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How do I reduce the gain of a mic preamp?

Discussion in 'General Electronics Discussion' started by MattP, May 21, 2012.

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  1. MattP

    MattP

    24
    0
    Oct 4, 2011
    Hello all! I have a microphone preamp, but when I try reducing its gain by having lowish value resistor short the output to the ground (like volume control does, right?), the volume is reduced but so is the bass. This is no good at all!

    Is there any other way that I can simply reduce the gain without affecting bass output?

    Thanks!
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,501
    2,841
    Jan 21, 2010
    you need 2 resistors. Both in series are connected across the preamp output and the input to the next stage is taken across the "bottom" resistor. The resistors should probably add up to something like 10k to 50k. (you might have 51k and 3k9 for instance, or 33k and 18k

    You can make this variable by the use of a device called a potentiometer :)

    If you do this, get one with a logarithmic (or audio) taper.
     
  3. MattP

    MattP

    24
    0
    Oct 4, 2011
    Hi Steve!

    So it should look a little like this?

    output>--------33k------18k----------->next stage
    ground>----------------------------------->ground

    How come two resistors are necessary? I have a feeling that I'm misunderstanding your directions.
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,501
    2,841
    Jan 21, 2010
    No, the the 2 resistors go from the output to ground, in series.

    then you take the attenuated output from the junction of the 2 resistors and ground.
     
  5. MattP

    MattP

    24
    0
    Oct 4, 2011
    Ohh, OK.

    Code:
    output>--------|
                   R1
                   |
                   |-------->next stage
                   |
                   R2
    ground>--------|--------->ground
    

    Is that right? Sorry if I've got it wrong again; I'm a bit of a dunce when it comes to this kind of thing. :)

    Thanks for your help so far Steve, I appreciate it!
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,501
    2,841
    Jan 21, 2010
    Yep, you've got it.
     
  7. MattP

    MattP

    24
    0
    Oct 4, 2011
    Cheers. :) I'll give it a go!
     
  8. MattP

    MattP

    24
    0
    Oct 4, 2011
    Thanks Steve, it works perfectly. :)
     
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