If it is variable 20:1, why even think about 1.18:1 cap change?

So you mean don't worry about the change? I did not get your meaning...

The filter is a Wien Bridge. The formula for F has root(1/(R*R*C*C)) and some pie.

https://en.wikipedia.org/wiki/Wien_bridge

https://en.wikipedia.org/wiki/Wien_bridge_oscillator

When R1=R2=R and C1=C2=C, the frequency of oscillation is given by:

The bridge works for unequal parts but 97% of designs use equal values for sanity. There is a variant with useful values of un-equal but only H-P had the brains to get anywhere on that.

OK, you lost me again... I tried understanding Wiki, but it just went over my head...

But after toying with Excel, I kind of figured it out (I do not get the EXACT values listed, but I am REALLY close those values!)

Band 1 (low end):

f1 = 1 / (2 X 3.14159265358979 X 0.000000047 X 104700) = 32.34Hz

Band 1 (high end):

f1 = 1 / (2 X 3.14159265358979 X 0.000000047 X 4700) = 720.48Hz

Band 2 (low end):

f1 = 1 / (2 X 3.14159265358979 X 0.00000001 X 104700) = 152.01Hz

Band 2 (high end):

f1 = 1 / (2 X 3.14159265358979 X 0.00000001 X 4700) = 3,386.28Hz

Band 3 (low end):

f1 = 1 / (2 X 3.14159265358979 X 0.0000000039 X 104700) = 389.77Hz

Band 3 (high end):

f1 = 1 / (2 X 3.14159265358979 X 0.0000000039 X 4700) = 8,672.76Hz

Band 4 (low end):

f1 = 1 / (2 X 3.14159265358979 X 0.0000000022 X 104700) = 690.96Hz

Band 4 (high end):

f1 = 1 / (2 X 3.14159265358979 X 0.0000000022 X 4700) = 15,392.16Hz

And then, according to the formula, my change would make the bands as follows:

Band 3 (low end):

f1 = 1 / (2 X 3.14159265358979 X 0.0000000033 X 104700) = 460.64Hz

Band 3 (high end):

f1 = 1 / (2 X 3.14159265358979 X 0.0000000033 X 4700) = 10,261.44Hz

If that is the case, I am 100% fine with this.

If it is variable 20:1, why even think about 1.18:1 cap change?

22:1 to be precise.

In stock form, the range would be (with the above mentioned figures):

32Hz to 720Hz = 22.3:1

152Hz to 3,386Hz = 22.3:1

390Hz to 8,683Hz = 22.3:1

691Hz to 15,392Hz = 22.3:1

Mi change would make band 3 461Hz to 10,261Hz, so 22.3:1

10:1 range is a bit more repeatable to adjust.

If you intend to use linear taper pots then it would be wise to reduce the range somewhat.

Perhaps 4:1 or at a squeeze 5:1.

Well, i am kind of stuck because I only got 100K pots... Sure, I could lower the range by increasing the resistor value in R, but I would lose my high end control if I do (for example, to go to 5:1, and keeping 100K pots, I would need to raise the resistor to 25K, which means the highest frequency would be 2.9KHz; if I go to 10:1, by using a 12K resistor, the highest frequency would be 6KHz. I loose all the "airy" frequencies). And the smallest cap I got (not counting ceramics) is the 0.0022, so changing cap is not the way either.

For high frequency spans like that you will need to use Reverse-audio/Antilog taper pots.

(If you are willing to compromise with back to front frequency scales you can use

audio/log taper pots.)

I have (in dual gang) Audio and Linear pots in 100K. I intended to use linear; why do you recommend reverse logarithmic?

your power supply makes no sense. what are you feeding in, and what are you expecting out?

I I was kind of following Rankot's advise... Remember, this is for vocals, not guitars!

It is also better to have regulated power supply with linear regulators.

So I added this in front of the power supply to insure no electrical noises: