highly unique offshoot of the Hall Passive Notch filter that provides
an adjustable - deep notch between 38 Hz and 86 Hz. Both R1 and R2 are
tracked equal. At the 38 Hz notch, shown on the left - both pots are at
100 % of their shown values with a suppressed value of -37.5 DB.
With both pots at their “0” % position, shown on the right, the notch
is -54.7 DB at 86Hz. In the left hand image the pass band is 300 to 10
KHz flat. The Right 1.5 to 10 KHz. The output must be fed into a
minimum 50K Load. Low frequencies below the notch values are also