Thanks for the answer tim.
ThIs may be a solution, but i have tried this the Guitar sound is more muffled than with the Hi-Z on.
I’ve got a 824 too, haven’t plug the guitar on this unit but I think that is the same circuit too.
the problem is that I have bought the UR22 only as a portable solution to play/record guitar directly on Cubase7 with Amplitube3 and it seems that is wasn’t the good choice (if there no solution to reduce the input gain). 
My old little Mackie Onyx do the job better, but it only records on 48 kHz and generally I use to record in 96 kHz.
I have tried the Babyface of a friend of mine, and not problem with the Hi-Z input level too.
I think I have to resell the UR22 and buy another portable unit.
Anyway, if there’s not UR22 update that will solve the hum problem when the phantom power is activated, this will be another reason not to keep this unit.
I was a not a Yamaha/Steinberg hardware user until I tried the UR824 that really seduce me… I have bought the UR22 without trying it, just because I was satisfied with the 824, and finally I was wrong with the UR22.