low power audio amplifier lm386n

sunil shetty

Other Parts Discussed in Thread: LM386

Hi all, I am using lm386n audio amplifier for increase voltage of (60mv ) with gain of 50 to the speaker .but out op -amp showing 1.2v instead of 1.5v volts. I am building amplifier circuit as same as given data sheet of lm386...

over 9 years ago

0 Dennis Eichmann over 9 years ago

Guru 74080 points

Sunil,

You have to provide a little bit more information about the circuit you have built up. Do you have a schematic? Or can you draw something? What's the amplifiers supply?

Dennis

0 sunil shetty over 9 years ago in reply to Dennis Eichmann

Intellectual 785 points

Hi Dennis ,

I build circuit as same as which is given in LM386N datasheet ,typical application in datasheet (gain 50) . supply voltage vs is 5V and input voltage is 60mv ..

0 Leo Bosch over 9 years ago in reply to sunil shetty

Guru 23000 points

Why do you expect 1.5V? 60mV x 50=3.0V+/- resistor and capacitor tolerances.

Which frequency and signal shape do you use for measurements?

Does the output saturates?

Do you have a scope picture?

0 Leo Bosch over 9 years ago in reply to Leo Bosch

Guru 23000 points

BTW: The external gain control is AC-coupled, the DC gain = 20, so when applying 60mVDC this will result in an output voltage of 1.2VDC.

0 sunil shetty over 9 years ago in reply to Leo Bosch

Intellectual 785 points

Hi leo ,

your right 160mv *50 =3.0V ,instead of 3.V ,I written 1.5v ..( manual error ) . I am using pure sine wave of 500 HZ frequency . output not get saturated ..

Thanks &Regards

0 Roberto Romano over 9 years ago in reply to Leo Bosch

Guru 27285 points

Leo Bosch said:
BTW: The external gain control is AC-coupled, the DC gain = 20, so when applying 60mVDC this will result in an output voltage of 1.2VDC.

Hi Leo, this is fully OT here but no way.. LM386 is not an operational amplifier but single supply operated audio/servo power amplifier, input can be symmetrical from ground offset compensated but output forever set to mid supply...

so DCOUT= 1/2VCC+(NI-INV)*DCGain. Ac coupled output cut away half VCC term so AC and DC gain are the same. Removing capacitor on feedback network also need adjustment of bias so some additional resistor are to be added to pin 7 to restore 1/2 VCC.

0 Roberto Romano over 9 years ago in reply to sunil shetty

Guru 27285 points

First place this forum is MSP430 related and this is OT.

sunil shetty said:
your right 160mv *50 =3.0V ,instead of 3.V ,I written 1.5v ..( manual error ) . I am using pure sine wave of 500 HZ frequency . output not get saturated ..

This is impossible many way..

You have selected AC gain of 50, feeding 60mV RMS to input of this circuits to be in linear region need generate 3V RMS at output, this cannot be true if this circuit is powered by 5 volt rail!!

3V Rms need a swing of twice the rms value multiplied by squareroot of 2 so 3*2*1.4142 -> 8.485V this require add one more volt to compensate for junction drop and at least 9.5V power supply are required to have non saturated output, so @60mV in 5VDC supply, output is severely clipped (saturated).

Max reasonable output @5V are less than 3.5Vpp so max RMS output -> 1.23VRMS divided gain give max input RMS voltage -> 24.7 mV !!!

So to not saturate don't apply more than 20mV RMS or +13dBmV