parametric filter to shelving

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Hi, got some books about op_amps and filter design, but still cannot handle it.
Dont get it which opamp does what.Is it possible to turn this section:
An externally hosted image should be here but it was not working when we last tested it.

//ibanez pql stompbox
into a shelving filter like this:
An externally hosted image should be here but it was not working when we last tested it.

//calrec pq1549
I like the design of the first schematic, using unipolar supply and having variable Q.
In general my idea is to remove the original low/high section from the ibanez pql and connect in series re-designed sections for low and high like the above mid section, with a shelving switch. Hope it won't introduce too much noise.
- - -
Don't get it also why the high parametric/shelving section of calrec pq1549 have one opamp more:
An externally hosted image should be here but it was not working when we last tested it.

Best Regards
 
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