Catalinbread Topanga Spring Reverb Guitar Effects Pedal A reverb pedal that functions just like a real deal outboard spring reverb unit The DWELL knob controls how much signal is going into and driving reverb 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 MIX knob extends beyond the original reverb tank units because they wanted you to be able to make the Topanga 100 percent wet.