@mglik You might take a look at my system page (here on agon)... I went through this exact same journey when transitioning from Coincident Super eclipse III's to Coincident pure reference extremes. Had the 8w Coincident Frankenstein 300b set monos and adored them, but they just couldn't power the PREs. I tried a Lyngdorf tdai-3400, pass labs xa-25, and atmasphere m60s, but couldn't give up the Franks. Then I got a pair of first watt f4s and finally found my replacement.
The f4s are unique in that they are a very simple circuit that has no gain stage and only add current to the signal. They are very transparent and just sound like whatever you use to drive them. That can be a traditional preamp (i use a 6sn7 based pre), or even the output of a low wattage set amp. I find the f4 mono blocks to be very clear and quiet, with an amazing holographic soundstage, and a touch of beautiful sweetness. I had planned on using the f4s as booster amplifiers being driven by the Franks, but loved them by themselves and ended up selling the SETs.
As a slight aside, over the course of my amplifier journey I have become convinced that I prefer amplifiers that have a distortion characteristic that is dominated by the 2nd harmonic. That is true of SETs and the f4, but not of the xa-25 or m60s, both of which are 3rd order dominated.
The f4s are unique in that they are a very simple circuit that has no gain stage and only add current to the signal. They are very transparent and just sound like whatever you use to drive them. That can be a traditional preamp (i use a 6sn7 based pre), or even the output of a low wattage set amp. I find the f4 mono blocks to be very clear and quiet, with an amazing holographic soundstage, and a touch of beautiful sweetness. I had planned on using the f4s as booster amplifiers being driven by the Franks, but loved them by themselves and ended up selling the SETs.
As a slight aside, over the course of my amplifier journey I have become convinced that I prefer amplifiers that have a distortion characteristic that is dominated by the 2nd harmonic. That is true of SETs and the f4, but not of the xa-25 or m60s, both of which are 3rd order dominated.