8910ADA-M/ST/SR — Instruction Manual
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Functional Description
The outputs of the swapping/summing stages are sent to the output stages
that buffer the signal and add another gain of 3.58 dB. This output is then
inverted to give the inverting output of the differential output.
Power Supplies
There are four regulated power supplies on this board for generating the
±5 V supplies for the processor and the digitally controlled gain stages and
the ±18 V supplies. These supplies boost the ±12 V from the frame up to
18 V for the output stages. The ±12 V raw voltages coming onto the board
are filtered with passive filters to be used by all audio stages except for the
digital gain stage and output stages.
Input Level Detectors
The input level is detected by taking the audio signal just after the input
stage and half wave rectifying it and then filtering it with a low cut off low
pass filter. This low pass voltage is then input to the four-channel A/D con-
verter. The software in the processor determines the user-selected
threshold for -20, -40, or -60 dBu level input.
Hard-wired Fine Gain and Balance Potentiometers
The hard-wired gain and balance controls uses a 10k ohm potentiometer to
ground on the two unbalanced BNCs J11 (Gain) and J12 (Balance) at the
back of the frame. These potentiometers adjust fine gain and fine balance
(± 6 dB range). U15 C&D buffer and offset the current created at their inputs
by the gain and balance potentiometers. The processor reads the A/D and
translates the reading into a gain or balance value to the digital potentiom-
eters and stereo volume control. The Local/Remote jumper on the module
circuit board must be set to LOC/POT for these pots to function.
