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Old 16th October 2009, 10:12 AM   #1
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Default Please, power amplifier active input filters needed

A friend asked me, he wants to build...but he wants active!... the one is already knowing i am doing passive input filters to amplifiers.... i do not know how to make it active...i have just an idea about...can you help posting schematics?

Yes..i have a lot of good operational amplifiers if needed... but i would be more happy with discrete, because less stages means lower distortion (normally)

Bass - 1 hertz to 200 hertz (-3dB) to the bass power amplifier unit (sub)
Mids - 200 hertz (-3dB) to 4 kilohertz
treble - 4 kilohertz and up.

thank you in advance by your cooperation...i can discover how to do it..but will take a lot of time..having your suggestion will be easier.... and faster!

Input and output impedance around 47K

Gain of one, input 1 volt rms ...or something more modern and up to date you suggest.

Volume potentiometer included into the input of these three filter channels..or active pré amplifier if you want to call this way.

Help!

regards,

Carlos

Last edited by destroyer X; 16th October 2009 at 10:17 AM.
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Old 16th October 2009, 11:21 AM   #2
AndrewT is online now AndrewT  Scotland
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esp shows active filters.
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Old 16th October 2009, 11:37 AM   #3
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I have a modular active filter project on my website
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Old 16th October 2009, 11:42 AM   #4
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Default Thank you Andrew T and Richie boy

To learn how to make it will spend a lot of time..and this is an issue..i had not too much free time time those last monthes.

You know....i have not the time to learn that..i have a dead line... this must be fast...i am searching for the stuff ready and tested..not to learn or develop.

Will take a good look at ESP pages..maybe the filters there are "ready to go"

regards,

Carlos
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Old 16th October 2009, 12:15 PM   #5
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Default Is this correct?... can you please observe if i made errors

thank you,

regards,

Carlos
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Old 16th October 2009, 05:50 PM   #6
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Linkwitz has complete active crossover designs as well as generic theory pages

Active Filters

http://www.linkwitzlab.com/xo_eq.htm

http://www.linkwitzlab.com/crossovers.htm
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Old 16th October 2009, 06:41 PM   #7
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"Is this correct?... can you please observe if i made errors"

It looks like you have made a series of nopass filters in that schemo (dead shorts across the op-amps).

There is more to designing a filter than just connecting resistors to capacitors. What characteristics are you looking for? The Chebychev characteristic gives the best skirt selectivity at the expense of amplitude response and phase linearity. The Bessel characteristic has the best phase linearity, the poorest skirt selectivity, and a fair amplitude response. The Butterworth -- a good compromise between skirt selectivity, amplitude response (the best) and a well behaved phase characteristic, except it goes a bit wonky near its cutoff frequency.

Here's what an active LPF ought to look like. The HPF simply interchanges the resistors and capacitors. (Attached). I'd always make the odd ordered filters, since it just costs you one additional resistor and capacitor. An extra -3.0db of roll off/on for cheap.
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File Type: gif Active_LPF.gif (3.4 KB, 148 views)
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Old 16th October 2009, 07:00 PM   #8
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Here is another theory page:
Body

And if you are building the amp from scratch for dedicated use one could sandwich PLLXOs between stages:
Passive High-Level Crossover

dave
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Old 16th October 2009, 08:05 PM   #9
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Default Thank you folks..i will read everything.

regards,

Carlos
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Old 16th October 2009, 08:16 PM   #10
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Quote:
Originally Posted by planet10 View Post
Here is another theory page:
Body
Marginally useful: I can sum up that entire article in two words: Butterworth filter. OK, so he's established he likes the Butterworth. All in all, not a bad choice. I don't know where he's getting this "Sallen-Key" nonsense. What's he's described is a Butterworth.

Quote:
Originally Posted by planet10 View Post
And if you are building the amp from scratch for dedicated use one could sandwich PLLXOs between stages:
Passive High-Level Crossover
Total bullocks. You don't make a second order filter by cascading two identical first order filters. Sure, it will eventually approach the -12db / octave asymptote, but that ain't no Butterworth characteristic no more. (attached)
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