VX Manual 1.2
check the power amp. If the Protect LED flashes at
three-second intervals, there is some kind of fault in
the connected load, i.e. either the impedance of the
connected loudspeaker system is too low for the
power amp or an output is short-circuited. Also
check the connected speaker system and the speaker
cords for faults. Here too, you don't have to power
the amp up again. After you've eliminated the source
of the problem, it will resume operation
automatically.
3.5 Clip LED's
These LED's illuminate to indicate that the amp has
run out of headroom and has exceeded its perfor-
mance threshold. Occasionally, this LED may flash
briefly. This is not a problem because the design of
the power amp makes it possible for peak pulses
such as a snare drum or similar signals to briefly ex-
ceed the normal threshold. If however this LED
lights up with just a few interruptions or if it illumi-
nates continuously, you should definitely lower the
level of the input signal. If you run the power amp
when it is clipping heavily, the distorted output sig-
nals can destroy the connected speakers even if the-
se are equipped with protection circuits.
Caution: HK Audio is not liable for damage to spea-
ker systems due to overload caused by improper
operation of the power amp.
3.6 Active LEDs
This green LED indicates whether this amp channel
is active, that is, whether an input signal is present.
(It is possible, however, for a very soft signal to make
it through the entire amp without even triggering the
LED to glow.)
4 Rear Panel
4.1 Inputs
The power amp is equipped with two input sockets
for each power amp channel: one XLR female (pin 1
= ground; Pin 2 = +; Pin 3 = --) and one 1/4" stereo
jack (tip = +; ring = --; sleeve = ground). Both jacks
are balanced and connected internally in parallel,
therefore making it possible to use these inputs to
patch the incoming signal out to more power amps.
We recommend that you use only balanced cabling
for the input signals in order to avoid noise induced
by electro-magnetic fields and radio frequency inter-
ference. If the signal source which you are connec-
ting to the VX power amp input is itself unbalanced,
we still recommend that you use a standard balanced
cable to connect between the two, but with one of
the ends modified. Modify the plug which is connec-
ted to the output of the unbalanced signal source as
follows: if the unbalanced source has an XLR output
jack, bridge pin 1 and pin 3 of the XLR plug; if the
unbalanced source has a 1/4” output jack, bridge the
ring and the sleeve of the 1/4" plug. This "quasi"
balanced arrangement will help eliminate possible
interference via the common mode rejection circuit
of the input.
4.2 Ground-lift Switch
This button separates the signal ground from the
chassis ground in order to eliminate hum caused by
ground loops. The chassis remains grounded so that
power amp safety is not compromised. The ground
circuit is severed when the button is pressed in.
Note: Hum is often a sign of a faulty power supply,
especially when your equipment is fed by multiphase
power supply circuits. In this case, do not attempt to
solve the noise problem by lifting the ground with
this switch; instead, check the cables and ground
circuits of your mains power supply.
4.3 Mode Switch
This sliding switch configures the power amp for
three different operating modes:
• Stereo:
This is the standard operating mode.
Two independent signals are patched to the amp,
amplified by the two power amp channels and sent
to two independent speaker systems.
• Mono:
The two inputs are connected in parallel, i.e.
a single input signal is routed to both power amp
channels, and the output signals of both channels
are identical.
• Bridge:
The two inputs are connected in parallel,
however, antiphase signals are routed to the power
amp channels and therefore the outputs. If you
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