Page 29
Macro-Tech 5002VZ
Power Amplifier
Reference Manual
pate. Also, the lower the
resistance of the power
transistors, the more
voltage you can deliver
to the load. But at the
same time that you lower
the resistance of the
transistors, you increase
the current passing
through them, and again
increase the amount of
heat they must dissipate.
5.2.2 The VZ Supply
An articulated power supply like Crown’s VZ design can
circumvent much of this problem by reducing the volt-
age applied to the transistors when less voltage is re-
quired. Reducing the voltage reduces the heat which
makes the amplifier runs cooler. This makes it possible
to safely pack more power into the chassis.
The VZ supply is divided into segments to better match
the voltage and current requirements of the power tran-
sistors. Remember that audio signals like music are
complex waveforms.
mode of the VZ
power supply.
When the voltage re-
quirements are high,
a VZ supply switches
into to a
high-voltage
mode to produce
higher voltage and
less current. The am-
plified output signal
never misses a beat
and gets full voltage
when it needs it—not
when it doesn’t need it.
Sensing circuitry monitors the voltage and current de-
mands of the signal and load to determine when to
switch VZ modes. The switching circuitry controls the
power supplies (not the output devices) which yields
the highest dynamic transfer function with no audible
switching distortion—you hear only the music, not the
amplifier. The VZ design gives you maximum power,
maximum safety, and power optimized for your load.
5.3 Circuit Theory
Each channel is powered by its own transformer, T100
or T200. The secondary of T100 is full wave rectified by
DB100 and DB101 and filtered by large computer grade
capacitors (C810 and C812 for Channel 1). The trans-
formers are protected against catastrophic failure by
fuses F700 and F701 and thermally protected by inter-
nal self-resetting switches.
Both channels share T1, a low-voltage transformer. The
output of T1 is rectified by diodes D709 through D714
providing an unregulated 24 volts. Monolithic regulators
U715 and U716 provide the regulated ±15 volts. T1 is
protected by fuse F702.
5.3.1 Stereo Operation
For simplicity, the discussion of stereo operation will re-
fer to one channel only. Mono operation will be dis-
cussed later.
Please refer to the block diagram in Figure 5.5 and the
schematics provided at the back of this manual.
The input signal at the XLR and phone jack input con-
nectors passes directly into the balanced input stage
(U100A). When the compressor is enabled, the com-
pressor control circuit (U101, U102 and U103) causes
a reduction in gain of the balanced input stage at the
onset of clipping in the output stage. The compressor is
POWER
TRANSISTOR
POWER
TRANSISTOR
SPEAKER
LOAD
POWER
SUPPLY
+
–
Fig. 5.1 A Typical
Power Supply
POWER
TRANSISTOR
POWER
TRANSISTOR
SPEAKER
LOAD
VZ
STAGE
+
–
VZ
STAGE
+
–
VZ POWER SUPPLY
Fig. 5.4 VZ High-Voltage Mode
POWER
TRANSISTOR
POWER
TRANSISTOR
SPEAKER
LOAD
VZ
STAGE
+
–
VZ
STAGE
+
–
VZ POWER SUPPLY
Fig. 5.3 VZ High-Current Mode
Fig. 5.2 Music Waveforms
For music the average level is always much less than
the peak level. This means a power supply does not
need to produce full voltage all the time.
The VZ supply is divided into two parts. When the volt-
age requirements
are not high, it op-
erates in
high-
current mode to
produce less volt-
age and more
current.
The power tran-
sistors stay cooler
and are not
forced to need-
lessly dissipate
heat. This is the
normal operating
