60
Theory of Operation
IC4A and IC4B [D2] provide buffers for the audio input, and provide the ability to accept bal-
anced or unbalanced inputs. The amplifier uses the inputs in an unbalanced 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:
To Next Page
Loading...
Need help?
General
