Quote Originally Posted by vuki View Post
the value of 4R7 resistor would give wide enough range for tuning high freq. energy.
That's cool.

Vuki did you know that your HP filter (before the contour) has the topology of a 3rd order, but the electrical function of a 1st? You might double check me, but it looks like the filter functions is very near 1st order at 4KHz. A single 5uF cap would do the same. The inductor and resistor do pull it down a little faster. Did you do that by ear?