Technical information

Page 27
Macro-Tech 5000VZ Power Amplifier
Reference Manual
nal (if it is turned on). If an input signal has too much
voltage, the input overload circuitry will light the IOC
indicator brightly, and the compressor will compress
the input signal regardless of the COMPRESSOR
switch position. 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
input 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 identi-
cal. 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 flash-
light. 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 con-
ditions change. Normally, the power supplies operate
in the high-current (low-impedance) mode for maxi-
mum thermal efficiency. When voltage demand
reaches highs levels, the supplies quickly shift into
high-voltage (high-impedance) mode. Because volt-
age and current requirements 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 degrada-
tion 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 activat-
ing 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 cool-
ing 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 nor-
mal 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 tech-
nician. Internal cleaning information is available from
our Technical Support Group.
Fig. 4.4 Channel 1 VZ Mode Switch (Behind Filter)