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Old 2nd December 2006, 05:22 PM   #1
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Default Roll off power amp low end?

To mate my main speakers and subs with a perfect L-R 4th order filter, I need to filter my amp output, -3 dB @ 70 Hz, 12 dB per octave. Amp input impedance is specified as 22kOhms.

What's the best way to roll off the bottom end of my power amp? A couple of caps in series on each input to the amp? A friend suggested a cap in series with the signal and an inductor bypass, as in a loudspeaker, but I don't know if you could even get an inductor with that low a value.

Right now I'm using a pair of FMod filters that do the job and are very convenient. Unfortunately they add the merest touch of roughness in the midrange, and I think I can do better with premium parts inside the amp.
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Old 3rd December 2006, 06:09 PM   #2
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Old 3rd December 2006, 06:29 PM   #3
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try searching google or the forums for active filter and op amp. WinISD even includes a calculator.
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Old 3rd December 2006, 07:17 PM   #4
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Default Active filter crossover xover 2nd order Linkwitz-Riley 12dB

Quote:
Originally posted by audiobomber
To mate my main speakers and subs with a perfect L-R 4th order filter, I need to filter my amp output, -3 dB @ 70 Hz, 12 dB per octave. Amp input impedance is specified as 22kOhms.

What's the best way to roll off the bottom end of my power amp? .
A Linkwitz-Riley 12dB (2nd order) active filter using Op-Amp
as already told.

This is placed BEFORE the amplifier 22kohm input.
So the load for this filter Op-Amp will be 22kohm
which is no problem for example for one OPA2134
which I recommend.
It is perfect to use for active filters applications.

To learn about such filters
you can find formulas and circuits
at LINKWITZ HimSelf website!
(yes, it is the very alive person that has given name to Linkwitz-Riley filters!)

Click the image to open in full size.
http://www.linkwitzlab.com/



Another great resource with good info about crossovers and filters
using op-amps is
ESP Rod Elliott projects and articles and tutorials website.
You will find articles about active filters and loudspeakers filters projects,
if you search a bit!
http://sound.westhost.com/site-map.htm



Regards
lineup active and posting diyaudio member
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