This circuit adds a treble shelving filter to Option B’s bass shelving C31 C 22nF filter. C32 C 22nF C33 C 680pF Easy to miss: Compared to Option A, R33 has been added. Don’t CF31 C 0.1uF forget it, or the filter will not work! CF32 C 0.1uF POT 100k, rotary, For treble, the maximum cut/boost is POT31 lin taper POT 100k, rotary, POT32 lin taper R31 R 22k R32 R 22k When the potentiometer is at its centre, the high-frequency R33 R 22k response is flat (gain of 1, or 0dB). R34 R 10k R35 R 10k The transition frequencies (from “low” to “high” frequency gains) R36 R 47k changes a little bit depending on the pot setting, but here are some NE5532 low-noise guidelines: U31 opamp, DIP8 IC When the pot is at the centre, there is a theoretical boost/cut that cancel out (to give a flat response). The cancelling happens at 3.72kHz. When the pot is at maximum boost or cut (fully turned to either end), the transition happens between 3.36kHz and 16.0kHz. References: Original paper: http://www.learnabout-electronics.org/Downloads/NegativeFeedbackTone.pdf A variation of this circuit: http://sound.westhost.com/dwopa2.htm
C31 C 22nF C32 C 22nF C33 C 680pF CF31 C 0.1uF CF32 C 0.1uF POT31 POT 100k, rotary, lin taper POT32 POT 100k, rotary, lin taper R31 R 22k R32 R 22k R33 R 22k R34 R 10k R35 R 10k R36 R 47k U31 NE5532 low-noise opamp, DIP8 IC This circuit adds a treble shelving filter to Option B’s bass shelving filter. Easy to miss: Compared to Option A, R33 has been added. Don’t forget it, or the filter will not work! For treble, the maximum cut/boost is When the potentiometer is at its centre, the high-frequency response is flat (gain of 1, or 0dB). The transition frequencies (from “low” to “high” frequency gains) changes a little bit depending on the pot setting, but here are some guidelines: When the pot is at the centre, there is a theoretical boost/cut that cancel out (to give a flat response). The cancelling happens at 3.72kHz. When the pot is at maximum boost or cut (fully turned to either end), the transition happens between 3.36kHz and 16.0kHz. References: Original paper: http://www.learnabout-electronics.org/Downloads/NegativeFeedbackTone.pdf A variation of this circuit: http://sound.westhost.com/dwopa2.htm