Audio Preamp Help

Discussion in 'General Electronics Chat' started by MDK, Mar 17, 2008.

  1. MDK

    Thread Starter Member

    Feb 1, 2008
    22
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    I'm working on a audio preamp that does not work all i hear is buzzing please take a look.
     
  2. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    567
    12
    There are many things wrong, most notably, no feedback. Please google "op amp design" or look at applications within a datasheet.
     
  3. Audioguru

    New Member

    Dec 20, 2007
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    The opamp without negative feedback has a voltage gain of about 200,000 to 1 million.
    Its ouput is over-amplified mains hum radiation that is picked up by the input wires.

    Your two 150 ohm input resistors are in parallel and will short whatever drives them.

    What is the input from? An electret microphone?
     
  4. cumesoftware

    Senior Member

    Apr 27, 2007
    1,330
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    It really depends on the amp, really. The LM386 has an internal feedback loop with a gain set to 20. Nevertheless if you are using other kind of amplifier, it might need a negative feedback loop. It will need a feedback network for sure if the IC is an operational amplifier.

    Please, could you specify the amp you are using?
     
  5. Audioguru

    New Member

    Dec 20, 2007
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    An LM386 is a power amplifier. It is not an opamp and it is not a preamp.
     
  6. MDK

    Thread Starter Member

    Feb 1, 2008
    22
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    The amp is a LM741CN
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
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  8. lespaul

    Active Member

    Jan 30, 2008
    49
    2
    True there are many issues with the circuit you attached. what type of audio preamp are you trying to build? Microphone preamp? Dynamic or hi-Z mic? line level or bnallanced level preamp?
    This will help determine the best circuit for the job...
     
  9. MDK

    Thread Starter Member

    Feb 1, 2008
    22
    0
    It is a mic Preamp
     
  10. Audioguru

    New Member

    Dec 20, 2007
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    You don't have a mic preamp.
    Instead, you have an opamp without any negative feedback so its AC and DC gain are way too high.
    The inputs are shorted together with two 150 ohm resistors in parallel.
    The input is not biased correctly.

    If the mic is an electret type then it needs to be biased.
     
  11. MDK

    Thread Starter Member

    Feb 1, 2008
    22
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    who would you di it?
     
  12. MDK

    Thread Starter Member

    Feb 1, 2008
    22
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    I mean how would you do it?!!!
     
  13. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Did you read the link?!? (???!!!?!???!?!!!???!?!?!?!??!??!!!?............ WTF)
     
  14. Audioguru

    New Member

    Dec 20, 2007
    9,411
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    You need to learn about opamps.
    The link tells you all about opamps.
     
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