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Voltage controlling the gain of an LM386

2 years ago 984
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Description

Three simple ways to voltage control the gain of an LM386.

1) Using a JFET as an AC coupled variable resistor from pin 1 to ground. This works reasonably well and has relatively low distortion.

See:

Vishay AN105. FETS as voltage controlled resistors.

http://www.vishay.com/docs/70598/70598.pdf

2) Using an NPN BJT in place of a JFET. This works but produces relatively high distortion.

3) Using an NPN BJT between pin 8 and in 1. This does not control the gain well. It produces high distortion and injects a high level of control voltage feedthrough into the output signal.

Note that in all cases the gain control range is only about 20dB (i.e. x10).

CTRL+R to run the simulation.

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Voltage controlling the gain of an LM386

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