I wanna create one, and share this on my school forum. The thing is, i cant find any circuit with explanation about its cut-off freq.

 

What's BSF?

You could built a Sallen-Key active filter using a BJT emitter-follower in place of the usual unity-gain op amp, (with perhaps some small reduction in its performance).
You can cascade a low-pass filter followed by a high-pass filter to get the bandpass.
Google Sallen-Key filter.

(A nit, but I find it difficult to take a technical post seriously when it contains the word "wanna". )

 

What's BSF?

You could built a Sallen-Key active filter using a BJT emitter-follower in place of the usual unity-gain op amp, (with perhaps some small reduction in its performance).
You can cascade a low-pass filter followed by a high-pass filter to get the bandpass.
Google Sallen-Key filter.

(A nit, but I find it difficult to take a technical post seriously when it contains the word "wanna". )

I think he means a Band Stop Filter, a Band Reject Filter.

 

The original Sallen & Key filter did use a single discrete device, the unity gain op-amp was a later adaption.
It was originally a triode valve connected as a cathode follower! Both bipolar transistors and FETs can be used successfully, although it does lead to an offset voltage of Vbe of Vgs.

 

Both bipolar transistors and FETs can be used successfully, although it does lead to an offset voltage of Vbe of Vgs.

I have used an NPN emitter-follower driving a PNP emitter-follower to reduce the offset to a low value.
That, of course, doesn't work so well with complementary FETS due to their inherent differences in Vgs(ths).

 

I think he means a Band Stop Filter, a Band Reject Filter.

It that's true, than the TS can consider the Twin-T filter.