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To put the Head One's preamp performance into perspective, I assembled a system around a low-powered valve amp of the kind Trafomatic makes—here Yamamoto's A-08S with Emission Labs 45s, then Sasa's Minueta for WLM—and a pair of properly matched loudspeakers, the same Rethms Sasa owns. My Zu Essence swapped in later to confirm bass performance (the Rethms use self-amplified woofers). After the valve amps, FirstWatt's J2 slipped in to account for customers with transistor amps who desire deliberate valve seasoning. The Head One's volume taper plus its overall gain left very little room before things got too loud on the Rethms and Zus regardless of amp used.  

At first, I ran into serious ground loop issues even when the Head One had no AC connection. As soon as the incoming and outgoing signal cables looped through the machine, there was unacceptable hum. Various cheater plug experiments on the amplifiers or preamp made no dent. Ditto whether the preamp's mains was tapped from the Walker Audio Velocitor S power block which fed the source components or the other one on the amplifiers. Once my customary Esoteric C-03 replaced the Trafomatic preamp, I was instantly noise free again. The culprit turned out to be my Yamamoto YDA-01 DAC. Once I replaced it with the Abbingdon Music Research CD-777 under review, the verkackte ground loop broke - with the tube amps but not the FirstWatt. Reintroducing the cheater plug on either the Pass amp, preamp or source power connection made no difference. Nor did floating the Saadhanas' bass amps which is my default mode.

Sasa had both explanation and solution: "When you don't connect the power cord, the relay is not switched on (RCA out connectors are not connected to the transformer) and your cables to the amp aren't coupled to the output transformers. The hum then derives from an open cable from the preamp. Ground loop effects are always possible so for the next production, I will add a ground post and perhaps even switch to float the power cord when the Head One is used as preamp."

I still had gain up the Yangtze even on my Yamamoto's 2-watt micro-power terminals. But no noise. I do strongly suggest however that Trafomatic adopt a shallower volume taper. This will expand the useful range for preamp applications. That covered, sonics were really quite spectacular. Even the EL84 integrated with its passive attenuator did audibly respond with slinkier elasticity, richer tone, greater presence and more articulated staging precision.

The slightly hallucinatory 45 amp with its 'perfect' balance of attributes usually runs off my Esoteric transistor preamp in passive mode—really a misnomer since even in zero gain, it runs off high-voltage rails—to not dilute its lit-uppity speed and energy with its simultaneously smooth textures. Active preamp insertion under such conditions tends to put the foot on the brake, fattens up girth and rounds over leading edges. The take on the tunes becomes cuddlier, warmer, less precise and less unputdownable for my tastes. That general direction could be desirable with certain amplifiers but I prefer Yamamoto's special 45 magic uncut. Even so, the Head One excelled. It contributed far more than it gently diminished. While the overall gestalt did mellow, the modest fill action was super benign and above all, linear. It didn't focus around the midrange waist in love handles but applied itself evenly top to bottom like an atomized drop of oil.

The impression of inner pressurization or color intensity increased and dynamics didn't suffer. While ultimate see-thru-ness did congeal a tad, the dimensionality of virtual bodies focused better. Particularly at low volumes, this added fleshiness was not only attractive but more intelligible. I particularly appreciated how this did not muck up the crystalline yet suave treble I so admire with the 45s. It's here where you expect the greatest losses from additive meddling but this unprepossessing small preamp acquitted itself very well indeed. While not as ballsy and resolved as the big two-chassis ModWright with its dual-mono external power supply, I'd give the Serbian the sonic—though clearly not functional—edge over Dan Wright's smaller SWL9.0SE. It performs more subtle texturizing than the latter's drier 5687s.

This becomes relevant for those who'd call the FirstWatt F5 or J2 texturally too matter of fact. These are finely honed machines. They walk the path of neutrality with elegance rather than blandness. Valve hounds might want more tonal billowing however. In such cases, the Head One contributes the perfect dose. It relegates my usual Esoteric machine into second place. In short, once the ground lift switch and post have been added—I very rarely encounter ground loops to believe that the Head One is unusually susceptible to really need those facilities—and the volume control is converted to ramp up shallower and pass well beyond 9:30 where I maxed out, this headphone amplifier doubles astonishingly well as a serious though minimalist preamp. It in fact has me curious what Mr. Cokic would do for a maxed-out preamp that ran the same Reflektor 6S45P high-mu triodes which once flew in the MIG-25 Interceptor's Smerch radar system and can output 2 solid watts of speaker-level power. These babies are crisp, accurate and linear like transistors but add that tubular cantabile.

As a headphone amplifier, the Head One is in a class by itself. More linear than the midrange-centric WE 408A Yamamoto which by comparison is clearly sculpted; faster than it and the mighty 300B Woo; texturally and harmonically richer than the transistors of the ALO Audio, KingRex and Red Wine Audio pieces; this Serbian makes a most compelling case to go tubes for low-level circuits. I'm clearly no longer exclusively dedicated to valves—both FirstWatt and ModWright make convincing arguments to the contrary—but for headphones, I continue to prefer them for the 'textural binder' which the absence of ambient room interactions minimizes. Harmonic leanness becomes even more objectionable when the transducers are close to hard-wired to the brain. Then I rather err on the side of 'caution', i.e. some extra padding.

To explain this better, power-line filtering can increase perceived silence for nearly stark blackgrounds. Similarly, transistors on headphones can lead to degrees of starkness which tubes—perhaps by virtue of subliminal noise dither—don't produce. Where powerline filtration can create overdamping like stuffed speakers which sound too stiff and unyielding, headphones react similarly when in spite of otherwise appealing grippiness and slam, the tunes seem military in their bearing.

If noise has been banished to create no background surf at the usual listening levels, tubes can have the advantage here. That's not necessarily a sonic trait as much as one of gestalt. Regardless of how caused exactly, valves for headphone applications really excel here and the linear quiet Trafomatic is a prime example. Transistor-attuned listeners might complain for example how Yamamoto's Western Electrics cause an uneven distribution of lighting or emphasis. This veers into the direction of 'deep triode' - deeply pretty but ultimately a fixed focal lens.

Big Woo was more evenly lit but against the small 6S45P triodes, even modern 300Bs by EAT were more voluptuous and 'girthy' at such millivolt levels. The Woo was thus subjectively slower and less incisive on the kind of blistering attacks Vicente Amigo's Paseo de Gracia is filled with. That relates very directly to the amount of excitement, inner tension and beat hipness which complex rhythmic fare thrives on. The Head One is a member of the PRaT Pack.

Just as the Rethms and Zus suggested already, treble extension was excellent. New Senn HD-800s displayed all their initial bite uncensored. This mellows over time but a superior aftermarket harness like ALO's 18-gauge proves how Sennheiser's own 36 job is really compromised.

With it, some hardness on top and a clear lack of weight and impact in the bass remain. Audio-Technica's 'Raffinato' W5000s proved to be deliberately voiced around the midrange which adored classical and voices but was somewhat less hip on modern fare. Despite their open backs, Grado's very pricey PS-1000s majored in slam beats and infrasonic wallop to show the close-backed Japanese a clean set of heels. After their quite endless break-in needs and despite their far lower price, the AKG K-702 with AOL harness hung in with the big boys but opted out sooner on wear comfort. On soundstaging, the HD-800 took the crown

Details about these various headphones remain reserved for their respective feature reviews. Let it suffice here to say that the Head One drove all of them with aplomb to become first amongst equals—and not so equals—from what I had on hand. As such, the Serbian dethroned my long-running Yamamoto HA-02 champ, out-sophisticated the excellent battery-power Red Wine Audio Isabellina HPA (whose integral NOS DAC becomes part of its sonics) and demonstrated by way of the two-box KingRex unit how premium triodes harnessed at micro-volt levels into 30-ohm plus loads still have an advantage over transistors that seems hard to bridge.

The rarely encountered Soviet 6S45P is a premium audio valve on par with the Russian military 6BQ5 equivalent. Its virtues are 70% transistor which dominate on extension and linearity, accuracy and cleanliness. Tubular contributions are limited to fine textures, more vibrant colors and nubility. Such a crafty balance of qualities should make friends on either side of the great divide. So make no mistake, this Head One is a masterpiece - small but Oho!

PS: 3.13MB owner's manual PDF here.

PS II: After encountering the Head One and its WLM Acoustic Minueta relative in the wake of prior reviews, I finally commissioned a pair of no-holds-barred 6P14P-EV monoblocks from this Serbian designer. This might underscore what I think of his abilities.

Quality of packing: Good.
Reusability of packing: A few times.
Ease of unpacking/repacking: No issue.
Condition of component received: Flawless.
Completeness of delivery: Perfect and remarkable for the quality of ancillaries.
Website comments: Recently revised and now perfectly informative.
Human interactions: Always timely and friendly.
Pricing: Fair value.
Final comments & suggestions: As a preamp, the Head One is highly susceptible to ground loops. Trafomatic has already affirmed a decision to install a relay which will automatically lift the ground as soon as the pre-out is selected with the front-panel switch. This removes the one potential reservation I harbored and is even more elegant than a separate ground-lift switch on the back would be.

Trafomatic Audio website