QSC Audio ISA 500T - Manual (Page 26)

OPERATION:
AC POWER SWITCH, LED INDICATORS, GAIN CONTROLS
NORMAL OPERATING LEVELS
The amplifier’s protective muting system guards against
excessive internal temperatures. With normal ventilation and 4
to 8 ohm loads, the amplifier will handle any signal level,
including overdrive. Lower load impedances and higher signal
levels produce more internal heating. When using 2 ohm loads,
frequent or prolonged clipping may trigger thermal shutdown.
AC POWER SWITCH
Before applying power, check all connections and turn down the
gain controls. When the AC power is switched on, the power
indicator LED will light at half brightness and the fan will start.
The outputs are muted. Then the power indicator fully
illuminates and the amplifier unmutes. The clip and signal LEDs
will flash briefly. When the clip LEDs go out, the amplifier is
ready.
After the amplifier has been powered up, slowly increase the
Gain settings for each channel and check for the proper
operation of all speaker loads. If you detect any problems with
speakers or wiring, turn the amplifier off, correct the problem and
try again. Once the system has been tested, adjust Gain levels as
required.
FRONT PANEL LED INDICATORS
At full brightness, the green power LED indicates that the
amplifier is operating. Half brightness indicates the amp is in its
muting mode.
As the input signal strength increases, the green signal LED
indicators will illuminate.
The red clip LED indicator flashes during overload (clipping). A
bright, steady glow indicates protective muting; if this occurs
during use, see Troubleshooting.
NOTE! Page 7 contains detailed descriptions of the LED’s and
how to interpret their indications.
A NOTE ON SOUND PRESSURE LEVELS- Sound is heard as the ear
converts vibration from sound waves into impulses in the nerves of the ear.
Sounds above 90 decibels, particularly if the sound is prolonged, may cause
such intense vibration that the inner ear is damaged. 90 decibels is about
the loudness of a large truck about 5 yards away. A jackhammer emits
sounds of about 120 dB from 3 feet away, and a jet engine emits sound of
about 130 dB from 100 feet away. Motorcycles, snowmobiles, and similar
engines range around 85 to 90 dB, and a rock concert may approach 100 dB.
A general rule of thumb is that if you need to shout to be heard, the sound is
in the range that can damage hearing.
Some jobs in the entertainment industry involving loud noise from music
carry high risk for hearing loss. In the U.S., the maximum job noise exposure
is regulated by law. Both the length of exposure and the extent (decibel
level) of exposure are considered.
If exposure is at or greater than the
maximum exposure, protective measures must be taken. The table at
right is referenced from OSHA’s Permissible Noise Exposure table G16.
The power switch is a rocker-type switch. To turn the
amplifier on, push in on the top portion of the switch. To
turn the amplifier off, push in on the bottom portion of the
switch. The green power LED should illuminate when the
switch is in the on position. The LED may takes several
seconds to extinguish when the power is switched off, this
is normal.
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GAIN CONTROLS
The Gain controls are located on the rear panel of the amplifier
as shown on page 6. The controls are detented (11 steps) for
repeatable adjustment. Surrounding the Gain control, the power
attenuation level is shown in dB. To operate the Gain control,
rotate the control’s knob so that the desired level is achieved.
There is a detent in the knob to indicate its position.