The clipping is strange. The maximum voltage swing might be dependent on the supplied voltage. The "standard" O2 comes with a 2.5x gain in "low" mode. But if the power brick does not swing 15VAC then things may indeed clip. I will try battery also. Some things come with 12VAC bricks and if that is the case I recommend getting a 15VAC one. It seems you had an underpowered O2. That said, not everyone is going to like the same stuff. Many don't like it. Such is life. As far as negative feedback and opamps, I don't see the use of those in a negative light. In fact I like negative feedback and opamps. But that's just me.