@andrewmg - I tried a Cary Audio preamp once. It was really noisy and had a ton of crosstalk between inputs. When I opened it up I realized why. Very poor PCB layout with ridiculously long traces and no ground traces between them.
I also did some analysis of the much loved CJ PV12 line stage. It had a circuit designed for 12AX7 tubes but they put 12AU7's in to lower the gain. They were biased in a totally non linear region at the bottom of the curves. It also oscillated for no reason at all.
I also did some analysis of the much loved CJ PV12 line stage. It had a circuit designed for 12AX7 tubes but they put 12AU7's in to lower the gain. They were biased in a totally non linear region at the bottom of the curves. It also oscillated for no reason at all.