Circuit Theory; Grounded Bridge Theory; Overview - Crown Macro-Tech MA-5002VZ Service Manual

130446-1 Rev. A

4 Circuit Theory

4.1 Overview

It should be noted that over time Crown makes improve-
ments and changes to their products for various rea-
sons. This manual is up to date as of the time of writing.
For additional information regarding these amplifiers,
refer to the applicable Technical Notes provided by
Crown for this product. Sketches have been added to
this section for clarification of the various concepts pre-
sented, as well as block diagrams for the amplifier and
specific portions of the amplifier. For detailed schemat-
ics refer to Section 6.
The Macro-Tech 5002VZ amplifier incorporates several
new technological advancements, including real-time
computer simulation of output transistor stress, low-
stress output stages, an advanced heat diffuser em-
bodiment, a programmable input processor (PIP) ex-
pansion system, and articulated VZ power supplies.
Custom circuitry is incorporated to limit temperature and
current to safe levels—making it highly reliable and tol-
erant of faults. Unlike many lesser amplifiers, the Macro-
Tech 5002VZ can operate at its voltage and current lim-
its without self-destructing.
Real-time computer simulation is used to create an ana-
log reading of the junction temperature of the output
transistors (herein 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, called ODEP (Out-
put Device Emulation Protection) maximizes the avail-
able output power and eliminates overheating—the
major cause of device failure. ODEP in the MA-5002VZ
also provides indication of amplifier thermal reserve
(front panel ODEP indicators) and may provide control
of VZ mode when the VZ mode select switches are
placed in the VZ-ODEP position.
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
signal and from turn-on and turn-off transients. It also
detects and prevents unwanted DC on the outputs.
Additional protection features include input voltage
sense as well as overvoltage (AC mains).
A mode of protection which may be switched on or off
©2000 Crown International, Inc.
is called Loudspeaker Offset Integration (LOI). The LOI
circuit, when switched on, prevents excessive bass fre-
quency cone excursions below the audible frequency
range. It operates essentially as a band-pass filter. The
low frequencies are rolled off at 18 dB/octave with a
–3 dB corner of 35 Hz (Butterworth response). Ultra-
sonics are rolled off with a second order Bessel response
and –3 dB corner of 50 kHz.
A compression circuit in each channel may be switched
off, on slow, or on fast by switches on the rear panel.
This compressor is activated by either input overload
or distortion (clipping). Input overload compression is
in fast speed when the compressor switch is in the off
position. The compression ratio is infinite (it operates
as a peak limiter).
The four-quadrant topology used in the grounded out-
put stages is called the Grounded Bridge, and it makes
full use of the power supplies. This patented topology
also makes peak-to-peak voltages available to the load
which are twice the voltage any output device is ever
exposed to. The Grounded Bridge is covered in detail
in Section 4.2.
The two channels may be used together to double the
voltage (bridged-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.
Macro-Tech amplifiers utilize a wide bandwidth multiloop
feedback design with state of the art compensation tech-
niques. This produces ideal behavior and results in ul-
tra-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, that extru-
sion technology doesn't perform nearly as well as the
cut fin radiator technology developed for the Macro-
Tech 5002VZ power amplifier.
Our thermal diffusers are custom cut radiator fins on a
solid heat sink block. They provide an extremely high
ratio of area to volume, or area to weight. All power de-
vices are mounted directly to massive heat spreaders,
which are electrically hot. Making the heat spreaders
electrically hot allows improved thermal performance
by eliminating the insulating interface underneath the
power devices. The chassis itself is used as part of the
thermal circuit, and this maximizes utilization of the avail-
able resources.

4.2 Grounded Bridge Theory

The Grounded Bridge topology is ground-referenced
MA-5002VZ Service Manual
Circuit Theory 4-1