Yes 2x OPA2227 in buffer and one DIP8 socket with 2xOPA627. an yeah, when I switch to 6,5x gain there are some instability issues indeed (i'm going to switch them today ) - thanks for advice! I'm using 2,5x low gain at all time. I have to say, I own my o2 for over a year and I can't really recally any background noise issues with any headphones I ever plugged into this unit. It's been always black background, kind of reference to me.