Tube Preamp Reviews

Anthony H. Cordesman followed-up his SP-10 review in December 1984 (Vol.7 No.7):

Audio Research hasn't formally changed the model designation on one of high-end audio's greatest status symbols, nor have they raised the price. They have "only" improved the phono section of each channel, improving that already-superb preamp so much that I felt justified in adding my own "II" to the model number. And you can convert your existing SP-10 for a quite reasonable $100–$150.

Now, let me whet your appetite: the improved phono stage of the SP-10 is superb. I won't go quite as far as William Z. Johnson—who called it "an order of magnitude" improvement. Live music is only 0.9387 orders of magnitude better than today's better preamps, and preamps don't really get 10 times better in a single step. The improved SP-10 is, however, 0.1936 orders of magnitude (nearly twice) as good in imaging and depth information, and has much better center fill, more transparency, slightly lower noise, and an improvement in coherence and apparent timbre. That ain't bad, considering we started out with one of the best preamps around!

In fact, you can lose yourself very quickly in the soundfield from this new version of the SP-10. The image "floats," with the instruments solidly placed in space. The sound is not etched. There are no surprising transients. Instruments don't suddenly have a new maker, nor do they change in character. In a darkened room, where the sight of your speakers and furniture do not remind you of the truly artificial nature of your listening environment, the SP-10 allows the best records and cartridges to make you forget where you really are.

Don't misunderstand me. I am not hyping the improvement in sound just to notify you that the SP-10 is the world's best preamp of the month. The competition remains strong: Krell and Klyne, just to mention the ~two new preamps beginning with the letter "K," have exciting new designs on the way. Buying for fashion or status is a sucker's bet at any time, and this is particularly true in a field that changes as rapidly as high end audio.

What I find special about the improved SP-10 is the prospect of being able to count on enjoying years of superbly reproduced music. The SP-10 is neither "dry" nor "romantic" nor "hi-fi," It succeeds in being both musical and analytical without calling attention to itself in any way. It gives records a coherence and mix of accuracy with natural musical warmth that I have never heard before in a tube preamp. It does not just do some things well, or what "tubes" do well, it does virtually everything well. It certainly provides all the sweetness of tubes, and only the most vestigial sacrifices in top- and bottom-octave performance.

I had been coming to feel that the electronic part of a phono system had been pushed reasonably close to the ultimate attainable. The new SP-10 is proof that it hadn't. I've run through well over 100 records with it so far, and it has always done two things: let me hear new detail, and let me hear new information thatis musically natural.

I should warn you, however, that this is only true when the input material itself is musical. The improved SP-10 serves as a new demonstration of the problems in Compact Disc players. I agree that the new CD players and the best CDs are getting better, and I now prefer them to cassettes and virtually all pre-recorded open reel tapes. They cannot, however, compete with a top-rank record playing system through the new phono stage on the SP-10. If you do a head-on comparison of the same performance on most phonos and CDs, you'll find the phono system will image better, be cleaner and more transparent in the highs, the depth will be much superior, you will get more natural deep bass, and you will hear more of the fine harmonic details or "air" that make music warm and relaxing enough for sustained listening (footnote l).

The improved SP-10 is also a grim reminder of the drawbacks inherent in the use of low-output moving-coil cartridges and step-up devices. The SP-10 now has less noise in its high-gain mode than it did, but it still cannot be used with many low-output moving-coils without incurring tube noise and hum. You can hear these effects much more clearly with the improved SP-10 than the old SP-10, just as you can hear the effect of changes in VTA, cables, and cartridge loading.

You will want at least a moderate-output cartridge, which may require experimentation. The Argent Diamond, for example, works fairly well, but the Dynavector 17DS is marginal, in spite of their identical output specs. Most Koetsus and Kisekis can work reasonably well, but some do not. The van den Hul EMT, the Decca van den Huls, the new Adcoms, the Argents of all breeds, the Goldring van den Hul, the medium- to high-output AudioQuests, and the high-output Alchemists, all have enough output to achieve the best results with the SP-10.

My advice is to only use a cartridge that can provide all the output needed for normal listening with the high gain stage switched on and the volume control set no higher than 12:00. As good as some of the ultra-expensive low- output moving-coils can sound using a transistor preamp, I suspect that you will be unhappy with any cartridge that doesn't meet the 12:00 test on the SP-10, once you have heard a really good higher-output cartridge through it.

Abuse during shipping can make one or more tubes go slightly noisy or microphonic, and this can lead to differences in sound between channels or a slight loss of the magic coherence that is the key merit of the improved SP-10. I suggest you check carefully for such tubes when you get your unit. Load the phono inputs, turn the volume control to maximum, and listen to the tube noise on each channel. Both should sound the same, with no clicks or rough noise. If you do hear problems, first try Tweak or Cramolin on all the tube pins. Second, gently tap each tube with a pencil eraser and see if any are unusually microphonic. If so, try replacing them. (Remember that the earlier the amplifier stage, the more microphonics you can expect from the tube in it.)

One strong word of caution, however: buy only Sylvania or Philips 6DJ8s if you don't have a reliable source of tubes, or buy extras from Audio Research. I tried a wide range of GE tubes, and they performed like every other GE consumer product I have tried in recent years, from steam irons on—abominably. Amperex tubes were better, but still sonically colored.

I can offer some alternatives to the SP-10 if you want many of the benefits but can't afford the SP-10. Much of the merit of its new phono stage seems to lie in the ability to provide more gain and linearity than other preamps, combined with extraordinary transparency. I've found you can get some of the same benefits by adding a really good tube pre-preamp to an existing tube preamp.

I've been using a tube pre-preamp designed by Murray Zeligman, that can add the gain of the SP-10, and much of its sonic clarity, to a good tube preamp such as the Conrad-Johnson PV-5. The Zeligman pre-preamp is largely hand crafted, requires a 47k-ohm load, and is suited only to the kind of moderate-output moving-coils recommended for the SP-10. It is very good, and can make it easier to live with the sound of that older tube preamp you know and love. Conrad-Johnson also has two new models of nuvister pre-preamps coming, and my tests of a prototype indicate they also can add much of the sound quality of the new SP-10 to an existing preamp, and give you more gain with a better signal-to-noise ratio.

All in all, however, my hat is off to William Z. Johnson for another job superbly done. The aforementioned tubed head amps plus the best old tube preamps can sound very good, but they are no match for the improved SP-10. If you even suspect that you can afford to buy it, you should hear the SP-10 before you make another major investment in audio. There is a lot of tough competition out there, and a lot more coming, but I haven't heard as revealing or exciting a piece of electronics in a long time.—Anthony H. Cordesman

---

Footnote 1: Here I must beg to differ with AHC. CDs have far greater channel–channel phase identity than any phono cartridges, although they do have severe phase shift at the high end. Except that cartridges introduce. to the sound a significant amount of random phase information, which can sound like added ambience, CDs should image better than cartridges. My observation is that they do. And AHC is the first person, to my knowledge, who has claimed that analog bass is better than digital.—J. Gordon Holt