With the re-design of the 3124 and the 3124M, we brought the phantom power switch to the front, added a polarity switch, added a transformer balanced stereo output option, added a little color, then Jeff wanted to call them the 3124 Plus and the 3124MB Plus. ..So, be it...The circuit is still the original 312 mic pre-amp card, with all of the stuff hooked up for you. ..Many have tried to copy it, but it still wins the shoot outs!!!