Crown Audio Macro-Tech MA-5000VZ - Manual (Page 31)

Page 32
Macro-Tech 5000VZ Power Amplifier
Reference Manual
steering diodes (D810 and D811) provide the two
modes of the power supply.
The VZ mode switch (S700) has four positions which
control how the articulated supply functions. (Two of
the four switch positions are identical because there
are only three VZ modes.) In the VZ position, the sup-
ply will automatically change as needed depending on
the signal demands. In the Lock Low position, the sup-
ply stays in high-current mode and cannot switch into
high-voltage mode. In the “VZ-ODEP” position, the sup-
ply operates as it would in the VZ position unless the
ODEP limit is reached. If the ODEP limit is reached, the
supply will be locked into high-current mode to lower
the thermal dissipation of the output devices until it is
cools enough to return to normal VZ operation.
The fan control circuit (U713, U707B, U712 and Q706)
uses the
ODEP thermal information to control the speed
of the fan. The summation of the ODEP signal and the
heat sink temperature is used to determine its speed.
In order to reduce the turn-on current needed by the
power transformers, a “soft start” circuit is provided
(U701B, U701A, U111, U700 and Q701) which limits
the maximum start-up current to less than 22 peak
amps per channel with 120 VAC mains. The primary
voltage is ramped up to the full voltage, then relay K700
closes across triac Q701 for normal operation.
5.3.2 Bridge-Mono Operation
By setting the back panel stereo/mono switch to
BRIDGE MONO, the user can convert the
Macro-Tech
5000VZ into a bridged mono amplifier. With a signal
applied to the Channel 1 input and the load connected
between the positive output terminals of Channel 1 and
Channel 2, twice the voltage output of a single channel
is achieved.
The Channel 1 output feeds the Channel 2 error amp
(U205). Because there is a net inversion, the Channel 2
output is out of polarity with Channel 1. This produces
twice as much voltage across the load. Each of the
channel's protection mechanisms work independently
and both
IOC indicators are operational.
5.3.3 Parallel-Mono Operation
With the stereo/mono switch set to PARALLEL MONO,
the output of Channel 2 is paralleled with that of Chan-
nel 1. A suitable jumper capable of handling high cur-
rent must be installed to gain the benefits of this
operating mode. The jumper should be connected
across a positive output terminal from each channel.
The signal path for Channel 1 is the same as for stereo
operation. The signal for Channel 2 is fed from the same
source as for Channel 1 and is paralleled at the input to
the error amplifier (U105 and U205). A signal from the
current sense circuit is also sent to the Channel 2 error
amplifier giving Channel 2 an electronic ballasting re-
sistor to better match the two outputs. In Parallel-Mono
mode, twice the current of one channel alone can be
obtained. Each of the channel’s protection mechanisms
work independently if a fault occurs and both
IOC indi-
cators are operational.
5.3.4 Terminator Module
The terminator module provides a high-frequency load
to the amplifier in order to maintain stability. It includes
a current sense circuit (U750) which is used for the
I
Load
/ I
Limit
display and in the Parallel-Mono mode.
5.3.5 Display Module
On the display module there are seven indicators. The
amber Enable LED shows that the low-voltage supply
is enabled. The green SPI/
IOC LED is driven by Q502
from the output signal and flashes with the output sig-
nal at normal brilliance. When the amplifier reaches
early clipping, the LED driven by Q504 will flash
brighter indicating an
IOC event. The amber ODEP LED
driven by Q500 normally lights at full brilliance and di-
minishes when thermal-dynamic power reserve drops.
This LED will stay off if the channel is put in standby.
The two-color I
Load
/ I
Limit
LED flashes green when
U500, U501 and Q505 see output current. It turns red
when the amplifier’s maximum current output is
achieved.