I have a power supply board that supplies 24-0-24VDC to two 20W power amps, this PSU also has a 15-0-15VDC output. I am now installing a pre-amp that requires 12-0-12VAC supply. Would it be ok to use the 15-0-15VDC to power the pre-amp? The pre-amp was a kitset that I assembled myself, would it be better is I bypassed the rectification part of the circuit?