Anderton Freq Booster - equalizing volumes?

[GibsonGM]

Hi guys,

I wanna put together one of them there frequency boosters...already have the basic one done set to 100Hz (the one with input buffer, running on 9V).  I'd like to have the first section 'always on', and switch in a 2nd section for mids (400Hz) when I use my thin-sounding Tele.  Of course, the gains are multiplicative and the volume will crank when I do this...any thoughts on how to get them equal in volume?   Trim pot somewhere, etc?   I've already tried playing with the feedback resistor values and a "2nd volume control" but don't get very far.  I think I need a switching idea to throw a trimmer in somewhere and short it when only the 1st section is on.  I have a DPDT toggle I'd like to use for this. 
I should know this 

Any thoughts appreciated!
Thanks

Mike 

[GibsonGM]

I guess the only good way to get this done is to build 2 of the circuits, with the input split with opamp splitters to feed the 2 sections.  Then the volumes can be equalized and re-summed, with a trimpot on the 2nd section to keep the volumes equa when the midboost section is switched in... 

[Ben N]

Do a search; I'm pretty sure Mark Hammer (who else?) has offered suggestions for combining multiple Frequency Booster sections tuned to different center frequencies. Depending on where their response curves overlap, I'm not sure you would necessarily get massive overall gain, rather like the ROG Mr. EQ, which also chains eq sections in series.

[Mark Hammer]

Each boost section is engaged by connecting the 10k resistor from the inverting pin to ground (or Vref).  Note that when that resistor is 10k and the feedback resistor is 10k, that stage will have a gain of 2x  ( [10k+10k]/10k ).  Since ungrounding the 10k resistor from the inverting pin makes the stage unity gain and nonfunctional at the same time, clearly the stage needs to have at least some gain to work.  But does it need a gain of 2x?  Let's try finding out.  Consider replacing the 10k to ground/Vref with a higher value, like 39k.  That will give a stage gain of  49k/39k = 1.25.  Let us know how that works out.