Two Band Parametric EQ

Thread Starter

GuitDud

Joined Apr 23, 2019
1
Salutations, most esteemed experts on circuit analysis.

I want to build this two band parametric EQ (one band consisting of frequency variation within it, Q factor variation, boost-cut in dB) for my guitar and my head is spinning these days trying to understand these many options for parametric EQ circuits. These circuits can be various, as I understand from different webpages. Problem is that some give its equations, some do not, and for these I cannot figure their equations, with which I would adapt its components to my EQ's needs.

Obviously I am no expert yet on these circuits and thus I ask for your help in interpreting these circuits.
Please bear with me while I try to understand and solve this.

I think this circuit could solve my EQ needs.



(Full circuit: http://byocelectronics.com/parametricEQschem.pdf)

This circuit was made with three bands and here is one band shown.

Are

fmax = 1/(2*π*R15*C5)
fmin = R10/(2*π*VR3b*R15*C5)

?

(This is by comparison with this circuit (https://damien.douxchamps.net/elec/param_eq/), in which I see some similarity for frequency, but not for Q and boost-cut.)

BYOC (owner of circuit) says that this circuit has three bands:
33Hz - 330Hz,
250Hz - 2.5kHz,
1.1kHz - 11kHz,
(1:10 ratio).
But with these equations we get
50Hz - 312Hz,
416Hz - 2.6kHz,
1.8kHz - 11.5kHz.
Should these be so?

To attain that 1:10 ratio either R10 needed to be 1kΩ or these equations lack something.

What equations then here for frequency, Q factor and boost-cut?

Also in this circuit there are many resistors with same value (5.1kΩ and 1.6kΩ). If one is changed, should all others be changed? (Damien Douxchamps thus seems to indicate.)

Most grateful for your help and time.
 
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