User's Manual

STEREO CODER BOARD OPT023

DESCRIPTION

The board contains the stages needed for the conditioning of the Left channel audio signal and for realising the

stereo encoding in compliance with the standard ITU racc. 450. The Right signal is provided through the

connection to the Mother board. The various sections are analysed below:

1. Balanced/Unbalanced Converter: the conversion from balanced to unbalanced and the input interface

of the audio signal are realised la electronically by the IC1-A operational circuit. This assures an high ge-

gree of immunity from disturbances and a perfect symmetry in unbalancing.

2. Pre-emphasis: after the level adjustment, there is the active pre-emphasis stage (IC1-B), with amplification

to high frequencies. The time constant is chosen between 25 and 50 microseconds by means of two jum-

pers (JP1-2). When they are both enables they give 75µs (for the FCC standard). The insertion of the

pre-emphasis is managed from the frontal panel by activating the electronic switch IC3.

3. Low-pass Filter: the use of two filtering stages with elliptical filters LP1 and LP2 assures the adequate suppres-

sion of input signals at frequencies 19k and 38kHz.

4. Peak Detector: before the emphasis circuit, part of the audio signal is sampled to provide the indication of

the LEFT channel deviation on the frontal display. IC4-A serves as buffer for the duplicator and peak de-

tector.

5. Stereo Coder: stereo encoding is realised inside the MPX1 block, providing the MPX signal in output.

SCH0378AR2 Component layout