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LM386
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Voltage controlling the gain of an LM386

3 years ago 1248
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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.

Documents

Voltage controlling the gain of an LM386

BOM

ID Name Designator Footprint Quantity BOM_Manufacturer Part
1 8 RSPKR1,RSPKR2,RSPKR3 1X02 3 ?
2 220u C3,C4,C7 CP_8X13MM 3 ?
3 SINE(0 10m 1k) V1 2P-5.0 1 ?
4 9 V2 2P-5.0 1 ?
5 LM386EE U1,U2,U3 DIP 3 ?
6 10u C1,C5,C8 CP_8X13MM 3 ?
7 47n C2,C6,C9 CAP_CERM_DISC_4.7N_3KV_VISHAY_564R30TSD47 3 ?
8 10 R2,R4,R5 0805 3 ?
9 2N5639 J1 TO-92 1 ?
10 1Meg R1,R3 0805 2 ?
11 sin(-4.2 4.2 100) V3 2P-5.0 1 ?
12 27k R6,R7 0805 2 ?
13 sin(4.2 4.2 100) V4,V5 2P-5.0 2 ?
14 2N3904 Q1,Q2 SOT23 2 ?

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