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Single-ended triode amplifiers (SETs) have a considerable following, but even their most devoted fans admit that its maximum power output is not among an SET's strengths. You'd be lucky to get an SET that puts out 7Wpc, and some (like those using the 45 tube) are closer to 2Wpc. Highly sensitive speakers (eg, horns) will tend to offset the power limitation, and SETs usually sound more powerful than their measurements indicate, but the laws of physics still apply: 2W is 2W, regardless of the kind of amplifier that produces it, and an amplifier's manner of clipping and recovery from overload…
Setup
I normally place amplifiers on a PolyCrystal stand that can support a good-sized stereo amp or a pair of smallish monoblocks. However, the pair of ATM-211s was too big to be accommodated, so I got hold of a second PolyCrystal stand so that each amplifier had its own. I first listened to the amps plugged directly into AC, but found that using a PS Audio High-Current Ultimate Outlet resulted in a slightly lower noise level, with no downside such as restriction of dynamics.
I normally place amplifiers on a PolyCrystal stand that can support a good-sized stereo amp or a pair of smallish monoblocks. However, the pair of ATM-211s was too big to be accommodated, so I got hold of a second PolyCrystal stand so that each amplifier had its own. I first listened to the amps plugged directly into AC, but found that using a PS Audio High-Current Ultimate Outlet resulted in a slightly lower noise level, with no downside such as restriction of dynamics.
The ATM-211 has what seems like an exceptionally rigid, well-built chassis; this, combined with the…
With the ATM-211s in the system, the bottom end of the Avantgarde Unos was as tight and extended as I've heard with any amplifier, including top solid-state units. Of course, bass in the Unos is handled by a powered subwoofer, so the bass you get is a function of the subwoofer amp as well as the main amp, but the quality of the bass I was getting showed that the ATM-211 was not letting its end down. The tonal balance of the ATM-211 was quite neutral, more so than that of the Quicksilver Horn Mono, a push-pull tube amplifier whose sound I've described as being more in the "classic tube…
SETs whose power outputs are in the low single digits pretty much require that you match them with high-sensitivity speakers like horns. The range of speakers that the ATM-211 can drive is not nearly as restricted. I did a brief trial with a pair of Paradigm Reference Studio/20 v.2s, which I still had around as part of the associated equipment for a review in Stereophile Guide to Home Theater. The Studio/20's claimed "in-room" sensitivity is 89dB (86dB anechoic), which is more than 10dB lower than that of the Avantgarde Uno. The normal recommended power for a speaker of this sensitivity…
Sidebar 1: Specifications
Description: Single-ended triode monoblock power amplifier. Tube complement, one each: 211, 12AX7, 12BH7A. Power output: 22W into 8 ohms (13.4dBW). Damping factor: 2.18. Input impedance: 22k ohms. No other specifications listed.
Dimensions: 15.2" (390mm) W by 14" (360mm) D by 10.1" (260mm) H. Weight: 66.1 lbs (30kg).
Serial numbers of units reviewed: 13003, 13006.
Price: $9800/pair. Approximate number of dealers: 18. Warranty: 3 years parts & labor, 90 days tubes.
Manufacturer: A&M Ltd., Osaka, Japan. US distributor: AXISS Distribution, 17800…
Sidebar 2: Associated Equipment
Analog source: Linn LP12 turntable (fully updated), Linn Ittok tonearm, AudioQuest AQ-7000nsx cartridge.
Digital source: PS Audio Lambda II CD transport; Perpetual Technologies P-1A and ModWright P-3A digital processors.
Preamplifier: Convergent Audio Technology SL-1 Ultimate.
Loudspeakers: Avantgarde Acoustic Uno 3.0, Paradigm Reference Studio/20 v.2.
Cables: I2S: Mystic Reference. Digital: Illuminati Orchid AES/EBU. Interconnect: Nordost Valhalla, Nirvana S-L. Speaker: Nordost Valhalla. AC: PS Audio Lab, Mini Lab, TARA Labs Decade.
…
Sidebar 3: Measurements
With the bright glow of its directly heated output tube lighting up the room, the Air Tight ATM-211 amplifier was very different from the products that usually pass through my measurement lab. I also had problems getting it to behave at first. When its AC supply lead was grounded, the amplifier was unstable at output levels of more than a few tens of milliwatts, going into bursts of ultrasonic oscillation. Keeping the Audio Precision System One grounded and floating the Air Tight's supply ground with a cheater plug solved the instability problem, though this did…
One of the biggest challenges in setting up any new listening room is getting the room to work with your equipment rather than against it. I faced this challenge in spades when Trish and I moved into our dream house in the California hills. What would serve as my listening room was a wonderful, open space with panoramic views of the surrounding hills—a space that bore no resemblance at all to a traditional, rectangular, dedicated listening room. Instead, there was a wall of glass, a huge marble-and-glass fireplace, a 20' ceiling—and did I mention that it isn't actually a "room," but one arm…
The verdict: Another winner. The Echo Buster is light and easy to use, even to hang on a ceiling. And the benefits, while sometimes subtle, are always audible and worth the work. At prices ranging from $130 for the smallest model to $285 for the largest, it's definitely worth having a few Echo Busters around.
Double Buster
The Double Buster is a panel diffuser similar in size and appearance to the Echo Buster absorber. But instead of an absorptive foam core, the Double's wooden frame is filled with a rigid panel of corrugated material. The idea is that they reflect high frequencies…
Sidebar1: Specifications
Descriptions: Bass Buster: Helmholtz quarter-round bass absorber, wood-framed with foam core. Echo Buster: flat-panel high-frequency absorber, wood-framed with foam core. Double Buster: flat-panel mid-to-high-frequency diffuser, wood-framed with corrugated core. Echo and Double Busters available in wall-hanging or floorstanding versions, with supplied feet.
Dimensions: Bass Buster: 5' H by 9" R to 6' H by 10" R quarter-round. Echo Buster: 4'-6' H by 12"-24" W by 3" D. Double Buster: 4'-6' H by 12"-24" W by 3" D. Weights not specified. Custom sizes available.…