A new parametric EQ?

Discussion in 'General Electronics Chat' started by AndrewCE, Jul 15, 2009.

  1. AndrewCE

    Thread Starter Member

    Jun 27, 2009
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    Ok, I know bandpass filters or bandstop filters are normally made with a capacitor and inductor in series or parallel, but would it be possible to make one with 2 RC filters? One would be highpass, the other would be lowpass. This seems like an extremely elegant solution, so the fact that i don't see it often tells me there's probably some really fundamental error that i'm missing. what is it?
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Here is a PDF on filter design with opamps.
    In there is a comparisson of band filters with high/low pass combinations.
    With opamps you will hardly use inductors.

    Greetings,
    Bertus
     
  3. AndrewCE

    Thread Starter Member

    Jun 27, 2009
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    i've done active filters, i'm looking for a passive filter. and i would like to understand WHY this particular one is not used.
     
  4. The Electrician

    AAC Fanatic!

    Oct 9, 2007
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    Design one and plot the response curves. I think it will be clear why it isn't done.
     
  5. AndrewCE

    Thread Starter Member

    Jun 27, 2009
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    I would've done that already, however i do not have any simulation software, nor do i have any tangible frequency response measurement devices. Maybe you could point me in the right direction with regards to software (free, preferably)?
     
  6. The Electrician

    AAC Fanatic!

    Oct 9, 2007
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  7. AndrewCE

    Thread Starter Member

    Jun 27, 2009
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  8. hgmjr

    Moderator

    Jan 28, 2005
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    This would be a good opportunity for you to learn how to analyze the circuit you propose without using simulation software. It is a valuable skill to learn if you have an interest in comparing different filter topologies.

    There was a time when there was no simulation software. Once you have analyzed a filter yourself you will have a deeper appreciation for filters as well as simulation software.

    hgmjr
     
  9. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    When connecting RC low and highpass filters together you will find out that the second filter acts as a frequency dependend load to the first one.
    In other words they interact with eachother and give an other frequency curve as expected.
    A great deal of this interaction can be solved by placing buffers between the filters.
    This can be transistors or opamps.

    Greetings,
    Bertus
     
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