Broadcast Electronics AM-2.5E, Руководство пользователя

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1-98. The battery backup system is equipped with a battery save function. If no fault
conditions have occurred during a power failure, NOR gate U55 will output a HIGH to
AND gate U71C. With a HIGH shutdown signal, U71C will output a HIGH to latch
U49D. U49D will output a HIGH to bias transistor Q52 off to terminate battery
operation.
1-99.
EXCITER CIRCUIT BOARD.
1-100.
LEFT/RIGHT CHANNEL INPUT CIRCUIT.
Left/right channel audio from the studio or
audio processing equipment is applied to the exciter circuit board left and right channel
input circuits (refer to Figure 1-2). The input circuits consist of: 1) RFI filters,
2) high-pass filter networks, 3) instrumentation amplifiers, 4) high frequency boost
circuitry, and 5) active PWM filter equalizers. The left and right channel input circuits
are identical. Therefore, only the left channel input circuit is discussed.
1-101. Left channel audio is applied to a balanced 600 Ohm resistive impedance network and an
80 kHz RFI filter network. The impedance and RFI filter networks are located on the
motherboard assembly. The output of the circuitry on the motherboard is applied to a
defeatable 10 Hz high-pass filter network consisting of capacitors C147 through C150 and
jumpers P12A and P12B. The 10 Hz high-pass filter is provided to remove low frequency
residual products from specific audio processing units. Jumpers P12A and P12B are
provided to bypass the high-pass filter networks. The output from the high-pass filter
network is applied to an instrumentation amplifier.
1-102. Integrated circuits U1A, U1B, and U2A are configured as an instrumentation amplifier
circuit. The circuit is designed to provide balanced-to-unbalanced signal conversion.
The output of the instrumentation amplifier is applied to a defeatable high frequency
boost circuit. The high frequency boost circuit is designed to increase high frequency
response to compensate for a Bessel filter in the pulse-width-modulation (PWM)
modulator circuit. If the high frequency boost circuit is enabled, the circuit will result in
a compromise between the frequency and transient response performance. If the high
frequency boost circuit is enabled, the transmitter frequency response will increase
approximately 2 dB at 10 kHz and the transient response will degrade. If the high
frequency boost circuit is disabled, the transmitter frequency response will decrease 2 dB
at 10 kHz and the transient response will improve. Programmable jumper P2 is provided
to bypass the left channel high frequency boost circuit if required. The output of the high
frequency boost circuit is routed to an active PWM filter/equalizer and a mono mode
switching circuit.
1-103. Integrated circuits U3A and U3B are configured as an active PWM filter/equalizer. The
PWM filter/equalizer is a fifth order low-pass filter. The filter is incorporated into the
circuit to match the characteristics of a filter contained in the pulse-width-modulation
(PWM) circuitry. The filter is required to provide: 1) accurate left and right channel
metering and 2) superior stereo equalization. The output from the PWM filter/equalizer
is routed for application to the stereo circuit board.