Bose OC-1 AWCS-II Service Manual download pdf (Page 4)

THEORY OF OPERATION

Overview

The OC-1 is a small plug-in module for use with Bose 502™, 402™, and 802

II controllers. The

OC-1 allows the use of the Cannon™ bass loudspeaker with these controllers and their

loudspeakers. Refer to the block diagram, equalization curves and OC-1 schematic for further

information.

The OC-1 provides three major functions:

A. Low frequency equalization.

B. Crossover filtering of the high frequency signals.

C. Protection of the Cannon against excessive power.

1. Low Frequency Equalization Circuit

U5's four op-amp stages provide low-pass crossover filtering, high-pass filtering to eliminate

subsonic material, and frequency contouring to optimize the overall response.

2. High Frequency Equalization Circuit

U3, section 1 and U5, section 2 provide two channels of high-pass filtering to remove bass from

the main loudspeakers.

3. Protection Circuit

The protection circuit consists of a compressor and a mute circuit. The protection circuit is

connected so that it can monitor the low frequency voltage applied to the Cannon driver. When this

voltage exceeds the power limit defined for the driver, a compressor begins to reduce the gain in

the low frequency path so that the power does not continue to rise.

4. Compressor Circuit

The compressor consists of the following functional blocks:

A. Differential input buffer

B. Full-wave peak detector/comparator

C. Averaging circuit

D. Voltage-controlled amplifier (VCA)

The differential input buffer (U1 section 1) features protection against Radio Frequency

Interference (RFI), Electrostatic Discharge (ESD), and overvoltage. It has a gain which is much

less than 1 so that it can attenuate the high level signals coming from the Cannon (over 40 volts at

full power).

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Bose OC-1 AWCS-II Service Manual Page 4