How do I add a bass pot to a...

[Robert]

 

[BurntFingers]

There's a James tone stack PCB available at oshpark under their shared projects. Super cheap, super easy. Just run the output of the pedal into the input of the tone stack PCB and voila, bass and treble controls.

 

[Chuck D. Bones]

And a 20dB signal loss.

 

[BurntFingers]

And a 20dB signal loss.

In some pedals that's more than doable.