Allen&Heath GL2400 - Manual (Page 16)

16 GL2400 User Guide
The MONO Input Channel
+48V Switches +48VDC to the channel input XLR for powering
microphones or DI boxes that need phantom power. The power is
current limited through 6k8 ohm resistors to pins 2 and 3.
WARNING: Do not connect unbalanced sources or cables to
inputs with phantom power selected. To avoid loud clicks always
mute the channel before switching +48V on or off and when
plugging or unplugging microphones.
POLARITY Reverses the polarity (+ and – connections) of the
input source. Useful when using the ‘above/below’ mic technique, for
example when miking a snare drum with two microphones, or for
correcting mic placement and cable wiring errors.
LINE (PAD) Press this switch to select the channel TRS jack LINE
input. Release the switch to select the XLR MIC input. The XLR
normals through the TRS socket. With nothing plugged into the line
input the switch therefore becomes a PAD for the mic XLR. It
attenuates the input signal by 20dB for connection to high level
microphone or line sources. This gives the mic preamp a massive
74dB range and headroom of +34dB to deal with the hottest signals.
GAIN Adjusts the input sensitivity to match the connected source to
the internal 0dBu operating level of the channel. Provides a variable
54dB range from +6 to +60dB gain (mic), or -14 to +40dB (line,
padded mic). The gain should be set so that the channel meters
average ‘0’ with loudest moments lighting ‘+6’. Reduce gain if the red
peak indicator lights.
Important note on setting channel levels: Use PFL to set the GAIN
controls for correct signal level through each channel. The main LR
meters provide a high resolution display of the channel signal level.
Use the faders to balance each signal in the mix. To ensure optimum
gain structure we do not recommend the practice of setting the faders
to ‘0’ and mixing using the GAIN controls.
HPF Switches in the channel high pass filter. This attenuates
frequencies below 100Hz by 12dB per octave. The filter is pre-insert,
pre-EQ. Select the HPF to reduce low frequency noise such as
microphone popping, stage noise and tape transport rumble.
EQ A responsive 4-band semi parametric EQ (equaliser) provides
independent control of four frequency bands. Use EQ IN to compare
the sound with the equaliser switched in or out of circuit.
HF and LF are shelving filters which affect high frequencies above
12kHz, and low frequencies below 80Hz respectively. HM and LM are
bell shaped peak/dip filters which affect frequencies around a centre
point which can be swept from 500Hz to 15kHz, and 35Hz to 1kHz
respectively. These have a width (Q) of 1.8 which provides effective
control for both creative and corrective equalisation. The EQ curves
shown opposite display the signal level response at maximum boost
and cut as the frequency varies from low (20Hz) to high (20kHz).
All bands can be boosted or cut by up to 15dB and have a centre
detent 0dB position. The overlapping frequency ranges let you deal
with challenging source problems easily using combinations of bands.
Check that you are using the best microphone type and placement
before using the EQ. Start with the EQ set flat and apply only as much
boost or cut as is really needed. When dealing with problem
frequencies cut rather than boost where possible.
PRE
AUX
AUX
4
3
AUX
AUX
2
1
O O +6
POST
O O +6
O O +6
O O +6
-15
LF -15
+15
+15
180
45
LM
35Hz
70
-15
400
1k
250
+15
3k
HM
700
500Hz
-15
1k
6k
15k
4k
+15
HF
GAIN
20
0
HPF
50
40
+48V
30
6
AUX
AUX
5
MUTE
+6 O O
PRE
POST
O O +6
EQ IN
POLARITY
LINE
(PAD)
100Hz
12k
80Hz
ODD
PAN
L
EVEN
R
=
6 -14 40 60