Hi Jax (No Pun intended
) A few things to try :
1. If you move the KN7000 away from the Hammond but still use the same connecting leads, is the hum still present? If the hum disappears when you move it, then it could be induced by pickup from equipment in the Hammond.
2. If the hum remains, I suggest you check the cables from the Line out of the KN7000 to the amplifier input - particularly the outer screen connection to the sleeve of the jack plugs. Also worth checking that the sleeves of the jack plug connections are clean and making a good contact with the jack sockets, at both ends.
3. If you have multiple items connected to your Rolands, try connecting them one at a time to isolate the problem.
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Willum