Just got a used Carver amp that has the 3 pin Cannon plug input or 1/4" 3 conductor phone plug.

What is best way to connect a pre-amp with RCA jack to this amp? Use 2 conductor shielded with red going from RCA center pin to Cannon + and RCA shield to Cannon -. What about the ground pin on the Cannon and the sheild in the cable? Same question for 3 conductor phone jack.