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F6 vs. F5. When Manolis Proestakis and I discussed amps for a review of his Tune Audio Prime widebander speaker—I could never get his big horns up my winding staircase regardless of lust—he explained that despite showing his top models with valve gear (Aries Cerat from Cyprus for years, at 2013's Munich HighEnd with Engstrom&Engstrom from Sweden) he listens very happily to an F5 at home. My lack of any remaining tube amps thus didn't bother him one wit. I felt tickled that another tube aficionado had discovered Nelson's transistor take on the subject. When I'd sold off my Voxativ Ampeggios, I'd demo'd them to the German buyer with my SIT-1 monos. When he returned months later to pick up the shiny boxes, he'd acquired his own SITs in the interim to enjoy the same combination. Zu's Sean Casey too has gone SIT-1 despite his penchant for very high SPL and the 16Ω loading of certain Zu where he can run out of steam. Contributor Frederic Beudot inherited my Yamamoto A-08S 45-based SET but now drives his French/Canadian Ocellia speakers with an F5. He loves the combo. This type of evidence is quite suggestive of the success various FirstWatt amps enjoy with the tube crowd. The sound isn't the same but has enough common ground with special attractions which make it a lovely alternative that routinely carries the day.


The F5 is slightly brash. It's fresh and vigorous. If one meant to tone down its brio, a valve preamp would suit. I'd stay well clear of 6H30 though. Every single one I've heard mimicked the F5's own tendencies rather than opposed them. 6SN7 would be the antithesis. If those proved too warm and dense, a 12AU7 as found in the super-expensive Concert Fidelity preamp or my Nagra Jazz could be just perfect. This isn't about changing tonal balance but shifting the relative needle setting of the general attack/sustain/decay meter. 3rd-order mode is more front heavy (leading edge), 2nd-order more back-loaded (trailing edge). On strings this quite literally means more metal for the former, more wood for the latter. Smart valve amp designers tune this needle setting with the THD interaction between driver and output tube. Smart solid-state amp designers add variability on this count with an adjustable bias meter like the SIT-1 has—its load line shifter— where the SIT-2 stereo is fixed at the center value.


Where the SIT2/F6 were identical twins, the M2/F6 mere brothers possibly from different mothers, the F5 and F6 were twins sharing a womb but not the same huevo. This added some brain fodder to the power Jfet vs. Mosfet assumption. It also showed other factors intrude when two Mosfet amps (M2 and F5) sounded more different than this particular Mosfet/Jfet match of F5 versus F6. The former's brashness mellowed a bit with the F6. It turned into something more suave and polished. Focus and separation power were quite evenly shared but the F6's lumens on the same scene contained more gold and less silver than the F5. In terms of subjective scale—that size thing which operates in a different dimension than centimeters—I found the F6 slightly bigger. On that count the sequence from plus to minus was SIT2, F6, F5, M2. The distance of flavor difference went the other way. It was smallest between SIT2/F6, slightly bigger between F6/F5, bigger between the F6/M2 and biggest between F5/M2. That's getting quite fussy considering that all of these amps are far more similar than not (with this word I always think of Robin Williams' timeless "fussy fussy" in 1996's remake of La cage aux folles).


Another way of approaching these fine distinctions would be a kind of sophistication index. Bed linens have thread count, woolen jackets worsted count. The finer the thread or yarn, the higher the count. Here the SITs are the super-costly stuff which has regular bedding shoppers aghast at what could possibly make it different from theirs to justify the price. It's also what separated the F6 from the F5. In textile terms it had the higher linear density, the finer thinner threads. This made it feel more elegant. If it were a suit it'd be cut the same and sewn by the same tailor but the raw material itself would be of a finer quality. In my view the upshot of it all is very basic. If you're a turn-key shopper without ability, interest or time to sling your own solder; and if a SIT2 busts your budget... then the J2 is your obvious choice. If you're a roller interested in higher power and drive who must decide between tackling the F5 or F6... I'd go with the F6 on sound (which completely disregards possibly dissimilar levels of skill required in building either one; and the potential to use Jfets for an F5). If you're a roly poly who'd never spend $5.000 on a SIT2 and needs more power in the first place... the F6 seems an ideal project. It probably means though that you'll want to get your hands on fancier power Jfets like the SemiSouth units my loaner had.


As I explained at the very beginning, this review differed from what we normally do by giving air time to a DIY project. The how is covered elsewhere. This was about why you should. Hopefully this added some grist for that mill. Happy grinding!
 

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