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Low frequency Amplifer

Discussion in 'General Electronics Discussion' started by Twodio, May 17, 2013.

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  1. Twodio

    Twodio

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    May 17, 2013
    Hey guys.
    I'm trying to construct a circuit that can convert litles vibrations into a more higher.
    I want to use only one transistor NPN one LED somes resistors, one capacitor, one electreto mic and one speaker.
    The problem is when i try put working doesn't happen nothing.
    Someone can help me or pass me another way to make.
     
  2. BobK

    BobK

    7,682
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    Jan 5, 2010
    One transistor is unlikely to get you from an electret mic to a speaker. Show us your circuit.

    Bob
     
  3. Twodio

    Twodio

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    May 17, 2013
    The schematic of my circuit is one like this
    [​IMG]

    With two NPN transistors and one adapted LED that doesn't disturb the power traffic
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,496
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    Jan 21, 2010
    The comment about the LED doesn't make any sense (especially since there is no LED there).

    the 220k resistor should be connected between the base and the +ve terminal of the battery.

    This circuit will draw significant power (it's class A) *and* a DC current flows through the speaker (which is generally a bad thing)

    edit: google for the LM380 or LM386 (depending on the power you require).
     
  5. Twodio

    Twodio

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    May 17, 2013
    Exist one class B or C ?
     
  6. BobK

    BobK

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    Jan 5, 2010
    Not necessarily, the way it is shown, it will have negative feedback to stabilize the bias. Otherwise, an emitter resistor is needed.

    Edited to add: I don't think you get anything like 200mV out of an electret mic, more like 5mV. And an electret mic needs a power connection, if it is not built in.

    Bob
     
  7. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    The bias resistor can be split into two resistors with their common node bypassed to gnd with a cap. This maintains bias stability while removing negative signal feedback. ;)

    Chris
     
  8. Twodio

    Twodio

    35
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    May 17, 2013
    Thank you everybody that try help me.
    I'll try simulate first until get something higher that 250mA and produce some loud.
     
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