PLLXO implementation

[lbstyling]

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

 

[lbstyling]

appologies- heres the guide http://www.t-linespeakers.org/tech/filters/passiveHLxo.html

 

[picowallspeaker]

May be that you'd feel uncomfortable with "big" capacitor values shunting to ground ?

 

[lbstyling]

May be that you'd feel uncomfortable with "big" capacitor values shunting to ground ?

its worth a go either way i think.

 

[PeteMcK]

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)

 

[Ipanema]

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.

 

[picowallspeaker]

Andrewwwww T ! Where are you ?
I think it's the Time Constant that had to be taken in consideration

 

[PeteMcK]

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...

 

[Ipanema]

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.

 

[planet10]

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

 

[lbstyling]

does it make any difference to the equasions though if you have the hp section before a split at line level to 3 power amplifiers?

do i add the imp of each power amp together and divide by 3 ,ie-no change??


ill post my individual calculations for you and where i get setting up for a standard single channel for each speaker.

 

[lbstyling]

ok for the 2nd order crossover i have the following values-

80hz crossover,

amp low pass imp- 20kw

amp high pass imp- 47kw.

lowpass--
r1=5kw, r2=50kw, c1=3.98nf, c2=13.93uf.

high pass--
c1=3.98nf, c2=0.398nf, r1=5kw, r2=783.6kw.

im not confident on the values being right here- sooo many oooooo's!!

 

[Ipanema]

Hi Dave,

Thanks for your explanation. If loading is a concern, would it be better to have R1=50 k W, R2=50 k W, C1=3.18nF, C2=3.18nF ?

 

[planet10]

For the high pass filter, amp impedance of 50k, just use the 50k as the last R. Set R2' to infinity (ie leave it out). That then means setting R1 to 5k, and calcing Cs accordingly.

dave

 

[lbstyling]

ll have a go and report back,
thanks peeps!