Some cartridges are color coded, some are not (like the Grado). Generally, red is right +, white is left +, green is right - and blue is left -. If the issue changed channels when you changed the connections, the problem is not the preamp. You might have a bad tonearm lead (from the tonearm to the cartridge or from the tonearm to the preamp. It could also be as simple as ensuring the cables are plugged all the way in.
1/23/17 at 9:10am