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But first, a quickie detour into headfi to satisfy a reader request. While discontinued, AKG's K-1000s remain a statement-level headphone. They're unusual by requiring speaker-type amplification to compensate for their own inefficiency. Hence their stock wire tail ends in speaker level connectors, not the usual 1/4" jack. Nelson's F1 current-source is ideally suited because the Ks lack a crossover. They cotton to transconductance drive without crossover shifts. Red Wine Audio's battery-powered Signature 30 is another ideal K driver - warmer and more relaxed than the F1 which counters with sharper articulation and accuracy. By eliminating room interactions, amp tests with headphones can be illuminating.

For a bit of nepotism, the above paintings are my wife's latest creations in her Geisha Series

Predictably, all prior speaker commentary applied to the headphones. The Ks lack intrinsic warmth and the F4 didn't really add any. But unlike the F1 which sharpens the presentation on the leading edge for that super-articulated, rhythmically driven flair, the F4 maintained its supremely relaxed poise to sound subtly sweet and thus borrow bits from the F3. Adding any so-called warmth would merely cause fuzz factor and opaquery. Thus it seemed neither necessary nor desirable.

The F4/K1000 makes no valve sound per se. Yet remarkably, even valve hounds won't fault it for that. It combines SET-type immediacy -- that lap-dance thang -- with low-level recovery that remains hidden in most SET's noise floor. The F4's lack of voltage gain stage becomes subtractive. It removes an audible action other amps insert. Coming from the high-power push/pull tube camp, you'll hear that as being finer yet slimmer, calmer, not being pushed outwards from within. The F4 feels less loaded, less enhanced, less massive. Entering that same p/p tube camp from the F4's crib, you'll hear tube-based additions and obscurations, a fattening and dulling. It'll entirely depend on your perspective whether the minimized 'action' of the F4 will seem loss or gain. Beyond argument? It sounds different. I'd strongly argue for calling it less signal manipulation and greater signal purity. Meanwhile my own penchant for "pleasurable distortions" also acknowledges that reactions are bound to differ. In the k-ontext of the 1000s, the F4 refuses to trigger any prima donna prissiness whereby the 'phones impress short-term but become fatiguing later. The F4 takes out their sting without diminishing any of their many virtues.

Versus the F3, the F4 injects a small dose of F1-erry to live somewhere between both, closer to the F3 to my ears and as such, wantonly perfect for the K1000s. If you already own an F3 in this context, I'd hold on to it. If you're still getting into this FirstWatt phenom, I'd pick the F4 (or build your own as DIYAudio poster traw has done). Which segues neatly into the mono equation and audibility of heightened current flow.

In parallel mono, the i/o ports become interchangeable so use whatever's closer

I began with a very simple recording, Anouar Brahem's Le Voyage de Sahar on ECM, a minimalist trio of oud, accordion and piano in the same vein as its gorgeous precursor Le Pas du Chat Noir. As predicted by theory and good sense, the output level remained unchanged. Nonetheless, there was a clear difference; the action of more current. It obviously expanded dynamics even on as macrodynamically relaxed a session as this. The microdynamic ripples were bigger for more expressiveness. The sonic gestalt in toto was more concrete - more embodied if you will. Very interesting. With zero shift in tonality and frequency response, the sound simultaneously acted bigger (even though the soundstage remained immobile and the images didn't grow) and the tones seemed more pressurized which had the effect of making things more colorful.

The title track to Angelique Kidjo's Djin Djin [EMI 94639 38012] with Alicia Keys and Branford Marsalis is a more complex affair on a rollicking groove and two F4s caused a wholesale densification of the images. The relaxed part of my prior characterization heated up for more muscular drive, more overt on this track than the prior one. However, with the Zu Definitions whose quadruple 10-inch woofer arrays are powered separately, the performance delta was narrower than likely justifying the added expense for most. The verdict was audible, hinting at what to expect with more realistic 'in need' loads but in this context, rather gilding the lily and arguably nearly over sharpening things a bit.

While the big green speakers were still hooked up, I took the opportunity to employ Nelson's custom RCA-to-bare-wire link with a resistor wired across the outputs to load the SET when followed by an F4 in booster mode. My Yamamoto A-08S drives the Zu Definitions with aplomb. Due to their bi-amp nature, the measly 2-watt 45 triodes have never yet telegraphed a desire for assistance in the power/drive department. As with the mono amp experiment in a setup where it wasn't needed, I was simply curious what'd happen while I still had the sound of one and two F4s on these speakers fresh in mind.

The most obvious difference of inserting direct-heated triodes into the signal path was the rounding-over action on transients which, depending on tastes, made the high-current F4-squared setup just slightly brutal on energetic fare into these high-eff speakers. 2nd-order distortion creates a modicum of subtle fuzz 'n' fluff between notes especially when things get thick and complex. The transistors sounded cleaner by comparison, the tubes more comfy. The big question was, what would change when the F4s were extracted from the chain?

Good grief, everything softened further and hazed over. From the midrange on down, grip loosened so considerably as to, from tube man no less, become unacceptably ill-defined by comparison. This sad truth transmitted uncut because the modified Eminence widebanders driven by the tubes are solidly good to 40Hz.
Arguably, the Raysonic C200 preamp would not be my first choice in this context. The ModWright LS-36.5 is faster and more dynamic. On the Yammy, it plainly makes a better match than the thicker, slower, warmer Ray. Still, this was a most instructive outcome, quite shocking in how unambiguously superior the buffer amp concept was to valves pure. It demonstrated in no uncertain terms what optimized invariant loading of a direct-heated triode (now merely seeing a resistor) plus transistor-sourced current into a far lower output impedance sounds like. To paraphrase Miller Time, it ain't about weak-ass suds, it's about Marcus slapping da bass.

It's cliché to invoke "sounded broken by comparison" but in this case, the Yamamoto solo was served humble pie à la burning mode. It didn't take more than two A/Bs to finish the last of this pie and wonder whether power tubes were needed at all. Not entirely vanquished, the Emisson Labs bottles did make a fine case for themselves if you didn't fancy increased leading edge definition and more while starker inter-note clarity but rather, a softer, gentler, more billowy infusion of character that retained the goodness the transistors bestow.

The final sound is a nouveau hybrid of power triodes + transistor buffer. Small-signal triode hybrids like Mike Elliott's Aria or Conrad-Johnson's ET250 have a long tradition. In fact, the Moscode and Abbingdon Music Research are merely the latest thereof (which includes the affordable Unison Research Unico). To my knowledge however, nobody yet has hybridized power triodes like 45s, 2A3s or 300Bs in the manner the F4 allows for. The justification for why is so sonically obvious that one would like to appeal to the global audio community: design a no-feedback single-ended triode amp with an F4-type current-gain impedance matching transistor follower stage all in one convenient enclosure. It would surely revolutionize the appeal of tubes. Only someone who hasn't heard the difference would shrug this off with a casual "why bother, class D is the future". The trouble might be that SET specialists don't know transistors well enough to pull this off and vice versa. Mister Pass, pretty please - a 101D output stage amp plus 100-watt F4 follower in one box? Who else would bother?

This proposition, for the first time perhaps and already available with the F4 in multiple boxes, really does give "the best of tubes and transistors" as we've been told before so often. As such, it's most assuredly not a classic valve sound. Adding the second F4 to the Yamamoto demonstrated how the sand/glass shares of the sound could be shifted. Raising current supply to the speakers firmed and toned further but -- and this was fundamental -- still didn't dry off the tube-sponsored textures completely. Only someone of exceptional fidelity in his marriage to vintage tube sound (to how such SETs soften and blur the bass by comparison and thicken and slow down the overall plot) would fail to apply for divorce. That said, hybridization does remove substantial portions of what's traditionally equated with (compromised as it turns out) valve sound. The notion of 'romanticizing' the sound matures into something less interpretive.

This transistor follower presentation is far more honest and linear. Its flavor is even top to bottom. What it adds over superior just-transistor sound of the F3 or F4 type is the softening (but decidedly not dulling or deccelerating) of transient emphasis and a 'controlled dispersion' of harmonic distortion (at least I assume that's what it is). That latter action is immediately obvious on voices especially during higher levels. They sound rather more real, more holographic, more sculpted in space. As you prime the pump, they don't flatten out or harden up in ways they never do in real life but often do with solid state. Is it a true 50/50 thing then, this sound - half solid-state, half valve? With two F4s hanging off the Yamamoto into the Definitions, I'd guesstimate more 70/30 in favor of solid state. With one F4, closer toward the middle. I think that's because tubes, by comparison, don't do current. Increasing current beyond one F4 shifts sonic attributes further into recognizable transistor milieu.

Even so, removing the Yamamoto altogether proved that the direct-heated triode contributions were more than resilient enough to not get swamped out. The absence of the Yamamoto was instantly felt. The linearization and superior drive effects of the transistors did not dominate such as to make the addition or removal of the triodes into minutiae you'd have to focus hard to notice. The only way one could approximate elements of this prior to the F4's appearance was with bi-(or more)amping. Then different amps were assigned to different frequency bands based on where the amps' relative strengths would shine the most. Traditionally, that's been the missionary position of tubes on top, transistors below. Anyone who's tried that will agree on the inevitable seams of discontinuity. The latter will be least disturbing if transistors enter below 80Hz such as they would in a monitor/sub array. Still, seams do remain. Plus, the F4 concept shows how the benefits of current and low output impedance extend far higher in range than just the bottom two octaves. Once heard, you want that definition, firmness and clarity also in the bands which are traditionally handled by tubes in biamp scenarios.

The SET/F4-follower concept doesn't just do that, it also extends the tube flavor down into the bass for a completely shaken, not partially stirred mix. The final cocktail no longer is a mix -- a little bit of this, a little bit of that, with a demarcation in the middle -- but a solid of-a-piece entity. While I had the Yamamoto/F4-squared threesome going, I moved the green towers to the sidelines and replaced them with the Mark & Daniel 85dB/4ohm Maximus Monitor. With gain to spare, I nonetheless suffered distortion, predominantly in the bass which seemed to break up. Swapping the 45s for the 2A3s in the li'l Trafomatic Audio Experience One integrated from Serbia, passive Alps pot fully opened, it banished any and all distortion for uncompromised Maximus sound. Headroom (unused range of the preamp volume control)
even during happy hour was flat silly. Removing the 2A3s still left SPLs to spare. This demonstrated unequivocally that a 20dB preamp into 100-watt/2ohm current gain into 85dB speakers works like a charm, no conditions attached except perhaps for standard to sizable rather than excessive room dimensions. Conversely, the 12dB ModWright into the 91dB DeVore Nines even with paralleled F4s required a 3:00 o'clock position on its volume control to produce standard SPLs. Having 20dB of gain in a preamp seems a good figure to aim for when an F4 is used without a preceding SET.

Why the distortion on the Yamamoto? "I speculate that the Yamamoto needs to see a specific load and I suggest procuring 16-ohm and 8-ohm resistors with which to load it and try both values to see what works best. This is interesting because it points to some design characteristics of the Yamamoto. Again speculating, the triode outputs would be working a specific load line which cancels the warps between voltage and current (the gain increases with voltage across the device and increases with current through the device). The load line is such that voltage across the triode declines as current goes up, so you get suppression of 2nd harmonic. Unfortunately, this only works with resistive loads so we would further speculate that the Yamamoto loves a particular resistive impedance. If this is true, you need only find that specific resistor value and it should work very well."

I confess to a rather evil grin - sales floor hype of power requirements, realistic dynamic range and all. Evil traded for pride while I was triangulating the above 4-watt triodes with the stout, supremely controlled low bass and intense levels gushing forth from the otherwise impossible load of the Maximii. Phat. Sick. Baaad. Street slang has any number of double-edged words to describe the only suitable reaction. Admittedly, adding $2,500 or $5,000 of invisible muscle to a flea-power affordable SET seems less than sane when the same cashish or less will buy a powerful one-box hybrid like the Moscode or AMR integrateds. Who perhaps would get the sanity behind this insanity are those experienced with direct-heated triodes who value their particular charms. As with any other religion, not everybody does. Those who do will agree that a 7308 or 12AU7 or 5687 such as you'd find inside a normal hybrid can't compare to a PX-25, 101D or 45 for audible action. The flip side is, F4'd DHTs no longer sound entirely like themselves. My personal take? My Definition Pros have never needed more than the Yamamoto's 2 watts to come on song. Yet adding an F4 equaled a wholesale improvement. Going back to triodes pure equaled devolving back down the Darwinian tree. The ideal scenario in this corner of esoteric hifi would of course be to get the present string of three boxes nicely wrapped up into a single enclosure. At which point the raw gain of the triode becomes irrelevant with regard to drive. Esoterica like PX4s and 50s would become viable. Such possibilities seem supremely attractive and wildly imaginative. Will such a beast ever come to market? It's nothing but wishful thinking at this point - my wishful thinking at that. Best to move on. Unless this morsel by Nelson is pregnant with meaning: "The beauty of First Watt is that there is no possibility of failure. Except failure of nerve."

Now enter the Supratek Cabernet Dual. It's the best preamp I've yet heard within my own four walls. It does exactly what reviewer peers report with Shindo and Kondo preamps: performance aspects that go well beyond raw measurements (though linearity, bandwidth and zero noise are a given at this level). They enter the highly subjective domains of inner meaning and heightened musical rapport. It's the black-art voodoo stuff that's impossible to correlate on the test bench. It's in outright defiance to the soulless bits and pieces of capacitors, resistors, chokes and wire that produce these effects. How much -- or little -- would adding power triodes into the above chain accomplish where a lot of transformative hifi-into-magic action was already covered by the preamp's 6SN7s and 101Ds?

Surprise! Adding the power triodes introduced sharpness, glassiness and the kind of crystallization that at first sounds ultra clean but quickly turns lean and whitish and annoying. Compared to my large Zus or the Mark & Daniel Maximii, the DeVore Nines needn't be pushed in that direction. Hence the transistor amps driven directly from the Supratek preamp sounded plainly superior and, this is no lie, warmer. This combination passed on the billowy, fluffy, spacious mien of the 101Ds instead of drying it up and leeching out tone. Admittedly unexpected for triode devotees, this was proof positive that low-level triodic action can be fully sufficient to transmit through the F4s into speakers such that tube guys won't want more - if the preamp delivers not just the voltage but also the juju package. Unusual about Mick Maloney in Oz is the use of DHTs in preamps that usually would show up in SETs. In this context, it's a rather idealized combination of hollow and solid state.

Interesting about this experiment was the far greater transparency of the F4s. It passed the preamp flavor uncut while the SET seriously and detrimentally modified it. Incidentally, the 91dB Nines were at about 9:00 o'clock on the Supra's dial when the Trafomatic Audio 2A3 amp was inserted, at 12:30 without it. I was playing trance/ambient-ethno by Bob Holroyd, Zohar, Cheb i Sabbah, Assembly and Third Planet for half a day and at stout levels. The attendant waves of truly low synthesized bass, deeply layered percussion grooves, tribal vocals and shards of sound effects swirling about in giantific artificial soundscapes became quite the antidote to the usual SET-approved fare of fainting female vocals.

Low-level valve hybrid vs. DHT hybrid
Comparing the 6SN7/101D path of the Supratek into two bridged F4s in one corner against the 180wpc 5687-based 'traditional' hybrid integrated from Abbingdon Music Research in the other was further confirmation. In such a context, the F4 does become an integrated hybrid functionally and sonically - just as considering it on paper predicts. Alas, a direct-heated triode like the 101D can do things a 5687 cannot. While clearly belonging into the same class of sound, the Supratek/FirstWatt combo came out ahead by offering more powerful bass and top-end energy; being spatially more expansive; and having a dynamic edge for more immediacy. For my money, the separates were the winner. And, the extra money spent was 2Gs.

Resistance at 8.3/2 is futile
Changing the load resistor on the Yamamoto to 8.3 ohms and 2 watt (the closest thing my Paphos electrical shop stocked) and Nelson was your uncle. The Mark & Daniels Maximii unleashed hell and the dainty triodes didn't flinch. Time for another very evil cackle. It worked beautifully just as the man said it would. Unlike the prior insertion of the Trafomatic amp (which perhaps wasn't ideally loaded), this one was sonically more than benign. Things got even bigger and juicier but they'd been so good before, this crossed the line of conspicious consumption. Then the voice of reason piped up. Supratek into Yamamoto into one F4 was just $500 more than the preamp directly into two F4s. Couldn't reason have its cake and eat it too? This became a tie depending on bias. The bridged F4s driven with a balanced signal took the lead in bass power and overall articulation. The Yamamoto pairing with the single F4 had more tone color and that lit, pressurized from within action triode hounds crave.
Season to taste would seem to be the lesson here.

Concluding the obvious
While a very basic and old concept, nobody in the commercial sector has had the guts or vision to issue a plain power buffer sans voltage gain. Just like fashion however, what was out is 'in' again now that high-output sources, high-gain preamps and increased speaker sensitivities are more common to occasionally meet up. When they do, they make such a basicality as this impedance converter follower the perfect tool for the job. Deathly quiet. Slightly sweet and thus, just a skoch warm. Ultra-resolved but supremely relaxed. Solid-state typical bass control (increases with bridging) which still avoids all cyborg brutality. Very transparent to the qualities of the preceding preamp which includes layering, dimensionality, airiness and enhanced timbres should those be passed on to the amp/s.
Perfectly suited for medium-sensitivity 4-ohm speakers. Calling on the carpet bull that's been perpetrated about actual power consumption in regular living/listening rooms if one uses 'normal' speakers rather than eccentricities that prey on the power-is-cheap mentality.
If you add up all the interesting things the F4 can be used for; and the abilitity to be paralleled or bridged... it's clear that this is the most universal FirstWatt amp yet. And by quite the margin. It's also an amp that tube lovers who are reluctant about power tubes can embrace while getting their thermionic fix in the preamp domain. The F4 will pass (consider who designed it) what comes before it to a higher than usual degree. If you've got a low-power SET and want to hear bass, definition and linearity you never knew you could, go humbucker and tie an F4 to its outputs (experiment with the load resistor value to keep the SET stable): "The supply voltages of the F4 are +/-23 volts and allowing a 3 volt margin, it means that you can feed each input +/-20 volts, which is 14V rms and equals 50W peak at 25W rms. Bridging doubles those voltages and quadruples those wattages. It is my presumption that any SET with a 16-ohm tap will get better leverage since it has half again more voltage output and will get twice as many watts out of an F4." These numbers should guide you about whether your current SET could be a candidate for the "F4 turbo injection mod".

As described, you can achieve a similar SET flavor (without that portion reliant on lack of drive and high output impedance) when your preamp runs power triodes like Supratek and Manley Labs do (there'll be others as well). No matter how you slice it, today's humble-looking machine with its plain black facade staring at you through those beady green-blue eyes is the real deal. It's also a one-of-a-kind deal. A simple class A circuit with no feedback, its harmonic distortion is predominantly the benign 2nd order kind which already inches it closer to triode ideals. That and its lack of additive 'action' from avoiding voltage gain might explain why I've unconditionally enjoyed a signal chain in which the only valves were in the preamp. Or as I confessed to Nelson Pass, "perhaps tube man is finally wigging out with age". Regardless, Mr. Pass was certainly overdue with an award for his FirstWatt venture. While brilliant in their own right, the F1 through F3 were too limited in application and power to be of relevance to enough folks. With the F4, the scope has expanded. It's an esoteric amp for mainstream speakers from a designer famous for no-nonsense bullet-proof circuits. As such, it's the exact opposite of a raw deal - whatever you want to call that, exactly. We'll simply call it nerve. And,

Quality of packing: Double cardboard with hard foam corners.
Reusability of packing: Can be reused at least once
Ease of unpacking/repacking: Very easy
Condition of component received: Flawless
Completeness of delivery: Includes power cord and owner's manual.
Quality of owner's manual: Tops, including hookup graphs, performance graphs and circuit schematics
Website comments: Contains all the necessary information.
Warranty: 3 years
Global distribution: Built personally by Nelson Pass, Mark Sammutt at Reno HiFi seems to have become FirstWatt retail central.
Human interactions: Nelson is very hands-on and answers even ignorant questions with patience though as a busy man, it could take 48 hours.
Other: Being class A, these amps run hot. They also sound best somewhere between 30 to 60 minutes after power up.
Pricing: Surely affordable for the performance offered.

Application conditions: Mandates preamp with sufficient voltage swing to amplify the source signal for desired SPLs.
Final comments & suggestions: Yet another left-field entry from the master of the unexpected that turns out to be extremely practical, realistic and just what the doctor ordered when your setup caters to its basic requirements.
FirstWatt website