simple sweepable Highpass Filter?

Hi,
sorry if I might have posted in the wrong forum. I wasn't sure where to post.
I am running an old Mackie CR16 Mixing desk which I like and which I am going to modify for the missing direct outs to track seperately into Ableton live.
Now the Mackie doesn't have Highpass Filters.
I really would like to add those (in a seperate 19 inch case) before the signals go into the desk.
Ideally would be a sweepable design going from very deep (dont know 20 Hz) to something like 100 or 150 Hz.
I have to build it for 16 channels so it would be great if there was a simple, effective and not too bad sounding solution for that.
On units like noisegates are sweepable Highpass Filters so I am hoping the construction wont eat up too much money.
Could anyone recommend a schematic for that?
My knowledge of electronics is very low but I am fine etching pcb's.
By loooking online this one comes up very often "20Hz to 200Hz Variable High-Pass Filter" however there seem to be two potentiometers to set the cutoff frequency which seems to be counterintuitive during mixing.
Help greatly appreciated.

Kind regards,

Jens