Tube Preamp Reviews

It says something for the state of technology that, after a quarter of a century, there still is no authoritative explanation for why so many high-end audiophiles prefer tubes. Tubes not only refuse to die, they seem to be Coming back. The number of US and British firms making high-end tube equipment is growing steadily, and an increasing number of comparatively low-priced units are becoming available. There is a large market in renovated or used tube equipment—I must confess to owning a converted McIntosh MR-71 tuner—and there are even some indications that tube manufacturers are improving their reliability, although getting good tubes remains a problem.

These trends have passed long beyond the cult stage. While tube amplifiers still cannot provide the high damping factors or woofer Control that is possible With transistor amplifiers, no one still claims that they soften highs or somehow romanticize recorded sound (footnote 1). There is a consensus among high-end magazines that the best tube units are exceptional in the areas of transient and harmonic detail, high frequency information, and imaging and soundstage data. Further, there is a similar consensus that the days when tube units provided superb midrange at the expense of the frequency extremes are long gone.

This brings me to the units under review: the Conrad-Johnson Premier Three preamp and H-la head amp combination. Unlike many tube units, they can be used With most moving-coil cartridges (more on this in a moment), and the preamp has sufficient output to drive most amplifiers.

The very best transistor units still win out in area of noise. The Premier Three preamp alone cannot be used with even moderately low-output moving-coil cartridges like the Accuphase, Argent Diamond, and Dynavectors without the noise and gain mismatch seriously coloring the sound. Even a Koetsu Black is marginal and tends to have its highs rounded and masked, becoming slightly dry and lacking in detail in the upper midrange. The Alpha-l is also marginal, although the problem tends to be a drying up of the upper octaves and a lack of proper warmth and midrange balance.

Like the Audio Research SP-l0, or Premier Three used with the HV-1a (which are remarkably close in price) has just enough gain so that you can use any moving-coil cartridge with a minimum of 2mV output. "Just enough," however, means detectable hiss and noise. I have recorded such noise and superimposed it on the sound of much quieter transistor units (this is a rough-cut approach since it is impossible to do this without adding some colorations to the sound), and it is clear that it matters. Ironically, one has an expanded impression of depth or air; the unpleasant aspects are a tendency to mask the softest musical detail and harmonics, while adding a dry coloration in the spectrum where the noise is dominant. Worse, the imaging tends to alter. There is a feeling of expanded soundstage size and detail, but it is not natural and, although it is initially impressive, it eventually has the same irritating effect as exaggerated highs.

The revised Conrad-Johnson HV-1a head amp offers more gain and less of this coloration than the SP-10. It is by far the best commercial step-up device I have heard, although Murray Zeligman has a new tube head amp in prototype that may well be major competition, and ARC's William Z. Johnson is working on a new transistor head amp design for use with the SP-8 and SP-10. Unlike most ARC and C-J gear, you can mix the C-J head amp with the ARC preamp and amp. Try using C-J preamps with ARC amps, or vice versa, and you get the worst of both sets of gear, not the best.

The HV-1a does not, however, permit input impedances much below 100 ohms without changing sound character and diminishing performance. This presents problems, because I am increasingly unhappy about high-impedance loading as a general solution to the moving-coil cartridge problem. Many of the best cartridges must be loaded down to well below 100 ohms for the best imaging as well as linearity of frequency and dynamic response. Furthermore, high-impedance loading often combines with tube noise to produce even more exaggeration of soundstage size, so that imaging detail is unnatural and irritating, with a tendency for the image to wander or appear in an unnatural location.

I should also note that both the SP-10 and the C-J head amp are sensitive to shock.

Sound Quality
I tested both the Conrad-Johnson and Audio Research combinations using top quality turntables like the Goldmund and SOTA-Sumiko arm combination, top quality cartridges, and speakers like the modified Quad ESL-63s, Thiel CS3s, Spica TC-50s, and Fuselier 3.3s. I have used them with Compact Discs and a wide range of FM Tuners. I have mixed and matched cables, including the Straightwire, Petersen, Discrete Technology, Audiosource, and Monster Cable Interlink Reference.

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Footnote 1: For a somewhat different point of view, see "As We See It" in this issue.—J. Gordon Holt