I'm a huge fan of this box. For the price it's excellent. My volume knob has gotten scratchy over time, but only when being turned, not when in a set position, and I've had it for a few years already now. The passive circuit sounds super smooth to me, I have no complaints on sound quality. The routing features are excellent as well. Forget the big knob and get the SM Pro. Nice headphone amp too, and nice small footprint.