Reverse the inputs on your op amp!
For harmonic analysis, you normally need a reasonable Q. This configuration only works at a low Q, and the Sallen Key filter has very poor performance (which can be minimized) as the frequency rises. If you only want low Q, use an inverting configuration.
You need to do more background reading, a link is enclosed.
http://www.ti.com/lit/ml/sloa088/sloa088.pdfIf you need high Q, the state variable filters are probably better, but have a lot more components. At high Q's you need high stability components, and Op Amps with a good GBW.
There is a free, limited program available from www.nuhetrz.com that will synthesis filters, and display the results. It is no substitute for reading the article from Texas mentioned above first.
Hope that helps,
cheers,
Richard
