Audio Amp

Discussion in 'The Projects Forum' started by crivoli, May 11, 2006.

  1. crivoli

    Thread Starter Member

    May 4, 2006
    26
    0
    I have built the following circuit but the sound quality is terrible.

    Any ideas on how to make the sound quiality MUCH better?

    I am using an electret mic and an 8 ohm speaker. Thanks

    [​IMG]
     
  2. Papabravo

    Expert

    Feb 24, 2006
    9,910
    1,724
    You might start by giving us some component values and part numbers. What are we supposed to do, use our extraordinary powers of extra sensory perception to read your fevered brain. Give us a break for pity's sake.

    Some questions you might want to ponder.

    What is the gain of the amplifier in this configuration?
    What do the input and output levels look like?
    What is the slew rate of the amplifier?
    Is the output being clipped?
     
  3. n9xv

    Senior Member

    Jan 18, 2005
    329
    1
    I think this is the amp in question. I copied & pasted from crivoli's other post under projects. I think parts of the circuit in the above attachment were missing.
     
  4. Papabravo

    Expert

    Feb 24, 2006
    9,910
    1,724
    Well OK, looks like the gain of the amplifier is 20 to 30 dB.
    He replaced the vlume control with a fixed resistor.
    What did he do with the other amp in the package? I'll bet he left the inputs wide open. A bypass cap on the Vcc pin couldn't hurt.
     
  5. crivoli

    Thread Starter Member

    May 4, 2006
    26
    0

    I am using

    1K resistors for Rb,
    a 1M resistor for R2,
    a 1K resistor for R1,
    a 10uF cap as already seen,
    a .47uF cap for the coupling cap from the mic to the IC,
    a LM741 IC and a 68uF cap out of the IC to the speaker....

    Sorry for not posting the specs
     
  6. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,590
    777
    gain as high as 1000 is way too much, use something more reasonable, like 20-200, which leads the R2 to 20k-200k.
    What is the amplitude of the input signal?
    If the input is the microphone like in the previous topic, than MAYBE the gain of 1000 is apropriate.

    What amount of power are you planning to get on the output? If you would look at the schematic, then you would see it is PREamplifier. It is not capable of driving an 8-ohm speaker. You should try either a speaker with higher impedance like 200ohm or more, or use some other amp like the good-old LM386, which can handle up to 1W into 8-ohm load, and is perfectly suitable for electret-mike amp.
     
  7. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    I suspect that the LM741 is unable to drive the speaker being used. The amplifier you have constructed constitutes an audio pre-amp. Now what you need is a buffer stage capable of driving the speaker.

    You may be able to get by with a push-pull transistor amp as shown in the link below. This push pulls stage would need to be incorporated into the feed back loop of the stage you already have. This is necessary to prevent the push-pull stage from introducing excessive cross-over distortion.

    Push Pull amp stage

    hgmjr
     
  8. crivoli

    Thread Starter Member

    May 4, 2006
    26
    0
    I switched over to a LM386 design from the datasheet and it works like a charm.

    I appreciate everyone's advice VERY MUCH!!

    Thanks again
     
  9. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    That is great news. Congratulations!

    hgmjr
     
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