# 6 Band EQ formula?



## irvmuller (Jul 23, 2021)

So, let’s say I wanted to change the frequencies on some of the pots for the 6 band eq. What would be the formula if I wanted to use a freq that’s higher or lower?


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## benny_profane (Jul 23, 2021)

The circuit comprises multiple bandpass gyrators. You can use this calculator to adjust the values to change the affected frequencies.


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## Chuck D. Bones (Aug 5, 2021)

Keep R2 above 470Ω and the ratio of R1/R2 <100.  There are four parts you can fiddle to change two parameters (F & Q), so there are many solutions.


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## irvmuller (Aug 31, 2022)

hey guys, I figured out how gyrators work. The info given was VERY helpful. Thanks!

However, the last freq, pot 6, seems to be doing something different. Could someone explain to me what's going on there?


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## Chuck D. Bones (Aug 31, 2022)

That last filter is a high-pass or low-pass filter, depending on whether POT1 is above or below noon.  It is a shelving filter, which means that above the cutoff freq, the gain is flat.  The cutoff freq is determined by R20 & C16 using the usual formula.  R20 determines the max cut or boost, so if you only want to change the cutoff freq, leave R20 alone and vary C16.

BTW, that Gyrator formula website leaves out an important piece of information: The impedance at resonance.  That impedance determines the max boost or cut.  In the case of the 6-Band EQ, the 470Ω resistors determine that impedance.


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## Mike McLane (Sep 14, 2022)

I mentioned something some time back about a "Tom Bukovac version" where the the bands were focused on the mid ranges.



Anybody have any interest in that?


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## Robert (Sep 14, 2022)

It sounds right up my alley.


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## benny_profane (Jan 6, 2023)

What modifications would be required to preserve the frequency bands while changing the pot values to B100k?


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## Chuck D. Bones (Jan 6, 2023)

The pot value doesn't affect the center frequency of each band.  It does affect the smoothness of the sweep.  If you want to keep the same feel, then scale all of the impedances up by 2x.  That means doubling resistors and halving capacitors.  This includes all of the components in the gyrators, R6 and R7.

You know I love building pedals, but sometimes I punt & buy one of the Chinese knockoffs.  I bought a Caline CP-24 10-band EQ pedal for $37 four years ago on the big A.


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## benny_profane (Jan 6, 2023)

Thanks @Chuck D. Bones 

I actually went that way myself too (MXR 10-band on wild sale though). I’m thinking about a combo build here though and would like to have the EQ control integrated.


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## Feral Feline (Jan 6, 2023)

Cross-referencing for people looking to mod the 6-band:






						6 Band EQ Mods
					

I would like to know if there are are any ways to modify the 6 band EQ.  Change the frequency of a knob?  Quiet component recommendations?




					forum.pedalpcb.com


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## Chuck D. Bones (Jan 6, 2023)

benny_profane said:


> I’m thinking about a combo build here though and would like to have the EQ control integrated.



I take it you've already tried this out by stacking the EQ with the other circuit you have in mind.  Do you plan on putting the EQ up front or at the end?


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## Feral Feline (Jan 6, 2023)

Stick it on a flip-flop so you can have EQ before or after the main circuit.


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## benny_profane (Jan 6, 2023)

Chuck D. Bones said:


> I take it you've already tried this out by stacking the EQ with the other circuit you have in mind.  Do you plan on putting the EQ up front or at the end?


Yep. A breadboarded version of the Unicab with the MXR ten-band—not the ppcb six-band. Planning on having it be a desktop end-of-chain interface with the EQ for adjustments before the cab sim.


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## Chuck D. Bones (Jan 6, 2023)

As long as you don't overdrive the Unicab or the EQ, the order won't matter.


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