High Q, ultra narrow band parametric filter

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4/6/2000 9:03 AM

Kremator

High Q, ultra narrow band parametric filter Hello,   I'm searching for something, that would work as the subject. I need it to eliminate feedback of my guitar pickups. It's resonance frequency is in the midrange, i estimate more than 1kHz (its a humbucker type pickup, i guessed this) it doesn't need to be very patametric, but it has to be VERY narrow. I can "notch" out the resonant frequency with my parameric mids on my pedal, but it's too wide, it cuts down more frequencies than needed. The thing should be also able to cut the second harmonic, beceause it's sometimes possible to hear it. (double band with single control - dual pot or something like that)   Thanks   K.

 

4/6/2000 9:49 AM
Liam	You could do it with a pair of op amp filters, since they can be amazingly sharp on low pass or high pass cut off ramps. I was looking at them in an electronics text book the other week, but I'm still trying to get the courage to try designing a parametric notch filter out of them.     Alternatively, LC. If you can get it narrow enough?

 

4/6/2000 11:46 AM
paul perry	When making very high Q analog filters, the problem is getting the components accurate, as this becomes more of a problem with high Q.   perhaps something could be done with the BurrBrown UAF series, which have precision capacitors inside them already, and are arranged so that various filter configurations can be made by adding precise resistors. I havn't done this myself.

 

4/6/2000 5:20 PM
R.G.	Bootstrapped Twin T filter is the standard in PA systems for this kind of thing, should work for guitar as well. See the article on building graphic and parametric EQ's at GEO for how to do this. Should be just one opamp and some R's and C's.   You can get infinite attenuation and very sharp notch filtering by tweaking the component values.

 

4/7/2000 10:25 AM
Kremator	Hello,   Thank you all. I found what i was looking for at www.ti.com in their application note LB-5. Which is a bootstrapped twin T filter.   bye,   K.

 

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