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Old 24th September 2009, 01:04 PM   #1
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Default PLLXO implementation

Afternoon all, (well it is for me anyway!)

i want to use a pllxo to cross over to my sub (2nd order-80hz)

im a little stuck though as i have my speakers tri-amped.

using this guide-im stuffed as i dont know wha to put in as a value for the high pass amp impedence- can anyone help me?

thanks people
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Old 24th September 2009, 01:05 PM   #2
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appologies- heres the guide http://www.t-linespeakers.org/tech/f...ssiveHLxo.html
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Old 24th September 2009, 01:52 PM   #3
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May be that you'd feel uncomfortable with "big" capacitor values shunting to ground ?
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Old 24th September 2009, 04:31 PM   #4
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Quote:
May be that you'd feel uncomfortable with "big" capacitor values shunting to ground ?
its worth a go either way i think.
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Old 25th September 2009, 04:53 AM   #5
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if your 'R2' to ground is small enough, say 10K or less, the imput impedance is unlikely to have much effect...
(i.e. just make R1=R2)
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency

Last edited by PeteMcK; 25th September 2009 at 04:57 AM.
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Old 25th September 2009, 05:27 AM   #6
Ipanema is offline Ipanema  Malaysia
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May I know why C2=C1/10 and R2=10R1? Can I use like C1=C2 and R1=R2 since they will have the same -3dB frequency. Thanks.
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Old 25th September 2009, 05:44 AM   #7
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Andrewwwww T ! Where are you ?
I think it's the Time Constant that had to be taken in consideration
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Old 25th September 2009, 05:45 AM   #8
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sorry guys, I was talking about the 1st order circuit,
R2 in the 2nd order schematic will be effected much more by the following input impedance if it's 10xR1
Ipanema, follow the link to Art Ludwig's site on the t-line speakers page link above if you want the gory details of the maths...
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Old 25th September 2009, 07:07 AM   #9
Ipanema is offline Ipanema  Malaysia
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In the example given for second order filter with equation f=1/2*pi.*R*C,

f=1kHz: R1=5 k W, R2=50 k W, C1=31.8nF, C2=3.18nF

and I will still get the same f even if C1=C2 and R1=R2, where

f=1kHz: R1=5 k W, R2=5 k W, C1=31.8nF, C2=31.8nF

I would appreciate if anyone can explain to me why Art Ludwig's prefer C2=C1/10 and R2=10R1. Thanks.

Another note is the above equation is only accurate assuming that source output impedance is 0 and the stage after filter input impedance is infinity for HPF.
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Old 25th September 2009, 07:44 AM   #10
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Quote:
Originally Posted by Ipanema View Post
May I know why C2=C1/10 and R2=10R1? Can I use like C1=C2 and R1=R2 since they will have the same -3dB frequency. Thanks.
This configuartion is to not have the secound stage loading down the 1st stage.

dave
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