Audio Notch Meter

Description:
A variable notch filter with both high and low pass filters.

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.