check this out

[pucho812]

An amplitude equalizer circuit utilizing active components in which unidirectional functional tuning of the amplitude, bandwidth and center frequency, may each be adjusted by varying a single resistance for each parameter. This eliminates the need for ganged-potentiometers or altering a plurality of interacting components.

http://www.freepatentsonline.com/4229716.html

 

[pstamler]

That bottom section with the five passive components in a vertical line and opamps connecting them -- I used to know the name of that. The topology was popular among folks designing circuits for various Audio Amateur publications in the eighties and nineties. Generalized Impedance Converter? (brief googling pause) Yes. It's a way of making a bunch of resistors and capacitors look like an inductor, and as Pucho said, it doesn't need ganged pots for tuning.

Peace,
Paul

 

[bcarso]

Or more frequently and generally, Generalized Immitance Converter usually abbreviated as GIC. Quite the rage due to low sensitivities, but note that the opamps have to have very good common-mode distortion performance to realize all the benefits.


(immitance meaning a combo of impedance and admittance)

 

[Svart]

any way to see it without signing up to that site?

 

[clintrubber]

[quote author="Svart"]any way to see it without signing up to that site?[/quote]
As always www.pat2pdf.org (note 'org', not 'com') comes to the rescue:


http://www.pat2pdf.org/patents/pat4229716.pdf

 

[Svart]

1980? that's not 17 years, that's 27 years..

 

[pucho812]

I saw it without signing up. weird...

 

[solder_city]

he said 'over 17 years'
pay attention

i think the point may be that more than 17 yrs have elapsed and the ckt may no longer be the subject of patent protection