Filter Schematic
http://www.commlinx.com.au/Filter.htm

Voltage Controlled State Variable Filter
Galaxy Noise Filter
RC Notch filter
Low-pass active filter
Filter Circuit for the Earthworm Seismic Data Acquisition
System
Active 2nd Order Filters
RC Notch Filter (Twin T)
Multiple Feedback Bandpass Filter
CW filters
Self-tune filter
SSB AF filter
Helical Resonator Notch Filter
3KHz low-pass filter plus audio amp (PDF)
Active bandpass filters
Bandpass filters
Butterworth filters
Narrow band audio bandpass filter
Single-Supply Sallen Key Notch Filter
Single-Supply Twin T Butterworth Low Pass Filter
Inversal notch and bandpass filter
DC Accurate, Active RC Lowpass Filter
Chebyshev Bandpass Filter
Bandpass filters
Chebyshev / Butterworth filters
Biquad Active Bandpass Filter Schematic
Voltage controlled filter and oscillator
"A" Weighting Filter For Audio Measurements
Multiple Feedback Bandpass Filter
Digital signal processor (DSP) for radio communications
29.85 MHZ bandpass filter schematic
29.85 MHZ notch filter schematic
LC filter design