Protech Audio 2000 - Manual (Page 7)

- Page 14 -
NOTE 1:
Always turn the ALC assembly off (switch down)
when adjusting any system gain controls, includ-
ing mixer inputs, master gain control, tone con-
trols, system equalizers, and amplifiers.
If this procedure is not followed, the ALC may
fade the gain back up when someone speaks
softly, and the system may go into feedback.
NOTE :
The automatic level control card assembly has
been aligned at the factory. Normally, no further
adjustments are necessary.
How It Works.
The ALC's function is to fade the master gain
down when the speaker is too loud, and hold it
there during pauses. When a quieter speaker talks,
the gain will be raised again. The ALC compares
the level of the mixer's output, measured with a
VU meter characteristic, with a threshold set by
the TARGET trimpot control. When the output
level is lower than the threshold, the ALC will
fade up the master gain. When the output level is
higher than the threshold, the ALC will fade the
master gain down. The speed of the fade is set
with the RATE trimpot control.
The gating action of the ALC freezes the master
gain when no one is talking. Normally it is con-
trolled by the logic outputs of the automatic
mixing input channels. Whenever a yellow logic
LED on any channel is on, the ALC action is
allowed to adjust the output level. The yellow
ALC ENABLE LED will come on when any
input's logic LED is on, and indicates when the
ALC is active.
Factory Settings- Recommended positions.
RATE Trimpot = 12:00, Counterclockwise =
Slower
TARGET Trimpot = 9:00, Counterclockwise =
Downward
WINDOW Trimpot = 12:00, Counterclockwise =
More Dynamic range
AUTOMATIC LEVEL CONTROL OPTION
ALIGNMENT PROCEDURE-
Unplug the power supply card. Unplug and remove
the master output card assembly (with ALC card
assembly). Plug the extender card into the master
output card slot. Plug the master output card assem-
bly into the extender card. Plug in the power supply
card
With the ALC switched to "OFF", adjust all input
gains, master output gains, tone controls, and adja-
cent channel input controls, as well as any other
equipment in the signal chain (equalizers, power
amps, etc.). Be sure to test with speech at all micro-
phones after any gain adjustment. Because of the
automatic mixing action, a microphone that may be
ready to feed back, will not have it's gain turned up
until someone speaks into it.
Turn the ALC "ON". Have someone speak loudly at
a microphone. Adjust the TARGET trimpot down-
ward (counterclockwise) until the volume is reduced
to a comfortable level. The middle green LED is
illuminated to indicate where the target level should
be. Now the ALC will fade the master gain down
whenever the output level is higher than the TAR-
GET level. When a quieter speaker talks, the gain
will fade up again.
Next adjust the RATE trimpot to 12:00 or lower.
This will increase the ALC fade time so that it
doesn't "pump". 100% counterclockwise is the
slowest setting.
If more dynamic range is desired, more difference
between loud and soft speakers, turn the window
control counterclockwise. This will create a "dead
zone" below the threshold level, where the volume
can vary naturally without ALC action. A WINDOW
setting of 50% gives a dead zone of 5dB, and 0%
(full counterclockwise), about 8dB.
Exempting Line Level Inputs From ALC-
Since the ALC works by varying the master gain
when a logic indicator is active, removing R23
prevents the ALC from changing the gain on the line
input, whenever any input becomes active.
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Gain Set
Bass Control
Treble Control
Adjacent Channel Mix-Minus L
Adjacent Channel Mix-Minus R
Adjacent Channel In
Adjacent Channel In
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Remote Control Voltage
Input Mute,
Ground.
Input Hi.
Input Lo.
48V Phantom From External Source.
Pre Mix Out
Ground
Direct MIx Minus Input (Resistor Isolate)
Gain Ind. Out
Logic Out
Post Mix Out, Used for Mix-Minus or Console Insert.
Ground
Mix-Minus Out Hi
Mix-Minus Out Lo
OUT
IN
HP
HI LO
GAIN
PRE
MUTE
POST
ALL ADJUSTMENTS ON
DAUGHTER BOARD ARE
MADE AT FACTORY.
DO NOT READJUST ANY
TRIMPOTS ON DAUGHTER
BOARD
AUTO
MANUAL
NORMAL
MUTE
DISABLE
ENABLE
GROUP MUTE
GREEN
YELLOW
RED
A
B
D
E
F
INPUT CARD ASSEMBLY
Switch allows individual channels to be connected to Group Mute. (Shipped "Enabled")
Switch allows individual channels to be muted for troubleshooting. (Shipped "Normal")
Switch allows either automatic or manual operation of individual input channels. (Shipped "Auto")
High-Pass filter (Rumble). (Shipped "Out")
HI-LO gain switch, 50 or 30 dB, for use with different microphone types. (Shipped "HI")
Placing RED push-on shunt on pins +48 and middle, allows external 48 volt phantom to be used.
(Shipped "15V")
Mic/Line switch, for determining input impedance and gain structure. (Shipped as MIC input)
Factory set, to allow mix-minus output
Placing RED push-on jumper determines whether pre-mix outputs are pre or post mute.
A =
B =
C =
D =
E =
F =
G =
H =
I =
LED's = Red indicates Mute Function.
Yellow indicates Logic function.
Green indicates gain function.
PHANTOM
+15 +48
INPUT FEATURES
TYPICAL INPUT CONNECTION, 1 OF 8
Line---Mic
LOG
M/M
C
G
H
I