are you able to put a calculation for l1 on the spreadsheet?

I have just been looking into this in some detail. One of the problems is that raising the impedance at which the EQ works (so we can use a 10K bridging transformer) means the value of inductance needed to provide a reasonable Q (small bandwidth) is correspondingly higher and the value of capacitance is correspondingly lower. For a modest Q of about 1.2 (which is roughly mid way between the sharp and broad setting on the Pultec) then the calculated values of inductance and capacitance are:

`Resonant f Inductance mH Capacitance nF`

3000 530 5.31

4000 400 3.98

5000 320 3.18

8000 200 1.99

10000 160 1.59

16000 100 0.99At the high frequencies, the capacitance values are becoming impractically low and at the lower frequencies I suspect the values of inductance are greater than can be obtained in a 5mm pitch inductor. If we aim for a more modest Q of 0.6 we get a more reasonable set of values:

`Resonant f Inductance mH Capacitance nF`

3000 270 10.61

4000 200 7.96

5000 160 1.37

8000 100 3.98

10000 80 3.18

16000 50 1.99There is little point in aiming for an even lower Q because you get a Q of 0.3 just using the normal hi boost and cut together.

So, right now I am not absolutely sure that the inclusion of an inductor actually offers much unless you want to have a 16KHz 'air' setting at position 1.

What do you think?

Cheers

Ian