6
A DEEPER LOOK: BALANCED OR UNBALANCED?
When cables are very long (e.g., over 6 meters/20 feet), the cable itself can
act as an "antenna" and pick up radio frequency noise, AC hum, or other types
of noises. To avoid these problems, many recording studios and live sound
installers use balanced lines. The average application may not require balanced
lines, but committing balanced connectors between the mixer and your A400.4
will cause less ground loops and hum in the system. Balanced lines carry two
signals, each one out of phase with respect to the other. To be converted back
into a single, unbalanced line, both balanced lines feed a differential amplifier
input that responds to the difference in levels between signals. In this way, the
out-of-phase signals are recombined into an unbalanced signal, but interference
induced into the cable will not be out of phase. Since the difference between
these signals is zero, the differential amplifier will reject the interference
completely.
4. OPERATION
1. Connect two pairs of PA cabinets or studio monitors to the output of your
A400.4. make sure that your A400.4 is switched off and that the volume
controls are turned down all the way.
2. Connect your A400.4 to a mixer, a preamplifier or another source making
sure that the gain and volume controls on the mixer are turned down.
3. Connect some source such as microphones, keyboards or CD player into your
Mixer or preamplifier and start to make some noise.
4. Adjust the output level of your mixer or preamplifier at a proper level. A very
low output level will generate unwanted noise.
At this point, gradually turn up the volumes in your A400.4 making sure that
the limit LEDs only flash occasionally.
OPERATION ADVICES:
4.1 TEMPERATURE CONSIDERATION IN RACK MOUNTING:
!
Notice
the special optional brackets.
Although your A400.4 generates almost no heat at all, you must secure proper
ventilation inside the rack to avoid overheating.
You can mount your A400.4 in only 1.5U with
A sustained high-temperature operation will adversely affect the sound quality,
and the amplifier may shut itself off for as long as the excessive temperature
conditions exist.
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