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Sometimes, a product review in Stereophile can breed additional reviews. Shortly after I reviewed the Audio Valve Conductor line stage in the July 2009 issue (Vol.32 No.7), I was contacted by NAT's US distributor, Musical Sounds: "Hey, if you liked the Audio Valve Conductor [$13,995], you'll love the NAT Symmetrical line stage at $8000! Would you like to review it?" Aside from Michael Fremer's review of the battery-powered NAT Signature Phono stage in the July 2007 issue, I was unfamiliar with this Serbian maker of tube electronics. But "Sure," I replied; "why not?"
Today, as I reflect on my recent experiences in my reference system with Audio Valve's Eklipse and Conductor, Audio Research's Reference 3, and the NAT Symmetrical, as well as time spent at friends' houses and audio shows with C-J's Art 2 line stage, I realize how dramatically things have changed. I felt that each of these designs presented a chillingly realistic reproduction of the musical experience, with no meaningful flaws, and with strengths that far exceeded those of designs of a decade or more ago. I found that, as a reviewer, it was nearly impossible for me to rank these products, to…
Listening to the recent remastering of the Beatles' Abbey Road (CD, Apple 382462 2), I focused on Ringo's drum work during the densely orchestrated chorus of "Something." Despite the complex mix of vocal harmonies, instruments, and orchestral backfill, I was able to follow every dynamic inflection of Ringo's clever snare and tom work, even though it was buried deep in the mix. And with Robert Silverman's reading of Beethoven's Piano Sonata 1, from his complete set of the sonatas (CD, OrpheumMasters KSP-830), I was able to analyze every movement of Silverman's stylized technique in a piece I…
Sidebar 1: Specifications
Description: Tubed line preamplifier. Tube complement: two OA2, two 6X4W, six 6N1P-EV, two 6N2P-EV. Frequency response: 0.07Hz–300kHz, –3dB; 20Hz–20kHz, ±0.01dB. Phase status: non-inverting (0°). Input impedance: >47k ohms single-ended, >94k ohms balanced. Stereo separation: >100dB at 1kHz. Output impedance: <70 ohms, single-ended, <140 ohms balanced. Signal/Noise Ratio: >95dB, A-weighted, ref. 1V RMS output. Maximum voltage gain: 15.5dB (x5.6). THD+N: <0.03% at 1V RMS, 20Hz–20kHz. Power requirements: 110 or 220VAC at 50–60Hz, maximum 100VA…
Sidebar 2: Associated Equipment
Analog Source: VPI TNT IV turntable, Immedia RPM tonearm, Koetsu Urushi phono cartridge.
Digital Sources: Lector CDP-7T, Creek Destiny CD players.
Preamplification: Vendetta Research SCP-2D phono stage, Audio Valve Eklipse line stage.
Power Amplifier: Audio Research Reference 110.
Loudspeakers: Alón Circe.
Cables: Interconnect: MIT Magnum & MI-350 CVTwin Terminator. Speaker: Acarian Systems Black Orpheus.
Accessories: Various by ASC, Bright Star, Simply Physics, Sound Anchor, VPI.—Robert J. Reina
Sidebar 3: Measurements
I used Stereophile's loan sample of the top-of-the-line Audio Precision SYS2722 system (see the January 2008 "As We See It" and www.ap.com) to examine the NAT Symmetrical preamplifier's measured behavior; for some tests, I also used my vintage Audio Precision System One Dual Domain.
The NAT Symmetrical line preamplifier is beautifully constructed, but I had some problems measuring its performance, as the right channel's balanced output was half that of the left's. I reseated all the tubes and ribbon cables, but this didn't fix things. The fact that the…
Denon Anechoic Orchestral Recordings
Music and Test Signals for Evaluation of Room Acoustics
Mashahiko Enkoji, Osaka Philharmonic Orchestra
Denon CD PG-6006 (CD only). Katsuhiro Tsubonou, Yoshiharu Kawaguchi, dirs.; Norio Okada, Katsuhiro Miura, engs. DDD. TT: 58:42
Music and Test Signals for Evaluation of Room Acoustics
Mashahiko Enkoji, Osaka Philharmonic Orchestra
Denon CD PG-6006 (CD only). Katsuhiro Tsubonou, Yoshiharu Kawaguchi, dirs.; Norio Okada, Katsuhiro Miura, engs. DDD. TT: 58:42
If this is supposed to be the age of communication, why aren't people communicating? If we can bounce a TV show off a satellite into the Soviet Union, or send an architectural plan along with the designer's signature from New York to London in 30 seconds by facsimile, why the hell haven't we been able to explain…
Way back in the mists of time, around 1980 to be exact, the Marantz company in Europe introduces a range of ostensibly cost-no-object solid-state electronics under the "Esotec" banner. Manufactured in Japan, but apparently designed in the USA, these ruggedly constructed components are noteworthy in that the power amplifiers are capable of being operated with the output stages running under class-A bias as well as class-B. The relatively expensive Esotec amplifiers sell in small numbers in the UK—remember that this is before the rebirth of the British high end—and pass into the history books…
Atkinson: Do you think that the correlation between good sound and low loop feedback is due to the basic linearity of the circuit? Or is it due to other factors? For instance, if you have very high amounts of loop feedback, you can then have time-domain problems.
May: Well, the basic amplifier is more linear. But there are a lot of aspects of it. You have to look at what the open-loop frequency response is with phase compensation. There you want to keep the energy storage in the loop as small as possible. In other words, get the widest bandwidth open-loop. But the phase-compensation…
May: I've got to say that it's pretty well broken up, distributed over the whole amplifier. It's a pretty stable power supply—not that any unregulated supply doesn't have its limitations—but it's a good transformer, a good power supply. I think the real breakthrough on Polaris was the linearity correction circuit for the MOSFET output stage. Basically what we do is compare an idealized output signal with the actual output signal of the amplifier. And introduce local error-correction networks within the output stage proper. It's a small feedback loop existing right around the output stage.…