Bose PACKLITE A1 Manual page 45

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Amplifier Section (continued)

IC4A and IC4B [D2] provide buffers for the audio input, and provide the ability to accept bal-

anced or unbalanced inputs. The PackLite

configuration.

R21, R24, R25, R26 [A/B3] provide resistive dividers to determine the under and over-voltage

protection thresholds.

R36 [C3] is assembled (0 Ohms), and R37 [C3] is not, which turns off the on-chip under-voltage

protection feature. See Pre-amplifier Enable Circuitry in section 6 for under-voltage protection.

N1 and R18 [C6] provide a temperature-sensitive voltage to protect the output FETs. The

voltage is fed to ICC1 [C3] where it can initiate a thermal shutdownof the amplifier above 120

degrees C, and is brought externally to J302, pin 1 [Input/Limiter PCB Schematic Sheet 1, C8].

Other signals provided externally on connectors:

•

Enable (bidirectional/open collector, can signal that the amp has shut down, or can be used

to shut down the amp)

•

OC – output, over current protection, or Zobel protection is active

•

TH – ouput – signals that the amp has shut down based on it's NTC input (N1)

•

Vdd – 5 Volts output for detection tht power is on

•

Control Ground

C45 [D2], C65 [C8], C66 [B8], and R40 [C8] are not assembled. L8 [C8] provides common

mode filtering of radio frequencies for FCC and EN55103 emissions compliance.

The voltage on the Zobel network is divided by R15 [C6] and R17 [C7] (and R31 [A6], R32 [A7])

and sensed by IC3 (ICC1) [C3], and will shut down the amplifier as represented below in the

following curve:

THEORY OF OPERATION

A1 amplifier uses the inputs in an unbalanced

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