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POSITIVE FEEDBACK ONLINE - ISSUE 33
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Nakamichi TX-1000 Self-Centering Turntable - The Reason Behind the Legend
by Roger S. Gordon

 

Amongst turntable aficionados the Nakamichi TX-1000 turntable and its smaller brother, the Dragon Computing Turntable (CT), are legendary. These turntables, like most classics, are rare. Both turntables were sold from roughly 1983 to 1987 before being killed off by the ascendancy of the CD. The TX-1000 sold in the USA for approximately $8,000 and the Dragon CT for approximately $2,000 (including a good tonearm). Estimates of the total number of these turntables sold worldwide range from 200 to 500 for the TX-1000 and 2,000 to 5,000 for the Dragon CT. These numbers are guesstimates as no one really knows for sure. While the TX-1000 and the Dragon CT are both Nakamichi turntables, they actually are quite different from one another in both design, appearance, and materials (cast metal versus wood). These differences are understandable when you realize that the TX-1000 was designed by Etsuro Nakamichi and built by Micro-Seiki, while the Dragon CT was designed by Junichi Okumura and built by Fujiya Audio Ltd. (Courtesy of www.thevintageknob.org)

Despite being so different from each other the TX-1000 and the Dragon CT share one incredible feature. Both turntables have a self-centering mechanism that eliminates the wow caused by the spindle hole being punched off center.(1) All of us who play vinyl records have seen the effect of an LP with an off-center spindle hole—the cartridge and arm swings horizontally from side to side with each revolution of the platter. Likewise, we have heard the pitch of a sustained note rise and fall with each revolution of the turntable. This is particularly noticeable on sustained piano notes contained in the last grooves of a side.

The reason for the rise and fall in pitch and its significance was explained in Dr. Robert Greene's review of the TX-1000 which appeared in issue 54 of The Absolute Sound (July/August 1988). Since Dr. Greene stated it so well, I will quote from his article which is posted at his site.

"Suppose we are listening to a groove that is, say, 75 mm from the center of the record; typically, this is still in the music groove region, but near the end of it. (Seventy-five millimeters is about three inches.) Since the record goes around once in 1/(33 1/3) minutes = 1.8 seconds, the velocity of this groove past the stylus is 2 pi (75mm)/1.8 sec. which equals 261.8 mm/sec.  Now suppose the record is 0.5 mm off center. (This is the limit of the correcting motion of the Nakamichi TX1000. Records further off-center than that have to be roughly hand centered before the TX1000 is applied. Most records that do not have badly worn spindle holes meet this standard of 0.5 mm.) Then when we are hearing the part of the 75 mm groove that is furthest from the platter center, the effective radius of the groove is 75.5 mm and the velocity goes up to 263.5 mm/sec. At the closest part of the groove, the radius is effectively 74.5 mm and the velocity goes down to 260.1. The ratio between the maximum and minimum velocities is 75.5/74.5 = 1.0134. Thus the pitch of a note recorded in this groove is a little more than 1.3 percent higher at the part farthest from the platter center than it is at the part closest. In another viewpoint, the wow is ±0.66 percent. Proportionately, smaller center errors give smaller pitch wow, with .25 mm giving about 0.33 percent, 0.1 mm giving .13 percent, etc. Smaller groove radii would give larger wow percentage (inverse proportion) for a given off-centeredness. Off-center wow is worst at the end of the side. A usually accepted standard for audibility of wow is 0.1 percent. This of course varies from person to person. The pitch discrimination level for A/B matching can be as low as 0.01 percent in people highly sensitive to pitch. This is of course a different, probably more sensitive kind of pitch audibility than wow, but in fact the repeated periodic pitch variations of off-center wow are seemingly quite close in nature to the A/B test. The TX-1000, in the process of centering the records, gives read-outs of how far the records are off-center before the correction. While most meet the 0.5 mm standard, few are centered within 0.1 mm and almost none at the level of, say, 0.03 mm or less. Moreover, spindle-hole looseness generates ambiguities that are often on the order of a tenth of a millimeter, varying with how you put the record on. And, as noted, better than 0.1 mm centering is needed to meet the nominal ± 0.1 percent wow threshold. (Precisely, at 75 mm groove radius, ±0.1 percent wow corresponds to .075 mm centering.) In short, it is numerically clear that some correction process is needed for the vast majority of records, if they are to be audibly pitch stable."

To summarize Dr. Greene, even if your LP is made with the spindle hole dead-centered, if your spindle hole is .1 mm larger in diameter than your spindle you will most likely have audible wow. Wow at this level will probably not be audible as a rising and falling pitch unless you are very sensitive to pitch instability. However, most people will notice that the inner details of the music will be blurred or indistinct. Also consider what is happening to your stereo image as the stylus is forced against first one side of the groove and then against the other side of the groove with each rotation of the LP—essentially anti-skating gone crazy. For those of us that listen to vinyl on a regular basis we are accustomed to hearing the consequences of pitch instability caused by off-centeredness. We just chalk these detriments up as just some of the inherent differences between digital and vinyl playback. This is what I thought also, until I found a TX-1000 lying on a shelf in the back storeroom of a shop where it had lain covered by dust and debris for eleven years. With some tender loving care and a lot of luck I was able to resurrect the TX-1000 and for the first time was able to hear the dramatic sonic improvement that is inherent with having the LP correctly centered.

With the TX-1000 you can play an LP without using the self-centering feature—this is called nominal centering. And you can switch back and forth between nominal and self-centered. Thus, it is easy to hear the difference self-centering makes. With an LP that is .5 mm off-center, the improvement in sound is very noticeable—more detail, a more natural, relaxed sound, and none of that annoying undulating wow on sustained notes. I never realized how much I hated that sustained note wow until it was gone.  With LPs that are less than .1 mm off-centered, the sonic difference between nominal and self-centered is not very audible. However, I think I can still hear the difference down to about .06 mm, though the difference is very slight. As Dr. Greene mentioned in the quote above, the TX-1000 gives a digital readout of the off-centeredness of each LP that it centers. Very few of the hundreds of LPs that I have centered on my TX-1000 are off-center by less than .1 mm. Thus, almost all LPs that I play on my TX-1000 sound better for having been self-centered. There is no doubt in my mind that self-centering an LP can significantly improve the quality of the sound during playback. However, self-centering is meaningless if the turntable itself is not a good sounding turntable. After all, putting delicious frosting on a mediocre tasting cake is waste of good frosting.

The specifications of the TX-1000 as published by Nakamichi in early 1984 (via a Google translated Japanese sales brochure) stated the signal to noise ratio as "above 78dB DIN-B". Wow and flutter were stated at "0.003% (WRMS/FG direct reading method) 0.02% (after WRMS and the center search)". I am not an engineer and I don't know what these numbers really mean. What I do know is that as my TX-1000 is currently set up, with a Van den Hul Colibri XPW mkIII mounted on a Schroeder Reference 9" jacoba tonearm and with the turntable supported on Stillpoints rather than on its original air bladders, the sound with nominal centering is wonderful. The sound is detailed, smooth, musical, has rhythmic drive and arises from a black, black background. With self-centering, things get even better. I wish I had a Teres Certus direct drive or a Walker Proscenium belt drive turntable in my listening room so that I could do a proper A-B comparison. However, I don't. I have heard both the Certus and the Proscenium turntables at audio shows. I suspect that both turntables sound better than the TX-1000 with nominal centering. To say how much better, I would have do an actual A-B comparison. However, if the TX-1000 self-centering feature were used, I believe that I would much prefer the sound of off-centered LPs played on the TX-1000 versus the same LP played on either the Certus or the Proscenium. I admit it. I am addicted to listening to LPs that don't have pitch instability. Having lived for months with pitch stability I really would not want to go back to instability.

Now I will qualify that last statement. For rock, heavy metal and certain percussive soundtracks pitch stability or instability is not really that noticeable. For this type of music I use my Garrard 401turntable with Moerch DP-6 12" arm and Empire 750LTD (moving magnet) cartridge. I find that this combination of table, arm and cartridge to be highly synergistic and produces music that has more pace and rhythmic drive than the TX-1000, Schroeder, Colibri combination. On the other hand, for classical music, small ensembles, and vocals the TX-1000 combination is, for me, the only way to go.

Now the above two paragraphs are not much of an equipment review. Besides how many readers of this article will ever see a TX-1000 in the flesh let alone be able to purchase one? The answer is - not many. Under the guise of a review, this article is really an editorial. Vinyl is making a resurgence. New turntables are coming to market and many of them are quite expensive—much more expensive than either the TX-1000 or the Dragon CT, which would have cost roughly $16,000 and $4000, respectively, when their original purchase price is adjusted for twenty years of inflation. Modern day turntable manufacturers are reluctant to publish the flutter and wow specifications for their turntables. However, the rule of thumb is that current belt drive turntables have flutter and wow of less than .1% and current direct drive turntables have flutter and wow of less than .05%. The inexpensive ($399 street) Technics SL1200 has published flutter and wow of .035%. So let us be generous. Let us say that your new $30,000 turntable has flutter and wow of only .015%—an incredibly low number. Now you put your audiophile approved $40 LP (with the spindle hole being .25mm off center) on your new turntable. Per Dr. Green's figures above, your flutter and wow just went up to .345% (.015% from the turntable and .33% from the off centered spindle hole). The manufacturer of your turntable just spent $1 million in research and development to bring the flutter and wow down to an incredibly low .015% and you just paid a portion of that R & D with your purchase. My question to you and the manufacturer is: Who cares if flutter and wow of the turntable is .015%? What is important is not the flutter and wow of the turntable by itself, but the flutter and wow of the turntable and LP combined. If the flutter and wow of the turntable was .05% that would mean the flutter and wow of the turntable with the LP would be .380% (.05% + .33%). Audibly, .380% is not much different from .345%. The difference between .380% and .345% may not even be audible because the .035% difference is being swamped by the .33% LP wow. To my way of thinking, the purchaser of a turntable would be far better off if the turntable manufacturer spent his R & D money on developing a self-centering mechanism for his turntable. That would dramatically lower flutter and wow on playback for the purchaser of the turntable. Who listens to a turntable spin with no record on it? What is important is the flutter and wow with the LP spinning and the stylus in the groove. This is the real world situation. Even if all of our LPs were off center by only .1 mm and all spindle holes were the exact diameter of the spindle, neither of which is the case, the .380% versus .345% flutter and wow would only drop to .180% versus .145%. This is still audible and the LP flutter and wow is still dominating the turntable flutter and wow.

So what does all this mean for the average vinyl lover. It means nothing if you are not going to buy a new turntable at some time in the future. However, if you might be buying that one last turntable some time in the future you might want to have a little chat on the phone or at the next audio show with your favorite turntable manufacturer. You might want to give him copy of Dr. Green's article and point out to him that while Mr. Manufacturer is spending all his time trying to drop his flutter and wow from .05% to .04%, there is a 400 kg gorilla rampaging though the listening room that is making so much noise that all of Mr. Manufacturer's time and money spent on achieving a .04% flutter and wow is meaningless and wasted. If enough of us talk about self-centering, maybe one manufacturer will actually do it. And if one manufacturer does it, many more will follow due to competitive pressure. If a dealer is demoing a self-centering turntable and a non-self-centering table and the tables are anywhere close in price, I believe the customer will choose the self-centering turntable the majority of the time. Building a self-centering mechanism is not as difficult or as expensive as it was in the 1980s. With current micro processors and servo motors the design and manufacturing of a self-centering turntable is easier and cheaper (in inflation adjusted dollars) than ever before.

If you love listening to your vinyl, do yourself and the rest of us vinyl lovers a favor and talk to turntable manufacturers about getting rid of the 400 kg gorilla and giving us true pitch stability by building a self-centering function into their turntables.

(1) Both the TX-1000 and the Dragon CT have a glass top platter on top of a metal sub-platter. A sensor arm is used by both turntables to measure the off-centeredness of the LP. The top platter is then automatically moved relative to the sub-platter to correct for the off-centeredness of the LP. The two turntables make the correction in different ways.

I have never seen a Dragon CT perform its self centering feature. However, from descriptions of it that I have read on the Web it seems you push down on the spindle which manually brings the glass top platter into alignment with the sub-platter and starts the self-centering process. In the photograph of the Dragon CT the arm at the back of the Dragon CT is not a tonearm. It is the sensor arm. Once the self-centering process has been initiated, the sensor arm moves over to the leadout groove area of the LP and slowly drops down. The sensor arm has a stylus at the end of the arm. Once the stylus is caught in the lead out groove, the sensor arm moves to the lead out lockout groove. The lead out lockout groove is in almost all cases, particularly for modern LPs, a perfect circle. As the LP spins, the sensor arm measures the horizontal movement of the stylus caused by the off-centeredness of the spindle hole. A small plunger then comes out of a housing next to the platter. The plunger gently nudges the glass top platter. You may have done something similar to this when you tried to center an LP with an oversize spindle hole by gently nudging on the rim of the LP as it spun on the platter. I have never had much luck trying to center an LP using this technique. The Dragon CT, however, is very precise and accurate. After nudging the top platter the Dragon CT measures again, applies another nudge and continues to measure and nudge until the LP is centered. Once centering is complete the sensor arm lifts up and retracts to its rest position.

For the TX-1000 the process is essentially the same. An LP is placed on the glass top platter and the 'center search' button is pressed. A 2" x 9" housing to the left of the platter rises up about 2.5", a brass rod (the sensor arm) rotates out, moves over to the lead out groove area and drops down. The stylus at the end of the brass rod drops into the lead out groove and moves the rod to the lead out lockout groove. The turntable measures the horizontal movement of the stylus and by means of two servo motors in the sub-platter adjusts the position of the top platter relative to the bottom platter. After moving the top platter the off-centeredness is again measured and additional correction applied. For most LPs, the self-centering measuring and adjusting process takes about ten seconds. On a few LPs, which are very off-centered, it can take up to thirty seconds. Once the LP is correctly centered the brass sensor arm lifts up, rotates back into its housing and the housing drops back into the turntable.

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