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12
Section III
SETUP AND OPERATION
PANEL CONTROLS AND INDICATORS
A brief description of the front-panel controls and indicators is given
here. Do scan this section to at least verify that our terminology agrees
with yours.
PLEASE NOTE
that all front-panel multiturn trim controls require
fifteen to twenty complete rotations
of the adjusting screw to cover their
total operating range. Depending on the trim-pot manufacturer, the end
of the range may,
or may not,
be identified by a “click-click” sound or
other audible/tactile sensation.
INPUT GAIN
These two controls, at the far-right end of the front
panel, adjust
DAVID-II
sensitivity for the nominal
program level applied to the
LEFT
and
RIGHT
channel
PROGRAM LINE INPUT
barrier strip terminals on the
rear panel. The controls have a 15dB range which is
multiplied by input gain range jumpering to an input
acceptance range of 30dB (see Page 8). The
INPUT
GAIN
controls are adjusted to maintain AGC gain in
the center of its operating region.
A G C GAIN
This series of five LED indicators displays the amount
of correction in effect for long-term variations in the
program input signal. The AGC circuit is left/right
correlated; that is, the overall circuit gain is controlled
by the
greater
of the left or right channel signals. This
prevents the stereo image from “wandering.”
The correction rate of the AGC circuit is intentionally
very slow, 10dB of gain correction will take
approximately 20 seconds. With a conscientious
operator on the console, the indicated
AGC GAIN
will
appear “stuck” at the center,
0dB
indicator.
The “safe” operating zone of the circuit is within the
central three green LEDs. If either the
+10dB
or the
–10dB
red indicator is lighted to full brightness, the
input program signal is
out of limits
and the reason
should be found and corrected.
GATE OPEN
The
DAVID-II
AGC is “gated.” This means that
during brief pauses in the program AGC gain is locked
to prevent background sounds from increasing to
unnatural proportions. The green
GATE OPEN
