Low output moving coil cartridges are more likely than moving magnet designs to exacerbate problems with hum, since the signal voltage generated by MC's is much weaker and has to be amplified significantly before going to the preamp. I have not had personal experience with the Coph Nia phono preamp, although I have read several good reviews of it that failed to indicate any tendency toward problems with hum.
Since you have installed two new components in your system (cartridge and phono preamp), you will have to do a little detective work to identify the source of the hum. If you still have your old Grado cartridge and Rotel phono preamp, try putting ONE of those components back into your system and see what happens to the hum. (For example, try running the Grado cartridge into the Coph Nia.) Depending on what happens, you may then want to try the new moving coil cartridge into the old Rotel phono preamp.
There are two other things you might try:
1. Try different gain levels with the Coph Nia, something that is close to the gain in your old Rotel phono pre. If gain is not set to the correct level (usually around 60 db of gain for a moving coil), it can contribute to the hum problem.
2. If you have also replaced the phono cable or interconnects between the phono preamp and the main preamp, you may want to try putting your old cables back into the system to see if it affects the hum.
One of these combinations of cartridge and phono preamp should either eliminate the hum, or substantially reduce it. After you conduct your "tests", come back on this forum with the results and one of the analog heads should be able to provide more specific advice. Hum in analog systems can be annoying, so be patient and experiment until you track down the culprit.
Since you have installed two new components in your system (cartridge and phono preamp), you will have to do a little detective work to identify the source of the hum. If you still have your old Grado cartridge and Rotel phono preamp, try putting ONE of those components back into your system and see what happens to the hum. (For example, try running the Grado cartridge into the Coph Nia.) Depending on what happens, you may then want to try the new moving coil cartridge into the old Rotel phono preamp.
There are two other things you might try:
1. Try different gain levels with the Coph Nia, something that is close to the gain in your old Rotel phono pre. If gain is not set to the correct level (usually around 60 db of gain for a moving coil), it can contribute to the hum problem.
2. If you have also replaced the phono cable or interconnects between the phono preamp and the main preamp, you may want to try putting your old cables back into the system to see if it affects the hum.
One of these combinations of cartridge and phono preamp should either eliminate the hum, or substantially reduce it. After you conduct your "tests", come back on this forum with the results and one of the analog heads should be able to provide more specific advice. Hum in analog systems can be annoying, so be patient and experiment until you track down the culprit.