ibility in maximizing the power available to the load.
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 heat
sinks in power amplifiers due to their low cost and rea-
sonable performance. However, measured on a watts
per pound or watts per volume basis, the extrusion tech-
nology doesn’t perform nearly as well as the heat sink
technology developed for Macro-Tech power amplifiers.
Our heat sinks are fabricated from custom convoluted
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 im-
proves thermal performance by eliminating the insulat-
ing 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
VZ means Variable Impedance. It is the name of Crown’s
patented articulated power supply technology. This
technology is what makes it possible to pack such tre-
mendous power into Crown’s Macro-Tech 3600VZ and
5000VZ amplifiers.
5.2.1 Background
A power supply must be large enough to handle the
maximum voltage and current necessary for the ampli-
fier to drive its rated power into a specified load. In the
process of fulfilling this requirement, conventional power
supply designs produce lots of heat, are heavy, and
take up precious real estate. And it is no secret that heat
is one of a power amplifiers worst enemies. Consider
the circuit in Figure 5.1.
According to Ohm’s Law, the bigger the power supply,
the more heat the power transistors must dissipate.
