Pass Labs AMP’s- What is the best Pass Amp Sound for You from past 10 years

So I have an XA-25 and its outstanding. I’ve tested the XA60.8 mono’s and there was not enough difference to move to them; no jaw dropping moments. Don’t get me wrong they were fantastic, but so is the XA25. Looking at the 350.8 or 250.8, etc.... even in comparison the Integrated INT-250... If you love it; want to explain what you like and why? I’m wondering what others are thinking... 
My set up: Wilson Sophia II’s, XA-25, Pass Labs XP-22 pre, Merging+NADAC. 
I took an X350 home one weekend in 2002 for an audition. 19 years later- this past February I switched to the new X260.8 monos. My son has the X350 now. I’m using these amps with an ARC Ref 5SE and Thiel CS6 speakers and Purist Audio cables throughout. I can play it loud for me and the needles don’t move. I was nervous that I might feel the loss of the few watts difference from the X350 but no. It took some time for them to break in. Every time I listen now the sound stage is startlingly clear and focused. The highs are crisp and fast. That’s the best way I can describe it.
The only solid state amp outside of Pass Labs that I would own is CODA, and that is what I own!

I got my first F4 (actually I built it) to serve as a zero-gain bass amp to augment my Coincident Franks, but unfortunately biamping on the PREs just kills their coherency (I've tried both active, with the Lygdorf, and passive, with the F4)... even with the Franks providing the F4's input signal from their speaker posts.  When I finally ran the F4 alone I was shocked to find that it was better than all the other amps I'd tried with the PREs. 

Previously, the Franks (currently up for sale) had won every shootout, but they simply don't have enough bass control for the PREs and I was forced to move on.  Super happy that I stumbled onto this amazing speaker/amp synergy, however. 

Thanks so much for sharing your power amp journey, probably the most useful I've ever come across-especially because it compares, at least in some important ways, respectable 300B SETs like the Franks with the First Watt F4. "They have a bit of the sweetness of my 300b SET amps, but both clarity and bass control that beats out all the other amps I've auditioned on these speakers.  The soundstage is expansive, imaging is precise, and there is absolutely no harshness or grain... an important quality with the accuton ceramic tweeters on the PREs.

Exactly what speakers do you have? I have two F4s that I had ordered from Reno Hi-Fi years ago. My speakers I'm have custom built from a proven design are ~ 94db/m/watt but only play down to 70Hz before my powered subs take over, so I can't see even one F4 having any problem driving them in my room and listening levels. I'm very glad you also mentioned the F4's "expansive" soundstage. Would that also be so in a 3D sense? And even if I use only one F4?

Also, very assuring is that you found zero "harshness or grain', as my tweeters likely be Raal ribbons.

Now the big questions are what is the ??db spl/m/w of your speakers, what preamp are you using and what's the approximate output  voltage usually needed to drive the F4 to make your speakers shine?




@ajant I have Coincident Pure Reference Extreme speakers.  I think they're around 92db/1w/1m (listed as 94db, but I don't believe it) and supposedly a flat 8ohm impedance. 

I'm sure you could get by with a single F4, mine worked fine that way... but I still believe in monoblocks for isolating right and left channels.  I have tried my F4 monoblocks in a bridged design and actually preferred just using a single channel.  Essentially you're doubling your power supply capacity that way.  I found that there was less distortion with an increase in clarity, smoothness, and sweetness from the amps using them in that configuration.  And yes, I find the amps very nicely 3-dimensional, at least as long as the source and preamp support it.  That's a key decisional factor for me for every component.

I've used two preamps with the F4s, a Bob Sachs 6sn7 pre and a custom Shiny Eyes EML20A DHT.  The Shiny Eyes pre is a simple single stage single tube DHT design... from Radu Tarta: "This is one of the simplest one stage preamps that is using an excellent sounding DHT and extremely low distortions, second harmonic being dominant. The gain is 14dB (5x) and with a 2Vrms source will provide 10Vrms at a Zout of 375 ohms. Measured THD was 0.02% at 10Vrms output (50Vrms on the plate)."

It gets plenty loud enough, but I do periodically wish I could be idling a little further down the volume control ladder.  

You can read more about my amps, speakers, and preamp on my Audiogon system page.  I personally couldn't recommend the F4s more based on all the amp comparisons I've done with my speakers.  I actually ended up rebuilding them with custom high quality parts and massively overbuilt power supplies (so now 4x the levels of a standard F4 for each channel) and they just got better and better every step of the way.  That information is all outlined on the system page if you happen to care.  I would only change amplifiers if I ended up with truly high efficiency speakers over 100db/w/m, or needed something with a lower damping factor.

Hope that all helps.