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Perspective: https://youtu.be/pdw7esZBbXEIt’s a nice video review as it answers some of the OP’s questions. From what I have read on Nelson’s FW webpages, the F6 is still in production.Best,Anand.
If you are interested in adjusting the harmonic structure in this amplifier, there is a nice easy place where you can do it. I have added low-value power resistors (R13 and R14) in series with the Source pins of the output transistors. Typical values for these would be 0.025Ω to 0.1Ω. If you leave R13 at 0Ω and put 0.05Ω for R14, you will find yourself with a positive-phase second harmonic. By this I mean there will be expansion as the wave goes positive and compression as the wave goes negative. If you have a negative-phase second harmonic, you could use this approach to null it out. If you leave R14 at 0Ω but set R13 at a small value, you do the opposite either creating a negative-phase second harmonic or nulling an existing positive-phase second harmonic.The two phases of the second harmonic do sound different. In fact the most consistent observation people have reported is that positive phase has a little more projection to it, that it's a little more in your face and immediate. Negative phase tends to add more depth. This is something you can play with and moving on to the next slide, for this one we credit Patrick (EUVL) on DIYAudio. What he did was come up with a variable version. Why not put a pot on it? So here you can adjust P3 and P4 up and down, trimming the relative perfection of the symmetry, creating or nulling the second harmonic...
Actually, the F6 is no longer made and really isn’t the same as an F5. The only FW amps in production currently are the F7 and J2. The SIT-3 is coming soon. If someone is looking for an F5, the F7 is Nelson’s simpler, updated, and more refined version of the F5 circuit. But to get back on topic : Of the OP’s options, the M2 should be an excellent match both in terms of power and sonic synergy.
At a typical 10 feet listening distance, 25W gets you 108 dB at your listening position with your 101 dB/1W/1m sensitive speakers. At 108 dB, your party guests will risk hearing damage, much less be able to have a conversation...
Well... that's not the whole story. 108 db with a full signal through the gear and not allowing any clipping room. When I would master our stuff I would shoot for 12 db of dynamic range from the average program level and the peaks. Now, others compress the daylights out their stuff so would be less. Also, how does the amp sound running full out. I think the Pass will get the volume most would want but how well it controls the large driver is another question. I would go with the Ampzilla, although never heard any of them. Rocket Ronny
capable of filling my big living room (12m x 6m) with powerful party levels sound - not necessarily ear splitting levels.
To say all of this differently, consider Zu speakers for a moment. Their Druid MkIV was famously dynamic, meaty and dark and really polarized opinion. Druid fanciers felt that the newer Essence with its ribbon tweeter veered too far from the house sound. They'd use the M2 on the Essence. Those for whom the Druid was too dark would run the F5 for maximum illumination of that speaker's deliberately subdued top end. This now gives us a generalized scale on which to place the M2. The F5 is jumpiest and cleanest. The J2 is sweeter. The M2 takes a backward step from ultimate resolution to go mellower, softer and just slightly voluptuous.
Locked into the F5/J2-type sound as a personal ideal, I'd initially weighted the M2 relative to that and keyed in on what it didn't do. Once I understood and then appreciated how Nelson Pass had indeed cloned the essence of a resolved and well-controlled direct-coupled valve push/pull sound of Kaivalya caliber, the proverbial bell tolled. The M2 doesn't emulate classic SET flavor. Rather, it approaches the kind of tube sound a gifted SET designer like Sasa Cokic gets when commissioned to employ pentodes in class A push/pull. To confirm that conclusion, I finally leashed up my Japanese 300B SET.
Thank you all for your opinions, I find them all useful and interesting. I only refer these three amplifiers because that's what there is available at my local shops. Not the F5 nor anything else; The M2, the 7150 and the Amp2000, being this last one twice the price of the other two - 2500 USD (new) against 1500 (used). I confess that I'm curious about the capabilities of the Amp2000, but my budget needs to stretch a bit beyond my wife's acceptance to get that one. And my speakers will stay with me for many years, so I think I won't need a lot of power in the future. That puts the Ampzilla a bit out of the equation, but I'd like to read opinions on this one as well. Regarding the McIntosh, I like the looks but I don't know about the sound and although the looks are important (again the WAF), I choose the sound. And from what I read across the internet, First Watt (as everything else out of Nelson Pass' hands) is an amazing sounding machine. I never heard one, but I have the chance to get this one now. It's a shame I can't try them in my system, but meanwhile I asked the opinion of Mr. Pass himself about the synergies, and according to him (the reply came in less than one hour. From Nelson Pass. Fantastic!) the M2 would pair very well with the rest of the gear. So I think I'll give it a try. They also sell well, in case I want to trade it in the future. I will listen to the different amplifiers anyway, even though in different systems. But at least I'll have a sample of the three. And my "party levels" are not crazy volume levels like in the club, but loud enough for head banging. I guess the 25W class A through my 101dB speakers are enough...
