Question on filters

[someone jr]

Hi, I'm currently building a couple of filters for an audio project I am working on.
I'm using this schematic as a guide: http://users.otenet.gr/~%20athsam/Circuits/Variable_filter.gif
However this design is 20hz to 200hz, I was wondering what components I'd have to change to make the filter operate until 1000 instead of 200hz.

I'm also going to need to build a low pass filter and was was wondering what components would need to be changed. Is it as simple as swapping around the 5.6k resistors and 150nF capacitors?

Thanks.

[Keppy]

To increase the frequency by a factor of five, reduce the filter resistance or capacitance by a factor of five. Change the 5.6ks to 1ks.

[someone jr]

Thanks, so all the other resistors would stay the same value apart from the 5.6k ones?

[Mark Hammer]

That would depend on whether you want it to have corner frequencies from 20hz-1000hz or the same 10:1 ratio but moved up (100-1000hz).

If the latter, leave the resistors and pots the same but make the two cap values 5 times larger (750nf).  If the former, then you would want to have a 50:1, rather than 10:1 change in resistance produced by the pot sections.

A possible arrangement might be 68nf caps, dual-ganged 100k pot, and 2k2 fixed resistors, rather than 5k6.  I should emphasize that none of these suggestions are precise, but simply use common values to get you relatively close.  Indeed, the values shown in the schematic only get you in the ballpark.

[Keppy]

Thanks, so all the other resistors would stay the same value apart from the 5.6k ones?

Yes. 1k resistors and 47k pots give you a 48:1 ratio. The lowest frequency would still be about 20 Hz, but the highest would be about 1k, assuming the original math is correct. Like Mark said, if you want the same 10:1 ratio (100Hz to 1k), just make the caps before the opamp 80% smaller.

[Thecomedian]

RC circuits are a multiplication of resistor size and capacitor size.

So if you want to have smaller resistors, go 1/10 for the resistor and 1*10 for the cap, and vice versa if you want to have smaller capacitor size.