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8910ADA-M/ST/SR — Instruction Manual
Functional Description
Inputs and Outputs
There are two balanced audio inputs. Each input has a three-terminal con-
nector.
There are four balanced outputs per channel making a total of eight out-
puts. Each output has a three-terminal connector. The output level
maximum for the 8910ADA_SR is +28dBu when working into a bridging
input.
Processor Section
The serial EEPROM is used to save the serial number of the board, model
number, revision level of hardware and software, and gain calibration. It
also saves the gain and jumper configuration settings that are used by the
board at start up.
Analog Audio Path
The balanced inputs for inputs 1 and 2 are part of a dual balanced receiver
IC. The output of the balanced receivers is routed to the front of the board
where it is inverted and sent back to the non-inverting reference point of
the input stage. This feedback causes the output of the receiver to have a
gain of -12 dB. It also makes available both non-inverted and inverted
signals which are selected by the second stage to correct for inversions at
the input.
The output of the Invert Non-invert Select stage feeds the top of the dual
digital potentiometers. These potentiometers are used to vary the gain in
0.1dB steps between the 0.5dB steps of the volume control that follows it.
High impedance unity gain amplifiers buffer the wiper on the digital
potentiometer to the inputs of the stereo volume control. The stereo volume
control has a gain range of +30 dB to completely mute and is controlled
through a three-wire interface to the processor. The digital potentiometer is
also controlled by the same three-wire interface with both devices daisy
chained together. The digital potentiometer is the first device in the chain
followed by the stereo volume control. When the DA is set for unity gain
(0dB), both the digital potentiometer and the stereo volume will have
approximately 0dB of gain through each device.
The next stage handles channel swapping, monaural, and summing
modes. The transmission switches control these modes for channel 1 and
channel 2 respectively. There is a gain of 10.4 dB through this stage for all
modes except sum. During sum the level of both channels are reduced by 6
dB. Each channel can separately output channel 1 or channel 2 inputs or
sum channel 1 and channel 2 to its output. To do a channel swap, channel
2 input is selected for channel 1 output and channel 1 input is selected for
channel 2 output. A sum of each channel can be done on each output sepa-
rately or at the same time.
