Allen&Heath PA28 - Manual (Page 24)

24 PA User Guide
The MASTER SECTION Controls
Master Control
For accurate control, the main house
and two foldback mixes are controlled using full length faders
and include mute and headphone monitoring functions. These
faders act as volume controls for the mix.
FB1, FB2, LR FADERS
100mm smooth travel faders
adjust the overall level of the mixes. Up to +10dB boost is
provided above the unity gain ‘0’ position, full shut off when
down. Normal operating position with the gain structure
correctly set is typically between ‘-10’ and ‘0’.
FB1, FB2, LR MUTE
Press this switch to turn the mix
off. The large red LED lights to warn that the output is muted.
MUTE does not affect the foldback mix AFL function.
FB1, FB2 AFL
Press this switch to listen to the foldback
mix signal in the headphones and display its level on the main
meters. AFL is sourced after the fader but before the mute
switch. This lets you check the mix while the output is muted.
AFL stands for After Fade Listen. It sends the signal
taken after the fader but before the mute switch to the
engineers personal headphones monitor and console meters.
AFL is more useful than PFL for output monitoring as it shows
you exactly how much signal will be sent from the console to
the connected equipment.
Gain structure is all about getting the signal levels
between the stages in an audio system correctly matched. If a
signal is too low then you are likely to hear the residual hiss
and noise that is present in all electronic circuits. If it is too
high then there is a danger that it will try to exceed the
maximum output and therefore be clipped causing audible
distortion. Get it right and you will achieve a noise floor too low
to be heard and enough headroom to allow for the typical live
sound peaks. You
need to consider the
matching between the
microphones and the
channels (gain),
inserted equipment
(operating level and
trims), channels to the
mix (faders), and
outputs into the
amplifiers (level trims).
The diagram here
illustrates the
principles of signal
dynamics.
☺
Checking the gain structure Start with the master faders
and amplifier level controls fully off. Having first used PFL to
set gain, route a test signal into the mix by bringing up the
channel fader to ‘0’ and raising the FB1 and FB2 sends to their
3 o’clock unity gain positions. Next, raise the master faders to
‘0’ and use AFL and the LR monitor to check each mix for
signal reading around ‘0’ or just below on the console meters.
Only then should you start to turn up the amplifiers until
maximum expected volume is reached. This means that the
console is operating at its optimum level for the desired
speaker volume. You should find yourself mixing with the
master faders between ‘-10’ and ‘0’. If you work with very low
fader settings you may start to hear some background hiss
associated with the console output stage. Correct this by
turning back the amplifier levels and raising the master faders.
☺
Using L and R in church sound A method popular
with some small to medium sized churches is to use the L
fader to control a mono “Live” mix for the house
reinforcement, and the R fader to adjust a “Recording” mix
for the ministry tape. It enables the operator to easily carry
out both jobs with one console. The channel PAN controls
are used to make adjustments between what is heard by
the congregation and what is recorded to tape. This
method offers several advantages which are described in
detail on the JdB Sound web site:
http://www.jdbsound.com/art/art511.html
TO
MIN MAX OO +6
POST-LR FADER
OO +6
PRE-LR
POST-LR