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|Power Supply||Variable Frequency Oscillator||Carrier Oscillator||Audio Amplifier|
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The receiver audio amplifier uses popular low noise IC LM386. Operational amplifier IC 741 is used as preamplifier. Both LM386 and 741 are available in 8 pin DIP.
LM386 is designed for operation with power supplies in the 4 V to 15 V range. Quiescent current is about 4 ma. Its input impedance is 50 K. Output automatically centers on a quiescent half supply voltage value. It provides 250 mw to 8 E speaker, which will be sufficient for comfortable listening level. The gain can be adjusted between 26 dB and 46 dB depending on the circuit at pin 1 and 8. Here LM386 is configured for 26 dB gain.
IC 741 is a very popular Op Amp. Many makes of IC 741 such as LM 741, AM 741, CA 741, UA 741, µA 741 are available in market. Op Amps have two input terminals. For IC 741 pin 2 is inverting input, pin 3 is non-inverting input. Supply voltage can be in the range of 5 V to 18 V. Input impedance is 200 K. Here Op Amp is configured as inverting amplifier. Its gain can be adjusted by changing the value of resistance between pin 2 and pin 6.
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