Leitch 880 Series, Инструкция по эксплуатации

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880 Series Audio Distribution Amplifiers Instruction Manual 39
Preliminary—Contents are proprietary and confidential. Do not photocopy or distribute.
Chapter 12
ATG-880 Audio Tone
Generator Module
Overview
The ATG-880 is a low distortion audio tone generator with high level-stability.
The module provides 8 outputs, that is, four pairs of outputs, each pair being at a
different level. One output of each pair can be pulsed off and on at a rate of
about once per second.
The basic tone generator is a Wien-bridge oscillator, chosen for its inherent low
distortion. The bridge consists of the RC network at pins 14 and 12 of IC4D and
ground. The network contains two arms. The top arm is series resonant at
400Hz when the switch is open and 1000Hz when closed. Similarly, the bottom
arm is parallel resonant at 400Hz when the switch is open and 1000Hz when
closed. At resonance, the voltage at pin 12 of IC4D is at a maximum with
respect to the voltage of pin 14 while the relative phase angle is zero. In order to
sustain steady oscillation, IC4D must be maintained at a gain of 3. This is
achieved by means of the circuit consisting of IC4A, IC4B, IC4C and IC1A.
The output from pin 14 of IC4D is amplified to a gain of 4 by inverting
amplifier IC4A. Its output at pin 1 is AC coupled through a 68
µ
F capacitor and
diverted to two places, that is, the control loop and the output stage later
described.