Sophia Electric 91-01 300B monoblock power amplifier
"We put music in the souls of our amplifiers. Every amplifier, every tube, every transformer has music in its soul."
Not to be cynical, but I've heard, over the years, countless variations on that sentiment. Not to be naïve, but it rang with somewhat-greater-than-usual sincerity when given voice by 45-year-old Richard Wugangfounder, with his late father, of Virginia-based Sophia Electric, Inc.
Wugang speaks with similar import of his audio upbringing: of the days he spent helping his engineer father disassemble and study some of the classic audio transformers that came their way, the older man noting in a green ledger the results of their experiments. Years later, after Richard had achieved success as a banker, there came a day when he looked up from his desk to see his father in the doorway, the old, green ledger in hand, asking to join him in starting an audio company. Neither looked back.
In 2001a year not known for coaxing tears of wistful nostalgia from the eyes of audio manufacturersSophia Electric began selling new mesh-plate 300B triode tubes. One year after that, Sophia introduced its first commercial-production amplifier: a US-made, single-ended, 300B design heavily influenced by the classic Western Electric No.91-A amplifier, multiple samples of which have been owned by both father and son. Today, this 300B amp endures in the Sophia line, in three different guises: the 91-01 monoblock ($4500/pair); the 91-03 stereo amplifier ($6500), which features higher-quality parts; and the 91-05 stereo amp ($10,000), which offers Sophia Electric's finest-quality parts, chassis, and transformers.
Sophia Electric's business model, in which audio amplifiers and component parts are sold via the Internet (home trials are available, the only requirement being for the customer to state that intent at the outset), doesn't satisfy the "five-dealer" rule regarding eligibility for a Stereophile review (footnote 1). Yet because that policy is motivated by the desire to focus our efforts on products from real companiesthus sparing readers the hassle of buying, on our recommendation, products that mightn't be supported a few years henceI was swayed by Sophia Electric's longevity to take a look at their level one Heritage Series 300B amplifier.
The Sophia Electric 91-01 300B is a single-ended power amplifier designed around the 300B directly heated triode tube, operated without negative feedback. Its input/driver tube is a Chinese-made 6SN7 dual-triode, implemented not in the rather common series-regulated, push-pull (SRPP) mode, but rather, according to Richard Wugang, in a manner that "allows enough voltage swing for the 300B to deliver 8W." According to Wugang, an SRPP arrangement "has some advantages, but it sounds too aggressive." The precise details of the 91-01's input circuit were kept from me by a smallish input-circuit board, containing four capacitors and seven resistors, that obscured from view the socket for the 6SN7 and much of the pertinent wiring.
The input stage is capacitor-coupled to the signal grid of one of Sophia's own Princess Mesh Plate 300B tube ($475/pair when sold separately). Rather than applying a fixed bias voltage to the grid, Sophia runs the 300B in autobias mode, the cathode held approximately 70V above ground. Thus, despite a highish 425V rail, the output tube sees considerably less than that between cathode and plate. Separate hum-reducing potentiometers, accessible from above the 91-01's top plate, are included in the heater circuits for the input and output tubes. (Sophia guarantees their output tubes for 1 year; Richard Wugang says that one can typically expect an output tube in one of his 300B amplifiers to last from five to seven years.)
The 91-01's power supply is built around a Chinese-made 5Z3PA full-wave rectifier tube, and the rail is smoothed by a pi filter of the usual sort, involving an unusually hefty choke, apparently made in-house. Filament voltages are all AC, supplied by dedicated secondary windings on the mains transformer, itself also a Sophia original.
The output transformer, too, is designed and made in-housea point of some pride, especially given the founders' years of research. Richard Wugang says it's wound on a standard IE core ("so we do not lose midrange magic"), using a mixture of vintage and "high-tech" core materials. According to Wugang, he and his father determined that, contrary to the prevailing attitude among designers and hobbyists, a smaller-than-average core produces a better-sounding transformerand he added that Sophia has "found a unique way to get wider bandwidth."
All of this is built into a steel chassis, painted black inside and out, with a separate interior subplate for the tube sockets and separate steel covers for the mains and output transformers. Apart from the input-circuit board, described above, all wiring is point-to-point and routed somewhat haphazardly. Indeed, while I greatly admired the ruggedness of the little chassis, and the transformer quality is presumed, through listening, to be superb (see below), I was a bit disappointed by the 91-01's build quality: A few solder joins between component leads were sloppy, the large choke was made to fit the chassis by bending its frame, and, most concerning of all, the leads of some high-voltage capacitors were overlong and underinsulated.
Setup and installation
Installation of the Sophia Electric 91-01 300Bs was straightforward: Separate loudspeaker terminals are provided for 4- and 8-ohm loads, and I used the latter with both the DeVore Fidelity Orangutan O/96 and my Altec Valencia speakers. I did not, during normal use with their standard output tubes, need to adjust the Sophias' hum pots. I did, however, have to make slight adjustments when I swapped in my own pair of Western Electric 300Bs, owing, no doubt, to the latters' very different current-draw characteristics. No big deal.
As with all such products, the 91-01 owner is advised to use these amps on a solid shelfnever a carpeted surfacein order to promote cooling. I complied, with no additional attention paid to mechanical isolation. The Sophias ran warm but not unduly so, although the smell of fresh paint was a bit of a nuisance after the amps had reached their operating temperature.
The sketchy owner's manual neglects to mention anything about the function of one control: a top-mounted toggle switch that turned out to be an AC ground float. (Its use proved unnecessary in my system.) The use of the hum pots was also, I thought, given short shriftalthough I was heartened that the manual warns the owner against doing such "silly things" as taking the 91-01 into a car wash or cleaning its tubes in the dishwasher.
Notwithstanding the manner in which the review pair matured and "opened up" over several weeks of use, the Sophia 91-01 300B impressed me from the start with its smooth, rich, warm, very well-balanced, altogether musical sound. It had decent color, very good (if sometimes a bit exaggerated) texture, and an acceptable sense of touch and force. From the moment I installed the Sophias in my system, I enjoyed them thoroughly, and though they didn't sound nearly as refined or as eerily human as my far more expensive Shindo Corton-Charlemagne monoblocks, I was never, during the review period, as anxious to return to my references as I usually am while reviewing strange gear.
With the musically brilliant and very well-recorded 14 Bluegrass Instrumentals, by Country Cooking (LP, Rounder 006), the Sophias' top-to-bottom balance was just about perfect, and their slightly warmish character served well an album's worth of fare that can get a bit glary with some gear. That said, the sounds of the twin (!) banjos of Pete Wernick and Tony Trischka did at times betray just a touch of clatter, and Kenny Kosek's fiddle had a little too much texture: qualities that might be associated with higher-than-average levels of harmonic products.
Footnote 1: Since this review was written, Sophia informs us that the company's products are indeed available through five US retailers.Ed.