Tone control

Another application of the "pan between two filters" idea.

Inspired by "A different sort of panning tone control" by Mark Hammer, at hammer.ampage.org

This filter does the same thing, but feeds one of the filters with an inverted signal, so the control allows for different kind of tones.
The inverted signal goes to a bridged-T filter, wich provides a wide notch at about 900hz.
The straight signal goes to a Wien network, for a gentle mid-boost, also at around 900hz.
Click on the image to enlarge

Frequency response plots

Thanks to the phase relationship and frequency response of both filters, we have a flat response when the Tone control is at the center position (blue line).
On the extremes, we have mid-cut on one side (red line), and mid-boost at the other (cyan line).
Note that the deepest notch is not found with the pot totally the bridged-T side, but at about 25% of the rotation. Weird.

For flipping the signal I used a FET phase splitter, wich also allows to adjust the relative level between the in-phase and out of phase outputs, by changing R2 and R3 values. This was needed to balance the filter action at the three settings.

v2.1 01/02/2006 corrected R2 and C2 values
v2.0 19/08/2005

Miguel Canel, Buenos Aires, Argentina bioroids.miguelNOSPAM@yahoo.com.ar (Quitar NOSPAM) http://www.bioroids.com.ar