Quest Engineering QA 1004 User Manual page 6

QA SERIES
User Manual
Notes for better
amplifier performance
• Amplifier gain
The amplifier should always be operated with the input
level controls set at maximum. The only departure from
this practice is where the internal filters/crossover is
engaged in a bi-amp configuration, where it may be
necessary to turn down the high frequency side of
the amplifier. If the amplifier needs to be calibrated, to
match a mixer line level output, the gain switch on the
back of the amplifier can be switched to the correct
line level.
The objective of correct gain settings is to have all the
segments of the audio chain from the preamplifier/
equalisers/compressors/crossovers matched to the
amplifier. A test tone should take every link in the chain
to 0 dB or +4 dB at the same input level. This way, a
mixer VU indicator is a real visual clue as to how hard
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the whole system is running and no single element will
be adding distortion before the system is at full power.
• High- and low-pass filters
The filter system in a QA series amplifier is a basic
switchable high/low pass crossover. It can also be
used to filter out sub-harmonic low bass frequencies
the speaker system cannot reproduce and waste
amplifier power. It is particularly recommended to
switch in the 35 Hz High Pass filter when the amplifier
is being used to power band-pass type bass boxes.
The amplifier can be used to power a bass system
without the need for an electronic crossover by
switching the high-pass to 35Hz and the low-pass to
80 or 110Hz. The input link A/B XLR connectors at the
back of the amplifier will remain full-range, so a full-
range signal can be daisy chained to another amplifier
or powered speaker.
• Amplifier limiter
The switchable limiter is designed to prevent the
amplifier from clipping or distorting, there by causing
speaker damage. It should always be engaged except
in the circumstance where the amplifier is being used
in conjunction with an amplifier sensing speaker
system controller.
User Manual QA Series
Power Amplifiers
Some brands of speaker system are designed to
be monitored and controlled by a dedicated system
controller that is wired directly to the output of the
amplifier. These systems measure both the input
and output from the amplifier and monitor the signal
for best results from the speaker system. To engage
the amplifier's limiter will interfere with the controllers
sensing circuit, so the amplifier limiter must be
disengaged.
• The air intakes
The two filtered air intakes have removable filters for
cleaning. The air intakes should be unobstructed and
allow the free flow of air.
The filters should be removed and cleaned as needed.
Running the amplifier without the filters will allow the
amplifier to fill with dust and foreign particles and could
void the warrantee under some circumstances.