Cloud Electronics VTX4400 - Manual (Page 9)

VTX Series User Manual v1.0 9
100 V/70 V-line operation
VTX amplifiers may be used to drive 100 V-line or 70 V-line
speaker systems with the addition of appropriate external
transformers. The Cloud CXL-100T is suitable for use with
the Model VTX4120, and one transformer will be required
per channel. A 2U rack-mounting tray (CXL-800) is also
available to facilitate the installation of up to eight
CXL-100Ts. Models VTX4240 and VTX4400 require
transformers with a higher rating.
Bridged Mode
VTX amplifiers may be operated in Bridged Mode to achieve
higher power outputs. Channels 2 and 4 are fitted with rear
panel mode switches; Channels 1 and 2 may be operated as
a bridged pair by setting the BRIDGE 1-2 switch on Channel
2 on; similarly Channels 3 and 4 may be bridged with
Channel 4’s BRIDGE 3-4 switch.
The principle of Bridged Mode is to feed the same input
signal to two amplifier channels, but with one input phase-
inverted. The “high” output terminals of the two channels
will therefore assume the same instantaneous voltage, but
of opposite polarity. In Bridged Mode, the load is connected
across the two “high” terminals, thus doubling the effective
voltage swing.
PHASE
INVERT
Ch. A
Ch. B
0 V
V
V
2V
0 V
+
+
When using pairs of channels in Bridged Mode, wire the
outputs in accordance with the diagram below:
CH 1 CH 2 CH 1 CH 3 CH 4
- + - + - + - +
Note that no connection is made to the ‘0V’ terminal of
either channel in the bridged pair. Note also that Channels
1 and 2 may be operated in Bridged Mode while 3 and 4 are
in Normal Mode – and vice versa.
Protection
The amplifiers include comprehensive protection circuitry
to prevent damage to loudspeakers, the output devices and
other components in the event of a fault condition.
Thermal Protection
The output device heatsink temperatures are monitored and
the protection circuitry activated if any should exceed 90°C.
The red front panel PROTECT LED for the appropriate
channel illuminates to indicate the fault condition.
DC Protection
Crowbar protection is provided to safeguard the
loudspeakers in the event of DC being present at the output
terminals. This is an emergency protection system, and
its operation is liable to blow internal DC rail fuses. The
amplifier must be serviced before any attempt is made to
use it further.
Short-circuit/reactive load protection
VI limiting is implemented in the amplifiers to protect
the output stage from excessive voltage or current at the
output. This condition can arise from a short-circuit (or
near-short-circuit) across the output terminals, or from an
excessively inductive or capacitive load.
Switch-on protection
The protection circuitry is also activated immediately
after the amplifier is switched on. This is to prevent any
voltage spikes due to start-up conditions from damaging
the loudspeakers. The duration of the protection period is
approx. two seconds. When the amplifier is powered on,
all PROTECT LEDs flash briefly; the POWER LEDs do not
illuminate until after the protection period (assuming no
amplifier faults exist).
fig.7: Bridged Mode Principle
fig.8: Output Wiring - Bridged Mode