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LM386: 250-350 hertz NOISE in audio amplifier circuit (LM386 )

mohit rai
Prodigy 40 points
Part Number: LM386

Hello,

I am using LM386 audio amplifier circuit for my application. My input for the LM386 amplifier is the DAC output (microcontroller). But when I  am playing my signal, 250-350 hertz sound is also present.

what can be the cause of this problem?

Before potentiometer 10 microfarad capacitor is also connected to remove DC signal. 

Thanks in advance.

Regards,

Mohit Rai

  • 0
    TI__Mastermind 20085 points
    Hello Mohit Rai,

    Welcome to E2E, thanks for your interest in our devices.
    You could share me more details about your application, and could you provide me a schematic of your system?

    Best Regards
    José Luis Figueroa
    Audio Applications Engineer
  • 0 in reply to José Luis
    Prodigy 40 points
    Hello Sir,

    Thank you for your reply. I am using the same schematic that is present in LM386 datasheet. I have designed that schematic on bread board.
    5 volt supply is used to power the amplifier circuit. Microcontroller board is used for power supply.

    Real time,I am recording sound using electret microphone using ADC (microcontroller board ) and playing that sound using DAC (microcontroller board). My DAC output is connected to LM386 amplifier circuit.

    is there any need to match the output impedance of LM386 amplifier to speaker input impedance(4 ohm)?
    or
    DAC output impedance to input impedance of LM386 audio amplifier circuit.

    Thanks

    Regards,
    Mohit Rai
  • 0 in reply to mohit rai
    TI__Mastermind 20085 points
    Hi Mohit rai,

    I have a question, which is the frequency present in the output signal? because 250-350 Hz is in the audible range, perhaps you mean 250-350 KHz.

    Best Regards
    José Luis Figueroa
    Audio Applications Engineer
  • 0 in reply to José Luis
    Prodigy 40 points
    Hello Sir,

    When I am playing 200 hertz sound, in output signal 250-350 hertz frequency component is also present.

    I have made some changes in my circuit.
    I have connected 16kohm resistance at the input pin of the LM386 amplifier to match the impedance of DAC(DAC impedance is 12.5 K-ohm). When I use 234 hertz low pass filter(R=68 ohm & C= 10 micro Farad) 250-350 hertz frequency component is removed.

    But my signal amplitude is also reduced.

    DAC OUTPUT--> LPF-->AC coupling capacitor--->LM386 input

    16Kohm resistance is also connected between the LM386 input pin and ground.

    Please, suggest if any changes needed on the circuit.

    Thanks

    Regards,
    Mohit Rai
  • 0 in reply to mohit rai
    TI__Mastermind 20085 points
    Mohit rai,

    It seems that the problem is in the previous stages. As you mentioned the low pass filter removes this undesirable frequency component, it means that the amplifier is not producing the problem.
    You must review the previous stages in order to track the issue.

    Best Regards
    José Luis Figueroa
    Audio Applications Engineer
  • 0 in reply to José Luis
    Prodigy 40 points
    Hello Sir,

    Thank you sir. I will check and try to find out the issue.

    Thanks
    Regards,
    Mohit Rai