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Audio Power Amplifier with tonal controls

Discussion in 'Homework Help' started by Yash_avengers, Sep 28, 2015.

  1. Yash_avengers

    Yash_avengers New Member

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    The requirements are a minimum of 8W RMS power to 8Ω speakers with a maximum of 1% second harmonic distortion and 0.2% third harmonic distortion.
    Can anyone help me decide the Class AB amplifier which fits the specifications! Also need help for tonal controls circuit design.
     
  2. Inquisitive

    Inquisitive Super Moderator

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    Is this a homework assignment?
     
  3. Yash_avengers

    Yash_avengers New Member

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    Yes, actually kinda project!
     
  4. dave

    Dave New Member

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  5. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Welcome to ETO!
    I suggest you research 'Baxandall'.
     
  6. Yash_avengers

    Yash_avengers New Member

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    Any suggestion for Amplifier?
     
  7. audioguru

    audioguru Well-Known Member Most Helpful Member

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    There are maybe 50 IC amplifiers available that are much better than the spec's you have. Or must you make an amplifier from transistors, resistors and capacitors and design the circuit yourself or find one in Google and simply copy it?
    You might find a circuit that works or you might find a circuit that does not work.
     
  8. Yash_avengers

    Yash_avengers New Member

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  9. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Read the datasheets for the transistors used in the hackaweek link. Consider that you want an 8W amp.
     
  10. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The hackaweek amplifier is a horrible design:
    1) The transistors are biased wrong so the output badly clips off the bottom of every waveform.
    2) The poor weak output transistors have a maximum allowed current of 200mA and perform poorly above 50mA but in this circuit if the output is trying to be 7V peak-to-peak which is 3.5V peak then their current is 3.5V/8 ohms= 438mA.

    The input impedance of that awful circuit is very low. If the signal source also has a low impedance then it shorts the negative feedback which causes the distortion to be much higher. So I added a series input resistor my R4.

    I simulated it to show you and changed the output transistors to more powerful ones and fixed the bias point. My fixes produce low distortion and 7.3V p-p output. 7.3V p-p is 2.58V RMS then the power into the 8 ohm speaker is (2.58V squared)/8 ohms= 0.83W.
    The amplifier output is only 1/10th what you need. It needs a higher supply voltage, more powerful output transistors and probably driver transistors.
     

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  11. audioguru

    audioguru Well-Known Member Most Helpful Member

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    To see if you know how to do the simple arithmetic:
    1) How much RMS output voltage is needed?
    2) How much peak-to-peak output voltage is needed?
    3) What supply voltage is needed for the 8W amplifier?
     

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