Filter Cleaning; Channel 1 Vz Mode Switch (Behind Filter) - Crown Macro-Tech 5002VZ Reference Manual

Macro-Tech 5002VZ Power Amplifier
brightly, and the compressor to compress the input sig-
nal (if it is turned on). If an input signal has too much
voltage, the input overload circuitry will light the IOC in-
dicator brightly, and the compressor will compress the
input signal regardless of the COMPRESSOR switch po-
sition. The OFF setting bypasses all drive sources for
the compressors except for input overload.
When the COMPRESSOR switch is set to FAST, the
compressors have an attack time of 4 milliseconds and
a release time of 300 milliseconds. When set to SLOW,
they have an attack time of 12 milliseconds and a re-
lease time of 600 milliseconds. When set to OFF, an in-
put overload will still drive the compressor which uses
the "fast" attack and release times to protect the input
circuitry.
The back panel input ground lift switch is located on
the PIP2-FXQ (see Figure 3.11). It reduces the chance
of ground loops by isolating the input signal grounds
from the AC ground (see Section 3.3.4). Slide the switch
to the right to isolate or "lift" the grounds.
The VZ mode switches are located inside the amplifier
behind the top dust filter on the front panel. To access
these switches, remove the top filter element (see Fig-
ures 2.2 and 4.4). Always turn the power off before
changing one of these switches. Each switch has four
settings (from left to right): VZ-ODEP, Lock Low, VZ and
VZ. Note: The third and fourth positions are identical.
The amplifier is shipped from the factory with the
switches set to "VZ-ODEP." Once the top filter element
is removed, the switch position label should become
visible on the grille below each switch. To access the
switches, reach through the grille opening with a long
narrow nonconductive object like a plastic pen. The
switches are about 1.75 inches (4.5 cm) behind the
grille. They are easy to locate with the aid of a flashlight.
VZ-ODEP VZ
Lock Low VZ
Fig. 4.4 Channel 1 VZ Mode Switch (Behind Filter)
Reference Manual
The switch for Channel 1 is located on the left side, and
the switch for Channel 2 is on the right.
The VZ (Variable Impedance) mode causes the power
supplies to automatically shift between high-current and
low-current modes of operation as operating conditions
change. Normally, the power supplies operate in the
high-current (low-impedance) mode for maximum ther-
mal efficiency. When voltage demand reaches highs
levels, the supplies quickly shift into high-voltage (high-
impedance) mode. Because voltage and current re-
quirements vary with the output level and frequency
content of the source signals, the power supplies are
designed to be able to continually switch between the
two modes as needed with no degradation to the audio
signal.
The VZ-ODEP mode is very similar to VZ mode. The
only difference is that the power supplies are forced into
high-current mode when ODEP is close to activating its
limiting circuitry. This reduces excessive stress on the
output transistors, and effectively increases the thermal
performance of the amplifier.
Note: When ODEP limiting begins, the IOC circuitry will
see that the input waveform does not match the output
waveform, and an error signal is generated. If the com-
pressors are on, they will see the error signal and com-
press the input signal to correct the problem. When this
happens, there is no audible signal degradation. Com-
pression is subtle, and not noticeable unless the sys-
tem is driven to extremely high levels.
The Lock Low mode locks the power supplies into the
high-current mode for low-impedance loads. This may
be desirable when driving high-frequency transducers
that must be protected from too much voltage, or when
driving loads with very low impedances.

4.5 Filter Cleaning

Dust filters are provided on the air intakes to the cooling
system (see Figure 2.1). If these filters become clogged,
the unit will not cool as efficiently as it should and may
produce output levels that are lower than normal due to
high heat sink temperature.
To clean, remove each of the five filter elements by gen-
tly pulling them away from the front panel. Clean with
mild dishwashing detergent and warm water. Replace-
ment filters may be ordered from the factory.
Dust filters are not 100% efficient—long term this may
require internal heat sink cleaning by a qualified techni-
cian. Internal cleaning information is available from our
Technical Support Group.
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