My problem is slightly different but possible related. I have a Neumann running in channel 1. The mix sounds great but if I am not singing into it for a few minutes -- maybe even less than a minute -- the channel goes flat with a roll off in the volume and the dynamics of the mix. Then after a second or two of singing into it it comes back to life, volume boosts back and effects kick in at the desired setting. Any ideas what's up with that?