Help with DIY dedicated circuit


I am wanting to install a dedicated circuit for my amp, but getting from my panel to the wall behind my amp is going to be difficult. As I was investigating in my attic, I realized that when I changed my stove from electric to gas, the unused 30 amp Romex 10/3 wire will reach within 15 feet of where I want the wall outlet. Do I install a junction box and run Romex 10/2 to the new wall outlet and use the 30 amp breaker? What is the best way to connect the wires in the junction box?
128x128jonandfamily
Sorry he deleted his posts it looked as though you were directing it to me as I didn't see his post. I can see I made a mistake going back and reading it again. 
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@djones51 is correct in his last post, except for the terminology of phasing. In residential electrical systems, it is actually called “split phase”, which is because the utility supplies only one leg of a three phase feed, via a center-tapped secondary on a step-down transformer, where the center tap is considered the neutral conductor, and bonded to ground at the main service panel.
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