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ONE GOOD TUBE DESERVES...
Even the most casual observer of the audio scene will have noted that, while many people can be classified as audiophiles, sub-groups within this fraternity have widely divergent views concerning reproduction of recorded music. Thus we have the "objectivists," who assess the quality of audio components by how well they measure in rigorous, standardized tests, and the "subjectivists," who judge sound quality on a more emotional and intuitive level, making no at tempt to technically account for the often elusive, ephemeral sonic qualities of audio components. Needless to say, the more hidebound adherents of both camps have endlessly argued the merits of their viewpoints. My feeling is that the well-rounded audiophile em braces the best qualities of both philosophies.
I raise this point because this month I'm going to report on a new, high-end tube preamplifier-the conrad-johnson Premier Seven. Nothing quite fans the flames of audio debate, even in the subjective camp, like the relative merits of solid-state versus tube equipment! Certain analogies can be made be tween the solid-state/tube controversy and the digital/analog imbroglio. For example, when transistorized preamps and power amps first appeared in the early '60s, they were widely con damned by audiophiles, mainly be cause of a "thin, shrill" high-frequency sound and a "cold, sterile, clinical" sound that was "lacking in musicality." Does this sound familiar? While solid state audio components are near-universal these days and have attained a very high degree of refinement, there are still those who prefer vacuum tube equipment. It is hardly a coincidence that tube gear is the "darling" of the underground audio press, the very same group which so adamantly op poses and condemns digital audio technology.
Please don't misunderstand--I don't mean to infer that those who prefer tube equipment and analog sound are part of some mysterious, dark cabal against progress in audio. Rather, it is the qualities the underground press ascribe to tube electronics and analog sound that make them philosophical and technological bedfellows. I myself have no bias in favor of tube equipment or, for that matter, analog sound, and I should also point out that tube equipment still has a loyal following in England and, of all places, Japan, where vintage McIntosh and Marantz tube amps command prices with five figures and no decimal point! If you reckon the introduction of the CD in 1983 as the de facto beginning of the digital era, such a dawning hasn't inhibited the development and marketing of new tube electronics.
Back in 1984, I reported on the conrad-johnson Premier Three tube preamplifier. Since then other "pure" tube preamps have been introduced, and we have seen the development of hybrid solid-state/tube preamplifiers, culminating in the very popular Audio Re search SP-11. Currently, Audio's Annual Equipment Directory lists about 20 high-end tube preamps, and now conrad-johnson has introduced the Premier Seven, which may well be the ultimate embodiment of the no-holds-barred, no-compromise, "pure" tube preamp.
The Premier Seven operates in a Class-A circuit topology utilizing one 6CW4 low-noise nuvistor input tube (which can accommodate fairly low-output MC phono cartridges) per channel and five 6GK5 single-triode tubes per channel. Each channel's gain blocks consist of a triode amplifier and a cathode follower. The phono stage of each channel has two gain blocks, and in between them is the passive RIAA EQ, which is accurate to ± 0.25 dB, 20 Hz to 20 kHz. The line stage consists of a single gain block.
Phono gain is 40 dB, line stage gain is 29 dB, and, unusually for a tube preamp, no negative loop feedback is used. At 1V output, THD and IMD are rated at less than 0.25%. Each channel's gain blocks are powered by discrete supplies, with a preregulator and two stages of regulation for very low noise. Proprietary polystyrene capacitors are used in all audio circuitry; even the power supplies use only polystyrene and polypropylene capacitors, and that includes the input condenser.
The first time you see the Premier Seven, you see striking evidence that Bill Conrad and Lew Johnson were determined to make a definitive design statement. The massive unit has a simple, uncluttered front panel that is singularly free of "bells and whistles" and is beautiful to behold in its gold anodized finish.
The Premier Seven is actually a dual-mono tube preamp. Each unit is in a separate chassis and has its own discrete solid-state power supply in another separate chassis. The preamplifiers are mounted left channel on top of right and are connected by a massive, 1/4-inch solid metal face- and endplate.
Although the power supplies are on separate chassis, they share a common enclosure. The units are completely separate electrically, to the ex tent of a separate a.c. line cord for each power supply and separate 5-foot umbilical cords which connect power sources to the units. In the preamps, all active circuitry is on the subchassis and shock-mounted to minimize microphonics. With filament and plate transformers for each preamp, the entire Premier Seven weighs 56 pounds and is surely one of the heaviest preamplifiers extant.
Throughout, the conrad-johnson uses "cost no object" parts and components. Precision metal-foil resistors are laser trimmed for accuracy. All internal wiring is 300-micron, linear-crystal solid silver. There are no potentiometers in the Premier Seven; level controls are stepped attenuators which switch discrete pairs of precision resistors. The controls provide attenuation in 23 steps from 0 to-54 dB. Individual LEDs on the front panel of each channel illuminate for the 23 steps.
Each preamp has solid metal controls for source selection (phono, tuner, CD, and tape 1 and 2) and a record selector for the same sources. To the right of this control is the level attenuator. On the extreme right is a small on/ off mute pushbutton. Each power sup ply has a separate switch, and the Premier Seven incorporates delay relays to suppress turn-on/off transients.
The rear panel has gold-plated RCA inputs for all sources, including the tape loops. Two pairs of main output jacks facilitate bi-wiring and biamping.
Each channel has a phono impedance control, ranging from 70 ohms to 47 kilohms, to accommodate both moving-coil and moving-magnet phono cartridges.
The Premier Seven claims a pass-band from 2 Hz to more than 100 kHz. It has a maximum output of 20 V rms and is an exceptionally quiet tube preamp, with phono noise 80 dB below 10 mV input and the line level noise 88 dB below 2.5 V input. Output impedance is less than 200 ohms. The Premier Seven is also rack mountable. No question about it, this is a physically imposing preamp, and I'm happy to say its performance was on the same elevated plane.
I set up this unit two ways. First, I decided to assemble a quintessential, tube-freak/analog-lover's system consisting of the superb Versa Dynamics 2.0 turntable with the new Ortofon MC3000 moving-coil cartridge alternating with a Cello cartridge feeding into the Premier Seven. The output of the Seven was fed into the conrad-johnson Premier Five 200-watt mono block tube amps and then to B & W 801 Matrix and new Duntech Sovereign Mark Two loudspeakers. Since the Premier Seven inverts polarity, I wired the speakers accordingly. I tried the Ortofon straight in, without its special step-up transformer. While the Seven has a lot of gain, the extremely low output of the Ortofon cartridge created some problems. I could get enough output for a fairly loud playback, but the Seven's tubes would go microphonic on some bass transients. Using the Ortofon transformer into a 47-kil ohm load gave plenty of level.
As most vinyl addicts are aware, cur rent classical LPs are almost invariably cut from digital masters, but in my tests with this system, I used many older vinyl records mastered from analog tapes. These included some from EMI and London Decca, and a few of my own recordings for Everest. I sought out the great Neville Marriner performances of Mozart and Haydn with the orchestra of the St. Martins-in-the Field Academy. Finally, for the ultimate in analog sound, I played some of Sheffield's direct-to-disc recordings of Lincoln Mayorga as well as my Crystal Clear direct-to-disc recordings of Arthur Fiedler and the Boston Pops and of the organist Virgil Fox.
Apart from the inevitable record surface noise, which fortunately wasn't excessive, reproduction was revelatory! The combination of the three-dimensional imaging of the 801 Matrix, plus the Premier Five and the Premier Seven, provided a wonderfully natural, very musical listening experience. The Premier Seven simply extracts every iota of hall ambience from decently miked recordings. The stage presentation is startling. The same can be said of depth perspective, which extended deep into the recording stage and was uncanny in capturing the off-stage brass in Mahler's Third Symphony. All this was heightened by the airy transparency of the sound and the enveloping space around instruments. In the percussion on the Sheffield discs, cleanness and transient attack were outstanding, quite crisp with no over hang. Bass response was excellent al though without the solidity, weight, and control of a top solid-state amplifier.
This was very beguiling, musically seductive sound. If some choose to call this reproduction "euphonic coloration," so be it. It is very easy on the ears, essentially non-fatiguing, and at least in my listening room, not amorphous. The results with the Duntech Sovereign were fairly similar, although the Seven didn't fully exploit this speaker's bass capabilities.
There are many people who like certain combinations of tube and solid state equipment. Some like to use a solid-state preamp to drive a tube amp. Others prefer to drive a solid state amp with a tube preamp because of the better-controlled, cleaner bass.
(Even most avid tube devotees usually admit this is a good idea.) My second setup consisted of Sony CDP-707ESD and Denon DCD-3300 CD players and a Sony DTC-1000ES R-DAT recorder all feeding into the Premier Seven, along with the same phono input. I then fed the Seven into Cello Performance solid-state, mono block amps and then to the Duntech Sovereigns. Here again was an impressively natural, highly musical listening experience, with a definite improvement in bass response. If you force me to choose, I'd have to pick the Premier Seven/Cello combination.
It had just the extra definition, better articulation, and tighter bass that add a touch more realism-although I have to admit the freedom from noise in the digital source material probably influenced some of my perceptions.
Obviously, either setup would have gladdened the heart of any audiophile of any persuasion. There is no question that a unit like the Premier Seven needs to be teamed with the very best equipment in order to fully savor its unique qualities. For those who are "into" tubes and can afford its $7,850 price, the Premier Seven is currently the ultimate expression of vacuum tube technology.
(adapted from Audio magazine, Dec. 1988; Bert Whyte)
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