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The Electronics of Radio by David Rutledge

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13Audio Circuits

There are two audio circuits in the NorCal 40A, the Automatic Gain Control, or AGC, and the Audio Amplifier. The AGC is an attenuator with JFETs that act as variable resistors. The Audio Amplifier is the LM386N-1, made by National Semiconductor. This integrated circuit appears in many different audio systems, and it costs about a dollar. The “–1” indicates a supply voltage range from 4 to 12 V. A “–4” version is available that allows a supply voltage up to 18 V. For the LM386N-1, the maximum output power is about one watt. In standby, it draws about 4 mA, which is a reasonable level for running off batteries.

13.1 Audio Amplifier

Figure 13.1 shows the schematic for the LM386N-1. It is more complicated than the previous circuits ...

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