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Old 13th August 2006, 07:06 AM   #1
barossi is offline barossi  Germany
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Default active crossover

Hi,
i woule like to build an active crossover or better called: protection!

I would like to protect my speakers form the ultra low frequency!
Therefore i need an active filter -24dB at 60Hz. I would like to install this filter on the input of my power amp.

The amp has got the following specs:
10 kOhm / 47 pF

Did anyone build this?

Greetings Barossi
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Old 13th August 2006, 10:15 AM   #2
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Have a look at this website:
http://www.beis.de/Elektronik/Filter/Filter.html
The usual way to do what you want is to use a Sallen and Key high pass filter
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Old 13th August 2006, 10:44 AM   #3
DorinD is offline DorinD  Romania
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Why you don't try a passive line level filter (2-nd order RC)? See there:

http://www.t-linespeakers.org/tech/f...ssiveHLxo.html

only for the high-pass branch. Your specs for the power input (10 kOhm / 47 pF) are perfect. Can use highest quality caps and res, nu power supply needed, no noise, highest dinamics, simple.
Can put all the parts in the power-amp box and activate on the need with a switch.
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Old 13th August 2006, 10:52 AM   #4
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Usually the filter is at least second order to avoid early roll off of bass. If you mean 24 dB/octave at 60 Hz, that is fourth order. As noted on teh page linked to above, passive filters have an insertion loss that may cause problems. I prefer an active solution. It is easy to build an active filter.

I have a group buy of active filter boards and power supplies that closes on August 18th. The boards offer more features than you require, but you can just leave the parts you don't use empty. A single power supply will easily handle two boards needed for a stereo high pass filter.

Filter board WIKI

Active filter on my page includes a spreadsheet to calculate values Here

PSU page here

odering page
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Old 13th August 2006, 02:41 PM   #5
barossi is offline barossi  Germany
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Hi,
i think i would like to try the passive version on t-line speakers!
Even i have losses, i could adjust the level of the Amp.
But the group buy is very very interesting!


Greetings Barossi
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Old 14th August 2006, 07:43 AM   #6
DorinD is offline DorinD  Romania
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See also:

http://www.audioc.com/accessories1/misc/hipass.htm

there are some of 2-nd order, I can't find the link to the producer of them, not the seller.
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Old 14th August 2006, 08:14 AM   #7
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I would avoid passive filters steeper than 2nd-order, because as well as the insertion loss it becomes difficult to stop the sections interacting and meet impedance criteria, and the response is very droopy as you can't get a decent q-value.
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Old 14th August 2006, 08:37 AM   #8
DorinD is offline DorinD  Romania
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Or some no so cheap RLC 2-nd or 4-th order passive filter with no insertion lost:

http://www.marchandelec.com/xm46.html
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