Gramophone Dreams #68: Lab12 Mighty power amplifier & Pre1 preamplifier

March 10, 2023 / By mobanmarket

In my realm, the most sophisticated, intelligent, difficult thing anyone can do is create something mysterious. It could be a poem, a photo, a movie, a song, a symphony, or a piece of painted wood. What’s most important is the mystery—and that experiencing the mysterious creation inspires in the observer a desire to probe its hidden realms, to somehow figure it out. Human cultures are founded on mysteries: Mysteries incite art, inspire science, and facilitate dreaming.

To me, mystery and beauty are synonymous. Consequently, I have steered my years so that I am always engaged in a search for, or a study of, the mysterious. And nothing—not books, nor museums, nor seas, nor forests, nor even my day job as a flâneur—has captured more of my mystery-seeking and -studying time than listening to recorded music in my studio.

I’ve spent 50 years developing my current viewpoint about audio system engineering, a set of beliefs about how sound systems work (and should work) and which engineering strategies result in the probing, high-engagement sound I seek. Historically, I’ve favored directly heated triodes powering large horns, or, alternatively, paper-cone drivers with powerful magnets on open baffles, or, less esoterically, class-A solid state amplifiers powering electrostatic, ribbon, or planar-magnetic dipoles.

Unfortunately, all but the smallest of those speaker types are too big for my apartment. Fortunately, my listening room works perfectly with small nearfield monitors such as my current references, the Falcon Gold Badge LS3/5a and the Genelec G Three. The Genelecs provide the cleanest window I know for examining line-level source components. And, during my 30+ years of almost continuous use, different versions of the LS3/5a have proven themselves worthy of being powered by the finest tubed and solid state amplifiers, low power or high. Who would have guessed an 83dB-sensitive, dome-and-cone, sealed-box loudspeaker could thrive on 8W from a single 300B tube? Or sound an equal but different kind of wonderful with 300W from Parasound’s A 21+? No loudspeaker I know shows me the nature of the components behind it with more clarity and certainty than the Gold Badge Falcons.

When differences collide
This month, my Falcons are being powered by a matte-black amplifier with recording-studio looks and round meters called the Mighty. The Mighty is a relatively small (12.6″ × 6.7″ × 11.4″) stereo amplifier that weighs just 20lb and is specified to output 10Wpc into 8 ohms. It is designed and manufactured in Greece by a company called Lab12 and costs just $2290 with tubes.

All last month, my system was anchored by Parasound’s monolithic A 21+ stereo amplifier, which I enjoy with the Falcons because its high-bias class-A/AB power layers copious amounts of well-ordered detail into an exceptionally deep soundspace.

When I switched to the 10W Mighty, those deep-space illusions closed forward some, but now the detailed insides of these shallower spaces were illuminated by a steady, beguiling light that rendered voices and instruments with a shimmering, Technicolor presence that in comparison made the A 21+ seem a bit stoic and gray. Both amplifiers recovered large quantities of recorded information, but the Mighty’s detail was presented with a measure of eye-popping Webb-telescope dazzle.

It’s Mighty simple
The Mighty is a simple, well-proportioned, small amplifier that uses solid state rectifiers and two tubes per channel: a 6N1P dual triode, which is a plug-in replacement for the 6DJ8, ECC88, or 6922 although it consumes more heater current; and a Russia-made Electro-Harmonix EL34 power tube operating at fixed bias (as opposed to self- or cathode-biased). According to the Mighty’s manual, users may substitute 6550 or KT88 tubes.

In an email, Stratos Vichos, Lab 12’s managing director, explained that the Mighty is a beneficiary of Lab12’s “Separate Rails, Separate Grounds” technology (SRSG), which means “We keep high current circuits totally independent from signal circuits. That means we use one star-grounding array for the high current returns and another star-grounding array for signal returns. They meet at only one specific point.”

Vichos explained that the Mighty benefits from another Lab12 technology, Fine Symmetry Design (FSD), which he described as a PCB-layout strategy in which “we take care about the technical symmetry of the two channels,” with the modest goal of keeping the two signal traces equal in length and the less-modest goal of “keeping the capacitance and inductance of both paths equal.” Implementing FSD involves labor-intensive parts matching and tube matching. I suspect that, like loudspeaker matching, the effort pays off with noticeably sharper image focus, more specific soundstage mapping, and superior transparency.

(Later in this essay, I outline my long-held misgivings about Ultralinear operation of pentodes and conclude that the Mighty somehow avoided typical UL sound. Something tells me that Lab12’s FSD “technology” may have played a part in that.)

Two small, unmarked switches between the Mighty’s power tubes and output transformers allow users to switch between Ultralinear (UL) and triode modes of operation.

Stratos Vichos says the Mighty is rated at 10W, but the “EL34 in single-ended triode mode can provide about 8–9W depending on tube. Then 10%–15% more power can be achieved using Ultralinear operation. Optionally, you add another 10% to 15% more power with 6550 tubes.”

On its secondary, the Mighty’s output transformer has separate taps for driving 8 or 4 ohm speakers. And Vichos swears “no feedback is applied.” Inputs are unbalanced (via RCA connectors), with a stated sensitivity of 600mV in triode mode and 400mV in Ultralinear mode to achieve full output power. The warranty is 5 years, one year on tubes.

Those meters I mentioned? They’re “mostly visual, adding to the retro-modern style of the Mighty,” Vichos said. “This is not a studio device.” The meters are functional, though, showing “a [Volt-Amps] measurement of an interstage point between driver and power stage. It perfectly corresponds to the output, and you can estimate the soft beginning of ‘tube clipping’ on red areas of the meter.”

Listening
Starting with the first recording I played, Maya Beiser and Evan Ziporyn’s Bowie Cello Symphonic: Blackstar (24/48 FLAC, Islandia Music/Qobuz), the Mighty found one way after another to mess with my head, sound better than I thought it should, and make me reconsider five decades of carefully cultivated engineering biases.

Familiar songs, like “When I Lay My Burden Down,” performed by Turner Junior Johnson on The Land Where the Blues Began – The Alan Lomax Collection (44.1 MQA, Rounder/Qobuz), came through with the unexpected vibey feeling of an electrified soundspace, within which I was forced to notice the Mighty’s unusually corporeal presentation of instrumental and vocal textures. Besides this surprising physicality, the Lab12 Mighty, operating in Ultralinear mode, made violin and acoustic guitar harmonics shimmer and linger seductively in the air.

Before I began these auditions, I was sure that generic pentodes like the EL34, though cheaper to buy and easier to drive than power triodes like a 211 or 300B, are generally good-sounding but never great-sounding: bleacher-seat tickets to the SET experience. That was bias #1.

I was also confident that when connected as triodes (screen grid wired to plate and suppressor grid tied to cathode), pentodes sound pure and nice but not starkly clear like real triodes.

I know pentodes generate distinct distortion spectra when wired as pentodes, triodes, and in that triode-pentode blend we call Ultralinear (aka UL), where the tube’s screen grid is connected to a separate, intermediate tap on the output transformer’s primary. This connection allows a portion of the tube’s output voltage to energize its screen grid—a form of local feedback.

Consequently, each of these operational modes sounds different. I’ve always appreciated the vivid energy, transparency, and sharp raw detail of pure pentode—likewise the radiant beauty of triode-connected pentodes—but I always felt there was something impure, something compressed and blurred about the sound of Ultralinear. That was bias #2.

Similarly, while I was building my own mostly directly heated triode amps, I felt that a fixed bias, in which a negative voltage is applied to a tube’s control grid, sounded crisper, cleaner, and more immediate than cathode bias, which is simply a resistor of a certain value inserted between a tube’s cathode and ground. I never used fixed bias because I thought it presented recorded energy with a stiff, slightly brittle viscosity that sounded more electronic and less natural than self-bias, which I thought presented recordings with a lower magnitude of internal friction. That was amplifier-design bias #3.

Listening to records with Lab12’s Mighty showed me that I was wrong about the focus factor of UL and about the viscosity of fixed bias. The Mighty played waltzes and reggae with Leica-lens focus and a thinner-than-water flow that let me believe that the sounds I was hearing were coming from instruments and humans with dense bodies—that pianos and sopranos stood solidly on floors near microphones. In UL, the Mighty came across as taut, focused, fast (flow and transient-wise), and über-transparent. Suddenly, I am listening to my favorite blues song ever, “When I Lay My Burden Down,” and digging it more than ever—with pentodes! In Ultralinear! And fixed bias!

Footnote 1: Lab12, K. Varnali 57A, Metamorfosi, 144 52 Athens, Greece. Tel: + 30 2102845173. Email: [email protected]. Web: lab12.gr. US importer: Fidelis Distribution, 460 Amherst St., Nashua, NH 03063. Tel: (603) 880-4434. Email: [email protected]. Website: fidelisdistribution.com

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