Confused by schematic...

Discussion in 'General Electronics Chat' started by ShockBoy, Nov 15, 2009.

  1. ShockBoy

    Thread Starter Active Member

    Oct 27, 2009
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    Hey, could someone explain what's going on in the upper left of this schematic? The mic only seems to be connected to ground.
     
  2. BMorse

    Senior Member

    Sep 26, 2009
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    It is connected as it should be, bias (red) wire connected to VCC, output going into the 741's - input, and ground....


    My .02
     
  3. ShockBoy

    Thread Starter Active Member

    Oct 27, 2009
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    Thank You. A little confusing seeing an unconnected pin.
     
  4. Audioguru

    New Member

    Dec 20, 2007
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    A 741 opamp is much too noisy (hissss) to be a mic preamp.
    Most electret mics have only two wires, the signal and power pin and a ground pin. A three wire electret mic is rare.
     
  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    What is the purpose of C2, Q1, and R4? Whatever it is, it won't work.
     
  6. ShockBoy

    Thread Starter Active Member

    Oct 27, 2009
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    Huh? Oh Dear God. Tell me it isn't so. Rare as in ... ? jackalope? what. All the electret mic's I have are 2 pin. Ron, Check ecelab.com, they have the copy/original there - though without the word 'red'. I'm just trying to use an op amp to boost mic signal to blink a light. I.E. led. Need help; that's why I'm here, you awesome folks you are.
     
  7. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    When you provide a link, try to be more specific. Ecelab has hundred of links on their main page.
    And it wouldn't matter if it were on God.com, it won't work without a resistor or diode (anode to GND) from the base of Q1 to ground. A resistor in series with C2 would be a good idea also.
     
  8. ShockBoy

    Thread Starter Active Member

    Oct 27, 2009
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  9. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Here's a place to start:
    Change the power supply to 9 volts.
    Add a 1 megohm resistor from the base of Q1 to ground.
    Add a 1k resistor in series with C2.
    Change R4 to 680 ohms, and add an LED in series with it.
     
  10. ShockBoy

    Thread Starter Active Member

    Oct 27, 2009
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    Thank You Very Much Ron. I will use your advice.
     
  11. ShockBoy

    Thread Starter Active Member

    Oct 27, 2009
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    Is it possible to swap the lm741 with a standard dual op amp like the 4580dd jrc?
     
  12. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    That should work. Disable the unused op amp if you're not using it. One way to do this is to connect the + input to the junction of R2 and R3, and the output to the -input.
     
  13. ShockBoy

    Thread Starter Active Member

    Oct 27, 2009
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    Thanks Ron, will give this a shot.
     
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