Tube Preamp Reviews

It is tempting to focus on short-term differences, and to ignore the fact that you're looking for equipment that gets the best out of a broad collection of records, tapes, CDs, and FM broadcasts, and on which you can listen for hours without reminders that your equipment is introducing unpleasant or constantly detectable colorations. By comparison, transistor equipment always has a distinctly less musical sonic fingerprint than does tubed equipment—either in the form of dryness or harshness in the upper octaves or a distinct loss of detail.

The end result was that both the Conrad-Johnson and Audio Research combinations provided a consistently more accurate reproduction of music, voice, and speech than any transistor unit I have heard in my own home. This accuracy shows up in several key areas, and is evident with a very wide range of source material and over a long period of time.

The C-J and ARC sets of equipment also offer amazing realism in the midrange. This is a function of coherence and the ability to reproduce an amazing amount of detail without hardening or softening, the ability to reproduce extremely detailed low-level harmonics, and the ability to provide wide dynamic range without effort—neither appearing to slow the music nor accelerating too far.

This superior coherence shows up clearly on those piano and violin records with both mechanical and musical detail: where the music is complex and covers the entire midrange; where scores are rustled, bowing sounds are clearly heard, the players move slightly, or there are extraneous sounds in the hall. To the extent that illusions are ever real, both the Conrad-Johnson and Audio Research systems seduce you into suspended belief: you listen as if it were live.

Tube units are famous for their imaging and depth, and for providing precise natural placement of the musician or singer. Again both these sets of equipment outperform the best transistors I've heard. Centerfill is excellent and the soundstage extends to the right and left of the speakers when the music permits it. Depth is natural. Imaging height is determined by the speakers and not by the electronics. Hall effects are clearer and less exaggerated. Transistor equipment can on occasion do a few of these things better, but never so many in combination.

Although neither the C-J nor the ARC equipment veil or roll off the highs, many audiophiles would enjoy simply to hear the upper octaves without the fatigue or irritation that comes from prolonged listening to their transistor equipment. The key subjective impact of the best tube units is that the highs will reveal any problems in the miking, but will sound natural with decent miking and on those records and tapes that actually do sound natural.

Comparisons
I tested both a new SP-I0 and one borrowed from a local audiophile who had retubed it to his taste. The GJ HV-I a and Premier Three preamp had just been retubed, and I tested two variants of the head amp.

Both preamps are nicely styled and have good basic features. The Audio Research SP-10, however, wins hands-down on ergonomics. You have switchable gain, a choice between two turntable inputs or Mute at the phono stage, and switchable cartridge loading. For most high-end audiophiles these are useful controls. The Conrad-Johnson combination has a slight advantage because its balance control is infinitely variable while the Audio Research control is stepped-and yes, dammit, there are times when the ARC's balance switch won't "lock in" at just the right place.

Both units are big and involve two rack-mountable boxes. The SP-10 has a separate preamp and power supply; the Conrad-Johnson a separate preamp and head amp. The ARC equipment is a muted silver grey with knobs that match the panel, and the C-J equipment is in burnished gold with gold knobs.

Both combinations seem to balance out in terms of the sonic impact of switches and wires. The Premier Three by itself is not particularly sensitive to grounding, but the C-J combination requires an interconnect between the head amp and preamp and is as sensitive to hum-field, grounding, and "AC polarity" as the SP- 10. To get proper AC polarity you need to plug each piece of equipment in individually to the AC so that each produces the lowest voltage from chassis to the ground on the AC line, with no interconnects plugged in to either the head amp or preamp.

Both preamps have the precise "feel" of expensive equipment, and both provide excellent sound. They do, however, sound different in several important ways. The Audio Research SP-10 has the flat, extended upper octaves of the very best transistor equipment, plus all the virtues of tubes; no transistor lover will feel slighted to own the SP-10. Its variable loading also allows a quick approximate calibration of the best loading for a given cartridge.

The end resylt is that the SP-10 almost seduces you into lisening to upper midrange detail while loading a cartridge for the most precise imaging. The outstanding merit of the SP-10 is in its top four octaves. You will hear more detail in a musically natural form in these octaves with the SP-10 than from any other preamp I've heard.

The Conrad-Johnson Head Amp and Premier Three, in contrast, do best in the three octaves above the bottom octave. They are strongest in the areas where tubes traditionally are strongest. You can, for example, hear the bowing sound on a violin more clearly than on an SP-10. Soundstage noises were clearer, because most occur in the frequency band where the G] does best, and the C-J combination has superior imaging in terms of stability and centerfill.

The units differ in depth presentation. The ARC provides more upper-octave depth information. The C-J provids more bass and lower-midrange depth information. This slightly favors the Gj for orchestral music, because more hall depth-information seems to be present in the frequencies the Gj favors.

Let me hazard another description of the two units. The SP-10 is ideal in reproducing closely miked chamber music, female voice, natural jazz, and other music where you might choose to sit within 30' of the performers. The CJ combination is ideal for reproducing the larger orchestra or musical combination, and opera. Both reproduce all music very well, but the two units tend to place you in different parts of the concert hall. The SP-10 brings you close to the music. The C-J is twentieth row center.

Another way of putting it is that the ARC preamp is "fast" and the C-J is "sweet." A pejorative way of saying the same thing is that the ARC is "hard" and the C-J is "rolled˙off." 50 much for semantics; the point is that they are audibly different, and you should pay close attention to their characteristics in making your choice.

I will ignore the issue of which is best; this is a matter of taste, and a choice you can make for yourself. They are as different in sound as fine wines from the same district. You may find that the C-J combination performs slightly better with cartridges that have extremely fast highs with a slight rise, while the SP-10 benefits from a cartridge that has flat frequency response.

Although both units performed without fault during my listening, they require care and sense. Shock and rough handling are no-nos. Mixing tubes to try to improve on the designer is a recipe for trouble both sonically and in terms of reliability. Cautious cleaning of the tube prongs with Tweek, according to the instructions that come with Tweek, can be recommended. Regular retubing at the manufacturer's recommended intervals is an unfortunate and expensive necessity.

Summing Up
I cannot tell you whether my love affair with tubes as the ne plus ultra in high end will last through the next year or the next issue. I have recently found the Krell solid-state equipment to be particularly impressive, and there is one hell of a band of designers trying to make tubes truly obsolete. I must say that I would not buy tube equipment if I didn't trust my dealer, as it is more trouble-prone than solid-state and you will need help and support.

Both the Audio Research and Conrad-Johnson electronics are, however, what the High End is all about. They are part of that elite group of equipment which leads the way towards filling the awkward gap between live performances and reproduced sound, and which allows you to explore nearly 100 years of recorded sound to its best potential. They, like virtually all high-end equipment, are luxuries and not cost-effective investments. While some of the best things in life may be free, none of them are cost-effective.