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Thread: Can someone spec some caps for me? Running active..

  1. #1
    Indecisive Tuner BowDown's Avatar
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    Can someone spec some caps for me? Running active..

    I don't like the turn-on thump I'm getting occasionally and while I troubleshoot that out I figured it would be piece of mind to put some spec'd bass blockers on my midrange and tweeters.

    Does anyone have the skills to spec out some caps for me?

    -Tweeters
    B&G Neo3
    4ohm
    50watts max
    Looking for 2khz-ish, I have the currently crossed over at 4.1khz but want the ability to cross lower.
    Bohlender Graebener Neo3W Planar Tweeter w/Back Cup


    -Midrange
    B&G Neo8
    4ohm
    100watts max (I am only pushing 60watts into them)
    Looking for 500hz-ish. Currently crossed over at 710hz.
    Bohlender Graebener Neo8-PDR Planar Transducer


    Thanks!
    2010 Fusion Sport: SQ Install w/Dash Sub - Build Log of the Month Winner | July 2011


    Nexus 7 | DAC | miniDSP | Aura MR2150 x 3 | NRT18-8 | RS180-4 | neo8-s

  2. #2
    Indecisive Tuner BowDown's Avatar
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    Alright. So the general consensus (by searching on the net) is that 80mfd will give me about 500hz @ 4ohm, and 20mfd will give me just shy of 2khz @ 4ohm. Seems like madisound has what I need...

    Bennic 80 mfd Electrolytic Caps
    $2.20 x 2
    Carli Mylar 20 mfd
    $5.95 x 2

    So about $22 shipped?

    What about voltage? How does that relate to wattage capacity? I would imagine at 65watts RMS I wouldn't exceed 10v?
    2010 Fusion Sport: SQ Install w/Dash Sub - Build Log of the Month Winner | July 2011


    Nexus 7 | DAC | miniDSP | Aura MR2150 x 3 | NRT18-8 | RS180-4 | neo8-s

  3. #3
    Founding Member
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    if you are worried about voltage, a zener diode will short any voltage above the cutoff you choose.

    I don't think I'd be putting that in or across the audio signal path though.

  4. #4
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    Ideally to avoid interactions at the xo, you would want to be at least an octave away from the xo point.

    I would go closer to 140 uf on the mid and 30 ufd on the tweeter.

    Check out what apex jr has in surplus...or Nebraska Surplus Sales has to offer.

  5. #5
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    And you can normally find some great deals on GE made motor run capacitors in the large sizes. However the caps are pretty large...would want to keep them near the amps The good GE caps are the 97F models.

  6. #6
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    These are pretty crazy prices. Just buy the regular nonpolar ones off PE. They're under $1 I think.

    Go with the 63v ones. Or I think they may have 50v too? 10v is probably too low.

  7. #7
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    If you are gonna buy 63 volt (and 50v for that matter) non polar caps, you can save yourself shipping costs and buy them at Frys if you have one local to you. I know they sell them cause I've got a few of those guys in my garage.

  8. #8
    Devil's Advocate Adam_MSS's Avatar
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    Adding the equation here for anyone interested in the method of calculation.



    R = load resistance (ohms)
    C = capacitance (uF)
    You don't use science to show that you're right, you use science to become right. - R.Munroe

    The important thing in science is not so much to obtain new facts as to discover new ways of thinking about them. - W.L.Bragg



  9. #9
    Indecisive Tuner BowDown's Avatar
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    Ya, no fry's around here. Didn't know any place would sell caps right off the shelf? So just any non-polar cap in the 50-63v range works? I notice there's a crap load of types when you're looking at digikey.com?
    2010 Fusion Sport: SQ Install w/Dash Sub - Build Log of the Month Winner | July 2011


    Nexus 7 | DAC | miniDSP | Aura MR2150 x 3 | NRT18-8 | RS180-4 | neo8-s

  10. #10
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    Pretty much. You are running audio or DC, not RF or digital signals. Factors like dielectric material, temperature sensitivity, and I'm sure much, much, much more play less a factor here.

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