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Old 28th August 2009, 06:29 PM   #1
kirk57 is offline kirk57  United States
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Default Anybody interested in checking my PLLXO?

I am designing a passive line level crossover, and using a few different sites have come up with the RC values for a simple 1st order crossover.

I was hoping somebody who has done this before would be willing to check my work.

The particulars are:
turnover frequency Low pass 400 Hz
Turnover frequency high pass 1600 Hz
1st order, 6 db/octave

(Some of you may recognize this as Magnepan crossover...)

input impedance of the HP amp is 47K
input impedance of the LP amp is 36K
Output impedance of the preamp is 600 ohms

I'd like to use .1 uF cap for the LP, and .01 uF for the HP, but that is not set in stone.

The most comprehensive site I've seen on this is here:

http://www.silcom.com/~aludwig/Sysde...ove_Design.htm

under the Multi-amping section.

Is anybody up for a little math? Not sure I'd want to bore the forum with all the calculations, but could do it this via e-mail. or I'm not too proud to have my math torn apart right here...

thanks

Kirk
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Old 28th August 2009, 07:46 PM   #2
frugal-phile(tm)
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Have you seen this one:

http://t-linespeakers.org/tech/filters/passiveHLxo.html

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Old 28th August 2009, 08:11 PM   #3
kirk57 is offline kirk57  United States
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Default Yes I have

Dave-

I started out with that one. I think the example on that site assumes the turnover frequncy for the high pass and low pass filters are the same, and looks like there is some dependency between R1 and R2 which I don't understand.

The formulas on the silcom.com site I referenced treats them separately, and accounts for the insertion loss of both filters. I think I need to take all those variables into account.

Of course I am new to this (other than a filters class I took 13 years ago)
so I could be making it more (or less) complicated than need be.

Kirk
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Old 28th August 2009, 09:19 PM   #4
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In that case, i just assume a 3-way and then toss out the bandpass only using the LP & the HP. Insertion loss shouldn't be an issue, you'll need a gain control on the amp that needs turning down.

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Old 28th August 2009, 09:44 PM   #5
kirk57 is offline kirk57  United States
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Default Do I need a Pot?

I was under the impression I could just fix the respective resistances of the LP and HP filters so the insertion loss was the same for both.

There is no gain control on either of the amps so it would have to be part of the PLLXO, in which case the R of the pot becomes part of the equation.

Would that go on the LP or HP?
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Old 28th August 2009, 10:44 PM   #6
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Depends on the sensitivities of the amps, their power and the relative efficiency of the speakers.

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Old 4th December 2009, 02:18 AM   #7
Pano is offline Pano  United States
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It's very tricky to run line level filters without volume control on the amps. Sure, it can be done, but it's a hassle.

Note what Dave said above and think about all that means, in depth.

EDIT: Oh, this is an old thread. How did it work out?

Last edited by Pano; 4th December 2009 at 02:19 AM. Reason: missed the date
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