In our project studio, we have several pieces of gear that use 9 volt AC wall-wart type power supplies. (When you have 16+ wall-warts, I think the term "infestation" is applicable). I thought it logical to assume that by purchasing a large current capacity transformer, I could replace the power supplies. I tried an 18VAC center-tapped transformer, and balanced the loads between the legs of the secondary. The hum rendered the project useless. I thought at first that the hum was induced by the transformer field, so I move it to 20 feet away, with no improvement. Any ideas on how I can make this work?