Mutchus

This simple and low pass  notch filter circuit. A variable notch filter with both high and low pass filters. Circuit Diagram: Notes: At first glance this circuit looks fairly complex, but when broken down,can be divided into high pass and low pass filter sections followed by a summing amplifier with a gain of around 20 times. Supply rail voltage is +/- 9V DC. The controls may also be adjusted for use as a band stop (notch) filter or band pass filter.

Component value sensitivity is extremely critical, as are temperature coefficients and matching of the components. Best performance is attained when perfectly matched components are used and when the gain of the amplifier is unity. 4.5 Mhz Notch Filter Schematic To illustrate, the quality factor Q is very high as amplifier gain approaches 1 with all components matched (in fact, theoretically it approaches infinity) but decreases to about 12.5 with the amplifier gain at 0.98.