Tube Preamp Reviews

The phono stage was particularly outstanding, allowing the audiophile favorite "Tiden Bara Gär" from the Opus 3 Depth of Image disc to be reproduced with a great deal of presence and a minimum of sibilant (over)emphasis. (The LP comparisons were done with the Bryston TF-1 in the system. With the AQ 7000 running straight into the phono input, there was just enough volume at maximum gain, but the noise level was too high for it to be listenable. I know that the phono stage in general is getting to be an endangered species, but I still wonder why Conrad-Johnson doesn't make this preamp in a version with an extra gain stage in the phono section to accommodate moving-coils.)

In terms of tonal balance, the PV11 was quite neutral (decidedly more so than the PV5), with extended, well-controlled bass, and, in comparison to the Threshold FET nine/e and the Audio Research SP9 Mk.II, just a hint of top-end rolloff. Combining the PV11 with a "soft"-sounding power amp (a descriptor that applies to the Luxman MQ 68C) requires that one pay careful attention to ancillaries like interconnects. I found the van den Hul D-102 III to be a bit too dull; some (now-obsolete) Randall TX was much better, as was AudioQuest's Lapis. Driving the Muse 100 amplifier, the PV11's sonic characteristics continued to be apparent, with results that were in some ways even more impressive. The Muse turned out to be quite a good match with the Quads, producing excellent dynamics, better control of the Quads' midbass resonance, and midrange/highs that were not too far from the delicacy of the Luxman tube amp. The PV11/Muse 100 combination would seem to be a good one for someone who wants the magic of tubes while avoiding the expense (initial cost plus tube replacement) of a tube power amp.

Guy Lemcoe has written extensively on the merits of the SP9 Mk.II; I can add little to his highly favorable assessment (Vol.14 No.6). This is a very fine preamp, with a lighter, brighter sound than the PV11, and with less of the hardness that tended to intrude into the sound of the FET nine/e.

Yes, but which one is most accurate?
My favorite definition of accuracy comes from J. Gordon Holt's The Audio Glossary (footnote 2): "the ultimate objective of an ideal sound system, which everyone claims they want but nobody likes when he has it." I think Gordon was not writing entirely tongue-in-cheek; a component with a very high degree of technical accuracy, but in which the remaining inaccuracy is of the conspicuously "electronic" sort, may be less preferred than a component that is technically not as accurate, but whose inaccuracy is the sort that sounds like it could have been part of the original sound rather than an electronic artifact.

In routine listening, we don't know what the original sound was like, so our judgment of "accuracy" is actually a measure of plausibility: how much does the sound resemble what we immediately recognize as real (produced by musical instruments, including the human voice) rather than reproduction? (footnote 3) Of course, when the listener was present at the original recording session, this provides another sonic reference, but here the comparison involves a memory rather than a readily available actual sound, and we know that memory is prone to a lot of error/distortion. A bypass test, where, for example, a line-level input signal to a preamp is compared to the signal after it's gone through the line-level stage, is a useful here-and-now comparison (actually, it's only short-term rather than long-term memory). However, I would still be reluctant to take the results of this test at face value if they contradicted the conclusions of the more conventional listening test; eg, if the product that ranked first in the bypass test turned out to be the one that rendered most records unlistenable.

With some skepticism, then, I conducted bypass tests on all three preamps under consideration. This was done by a) feeding the signal from the output of the Aragon D2A to the CD input of the PV11, b) taking the signal from the tape-out jacks of the PV11 to the input of the Stax CRM-T1 headphone amplifier (footnote 4), and c) comparing the sound of this relatively direct connection (the signal at the tape-out jacks has gone through the input selection switch but no amplification or buffering) with the signal taken from the main outputs, the volume control of the preamp set to provide approximately unity gain (footnote 5).

As it turned out, the results of the bypass tests were not that dissimilar from the results of long-term listening tests. (Whew!) The PV11's line stage showed some loss of transparency compared to the tape-out signal, with some added warmth and a very slight softening of the sound. Ironically, this softening gave a more natural effect, apparently compensating for the Stax headphones' rising top-end response. The SP9 Mk.II line stage was close to neutral in tonal balance, with some (inevitable) loss in transparency and a slight lightening of the sound.

The bottom line
It should be obvious to anyone who hasn't skipped the body of this review (If you have, go back and read all of it RIGHT NOW!) that I was extremely impressed with the Conrad-Johnson PV11. If the term "musicality" has any meaning in the context of reproduction rather than production of music, then surely the PV11 can be said to embody this characteristic. That is, with the PV11 in the system, I found it easier to sustain the illusion that I was listening not to the product of a complex electromechanical encoding/storage/playback technology, but to music, played and sung by people.

---

Footnote 2: The Audio Glossary used to be published by Old Colony Sound Lab, Peterborough, NH 03458-0423.

Footnote 3: Roaming the halls of the New York Penta at the 1990 Stereophile show, I heard a faint sound emanating from one of the rooms in the distance. "That's it! Those are the speakers I want!" I thought as I rushed down the corridor. I threw open the door of the room where the sound system of my dreams was apparently playing. It was Igor Kipnis, practicing on the harpsichord.

Footnote 4: It might seem that it would have been more reasonable to take the output of the D2A straight to the CRM-T1, but this would have left uncontrolled the possible effect of the additional cable and contacts. (The PV11 in the control condition was acting as—no disrespect to Conrad-Johnson intended—a "dummy preamp.")

Footnote 5: Absolute polarity was maintained by using the polarity-reversal switch on the D2A.