User manual

TROUBLESHOOTING
6
Trouble shooting
Buzzes and noises in the sound system.
Getting rid of unwanted noises is a study in
itself. Most of the noise, (apart from undesir-
able program) will fall into three categories.
(A) White noise. This is the hiss that suggests
that the gain structure is set incorrectly.
Something in the signal chain is boosting too
much or an input is set too sensitive. If your
equipment has gain switches on it, set them
all the same. If the switch is labelled +4dB,
set them all to that gure. If one piece of
equipment seems to be overloading, set them
all to -10/-20dB and be prepared to boost
the input level of the QSA input. The last unit
in the chain should be set to +4 dB at the
output stage if possible when connected to
the line level input of the QSA series input.
(B) Low frequency hum. This is often
caused by noise from the power leads being
picked up by the audio signal cables. The
preferred solution is to connect up your
system with “balanced” XLR microphone
cables. Especially if you are running the
cables a long distance, (more than 5Mtrs
/15 Ft). The other solution is to make sure
that your audio cables are as far from power
cables as possible.
(C) Buzz. Sometimes you can experience
a hum and buzz together. A buzz is almost
always a problem with the “earthing” of the
system. It will often occur when you have the
system powered from sperate power outlets
in the same building or audio and lighting
sharing a common power circuit. Even when
the audio and lighting systems are powered
from separate sources, there can still be a
common earth between them. For example,
a smoke machine may be powered from the
lighting system, yet the trigger mechanism
could be connected to the audio system
through the audio multi-core/snake. An earth
connection between the audio and lighting
will now exist and a buzz could be amplied
in the audio system. The simple solution is to
power your audio circuit and everything con-
nected to it from the same source. If the buzz
persists, check your signal cables, one may
have an earth/shield disconnected.
A cheap but possibly life saving investment
is a domestic power tester to check that the
power supply sockets are correctly wired.
Faulty or incorrectly wired power is a booby
trap that is more common than you think.
It is wise to avoid switching on or off devices
in the signal path while the speaker system
is powered and turned up. Otherwise loud
clicks and bangs could result. When shutting
down the system, always turn the speak-
ers off rst. This is to prevent the speaker
amplifying the sound of the other equipment
in the chain being shut down. The reverse is
true when powering up. Mixers and effects
on rst, power ampliers or powered speak-
ers on last.
QSA 300
Active Speakers
User Manual
QSA 300
User Manual