Bose OC-1 AWCS-II Service Manual download pdf (Page 5)

U4, sections 1 and 2 form a full-wave peak detector. When the input to these stages exceeds

+/-2V peak, the outputs go high and a control voltage is created in the averaging circuit (C27, C28,

etc.). The averaging circuit captures peaks with a short attack time and holds them with a longer

release time. U2, section 2 inverts and scales the averaged control voltage and applies it to the

VCA control input.

U7 is a current-in/current-out VCA which is controlled by the voltage on pin 2.

5. Mute Circuit

The mute circuit acts as a watchdog, and prevents the Cannon™ from operating unless the

feedback signal from the Cannon is connected properly to the controller/OC-1 protection input.

When the mute circuit detects that no audio has occurred for about two minutes, it reduces the gain

in the low frequency path.

The mute circuit consists of a gain stage and a comparator. U1, section 2 amplifies the signal from

the protection circuit differential input, and U2, section 1 compares it to a reference. When the

sensed level exceeds the threshold, a control voltage (generated in U2, section 2) causes U2,

section 1 to go from high to low and reduces the compressor gain by about 40 dB.

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Bose OC-1 AWCS-II Service Manual Page 5