Steinberg UR22 MKII - bad Keyboard Sound

Hi guys,

today I activated my new Steinberg UR22 MKII and I connected it to my Rode NT1A. It is working properly (except of a quiet background noise), but now I tried to connect my Keyboard in the Mic/Line input and it sounds horrible. If I connect my headphones directly to the Keyboard the sound is great, but when I connect my Keyboard to the Steinberg UR22 MKII Line/Mic Input it sounds bad.
Can someone help me?

(Sorry for my bad English)