Thank you to all. Actually, comparing to McIntosh C20 preamp, ARC LS22 ( I just bought) is lacking of high and low frequency. It is OK in term of noise ( I think it is better than Mc Intosh C20). So, I am not sure what causes the problems I hope replacing tubes will fix the problem! I am going to try some tubes and let you guys know the results. Feel free to recommend.
Thanks
Thanks