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simple amplifier for LME49710

Discussion in 'General Electronics Discussion' started by solder_flux, Jul 22, 2013.

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  1. solder_flux

    solder_flux

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    Jul 22, 2013
    I have this high quality, hi-fi amplifier called LME49710 (http://www.ti.com/lit/ds/symlink/lme49710.pdf). I want to have an amplifier (not preamplifier) circuit that's very simple and bare minimum, yet still high quality enough to amplify mostly the audio frequency that a human ear might pick up... (for music). There is a demo circuit for a "NAB Preamp" at pg 19 of the manual... would that do??
     
  2. BobK

    BobK

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    Jan 5, 2010
    That part is an operational amplifier that is used for low-level to line-level signals. It is not a power amplifier that can drive a speaker, if that is what you are thinking of. There are plenty of IC power ampliifers out there.

    Bob
     
  3. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
  4. solder_flux

    solder_flux

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    Jul 22, 2013
    i simply want signals as low as the ones coming from my headphones jack to be amplified to drive an 8ohm, < 0.5W speaker (quite small) driven with a small voltage (around 3V), with almost no loss in quality and very, very compact. which is why i picked that opamp.
     
    Last edited: Jul 26, 2013
  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Ah, some information about what you want to do! That's a help. but it's not enough.

    How compact is compact?

    What is your power source? You mentioned 3V, is that your power source? Are you planning on powering it from a coin cell?

    Generally, small eight ohm speakers have very poor sound quality - specifically, a narrow frequency range and a mountainous frequency response graph. So even with a very high quality amplifier you will not get good sound from a common small speaker.
     
  6. BobK

    BobK

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    Jan 5, 2010
    To get a 1/2 W into 8 Ohms, you need:

    Vrms**2 / R = 1/2

    Vrms**2 = 4

    Vrms = 2

    But that is the RMS voltage, so you have to multiply by sqrt(2) to get the peak voltage, so

    Vpeak = Vrms * sqrt(2) = 2.828V

    In a perfect world you could get this by using a bridged amp at 3V, but not in reality. There are chips out there that use a bridged configuration to get as much as 1/4 W out of 3.3V in. Here:

    http://www.mouser.com/ds/2/405/slos229d-122109.pdf

    Bob
     
  7. solder_flux

    solder_flux

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    Jul 22, 2013
    just let me worry about the speakers -- those are just the approximates. anyways, let's pretend that i'm stuck with the LME49710. for the sake of minimal size and component count, would the configuration of NAB Preamp in p 19 do?

    could we make it more responsive or have higher gain by adding just 2 to 3 more components??
     
  8. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    You're asking strange questions. How about first answering some of the questions on this thread that are directed at you. Some of mine, perhaps. Maybe even ALL of them! Go on, make my day!
     
  9. BobK

    BobK

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    Jan 5, 2010
    As I told you before, that part cannot power speakers. It is not a matter of quality, it just cannot do it. If you read the datasheet, it is designed to power loads down to 600 Ohms. A speaker is 8 Ohms.

    And about size: the part I linked to is tiny, about 1/4 in square, and requires only 2 resistors and 2 capacitors to complete the circuit. I could build this on a 1/2 in square pc board.


    Bob
     
    Last edited: Aug 1, 2013
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