Technical Information; Overview; Vz Power; Background - Crown Macro-Tech 5002VZ 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 simulation of output transistor con-
ditions, advanced thermal management, a modular
system for signal input and processing, multispeed
compressors, Loudspeaker Offset Integration, split
feedback paths, modular internal construction and ar-
ticulated 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, in-
put-overload damage and high-frequency blowups.
The unit protects loudspeakers from DC in the input sig-
nal, output DC in the output, and turn-on/turn-off tran-
sients. The amplifier is also protected from internal
faults.
The four-quadrant topology used in the grounded out-
put 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 de-
vices 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
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
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Macro-Tech 5002VZ Power Amplifier
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 synchronously.
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 amplifiers.
The heat sinks for the Macro-Tech 5002VZ are fabri-
cated from custom milled fin stock that provides an ex-
ceptionally high ratio of area to volume, or area to
weight. All power devices are mounted directly to mas-
sive heat spreaders that are electrically at the Vcc po-
tential. Electrifying the heat spreaders improves thermal
performance by eliminating the insulating interface un-
derneath the power devices. The chassis itself is even
used as part of the thermal circuit to maximize 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 VZ 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's 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 higher the power supply
voltage, the more heat the power transistors must dissi-
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