Sallen-Key vs Multiple Feedback Filter Design

[mimmotronics]

I read a white paper some time ago on implementing active filters in both Sallen-Key and Multiple Feedback topologies so I'm wondering if you guys have any preference on which to use.

[Kipper4]

Hi Mimmotronics and welcome.

It's a hard one to answer since we have no clue of the operation of the circuit and intent.
Perhaps if you expand much more the guys could maybe advise.

Point us to the white paper.
Tell us what is your intended use of the filter.
Show us a potential schematic.
Give us some more to go on please.

[mimmotronics]

Hi Mimmotronics and welcome.

It's a hard one to answer since we have no clue of the operation of the circuit and intent.
Perhaps if you expand much more the guys could maybe advise.

Point us to the white paper.
Tell us what is your intended use of the filter.
Show us a potential schematic.
Give us some more to go on please.

Hi Kipper4,

Thank you, I am planning on constucting a graphic EQ with some active filtering. The white paper is from Texas Instruments: https://focus.ti.com/lit/ml/sloa088/sloa088.pdf

But I'd imagine they could be used in any tone control setting, just wondering if anybody has any experience with the two topologies.

[mimmotronics]

Mainly section 16.5 is what I'm studying. I think I'll take the liberty in documenting my findings on this thread!

[R.G.]

Better for rough and ready work: Active Filter Cookbook, Lancaster

[PRR]

+1 for Lancaster.

> a graphic EQ

First find RANE's library of both white-papers and product schematics. It's a bit harder since Dennis left, but I think all the stuff is still there. Read it! Dennis' exploration and exploitation of audio EQ techniques was comprehensive, a good guide into the woods.

However Octave graphic EQs are almost all implemented with L-C or C+Gyrator on the same boost-cut mixer. 1/3rd octave is actually 9X more work and pretty overwhelming for an individual builder; pointless since fine 27-band graf EQ show up in pawn shops.

Don't take the TI paper as "Word!". The engineering is probably OK. The application to audio... TI does employ several good audio-persons, but they do not write all the papers (they work on the chips and implementation).