Hi, I've been here for a while, great forum. I got a voodoolab guitar preamp, the clean channel sound funny and unstable, sometimes it produce high compress or clipped and distorted sound even in extreme low gain setting, it's currently using 4 Sovtek 12ax7wb, after I change the order of the tubes randomly and the sound improved abit, sound much normal now, so I am thinking replacing the tubes, but I don't know anything about tubes, I've read alot of post in here and got some general idea of it, but I still have some questions, please help. 1. there are four sockets labeled v1 through v4, as I check the old post here and saw some people talking about v1 and v2, at first I didn't know what they are talking about, does every preamps have these, can some one explain to me what's the meaning of them. 2. can I install different tubes in the pre? like two JJ's and two Sovtek, or I should put 4 same tubes in it? 3. the current sound of the voodoolab pre works for me, but I would like to make it more open sounding if it's possible, can anyone recommand some tubes where I should start looking? thanks in advance!