Audio Developments AD149 - Manual (Page 41)

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The microphone amplifier has been described in detail in the introduction. Switches
(1) and (2) select 48v phantom and 12v tonader power for condenser microphones.
The switches are interlocked with tonader taking precedence over phantom.
Powering may be selected before or after connecting the microphone, but switch off
all powering on unterminated modules to ensure unconditional stability of the mixer.
When switched to line input (3), no damage will occur to external equipment should
microphone powering remain selected momentarily.
Such is the isolation, a microphone and line-level input may remain connected
simultaneously (when separate input connectors are employed).
Phase change (4) is pre transformer and operates on both microphone and line
inputs.
The first high-pass filter (5) is pre transformer and, likewise, operates on both
microphone and line inputs. In this position, the high-pass filter protects the
transformer from low-frequency saturation caused by wind, traffic, air conditioning etc.
The second high-pass filter (6) is placed after the microphone amplifier for correct and
predictable combining of the two filters when selected simultaneously. Operating
frequencies are to be found in the TECHNICAL SPECIFICATION - as are all
parameter details. High-pass filter (HPF) 2 operates independently of the equaliser.
To control the gain of the input amplifier, a limiter may be switched into circuit (17) -
limiting action being indicated by LED (22). Limiter release time (23), attack time (24)
and threshold (25) may be adjusted externally: factory settings and values at the
clockwise and counter-clockwise positions of the presets are detailed in the
TECHNICAL SPECIFICATION. Despite the limiter on the input amplifier, overload
can still occur in later stages. (The limiter also operates on a line input.)
On the mother board, a DIL switch will be found between module positions 1/2, 3/4
etc. When selected - to right - the DIL switch will link the limiters of the pair of
modules for stereo operation. (The presets of each module should have the same
settings for perfect parallel tracking.) The mixer is supplied with the modules
unlinked.
All limiter-link DIL switches are accessed by removal of the back panel covering the
mother board. (There is no requirement to remove input modules.)
It is ESSENTIAL that X, M, L signals are inserted in odd-numbered channels and that
Y, S, R signals are inserted in the even-numbered channel ABOVE.
Following the microphone amplifier is the equaliser - switch (9). Within the equaliser,
it is possible to select - (7) and/or (8) - four frequencies for the peak/dip mid-frequency
band.
Because of the inherent inaccuracy of the centre-detent mechanism, it is not
Audio Developments' practice to fit such devices to equaliser amplitude controls -
HF (28), MF (29), LF (30).