a switch would be fine if i just wanted to a/b phase and vibrato, but i thought that a blending of the two would be interesting for the sake of experimentation.
any explanation on why you chose the value pot you did in the diagram you posted? is it just trial and error, or is there a particular electronic reason?
The values I chose are for the sake of unity gain (keeping the ON signal the same volume as the BYPASSED signal)
My thinking behind it is that the total resistance to both the wet and dry signal is 300K ohms. THey are also divided evenly, so that makes it even easier. So if you cut the dry signal by increasing the resistance to 250k, then you want to boost the wet by decreasing the resistance to 50k.
I have not tried this mod myself. I have tried it with just the straight 250k pot. It worked, but the taper became uneven on either side towards full turn, which suggested that some sort of limiting resistors were needed on each side. It appeared that as you approached zero resistance after about 50k, the signal would boost. So a 27k - 47k resistor on each side should do the trick. You'll have to experiment with the value of the resistors.