Audio amplifier using only 1 op-amp [single supply]

  1. As the thread suggests, I am trying to amplify the signal from a microphone.

    Now, I have a circuit which uses 2 op amps with dual supply.

    That circuit works pretty well.


    I have to make now, a amplifier using only one op amp, single supply.


    The sound itself isn't of much importance, I just need the signal, it can be distorted(a little),

    because I am not sending that signal to a speaker, but to a LED driver, in bar mode.


    I attached a circuit.

    Can this be done with only 1 op amp, and if it can, can somebody suggest me a circuit?

    Thank you.

    p.s. I am using elecrtet microphone.
     

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    Last edited: Feb 20, 2012
  2. jcsd
  3. jim hardy

    jim hardy 5,139
    Science Advisor
    Gold Member
    2014 Award

    my browser is giving trouble cant see your sketch
    anybody else getting 502 errors on IE?

    anyhow,
    check LM386 it's a versatile little audio amplifier
     
  4. Hmmm. I will buy it tomorrow. This may as well solve my problem!

    It even works with single supply! Thank you mr. Jim!
     
  5. psparky

    psparky 884
    Gold Member

    Not sure I get your question.

    Why not just use any op amp with a resistor in the feedback and a resistor in the input? Gain will be -RF/Ri if the + terminal is grounded. If the negative output is a problem.....put your input into the positive terminal.....ground the former input resistor....and the same feedback resistor. Gain will be (1+ RF/Ri)

    If you need to filter out high end frequencies....put a capacitor in parallel with the feedback resitor. If you want to get rid of lower frequencies....put a resistor in series with the input resistor?

    Break frequencies happen at 1/(2*pi*R*C)?

    The basics of op amps right? Am I missing something......probably!!!

    I'm more than sure the LM386 will work great....but wouldn't pretty much any op amp work as long as it has the required power you need?????
     
  6. Problem was mainly because, my microphone was driving the op amp into negative saturation.

    So I had to raise the voltage on the +ive lead. That solved the problem. Or so I thought. Now I had problem with gain. I put a 100 000 ratio resistors, but op-amps frequency characteristics knocked in, and I was pretty much nowhere. Then I thought, why not use again 2 op amps with single supply. I tried that, with different resistor ratios, and I was almost there, but I couldn't get the gain needed. I wasn't amplifying all frequencies equally enough(I think that was the problem). I did work on this like half an hour(spent 4h working on other parts of this project), was really tired, I will try again tomorrow(this with 2 op amps)

    So I will probably go with this IC mr. Jim suggested. That looks like a winner, and I don't have to bust my head with 2 op amps.
     
  7. psparky

    psparky 884
    Gold Member

    Wow....the LM86 costs a whopping 2 dollars! Not bad.

    For fun....play with some capcitors in the feedback in paralell.....and some capacitors in series to see if you can cut off low and high frequencies outlined to what I said above.

    If you get it to work....you just designed a basic "equalizer". Put in a variable resistor in the feedback and you now have a volume control.
     
  8. psparky

    psparky 884
    Gold Member

    Oh....I was just able to really zoom in on your drawing......you certainly did use to op amps as non inverting amps.....cool.

    I guess having an op amp powerful enough is your only issue. Might wanna check the specs on the LM386 before you get it. Then again...for $2, no biggy.
     
  9. Yes I am enjoying this very much. And here at my store, LM386 is a dollar :P

    Will try that!

    This project was something my teaching assistant gave me, you know, for fun. Problem is, I don't have oscilloscope at home, nor dual supply, so I am limited to my lab at university.
     
  10. jim hardy

    jim hardy 5,139
    Science Advisor
    Gold Member
    2014 Award

    LM324 is a great little single supply opamp but not much current drive and not real fast.

    It'll run from a 9v battery or wall-wart .

    I bought a tube of them, lifetime supply, for just a few bucks..
    4 amps in a 14 pin DIP!
     
  11. It's been bad the last few days, I couldn't get in for a few hours two days ago and this is the first time I can get in today. Yes, 50x error.
     
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