The DWELL knob controls how much signal is going into and driving reverb springs. As on the original unit, cranking this knob up can cause clipping on the wet side due to the signal crashing the springs. Though it seems to imply reverb length (and sort of functions this way), this control is quite literally a volume knob for the springs.
The TONE knob allows you to roll off just the right amount of high end from only your wet signal. Roll this knob back if you want the reverb to appear to more distant and out of the way of your dry sound.
We took liberties with the MIX knob extending beyond the original reverb tank units because we wanted you to be able to make the Topanga 100% wet. Otherwise it is much like the knob on the tanks, allows you to balance between your wet and dry signals.
Original spring tank units had a big feel to them that encourage a lot of attitude from the musician playing through them. We asked ourselves, “how can we make the Topanga even bigger sounding?!” The only answer to that question was add a VOLUME knob that pushes the entire circuit! This is a modification that we have actually performed on the big tube tank units!