(2)  
AIRPLANES WITH LORAL/FAIRCHILD SOLID STATE VOICE RECORDER; The voice recorder contains these printed wiring assemblies: aircraft interface, audio processor, and the store processor. The aircraft interface card connects the airplane wiring to the voice recorder. The audio processor card accepts the four channels of data and converts this to digital data to store into the solid state memory. The store processor card encodes the data and supplies it to the crash protected memory.

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A 737-300/400/500MAINTENANCE MANUAL
 4.  Operation (Fig. 3)_________
 A.  The voice recorder system automatically records the latest 30 minutes of communications and conversation in the flight compartment. The system is in operation whenever 115-volt AC power is applied to AC bus No. 1. Communications and interphone audio from the first observer's, the first officer's and the captain's audio selector panels is applied to channels 1 through 3 respectively of the voice recorder. Conversation in the flight compartment is picked up and amplified by the microphone and preamplifier in the voice recorder control panel and applied to channel
 4.
 NOTE:____Hot microphone recording is used. That is, audio from the captain's, first officer's, and observer's boom or oxygen mask microphone will be recorded even with all control wheel and audio selector panel PTT switches in the off positions.
 B.  AIRPLANES WITH LORAL/FAIRCHILD TAPE BASED VOICE RECORDER; The 65-kHz bias frequency for all four recording amplifiers is generated by a common bias generator. This frequency is also used to drive the erase head, that removes previous information from the tape before recording.
 (1)  The bias frequency is used in an audio frequency tape recorder to shift the audio band upward to a frequency range suitable for operation of ac amplifiers, inductive recording and playback heads. The bias frequency is introduced in the recording amplifier and removed in the monitor amplifier. Each recording amplifier drives an inductive (electromagnetic) recording head which produces a varying magnetic field. As the tape transport moves the tape past the recording head at a constant speed, the varying magnetic field produced by the head magnetizes the magnetic oxide film on the tape producing a magnetic track of varying strength. As the magnetic track moves past the playback head, it induces a small varying current in the coil of the head. The monitor amplifier amplifies this signal, removes the recording bias frequency, and furnishes the audio to the recorder output.
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A 737-300/400/500MAINTENANCE MANUAL

LANDING GEAR ACCESSORY UNIT

TEST SWITCHES FOR FAIRCHILD VOICE RECORDER UNIT MODEL A100 ONLY
Voice Recorder System Schematic Figure 3 (Sheet 1)
F13431
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UNIT
Voice Recorder System SchematicFigure 3 (Sheet 2)
C37766
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A
737-300/400/500MAINTENANCE MANUAL
 (2)  
The playback head and monitor amplifier are used to monitor information recorded on all tracks of the tape. The audio output of the monitor amplifier is available at the MONITOR jack on the front panel of the voice recorder and at the HEADSET jack on the voice recorder control panel. This audio is also supplied to the test meter on the voice recorder control panel.
　
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