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Positive Feedback ISSUE47
2A3 SET amplifier
as reviewed by John Hoffman
Another summer has passed us by in Eastern Washington, and winter is fast approaching. Winds are whipping down the Columbia Gorge, and stripping leaves from the maple tree in my front yard at an astonishing rate. Of course these leaves never leave my property, but instead pile up by a hedge, patiently waiting to be cleaned up. Thoughts inevitably turn to indoor activities and the upcoming holidays; as the hundred-degree summer days are only a fading memory. Currently, I am spending my evenings listening to the Arte Forma 2A3 SET amplifier, who's glowing bottles have been responsible for several enchanting evenings. Beautifully textured music cascades into my library from a pair of 12-inch, full range drivers, powered by this robust 3-watt per channel amplifier. Before delving into the description of the Arte Forma amplifier, I think it is important to discuss where the amplifier comes from, and who builds this excellent product.
A new breed of electronics manufacturers has risen from East Asia, who has established a significant presence in the two-channel market place. A fundamental realignment of the status quo has occurred, especially in the strata where the price conscious consumer resides. These new found offerings also bring a new element of risk, since a notable percentage of these new world products have developed a reputation for having technical issues. When the enthusiasm for the unbelievable price, and striking appearance has faded, many buyers discover that their latest acquisition is, in reality, a mediocre sounding component.
For several years I have been waiting for a company such as Arte Forma to make an appearance. I felt that eventually a company would surface that valued the presentation of music over the visual appearance and rock bottom prices. These amplifiers are hand built, carefully evaluated, and produced by people who value the art of music reproduction. Arte Forma is the name given to this product line by Michael Gill, who is the US marketing representative. In Taiwan the manufacturer is known as Hans Lab. This company started out as a collection of experienced DIY hobbyists who came together to form a company that embodies the spirit of the DIY movement. The founding members have a diverse background, but the common factor is that each person is passionate about the reproduction of music.
In the early days, this group studied the designs of McIntosh, VTL, Audio Note, and Audio Research, looking to understand the framework of what lies underneath a successful amplifier design. Exposure to the work of the Uesugi Brothers injected a different perspective to their design philosophy. Specifications and component brand names were no longer important, now the optimization of every stage within the circuit becomes the focal point. The primary concern is the preservation of the incoming signal, which is a challenging task that to some degree or another has thwarted many an amplifier designer.
The Arte Forma 2A3 amplifier has a factory direct price tag of $2000. This price is quite reasonable, especially once you examine the quality of parts contained in the amplifier, and the fine craftsmanship that is required to produce it. Once the amplifier beings playing music, the price is more in line with outright thievery.
With a foot print of 17"W x 14"D x 9"H and a weight of 65 pounds, the Arte Forma 2A3 is a substantial amplifier. A great deal of the weight resides in the potted James Audio output transformers. The chassis is built from heavy gauge steel, with an attractive painted gray wrinkle finish. The front panel contains an on/off switch and a pair of dual mono volume controls. Located on the back panel are speaker terminals for 4 and 8-ohm taps, and a single pair of RCA inputs. An IEC plug allows the owner to experiment with different power cords, and find the correct match for their system and tastes. A set of hum pots are located in front of the output transformers, and are used to achieve the correct ground value on the AC filament side of the output tube. The amplifier is hand assembled, with point to point wiring, and the layout is neat as a pin.
The tube complement for this amplifier is a pair of 2A3 Shuguang output tubes, Mullard 12BH7 pre-driver tubes, and a Shuguang 5U4G rectifier tube. These tubes are a reasonable balance between price and performance, although there is an opportunity to improve the sound by upgrading the rectifier and power tubes. The more adventurous hobbyist can spend the money needed to acquire NOS output tubes, and will advance at least one level in sound quality.
Three watt amplifiers need to be used with efficient speakers, that much is a given. I paired the Arte Forma amplifier up with a set of Audio Nirvana Super 12 speakers. These speakers are 96dB efficient, have a stable impedance curve, and operates as a point source. There were a few instances where I did swap in a moderately efficient set of bookshelf speakers in order to see what the amplifier could drive. While the sound was acceptable, I do not believe that this would be considered an optimal arrangement. This amplifier should be used with a minimum of 94dB efficient speakers. Fortunately there is a wide array of affordable high efficiency speakers currently being offered. There are several designs using drivers from Fostex, Lowther, Audio Nirvana, and Hemptone. Of course horn based designs would be a natural pairing, and high output multi-driver speaker designs are also an option. In the past, it has been difficult to find affordable high efficiency speakers to use with Single Ended Triode amplifiers, but thankfully those days are gone.
A properly designed Single Ended Triode amplifier has the ability to reproduce instruments with a level of realism that is difficult for traditional amplifiers to emulate. Music played through the Arte Forma amplifier has clarity, definition, and purity that are the hallmarks of a properly executed SET design. Early on in my listening sessions, I began to get the impression that the Arte Forma amplifier was something special, and not just another Johnny come lately amplifier. The opening track on Peter Fingers' Open Strings disc is "101 South" (Open Strings; Acoustic Music Records AMC 1173) and from the moment I hit play music began to flow into my listening room. The tone of the steel stringed acoustic guitar is beautiful, and even though individual notes flew by at a rapid rate, they were always clearly defined. The texture of the guitar was warm and full-bodied, yet the various colors of the guitar strings could easily be discerned. At times the sheer density of music coming from my system was unsettling; no other affordable amplifier that has graced my listening room could unveil all the detail in a recoding in the manner that the Arte Forma does.
With an impressive performance turned in during the early listening sessions, I was determined to find out if this amplifier has the depth of character that audiophiles require for a long-term relationship. The Arte Forma amplifier excelled with the small venue style of music, so I decided to throw a challenging large-scale piece at it. I figured that big band jazz would fit the bill, so out came a rendition of "Boogie Woogie Bugle Boy" by the Randy Scott Orchestra (Swingin' To The Big Bands; Compose 9943-2). The opening trumpet solo has excellent tone, with a metallic sheen that achieves a realistic presentation. When the band hits its stride, the amplifier easily handles the dynamic swings in the music. Each section of the band can be clearly heard, and at no time could I discern any signs of compression as a result of the amplifier running out of power.  A trio of singers is situated in front of the band, and even when the orchestra is at a full head of steam, the ladies voices maintain their individuality. I thoroughly appreciated this disc on the Arte Forma amplifier, and several times I found myself listening to this music for just the enjoyment of it.
The 2A3 output tube has a reputation for rendering excellent presentation of spatial dimensions. While this attribute may be inherent in the tube, the amplifier circuit has to be properly laid out to exploit this advantage. Not every amplifier that uses this tube is guaranteed to have a highly defined soundstage, and the 2A3 tube is not a magic bullet by any means. The design team at Hans Lab has certainly worked hard at optimizing their circuit, and I can vouch for their efforts. Lucia Hwong is an artist who melds traditional Chinese and Western composition techniques to create an intriguing style. Hwong also blends Chinese and Western acoustic instruments with synthesizers to form a combination of ambient and environmental music. "Everest at Sunrise" (House of Sleeping Beauties; Private 2006-2-P) is a song that fills the room in all three dimensions, with synthesized chimes, violins, haunting wooden flutes, and Hwong's otherworldly vocals. Up until this point the Arte Forma amplifier has performed remarkably well, and I looked forward to hearing what it could accomplish on this song. The soundstage has a panoramic presentation from left to right, and has excellent front to back layering. The height of the stage extends well above the speakers; and there is sharp definition along the edges of the recording. All the instruments are realistically fleshed out, and have the elusive "in the room" quality. While this recording is a fabrication of a talented recording engineer, the illusion of a diverse set of musicians is breathtakingly realistic.
As a general rule $2000 amplifiers are going to have a discernable personality, which affects the music in some manner. The Arte Forma 2A3 amplifier is as evenly balanced a component as I have encountered at this price level. Over the years I have owned several SET amplifiers, and thoroughly appreciated each and every one of them. I have spent many an hour in front of the dynamic and detailed Art Audio Diavolo, and the graceful and sophisticated Electra-Print 300DRD amplifiers. I can say that the Arte Forma amplifier is competitive with these products, although it does have its own distinctive sound. The personality of the Arte Forma amp is a melding of the positive attributes of these other two amplifiers. There is a clarity that is reminiscent of the Diavolo, and a refinement that is characteristic of the Electra-Print. Perhaps the only notable limitation of this amplifier is its power output. The 2A3 output tube is only capable of a few watts per channel; so high efficiency speakers are almost mandatory. Team the Arte Forma amplifier up with an appropriate set of speakers, and this amplifier is going to challenge your preconceptions of what affordable electronics are capable of.
The members of Hans Lab should be proud of what they have accomplished; this amplifier has all the attributes of a successful product. The fit and finish of the product is neat, and it is obvious that great care has been taken during the assembly process. The quality of parts found in this amplifier is a cut above what one would expect for a $2000 unit. As an exercise in engineering, the Arte Forma would certainly be considered a success. In reality, it is the sonic performance of a component that an audiophile cares about, and this is where the Arte Forma 2A3 amplifier proves that it is belongs in the high-end arena. This amp gets high marks in every category I consider important. The amplifier is quiet, with a low noise floor that can be attributed to a sturdy power supply, and proper circuit layout. I appreciate the natural tonal balance and timbre of the Arte Forma amplifier. Even the presentation of acoustical space is top shelf, and far better than what other products in this price range. I could easily live with the Arte Forma, and would recommend it to anyone considering the purchase of an affordable 2A3 based amplifier. John Hoffman
 Members of Hans Lab are computer engineers, electrical engineers, retired air force and navy technicians, and communication industry specialists. Hans Lab is composed of 26 members. Each person is capable of building an amplifier from start to finish. This includes the CNC production stage. This is not a company headed by one or two engineers and a gaggle of workers assembling a product.
 I prefer the dual volume knob set up the Arte Forma amp uses. However, this is an early production unit, and the knobs are a smooth rotation, which makes balancing the signal a tiresome task. New production units will contain détente volume knobs. I believe this is an excellent design, and would choose this arrangement over a traditional stereo volume pot and balance control.
 The design team at Han Audio is going to add a selector switch and an increased number of RCA inputs. While the single set of RCA inputs is the purest design implementation, it does not meet the needs of the hobbyist who uses more than one set of source components.
 The Shuguang 2A3 tube is surprisingly good for the money. NOS tubes will outperform them in the right application, but the laws of diminishing return can be applied to this expenditure.
 It is essential to use a high efficiency speaker with a stable impedance load with this amplifier. In the end, the amplifier produces 3 watts per channel, which is plenty of power if it is mated with the proper speaker.
 Well at least at any sane volume level, the Arte Forma amp is rock solid. When the amplifier finally does clip, the Audio Nirvana speakers are at a volume level that is reminiscent of a college frat party.
 There is a balancing act of parts selection that goes into the Arte Forma amplifier. With a $2000 price tag, not every part can be best of class. Certainly the output transformers, power supply capacitors, and volume pots are of excellent quality in this amplifier. The other parts are role players, and the design team had to take into account the quality of performance offered versus the incremental cost of each part to the amplifier.
Arte Forma Audio