Less is often more when it comes to audio excellence. A case in point is the 2A3 directly-heated triode (DHT). In single-ended applications, about 3 wpc is about all the power this puppy can muster. Don't even think about owning a SE 2A3 based amp, unless your speakers are at least 96 dB sensitive. It's shameful that some manufacturers, in an effort to increase market reach, have pitched these amps at owners of moderate sensitivity speakers of 88 dB to 90 dB. Such a pairing would be highly inept and only makes sense if you plan to use your speakers like giant headphones. With my own BassZilla speakers, which is what I use to enjoy the music with these days, one watt goes a long ways - even in a large room. The BassZilla has proven to be a wonderful testing ground for a host of low-power SE amps.
My samples of the Seduction were outfitted with a pair of KR Enterprise 2A3 tubes, though the amplifier may be purchased sans output tubes. I used to be schizophrenic about "Boutique tubes," that is, high-priced, low volume production from an exclusive source, but now we're OK with the concept. KR Enterprise is a small tube manufacturer in the Czech Republic, which specializes in directly-heated triodes for purely audio purposes. The KR 2A3 features a mono-plate with ribbon filament construction and an exclusive multi-cathode design. It is a direct substitute for both bi-plate and mono-plate 2A3 tubes, but can be operated at a higher plate dissipation for increased power output. The KR tube line is distributed exclusively in North America by ADYN. A less expensive alternative, which I have not auditioned, is the Sovtek 2A3 single plate type at about $50/pr.
The DIVA line is the result of a collaborative effort between Richard Seah, owner of the Soul of Music high-end audio store in Singapore, and designer T. S. Lim, who would rather be known as a musician and music lover. Richard Seah, a partner in a natural foods store, surprised his friends in 1997 by changing his lifestyle from "hi-fiber" to hi-fi. Lim, who is active in the Singapore Mahler Society, also sings tenor and plays the harmonica extremely well. It is this commitment to music that makes him such an effective high-end audio designer. "Anyone with electronics knowledge and a computer, can design hi-fi," Lim points out. "But not many are as deeply involved in music as I am. Not many know how to make the sound more musical, more human."
As you might expect the circuit topology is quite simple. The input stage consists of a 12AT7 ( ECC81) dual triode operated as a SRRP (aka totem pole or Mu follower) gain stage. This is essentially a push-pull stage with the upper triode being used as both a cathode follower and as a current source for the triode below. Its popularity over the past decade or so has given it considerable momentum going forward into the new millennium. The driver stage is also configured as a SRRP using a 6SN7. The output transformers are sourced from Tango in Japan. Global feedback is applied from the secondary of the output transformers. All components are claimed by the manufacture to be carefully tested and selected to ensure synergy, since "best" components do not necessarily produce good sound in a given application.
Over the past couple of years I've developed a ravenous appetite for low-powered SET amplifiers. This time frame coincides with the design and development of my BassZilla loudspeaker - a platform designed to showcase the magic of full-range drivers such as the Fostex Sigma 208FE and the Lowther DX4. With a high-efficiency loudspeaker in the house (up to 98dB/W/m), it became possible to enjoy the performance of even a 1 wpc amp such as the Berning microZOTL. More so than ever before, I came to realize that the ultimate musicality of a particular amp transcends conventional engineering models. In an audiophile culture fixated on the notion that bigger is better, that more watts equates with better dynamics, the truth is hard to accept. Listen and believe: it's that first watt that makes all the difference in the world. The microdynamics of the music are all encoded in the initial power rush. Get it wrong out of the starting block and another 99 boring watts are hardly going to compensate. That's why a low-powered amp, when mated to a high-efficiency speaker, can actually sound much more dynamic than a conventional high-power amplifier.
Not all SET amps are created equal. The circuitry is fairly simple in most cases, and aside from issues of power supply and output transformer quality, the biggest sonic variable is the power tube. The harmonic signature of the output tube tends to dominate the amp's voicing. Take for example an EL34 power pentode. Even when operated in triode mode, with the screen grid connected to the plate, it still projects a full-bodies bluesy sound - far different than that of a 300B or 2A3 DHT. The harmonic flavor and distortion spectrum of an EL34 make it a great choice for guitar amplification, but not necessarily for music reproduction. Joe Roberts, the progenitor of the now dormant Sound Practices, once remarked something to the effect it's hard not to make a good sounding 2A3 based amp. My sentiments exactly. I've certainly never met a 2A3 SE amp that failed to appeal.
So what's the big deal about a triode that was already being eased out of mainstream audio in the late 40s? The attraction has to do with harmonic purity and clarity of expression. The 2A3 has the potential to reproduce the midrange with astounding purity and verve. It is to the tube world what Champagne is to the wine world. The music's drama bubbles to the surface with little effort. Nuances float to the surface naturally, without overwhelming the auditory system. A good 2A3 gives the midrange, the core of the music the Windex treatment. It is prodigious in clearing away the cobwebs and elucidating the music's passion. Its direct presentation is in contrast to that of an EL34 pentode, which while sounding rich, tends to muffle and blunt the music's spontaneity.
The DIVA "Seduction" does an excellent job of giving the KR Enterprise 2A3 plenty of room to breath in the midrange. Soprano voice and violin overtones were particular joys with the DIVA in the chain. The NOS Tungsol 6SN7s helped in fleshing out a credible soundstage with excellent width and depth dimensions, but just shy of the BassZilla's full potential in this area. In addition, image outlines lacked the ultimate in focus and delineation. I obtained the best results with the Air Tight ATC-2 preamp, whose harmonic integrity complements that of the DIVA very nicely. DIVA's own M-7 preamp brightened the upper octaves far more than I could tolerate in the long run.
I was surprised by the DIVA's strong control over bass transients. It doesn't exactly come outfitted with buffalo testicles, but its speed of attack and pitch definition were superior to the bass performance of the Cyrus Brenneman Cavalier - a cathode follower output stage design. Unlike a host of SET designs with mushy bass lines, the DIVA does not hold its punches. Kudos to designer Lim for being able to incorporate global feedback and improve bass damping without significantly impacting microdynamics. Only when compared with the much more expensive Art Audio PX-25 amplifier does it become clear that dynamics are in fact slightly blunted.
The overall tonal balance with the NOS 12AT7 tube type supplied by Richard Seah was too bright for my taste. This British 12AT7 equivalent, branded CV6091, apparently has a good reputation in the Far East, but in my system, it seemed to get worse with time. I finally replaced these with British made Amperex types with a much more mellow sound. This was just what the Doctor ordered in this case. Even so, I still wasn't entirely happy with the tonal balance. What I observed repeatedly was a lack of weight in the lower midrange. Both the microZOTL and the Art Audio PX-25 are better integrated and better balanced through the power range of the orchestra. The DIVA is not a romantic sounding amp. It's midrange clarity isn't matched by a lush and robust harmonic foundation. In other words, it is slightly lean in character, which argues for careful speaker matching. It worked very effectively with the Fostex BassZilla, benefiting from the latter's full-bodied lower midrange.
The DIVA Seduction along with Lim's other designs deserves wider recognition, and a serious audition is mandatory if you're shopping for that fabled 2A3 sound. There's considerable magic in the midrange, and the overall sound is spacious with good treble extension and bass control. In case you're wondering, I have not as yet had a chance to compare the DIVA with Moth Audio's si2A3 ($1,695 plus the cost of output tubes). Recall that this is the amplifier that our own Steven R. Rochlin took to like a "Moth to a flame." Current distribution in the US is very limited (only three dealers as of this writing), but DIVA Classic Audio will sell direct via the Internet to customers not serviced by a local dealer.
The Soul of Music / DIVA Classic Audio
Retail Price (w/o output tubes): $2,800 USD