Question For My Electrical Expert Friends

I want to move my amp, which is on a dedicated line/circuit. I only need to move the amp eight feet, but I don't want to have to use an eight-foot power cord. Will I negate the effectiveness of the dedicated line (which is one run of Romex from the receptacle to the breakerbox) by coming off of the dedicated line/receptacle with an additional eight-feet of Romex to a newly installed receptacle located eight-feet away from the existing dedicated line/receptacle?

Thanks guys...(and gals!).

_Ben