Setting Q for Mercurial Boost?

[bn40]

Looking at an ebay review of the new Chase Bliss super duper preamp, it occurred to me that some of the functionality--semi-parametric mids either pre-or post-gain and three Q settings--can probably be had very easily by modding the old Mercurial. The first thing, assuming a big enough enclosure and careful fitting, can be achieved with an extra couple of jacks and a 3PDT toggle--basically an FX loop for your other gain pedals and an order switch so that the Mercurial is either before or after them. I think this would be a very useful mod, since this pedal obviously has its uses at both ends of the signal chain. Since I currently have mine in a 1590B, I think I might be able to pull it off in a 125B.
But the second part--a switch to select different Q settings--I need some help with. Any thoughts?

 

[Chuck D. Bones]

It's quite easy to change the Q on this pedal. Make R5 a pot. 22K in series with a C50K pot will vary the Q from 1.3 to a little over 6. Don't go under 22K unless you want an oscillator.

 

[bn40]

Thanks!

 

[phi1]

It's quite easy to change the Q on this pedal. Make R6 a pot. 22K in series with a C50K pot will vary the Q from 1.3 to a little over 6. Don't go under 22K unless you want an oscillator.

cool, I’ve often considered building this and would be interested in the Q knob. I’m confused though, you said don’t go below 22k... but the original R6 value is 10k, am I mis-understanding something? Did you possibly mean R4 or R5? just speculating since they are originally 47k. Unfortunately I’m not really up to speed on how this filter circuit works.

 

[Chuck D. Bones]

Yeah, I meant R5. Hit the wrong key. I have the same problem with guitars. ?

I just corrected my original post, nor sure if that will reduce or increase confusion.