Macro-Tech 3600VZ
Power Amplifier
Page 26
Reference Manual
Fig. 5.1 A Typical
Power Supply
voltage require-
ments are not
high, it operates in
a
parallel mode to
produce less volt-
age and more cur-
rent.
The power tran-
sistors stay cooler
and are not forced
to needlessly dis-
sipate heat. This is
the normal operat-
ing mode of the
VZ power supply.
When the voltage requirements are high,
VZ supplies
switch to a
series mode which produces higher voltage
and less current. The amplified output signal never
misses a beat and gets full voltage when it needs it—
not when it doesn’t need it.
Sensing circuitry watches the voltage of the signal to
determine when to switch
VZ modes. The switching cir-
cuitry is designed to prevent audible switching distor-
tion to yield the highest possible dynamic transfer
function—you hear only the music and not the amplifier.
You get not only the maximum power with the maximum
safety, but you also get the best power matching to your
load.
5.3 Circuit Theory
Each channel is powered by its own power transformer,
T100 or T200. Both channels share TF-1, a low
voltage
transformer. The secondary outputs of each transformer
are full-wave rectified by heavy duty bridge rectifiers
and are filtered by large computer grade capacitors. A
thermal switch embedded in each transformer protects
them from overheating.
The low
voltage transformer TF-1 uses a separate fan
motor winding. The TF-1 output is rectified by diodes
D1-4 delivering an unregulated 24 volts. Monolithic
regulators U1-2 provide a regulated ±15 volts.
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.
See the block diagram in Figure 5.5.
Also, the lower the
resistance of the
power transistors,
the more voltage
you can deliver to
the load. But when
you lower the resis-
tance of the transis-
tors, 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
VZ avoids much of this
problem by reducing the voltage applied to the transis-
tors when less voltage is needed. Reducing the voltage
reduces the heat, so the amplifier runs cooler and more
power can be packed in safely.
The
VZ supply is divided into segments to better match
Fig. 5.2 Music Waveforms Are Complex
the voltage and current requirements of the power tran-
sistors. Remember that audio signals like music are
complex waveforms.
Fig. 5.4 VZ Supply in
Series Mode
Fig. 5.3 VZ Supply in Parallel Mode
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
