Open "...\rathena_RENEWAL\db\re\level_penalty.txt" and change all "2,CLASS_NORMAL" value to "0,100":
// Drop rate modifiers due to level difference
2,CLASS_NORMAL,0,100
2,CLASS_NORMAL,0,100
2,CLASS_NORMAL,0,100
2,CLASS_NORMAL,0,100
2,CLASS_NORMAL,0,100
2,CLASS_NORMAL,0,100
2,CLASS_NORMAL,0,100
2,CLASS_NORMAL,0,100
2,CLASS_NORMAL,0,100
2,CLASS_NORMAL,0,100
2,CLASS_NORMAL,0,100