Low pass band

Discussion in 'General Electronics Chat' started by steven reneker, Nov 18, 2008.

  1. steven reneker

    Thread Starter New Member

    Nov 18, 2008
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    I am making a stomp board and need to make a passive band.Need to block all but 33hz to 100hz any ideas:confused:
     
  2. steven reneker

    Thread Starter New Member

    Nov 18, 2008
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    What can i use to make a passive filter or band to allow only 33hz to 100hz
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    See the attached.
    Input/output impedance of 50 Ohms assumed. If yours is different, change it.

    I used a Butterworth design for a nice smooth roll-off. It's a bit wider than you asked for, but usually folks want the passband a bit wider. Otherwise, your response at both 33Hz and 100Hz would be 3dB down.

    Filter created using AADE Filter Design, available for free here:
    http://www.aade.com/

    [eta]
    You're going to have to wind your own toroidal inductors. Amidon's FT-87A in Material "J" (75) should work OK.
    Amidon's "J" toroids are on this page:
    https://www.amidoncorp.com/items/21
    The FT-87A-J is the last item on the page; $2/ea
    L2 is 245mH; that's 201 turns of wire.
    L3 is 200mH; 182 turns of wire.
    L4 is 100mH; 129 turns
    L5 is 85mH; 118 turns.
    Each pass through the center of the toroid counts as 1 turn. Wind it on as evenly-spaced as you can.
    Inner diameter of the toroid is only 0.54", so you'll have to use fairly small magnet wire. AWG 28 or AWG 30 would be a good bet, if you're working with line-level signals.

    Use poly caps for reliability and better frequency response.
     
    Last edited: Nov 18, 2008
  4. steven reneker

    Thread Starter New Member

    Nov 18, 2008
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    Thanks so much i have been working on this for weeks. Now to find someone to build it for me. I am good with music this is out of my abilitys.
    Thanks again
     
  5. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    I have an original Vox Crybaby, with the variable Q, that does it all. I don't see any reason to reinvent the wheel. :) But as Sarge says, it's a pretty simple matter to design a filter prototype for that. A great filter design tool is ELSIE, which is bundled with the ARRL Handbook. It has a GREAT optimization routine in it.....makes it a snap to twiddle filter parameters.

    Eric
     
  6. SgtWookie

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  7. mik3

    Senior Member

    Feb 4, 2008
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    You can combine a low pass with a cutoff frequency of 100Hz and a high pass with a cutoff frequency of 33Hz.

    Here is a link for more information:

    http://www.play-hookey.com/ac_theory/band_pass_filters.html
     
  8. SgtWookie

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    Jul 17, 2007
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    Mik3,
    Those are RC filters. While much easier to build than LC filters, our OP will require an active amplifier to boost the signal back up to where it's supposed to be. A properly tuned LC filter won't lose much of the passband signal at all; a mere fraction of a dB.
     
  9. steven reneker

    Thread Starter New Member

    Nov 18, 2008
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    Sarg.
    Does it matter which direction i wind them clockwise or counter?

    Material is ordered and thanks so much.:D
     
  10. SgtWookie

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  11. steven reneker

    Thread Starter New Member

    Nov 18, 2008
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    Once i have all the windings that will fit on the core and i still do not have the count do i keep going over the other windings?
     
  12. steven reneker

    Thread Starter New Member

    Nov 18, 2008
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    Once i have all the windings i can get on the core but still need more windings do i wind over the other windings?
     
  13. steven reneker

    Thread Starter New Member

    Nov 18, 2008
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    Once i have the core covered and i still do not have all the windings on do i keep going back over the first windings????:eek:
    Help please this is all new to me but fun:)
     
  14. KL7AJ

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    Nov 4, 2008
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    At audio frequencies, it's okay to overlap windings, but it becomes a bit more complicated to calculate the inductance. Also, your chances of having some parasitic resonances increases. To be on the safe side, us a smaller gauge wire that you CAN fit on in one layer.

    Eric
     
  15. SgtWookie

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    Yes. It was a given that you'd have to go another round. Still, try to distribute the turns as evenly as possible once you're done.
     
  16. Ron H

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    The filter you posted is terminated in 50Ω on each end, and will attenuate signals in the passband by 6dB. Am I missing something?
     
  17. SgtWookie

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    I made the assumption that the impedance of the circuit was 50 Ohms, which is typical for RF stuff. Without the termination resistors, the filter would be seen as somewhere between an open circuit or a dead short, according to the length of the transmission line. The resistors assure a good match.

    If his input or output impedance is not 50 Ohms, he needs to say something.
     
  18. Ron H

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    I was disputing your claim that it has negligible loss. With both ends terminated in 50 ohms, it has 6dB loss in the passband.

    With a 50 ohm source and a high-Z termination, or a low-Z source and a 50 ohm termination, it still looks fairly good, and the attenuation is negligible. With a low-Z source and a high-Z termination (typical in audio, but not essential), it looks terrible.
     
  19. SgtWookie

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    Why don't you upload your simulation of it, so that I don't have to re-create it in LTSpice?

    Alternatively, you could download the freeware version of Elsie from this page:
    http://tonnesoftware.com/elsie.html
     
  20. Ron H

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    You have to correlate the plots with the schematic.
     
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