Unidrive dissection?

[Vince]

I've seen these with an added bass 'filter' knob. So rather than socket everything and experiment, I thought I'd be lazy and ask instead. (and it's too damn hot here for stressing)

I'm looking at the 33k (R2) that leads to the 150n (C1) cap from the input? I know it can be switched but I'd rather have a control knob.

Thanks in advance

[alex.s]

You could put a potentiometer as a variable resistor followed by a large value cap (1u could be a good one) in parallel with C1 and perhaps even lower the value of C1.

By doing this you are effectively creating a "variable" input cap that will range from C1's value to the sum of C1 and the aforementioned large value cap you added.

This is an easy and fairly common way of controlling the amount of low frequency entering the pedal. DAM, for instance, uses it quite a lot, as in the Meathead Deluxe, Drag'n'Fly and Red Rooster.

Hope this might be of some help!