the km183 is a diffuse field omni, with an 8dB rise in the upper freqs, and will not give you a flat natural sound in the near field. the km131 is a near field omni which is superb for your application. another approach is to stereo mic the solo violin with an ORTF pair of KM184s anywhere from 4-10 feet out. while the 184 does have a slight rise at aroun 6k, turning the mic(s) off axis somewhat (like ORTF does) will result in a natural flat response at short to medium distances.