November 2005 - Less is More
Or the Beauty of Single-Ended 2A3 Amps

My first experience with live music was back in '68, when my father, a carpenter at the Vienna State Opera, took me to a performance of Mozart's Magic Flute. Little did I realise the lifetime impact that evening would have.

How riveting to sit in the grand hall, feeling the texture and nuance of each note. I'd never had as much fun or involvement in music before - I was hooked. But how to achieve that same magic at home?

My first pay-checks went towards a Marantz 2235B receiver, an Onkyo direct drive turntable, a Kenwood cassette recorder and a pair of Braun loudspeakers; in the decades that followed, many audio products (medium- to higher-priced gear) became part of the quest for musical pleasure as close as possible to live.

But there was always something missing when listening to vinyl at home. My system's front end was high quality, a suspensionless granite-based turntable equipped with a Helius Cyalene tone arm and Denon DL-103 mc cartridge (which bettered my Linn LP12, Ekos, Lingo, AT-OC30 mc combination by an audible margin) but music played through the system lacked emotion and drama - flesh and blood, if you will - in comparison to a good acoustic live performance. My gut feeling said it could get better.

During those years, I mainly used transistor-based power amplification (such as Audio Research, Bryston and Krell) which the speakers' low efficiency required (TDL 3-way transmission line speakers with 85dB sensitivity). Preamplification was tube-based (Audio Note pre amp kit with choke and tube rectification, high quality Audio Note paper in oil capacitors with ECC83 tubes in the phono stage and ECC82 in the line stage as well as a wonderful German tube line/phono stage based on ECC83s from Mr. Mollenhauer) which helped improve the system's sound quality. It also awakened my interest in tube gear.

I scoured for information on tube power amplification, and especially appreciated the late great Harvey Gizmo Rosenberg's inspiring home page. His love for single-ended triode (SET) amplifiers was legendary, and the so-called "Triode Guild Master" inspired others to explore the magic of SET amps, 300B and 2A3 amps in particular. The stories I read about the latter of these triode power tubes, rated to provide 3 to 3.5 watts, enthralled me like a glass of single malt on a cold winter's night. Although you need "efficient" speakers with a sensitivity of about 91dB or greater (combined with an impedance behaviour over the audio band that comes as close as possible to a pure resistor, possibly above 8 ohm, to ensure that the high output impedance of single-ended designs doesn't modulate the frequency response through the impedance response of the speaker) it was clear a 2A3 SET amp was the way to go.

Just a brief technical note: differing from push-pull designs where the crossover distortion increases with decreasing acoustic level, single-ended designs have distortion behaviour similar to the acoustic medium (the air!) which means distortion smoothly decreases as the acoustic level decreases, resulting in a more natural and musical presentation to our ears.

Thanks to my beloved father, the speakers on hand were close to the 92dB range (a vintage pair of Altec Lansing Model 15, rated between 90 and 91dB and an easy load to drive) and sensitive enough to give the project a try (+100dB horns would have been the ultimate partners, of course).

Next came choosing among the variety of affordable and great sounding 2A3 amps on the market, such as Wright Sound WPA 3.5 monoblocks and Antique Sound Labs' Tulip stereo amp. For the extra thrill, not to mention savings, of assembling one's own amp, some are also available in kit versions: Sun Audio 2A3 stereo amp, and Welborne Labs Moondog monoblocks (now replaced by a new design), for example. These amps will set you back $1,400 to $2,800 depending on the quality of parts and 2A3 tubes ordered. There's a big advantage to 300B SET amps though, because an excellent pair of 2A3 triodes, like the new production Sovtek 2A3, runs under $80 for a matched pair - good news if you know what a 300B triode can cost. There's also the rumour among SET amp aficionados, that it's hard to design a bad sounding single-ended 2A3 amp.

After much deliberation, I chose the kit-version Welborne Labs Moondog 2A3 monoblocks and never looked back.

So what's the sound of a good 2A3 SET amplifier?

Connected to the right speakers, even a low-powered SET amp delivers unbelievable bass performance. Of course my Altec Model 15 and Moondogs don't rock the house, but at moderate listening levels they produce a well-defined, dynamic and powerful bass that's hard to beat. The soundstage is huge and instruments authentic - music fills the room with big sound. The mids are the sunny side of 2A3 single-ended triode amps. Smooth and creamy, human voices shine and if the recorded performance captured it, 2A3 amps deliver the emotion and drama that define a music lover's Mecca. Take "Amazing Grace" from Joan Baez's live album From Every Stage (A&M SP6506) - the recording quality isn't first rate, but the sheer magic between Joan and her audience is delivered with such beauty that when the enraptured audience sings the last verse alone towards the song's end, it never fails to give me goose bumps.

The top end is another strength of a good 2A3 amp: clean and sweet, extremely detailed and absolutely grainless. A good example is how violins are reproduced in an extremely natural way. Rossini's String Sonatas for instance, performed by Sir Neville Marriner and the Academy of St. Martin in the Fields (ARGO ZRG 506), have beautiful and sweet string tone but also the same tendency to harshness in the extreme highs you're accustomed to when listening to live violin music. Another strength becomes visible with the colour of instruments; Joaquin Rodrigo's Fantasia para un gentilhombre, performed by Angel Romero & the LSO under André Previn (EMI ASD 3415), for example, delivers a full palette of classical instruments (guitar, strings, woodwind and brass instruments) delightfully and accurately presented by these triode beauties.

Summed up, the overall performance of 2A3 SET amps is awesome over the whole audio band, with no audible weaknesses. You're invited, if not compelled, to play music over and over with these low-powered SET amps because they're so fluid and realistic. My evening listening sessions often last much longer than planned; I get lost in music until the early hours.

The only downside is the reduced variety of appropriate speakers on the market. Besides horn systems, and most of them are quite expensive, there are only a few companies (Loth-X and Triangle, for example) offering highly sensitive speakers with the moderate impedance behaviour needed to enjoy the beauty of 2A3 SET amps.

There's movement on the loudspeaker-builder scene here in Austria. David Haigner, a young engineer and acoustic expert, designs and builds made-to-order speakers especially designated for use with low-powered SET amps. I tried one pair (92dB sensitivity) with my Moondogs, and the results have been superb; in the meantime I bought a pair of these  awesome speakers for myself (but that's another story...).

The next frontier for talented designers should be horn systems (and I can tell you that David Haigner has detected his love for such systems... more to come); with the technical knowledge and high tech materials available these days, the improvements could be amazing, perhaps even eliminating the often criticised coloration of horn-loaded systems. The fitting amplifiers are out there waiting...

Give 2A3 SET amps a try and you'll experience a new level of musical reproduction. Less power is sometimes more. Music played with a 2A3 SET amp is more real, more involving, more fun ... and that's what our beloved hobby is all about, isn't it?


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