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the_ufo
Joined: Nov 02, 2010 Posts: 15 Location: edinburgh
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cloudscapes
Joined: Feb 09, 2004 Posts: 100 Location: Montreal
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Posted: Sun Nov 14, 2010 8:14 pm Post subject:
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maybe I'm missing something
I'm looking at an analog filter. _________________ Sonic Crayon DIY effects lab |
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yusynth
Joined: Nov 24, 2005 Posts: 1314 Location: France
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Posted: Mon Nov 15, 2010 6:14 am Post subject:
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As stated by cloudscape it is a basic 6dB/octave ANALOGUE lowpass filter. The triangular component with the + and - symbols is an operational amplifier (stuffed with BJT transistors). The cut off frequency is set by R1 and C. F = 1 / (2xPIxR1xC) ; However you must be aware that the ratio R1/R2 sets the gain as well. Therefore if you vary the value of R2 to change the cut-off you must change equally R to have a constant gain. The best way to do this is to use a dual gang pot for R1 and R2.
By the way forget about valves _________________ Yves |
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the_ufo
Joined: Nov 02, 2010 Posts: 15 Location: edinburgh
Audio files: 1
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Posted: Mon Nov 15, 2010 5:23 pm Post subject:
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awesome, That is what I wanted to know.
I now realize it's an analogue component even though it's made of semiconductors.
If somone could reccomend such a dual-gang pot, i'd appreciate that greatly and defo use it. i've never ordered electronic components before.
w0000000000t, get the soldering iron out! |
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DrJustice
Joined: Sep 13, 2004 Posts: 2114 Location: Morokulien
Audio files: 4
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Posted: Mon Nov 15, 2010 7:41 pm Post subject:
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the_ufo wrote: | If somone could reccomend such a dual-gang pot, i'd appreciate that greatly and defo use it. i've never ordered electronic components before. |
Since you're in the UK, maybe Maplin is a good place to shop. You can even pop down to your local branch. Hopefully they have these dual gang pots in stock.
Oh, and to electro-music.com
DJ
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yusynth
Joined: Nov 24, 2005 Posts: 1314 Location: France
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Posted: Tue Nov 16, 2010 2:11 am Post subject:
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the_ufo wrote: | I now realize it's an analogue component even though it's made of semiconductors. |
Semiconductors are components, analogue and digital are working modes, analogue circuits can be built with either semi-conductors or valves and digital circuits as well can be built with either semi-conductors or valves. _________________ Yves |
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the_ufo
Joined: Nov 02, 2010 Posts: 15 Location: edinburgh
Audio files: 1
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Posted: Tue Nov 16, 2010 5:41 pm Post subject:
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brilliant!
thankyou everyone!!
I am finding electro-music.com to be most welcoming!!! |
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enomys
Joined: Dec 19, 2010 Posts: 11 Location: italy
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Posted: Sun Dec 19, 2010 12:06 pm Post subject:
2nd order lowpass filter |
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Hi, just a question... For a 1rst order lowpass filter I can use a double pot to change the cutoff, but if I would like to change the cutoff in a 2nd order lowpass filter? thanks
Simon
yusynth wrote: | As stated by cloudscape it is a basic 6dB/octave ANALOGUE lowpass filter. The triangular component with the + and - symbols is an operational amplifier (stuffed with BJT transistors). The cut off frequency is set by R1 and C. F = 1 / (2xPIxR1xC) ; However you must be aware that the ratio R1/R2 sets the gain as well. Therefore if you vary the value of R2 to change the cut-off you must change equally R to have a constant gain. The best way to do this is to use a dual gang pot for R1 and R2.
By the way forget about valves |
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yusynth
Joined: Nov 24, 2005 Posts: 1314 Location: France
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Posted: Sun Dec 19, 2010 12:18 pm Post subject:
Re: 2nd order lowpass filter |
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enomys wrote: | Hi, just a question... For a 1rst order lowpass filter I can use a double pot to change the cutoff, but if I would like to change the cutoff in a 2nd order lowpass filter? thanks
Simon
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It depens very much on the type of 2nd order filter you intend to use. If you intend to cascade two of the above circuit th'at's a bad idea because you would need a quad pot for this. If you use a Sallen and Key or another topology such as those explained in detail here http://focus.ti.com/lit/ml/sloa088/sloa088.pdf _________________ Yves |
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enomys
Joined: Dec 19, 2010 Posts: 11 Location: italy
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Posted: Mon Dec 20, 2010 4:32 am Post subject:
Re: 2nd order lowpass filter |
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thanks, i just checked the second order Sallen and Key, but my question still remians, I don't know to change the cutoff....
Simon
yusynth wrote: | enomys wrote: | Hi, just a question... For a 1rst order lowpass filter I can use a double pot to change the cutoff, but if I would like to change the cutoff in a 2nd order lowpass filter? thanks
Simon
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It depens very much on the type of 2nd order filter you intend to use. If you intend to cascade two of the above circuit th'at's a bad idea because you would need a quad pot for this. If you use a Sallen and Key or another topology such as those explained in detail here http://focus.ti.com/lit/ml/sloa088/sloa088.pdf |
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the_ufo
Joined: Nov 02, 2010 Posts: 15 Location: edinburgh
Audio files: 1
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Posted: Mon Dec 20, 2010 12:30 pm Post subject:
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Yusynth explained how to do it for a first order filter... I dont know its applicable to a 2nd order. I haven't had chance yet to play around with this myself, so I can't really help. |
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