Narco, yes, passive DI boxes do use transformers to eliminate hum and other noise. The JDI has a Jensen transformer and the JDI Dual has two, which allows for LOTS of other possibilities (ground lift, phase shifting and reverse polarities among others). Yes, Hi-Z equipment aren't required to have a transformer in the front for various reasons including size restrictions and complications that it would introduce to their unique designs and engineering - there are a lot of reasons. EBtech is great, but Radial offers more 'musical' options. They are THE go-to DI boxes for many artists for good reason.

Numb, yes, there are quality UPSes and high end power bars that can solve problems that you may have in your outlets. We have a couple of great music shops that carry them for that very purpose. However, the solutions for ground loop hum and interference noise are not interchangeable, as the same noises can be from a plethora of causes. A good music store will have gobs of gear to address these, but they'll be the first ones to tell you that there isn't a silver bullet. Nonetheless, good you mentioned the UPS option.

Edited 1 time by hoisin Nov 2 13 3:13 AM.