Hum causes: MC cart, arm cables or phono stage ??

Dear ALL, I have a Denon D 103, Sme 309 and its cables, plugged to a brand new Phono stage from Coph Nia.
I have a consistent hum that I was not listening with my previous system (Grado cart+ Rotel phono stage).
It does not harm when listening to medium level rock music but I think it will be listenable when playing low level piano music for instance.
Shall I investigate and how in all the rest or the pre stage can have its part of responsibility ??
My feeling says that this MC cart is quite sensitive and probably the previous one (MM) was not at all.
I would like to know if the hum is due to the pre so I can try to give it back as it is new.
How can I check if it is part of the problem ??
Tks so much
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.
Make sure your ground wires are well connnected and have clean connections.
If the Coph Nia has a three-prong A/C cord, try using a "cheater plug" to lift the ground connection. Also, is the turntable well away from power amps or other large transformers, ie power conditioners? Hopefully, the phono cables are shielded, but even so, keep them away from power cords. Good Luck.
Well , I am not sure how to cheat. The Coph has a 2 way plug Schuco without the ground.
On the contrary the turntable has a 3 way grounded plug.

All goes to the main via grounded plugs in the wall
High power gear are not next to the TT or phono stages.
Tks for further development
Try unplugging the tonearm leads from the Coph Nia, and see if the humming goes away. If it does not, then you know it is in the phono stage or cabling. If it does go away, then it is something in the cartridge or tonearm wiring.
I tried , It went away almost totally (only a small hiss)
This means coph nia is OK.
I will concentrate on the cart and tonearmcable.
I will now try to remove the cart hold by its shell,leaving the tonearm cables oplugged to the coph without the cart.
This should help to go to the Hum point
Tks anybody.
The investigtions ended.
My mistake as I had inverted one of the cart plugs.
Stupid me, but I learned the lesson.

Coph Nia sound splendid now
Tks anybody that drove me to the solution