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Old 20th November 2012, 01:22 PM   #1
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Default analogue active filter: MFB or Sallen Key?

A noob question. Is there any sonic advantage to either of the filter topologies? Is there a clear reason to pick Sallen and Key over MFB? and vice versa.
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Old 22nd November 2012, 11:36 AM   #2
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Old 22nd November 2012, 11:46 AM   #3
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You may also find this article helpful http://www.analog.com/library/analog...inal_PtB_F.pdf starting at section 5-6.

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Old 22nd November 2012, 10:16 PM   #4
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thanks guys. Ive made Sallen Key types before, but this would be a 1st design effort. Resources like those are useful thanks again. Im studying analogue EE at the moment, and I have to admit MFB were until last week, unknown to me Currently reading R. Mancini and J. Karki.

Edit: this is for my own interest, NOT an coursework assignment.

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Old 23rd November 2012, 06:08 AM   #5
seanvn is offline seanvn  Viet Nam
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You can just use LTSpice IV and EvoSpice 4.1 and let them decide the best component values for a filter. You still have to give a specific circuit arrangement though.

Linear Technology - Design Simulation and Device Models

http://www.evospice.site88.net/

1960’s Style Speech Filter Circuit
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Old 23rd November 2012, 07:13 AM   #6
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i was originally thinking of going state variable but after reading the chapter i linked above, I decided to go gic and fdnr. I really do need to move beyond the breadboard stage though

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Old 23rd November 2012, 07:54 PM   #7
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state variable and biquads are others ive heard of, in fact it may have been a biquad circuit i build from an ETI article long since lost

the fdnr is very intriguing circuit, i was reading the blurb and thinking of using it for a different app altogether. Basically a device to measure 2 independant frequencies and output a voltage from each, and display the percentage difference. Long story lol

I have a beringer GEQ3102 31 band EQ, this also has low and high cut 2nd order butterworth circuits. Low cut is variable between 10 and 400hz, but via a rotary switch or digi pot. 10 clicks between 50 and 200hz, so perhaps not continuously variable, but not bad.

The aim being to make a 2nd order Butterworth low pass, perhaps variable over a similar range, for a cheap active 2way or assisted fullrange system.

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Old 23rd November 2012, 08:12 PM   #8
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Quote:
Originally Posted by seanvn View Post
You can just use LTSpice IV and EvoSpice 4.1 and let them decide the best component values for a filter. You still have to give a specific circuit arrangement though.

Linear Technology - Design Simulation and Device Models

EvoSpice 4.1 & 4.2

1960’s Style Speech Filter Circuit
I agree. I think i could use most of the Linear software Thanks for the great links!
I have multisim and im getting to grips with it the last few weeks. I used circuitmaker for a long time, great free program, perhaps lacking in features but so easy to use. Im computer savvy and mid 30s but even so I find so many 'serious' softwares to be stupidly counter intuitive.

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Old 27th November 2012, 11:34 PM   #9
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You might want to check the last page of:

http://www.jensen-transformers.com/an/an001.pdf
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