Audio driven led question

Discussion in 'General Electronics Chat' started by ShockBoy, Apr 14, 2010.

  1. ShockBoy

    Thread Starter Active Member

    Oct 27, 2009
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    Hi. Would I use an inverting or non-inverting op amp design for using an electret mic to flash a single led?
     
  2. Audioguru

    New Member

    Dec 20, 2007
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    An electret mic and the resistor that powers/loads it are a faily high impedance (about 2.5k). If an inverting opamp is used then its low input impedance might reduce the output of the mic.
    So a non-inverting opamp with a fairly high input impedance (12.5k and higher) is the best preamp circuit.
     
  3. ShockBoy

    Thread Starter Active Member

    Oct 27, 2009
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    I will go with the non-inverting opamp then. You mention the preamp circuit, isn't that just the use of a vcc to a resistor and capacitor off the positive point of the mic? Are you talking about using the opamp as the pre amp?
     
  4. Audioguru

    New Member

    Dec 20, 2007
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    Yes, the opamp is the preamp. It can also turn on the LED when the input signal is high enough.
     
  5. ShockBoy

    Thread Starter Active Member

    Oct 27, 2009
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    Would I need a dual opamp for this?
     
  6. retched

    AAC Fanatic!

    Dec 5, 2009
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    If the output of the first opamp isn't high enough, you can trigger an NPN or use another opamp.
     
  7. ShockBoy

    Thread Starter Active Member

    Oct 27, 2009
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    Thanks. I'm planning on using the LM358n. I might need some assistance on the schematic for this circuit.
    Question: Does the electret mic create AC? Impedance relates to AC from what I understand. I plan on using a 9v battery for this, that's not AC.
     
  8. Audioguru

    New Member

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    An LM358 is too noisy (hiss), has high crossover distortion and has a bandwidth too narrow to be used as a mic preamp. Many low noise opamps are made. I use a TL071 single, TL072 dual or TL074 quad opamp that are low noise, have very low distortion and have a bandwidth that goes high enough for audio.

    Here is a preamp for an electret mic:
     
  9. ShockBoy

    Thread Starter Active Member

    Oct 27, 2009
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    Thank you for the preamp schematic. Would the 'hiss' of the 358 cause the led to flicker uncontrollably? I will look for the 071.
     
  10. Audioguru

    New Member

    Dec 20, 2007
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    It depends on the amount of gain you set for the opamp.
    What sounds and how far away are they from the mic?
     
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