I have a OPS1 Mk4 and it is super silent! Even more details and a much better soundstage than my older Xono. Better defined, meaty players in the stage, more hall info, better layering and seperation of players in the stage - example: much more detailed with better seperation and localization of the inner details of large symphonic works ie able to seperate/layer the 1st vs 2nd violas, hearing the 2nd cello's vs double basses.....(ie not just with small emsembles). And boy can my OPS1 rock out too - Big bass drum kicks. I have a Basis/Vector/Sumiko Celebration cart (.5mv) and with high gain, loaded at 1kohms, it is super silent - no tube noise. Both with the stock A-frame Ei Yugo 6dj8 and Sylvania 5751's, or with my cv2493 and Raytheon windmills. Now I also have the external power supply option for the OPS1 so that may be part of why it is so quiet even at the high gain setting. And Herbies Halo's are great - but they can over damp the sound a bit (as the circuit and tube sockets are already well isolated from the chassis) - so I slide the Halo's down closer to the pins - this allows more of the tube character and wetness of the stage to remain - yet damp any microphonics and maintain that focus of stage the herbies provide. Check out the Review on Soundstage.com - it really nails the OPS1 as well as OPS2. Dynamic, ppp to fff in a downbeat; big stage, great mids - super musical yet very detailed, I have nothing but positive things to say here. (previous stages owned are Camelot, Xono, M3A, bc23.....)
Anyone care to give voice to their tube rolling experince in the OPS1 or OPS2? Esp with the 6350 Mu Follower? I have a RCA Black plate 6350 in there now - I have a Sylvania or 2 here as well but have not ventured to roll this tube yet.