Passive EQ filter (Caps topology)

Has anybody tried some filters with the caps topology that is in the Forssell white paper. Evolution of an EQ design.

Curious as I am trying to find more info on it.
It's a passive filter akin to the gyrator (DOA) with control Q and +/- independently from what I gather.


Anybody with any more info.

I reverse engineered the Millennia NSEQ once and with a few small value changes it is almost exactly the CAPS circuit described.

Look for the Steve Dove console design articles, much more info in there about that topology.

Thanks ruairi.

I will have a search for those Steve Dove articles. Is that NSEQ stepped switches or not it's probably worth having a gander regardless at it's filters?

Hi Peter

The link to the Streve Dove articles is in this thread.

http://groupdiy.com/index.php?topic=56256.0

Peter

Thanks so much pete.
Part 9 was exactly what I was looking for.

Thread bookmarked.
Thanks guys.

I can't figure out why "passive" is used here?

To me that means something very different?

Jakob E.

gyraf said:

I can't figure out why "passive" is used here?

To me that means something very different?

Jakob E.

Click to expand...

I think Peter is a little mixed up, Fred was referring to the earlier circuits in his paper as passive, not the CAPS.  That said he still references the swinging output negative feedback eq as passive which most wouldn't designate as such.

petermontg said:

Thanks ruairi.

I will have a search for those Steve Dove articles. Is that NSEQ stepped switches or not it's probably worth having a gander regardless at it's filters?

Click to expand...

No, the NSEQ is pots for gain and freq and Q on the parametric section, the freq was switched on the shelves which use a different topology.

I don't love the NSEQ, it's fine but there are lots of eqs I'd prefer.

The Dove articles are awesome, print on paper and enjoy.

ruairioflaherty said:

(..) he still references the swinging output negative feedback eq as passive which most wouldn't designate as such.

Click to expand...

Makes sense to me now. This is probably also why the EAR825 is claimed by manufacturer to be a passive Eq, which always puzzled me:
http://www.gyraf.dk/schematics/Ear_825_EQ.GIF

Jakob E.

Me too.  Passive filters I guess.