PREMIER PERFORMERS
In the December 1983 issue, I discussed tube amplification technology--past and present. I reported on some of the lower priced tube equipment, and promised that down the line I would cover high-end tube equipment-specifically, Conrad-johnson's Premier One amplifier and Premier Three preamplifier. These units are generally considered as being at the "cutting edge" of tube amplification design.
As I pointed out in my previous column on tubes, these conrad-johnson units are particularly prized by the underground audio press and their readers. I wondered what these people found so attractive about tube equipment. I know a number of individuals who are devotees of the technology, and asked them to express their opinions on why they favor tube sound.
Their answers were pretty much as I had expected. They talked of the "smoothness" of the sound, the absence of "graininess" and "overbright, tizzy" top end. The sound had an "open, airy, and transparent" quality.
They liked the "imaging," "stage width," "sense of depth" and "ambience preservation." Above all, they stressed that these qualities added up to what was reverently described as "musicality." These people contend that even with the most sophisticated and expensive solid-state preamps and amps, this vaunted "musicality" is missing.
Acting on a hunch, I asked these tube aficionados what they thought of digital sound, and most especially the Compact Disc. Almost to a man, they turned out to be vociferously anti-digital! I asked them if it had occurred to them that the negative qualities they had ascribed to solid-state equipment over the years was somewhat akin to what they disliked about digital sound.
Well, we won't get into that can of worms! Suffice to say, some people like vanilla, and some like chocolate. A number of my friends knew I was gently needling them, and I would never summarily dismiss their notions about "musicality" as mere self-delusion.
The conrad-johnson Premier One is a big amplifier. It measures an imposing 19 in. W x 10 in. H x 21 in. D and, at 135 pounds, is one of the heaviest amplifiers--tube or solid-state--extant.
A large part of this weight is due to the massive power and audio transformers. The main power supply provides more than 4,000 µF at 550 V. After the input condenser, the power supply is separated for each channel to reduce stereophonic cross-coupling. A cascode triode pair of 5751 tubes is employed at the input as a voltage amplifier. As described by Bill Conrad and Lou Johnson, "This high-gain, phase linear single stage is direct coupled to a cathode-coupled, differential phase inverter made up of paralleled sections of high-current triodes (6FQ7) to provide balanced low-impedance drive to the push-pull output stage. The output stage utilizes paralleled 6550 tubes, a total of six per channel." The arrangement features ultralinear operation at high power levels, while reducing the source impedance of the stage. Thus, the amplifier is capable of the high current necessary to handle high-amplitude transients.
Power output of the Premier One is rated as 200 watts per channel rms at 4, 8, or 16 ohms from 30 Hz to 15 kHz, with no more than 1% total harmonic or intermodulation distortion. Two hundred watts is a high output for a tube amplifier, and for many years, the only tube amp with that kind of power was the 200-watt McIntosh. George Piros, the disc cutter for the late Bob Fine, used a Mac to drive the special Miller cutter head when the superb Mercury Olympian Series recordings were made.
It is interesting to note that Conrad-johnson uses domestically manufactured tubes (including the 6550 output tubes) in the Premier One. Many owners of tube equipment are always looking for esoteric Russian or other foreign tubes which purportedly are better than American tubes. The folks at conrad-johnson say they have extensively researched the performance of U.S. versus foreign tubes, and, for their purposes, the American tubes are superior. In fact, they state that substituting foreign tubes in the Premier One will significantly degrade its performance. The company also points out that their tubes have been tempered by a controlled burn-in procedure, permitting extended performance of up to two years without sonic degradation.
A nice feature of the Premier One is its output-tube bias-adjustment system. The amplifier is connected to a loudspeaker, the preamplifier to the amplifier with the volume control fully off, and no signal is applied to the amplifier. Through the perforated metal cover of the Premier One, screwdriver adjustable controls (one for each output tube) are turned clockwise until an associated red LED is illuminated.
Next, the controls are turned counterclockwise until the LED is just extinguished. After a 30-minute warming period, the procedure is repeated and that is all there is to do. With this biasing system, it is not necessary to buy output tubes in matched pairs. In use, the Premier One generates quite a bit of heat, but not as much as some Class-A amplifiers; it operates in Class AB. Considering that this Premier One is a tube amp, its rated hum and noise figure is extraordinarily low, 100 dB below full power output. That is right in line with noise figures of top-quality transistor amplifiers. Frequency response of the Premier One is rated within ±0.5 dB from 20 Hz to 20 kHz.
This unit costs $4,350. The conrad-johnson Premier Three is the Premier One's companion preamplifier. It measures 19 in. W x 5 1/4 in. H x 12 1/4 in. D. The unit has an attractive gold finish and solid-metal control knobs for volume, balance, and mode and input selection. Pushbuttons control on/off, muting, and tape monitor. There are two tape monitor functions and two main outputs. The rear panel has inputs for phono, AUX, tuner, and tape record in and out. Two switched and two unswitched a.c. receptacles are provided. Herewith is conrad-johnson's description of the Premier Three preamplifier circuit: "The Premier Three phono stage consists of two stages of cascode triode pairs. This provides sufficient open-loop gain to achieve optimum feedback ratios even at bass frequencies. The second stage is direct coupled to a cathode follower which drives the feedback loop as well as the output. Phono equalization is accomplished by RC networks in the feedback loop. A generalized anode follower configuration on the second cascode stage tailors the circuit's open loop response to maintain a constant feedback ratio across the audio spectrum.
"The line amplifier stage uses two triode amplifiers, separated by a cathode follower which maintains open loop phase linearity at high frequencies. The second amplifier stage is direct coupled to a cathode follower to achieve low output impedance.
"Plate voltages are supplied by a separate circuit for each channel. Special voltage regulators effectively isolate the two channels as well as eliminate line voltage fluctuations. The regulators achieve an extremely low impedance supply for the audio stages.
"Filaments are operated at a regulated d.c. voltage to eliminate coupling of subsonic line voltage disturbances to the audio signal." Phono input is the industry standard 47 kilohms and 100 pF. RIAA equalization is within 0.25 dB from 20 Hz to 20 kHz. Phono overload is in excess of 500 mV at 1 kHz. Phono gain is 40 dB, and phono hum and noise is 72 dB below 10 mV. The phono input is for moving-magnet cartridges, but I am a bit surprised that no moving-coil phono input was provided on a preamplifier of this price ($2,850) and sophistication.
As in the Premier One, the Premier Three's tube complement (two 12AX7s, five 5751s, and two 5965s) has undergone the special burn-in procedure for extended life. And here, too, conrad-johnson does not recommend the use of foreign tubes.
The high-level gain for the Premier Three is 28 dB, and maximum output is 25 V. Response bandpass is 2 Hz to more than 100 kHz. High-level hum and noise is 84 dB below 2.5-V output.
Total harmonic and intermodulation distortion are specified as less than 0.05%. I hooked the Premier Three into the Premier One and added a Sota Star Sapphire vacuum turntable with Sumiko's The Arm and a new Grado Signature Eight phono cartridge. I also used Technics, Kyocera and Sony CD players, the Sony PCM-F1 digital processor, and my Ampex 440C open-reel recorder. In other words, I had plenty of top-quality input sources. I used a number of speakers, ranging from Quad ES-63s and B & W 801s, to IMF Monitor Sevens and the new Duntech PCL-3 planar wall loudspeakers.
Did I perceive the same qualities of performance as the "tube freaks"? It is best to remember I had not listened to a tube preamplifier/amplifier combination for many years, especially units with this degree of sophistication and quality. I was very pleasantly surprised by many of the things I heard, less so with some other things. The conrad-johnson Premier Three and Premier One did, indeed, present a broad sound stage, a great sense of depth, and more retrieval of hall ambience (with selected recordings). There was an airiness, a transparency, and a' more evanescent quality to the sound, especially notable with strings and woodwinds. The smoothness tube lovers prefer was certainly evident. Transient response from piano, percussion, and guitar was fast and clean but not with the super-fast attack of amplifiers like the Levinson, Krell, and Citation XX. Bass response was better than is traditionally expected of tube amplifiers. It was clean and extended, but the lower damping factor meant less control and a thickening in the lowest frequencies. However, it was not tubby and should be fine except with speakers which produce a really lumpy low end. Vocal and choral work fared very well, with a fine sense of presence and no blurring.
With digital vinyl, CDs and digital tape, did the tube equipment produce sound any different than solid-state units do? Not appreciably. In some of the shriller CDs, the sound did seem to smooth out somewhat. Did all the nice things I heard add up to this much abused term, musicality? Can musicality equate with accuracy? Is it more of a euphonic coloration (a phrase beloved by the little magazines) than a superior reproduction of sound? Perhaps it is like a well-known and expensive phono cartridge, of which auditioners say, "If it doesn't sound like music, than that is how music ought to sound." In several months of use, I found the conrad-johnson Premier One and Premier Three very reliable, and all controls were very smooth and positive in operation. These components reproduce recorded music with all the parameters so beloved by the tube cultists. Their sound falls extremely easy on the ear.
(Note: In my April and May columns, I inadvertently caused some confusion as to the location of two companies. Duntech loudspeakers are imported by: W & W Audio, 4821 McAlpine Farm Rd., Charlotte, N.C. 28226. Components developed by Win Labs are available through Tru-Sonics Marketing, 7320 Hollister Ave., Goleta, Cal. 93117. -B. W.)
(adapted from Audio magazine, Bert Whyte)
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