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# How to calculate gain of the LM386 in this circuit?

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#### danesh

##### Full Member level 3
calculation of the lm386

hi ,

do anyone know hw to calculate gain for this circuit?

lm386 gain control calculation

LM386 is not operational amplifier. It is Low Voltage Audio Power Amplifier and you must look at the datasheet for this chip. Then all will be clear.

op amp calculation

GAIN CONTROL
To make the LM386 a more versatile amplifier, two pins (1 and 8 ) are provided for gain control. With pins 1 and 8 open the 1.35 kΩ resistor sets the gain at 20 ( 26 dB ). If a capacitor is put from pin 1 to 8, bypassing the 1.35 kΩ resistor, the gain will go up to 200 ( 46 dB ). If a resistor is placed in series with the capacitor, the gain can be set to any value from 20 to 200 ..

Regards,
IanP

op-amp calculation

danesh said:
hi ,

do anyone know hw to calculate gain for this circuit?

If you neglected the fact that the LM386 isn't ideal opamp, and you just want to calculate gain of the circuit assuming block of ideal opamp, then i think it's easy to get gain of the circuit..

You can start with assuming no input current to the opamp, and that equal voltages are there on positive and negative input terminals of the opamp, and go with it, you will find the gain,
BR

op-amp gain calculation

You shouldn't use the resistor divider though. You should use pins 1 and 8 to vary gain.

calculation = gain = (gain of op amp) * (r2/(r1 + r2))

ideal opamp current calculation

The variable input resistor is presumably volume control. The overall gain of the amplifier, assuming you leave pins 1 and 8 open, can therefore vary from 0 to 20. As kevinj said previously, the overall gain is 20 (gain of the amplifier) times the voltage divider ratio.

Re: Op amp calculation

I'm agree with opinion of Kenivj

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