2.6 Output Circuitry - Tandy 1000 HX Technical Reference Manual

2.6 OUTPUT CIRCUITRY
The NCR 8496 Sound Generator output circuitry, emulating a
conventional op amp summing circuit, sums the three (3) tone
and one (1) noise generator outputs, and will source/sink
current to 2 mA. The 0 dB output signal per generator is
nominally a 450 mV square in the negative direction from a
2V quiescent level. The output should be OR coupled into
the application audio circuit via a filtering network
similar to the following:
The upper and lower frequency poles for the application are
determined from the following equations:
Typically R
B
^ 10 R* so that the attenuation can be small
while achieving desired filtering at the same time.
2.7 AUDIO INPUT CIRCUIT
This input node can be biased on with a current to give an
approximate transfer function at the output of :
R
fi
provides the bias current to put the amplifier in the
linear range.
R
sig controls the input current causing the signal swing.