A turntable is simply a mechanism for converting the mechanical energy supplied by the turning of the platter by the motor into electrical energy. The conversion occurs when movement of the stylus generates an electrical signal. All movements of the stylus are converted to electrical energy, not just those related to musical information impressed into the record groves. Any movement not directly related to the musical information is detrimental to the recreation of the musical event. The motor in many instances creates more energy than is needed to turn the platter. This energy must be dissipated by the turntable. Much of it is transmitted through the bearing and dissipated as heat. Some is undoubtedly absorbed by the platter. A related problem is that not all motors are created equal. Some exhibit cogging and other non-linearities. Even if the motor is well designed, it may be affected by the distortion products contained in the electricity used to feed it. In the main, the design of the turntable, if properly executed, should minimize this type of noise; however, even in a turntable like the Rockport Sirius, it is never completely eliminated. A properly designed record clamp can serve as an energy sink for some of this energy by providing a low impedance path for energy to migrate away from the stylus as well as a mechanism to convert that mechanical energy into heat. In the case of the Lurne, the designer has chosen to use a material with an impedance close to that of vinyl (methacrylate) for the surface of the clamp that contacts the record and brass and lead to provide the energy sink.
The clamp is also designed to address another problem inherent to the vinyl medium – records are seldom flat. In many instances, they are warped. Unfortunately, these warps are often close in frequency to the resonant frequency of the arm/cartridge used and the combination can generate distortion. These warps also contribute to premature failure of the suspension of the cartridge. A further benefit of flattening the record is that it brings it into intimate contact with the platter which, if properly designed, will allow spurious energy in the vinyl to be dissipated. This effect can be rather significant with some of the thinner records.
Pierre Lurne manufactures a state-of-the-art turntable and tonearm and two record clamps in addition to digital equipment. In order to evaluate how effective these clamps were in each of the above areas, I chose to compare them on three turntables: two which had no vacuum draw down mechanism (Linn Sondek LP – 12 and Technic’s SP – 10 MK3), and one with a sophisticated vacuum draw down mechanism – the Rockport Sirius. The clamps were also evaluated against a number of other clamps. The two PL clamps appear to be identical except that one has a thin layer of felt between the bottom of the clamp and the record, while the other allows the methacrylate to rest directly on the record.
I knew from experience (after many comparisons with similar clamps) that the felt clamp worked very well with my own Rockport turntable. Just to get a different perspective, I chose to begin my listening on a partially upgraded Linn LP12 owned by a friend. We began the session (after warming up the turntable) with Thelonious Monk’s It’s Monk’s Time (Columbia CS-8984, 2-eye pressing). Without the clamp, the record sounded perfectly pleasant and musical, but a bit soft around the edges, and somewhat ill-defined (by my standards). Then we introduced the felt clamp. The effect was immediate and unmistakable: more solid bass, more secure soundstage, and better definition and air in the top-end. Overall, however (and I mean this in a positive sense) the basic sonic profile was not altered; the end result was still very musical and enjoyable, yet better defined.
We then switched to the “nude” clamp, the one with no felt between the bottom of the clamp and the record. The immediate impression was that there was more of the same result, and it was impressive. My friend expressed surprise at the amount of information the Linn was now retrieving from the LP. With the nude clamp in particular, one very fortuitous side effect was that the surface noise (such as it was – and it is hard to find these early Columbia jazz sides without a few odd ticks) seemed to float to the sides of the soundstage as if completely unconnected to the music.
Over the course of the LP side, however, we could begin to detect just a bit of hardness in the transients, particularly in the piano, which, frankly, did not seem to be particularly well-recorded, and in fact gave the impression of not being a particularly good piano, either. For some, this effect might become fatiguing, depending upon the circumstances, although my own reaction was not particularly strong.
I was curious, though, how the hardness issue would shake out in a more electric setting. We listened to John Scofield’s Still Warm (Grammavision 188j508-1). The various observations were completely consistent with the last round, though the Teflon clamp seemed clearly superior, with no downside of the hardness apparent. The recording, from 1985, was somewhat typical of its day and genre; though apparently not digital, it had some of that “trying too hard” sound that included somewhat splashy highs and, at times, a little too much (perhaps electronic) reverb and piano/guitar effects. Certainly, the turntable had some work to do, and with the nude clamp in particular, the wheat was clearly sorted from the chaff. Case in point, it is an excellent record, as the auction prices attest.
The Scofield record is fun to play loud. Here, we noticed a particularly beneficial effect of the Teflon clamp, and likely true of the felt clamp as well: We could play the record up to a volume level about as high as one might reasonably desire in a typical living room without a sense of strain or edge. And the soundstage was huge – really eye-popping for a Linn.
Next, we turned to an old Columbia 6-eye mono release of Francescatti, Casadesus and the Guilet Quartet’s recording of the Chausson Concerto for Violin, Piano and String Quartet. With this early pressing, the issue of occasional surface noise was again side-stepped by the effect of disassociating the music from the noise such as the clamp brought about, which certainly increased the listening pleasure. However, again, with the nude clamp, we noticed what some might hear as a bit of hardness in both the piano and violin. Columbia LPs tend toward brightness in many examples, and some might feel that the nude clamp was simply allowing what was on the record to be heard clearly. Perhaps so. However, my friend reported that, in the end, he preferred this LP without the nude clamp when he listened again a few days later. (He did not have the felt clamp to compare at that point.)
Finally, we tried the Classic Records 45 rpm reissue of Paray’s version of Ravel’s Rhapsodie Espagnol (formerly Mercury SR90313). We only listened to this disc with the Teflon clamp, and the soundstage was truly amazing in its breadth, and exceptionally coherent. With this record, hardness was not an issue. My friend summed up the experience simply: “It’s like a new turntable.” I agreed.
I have utilized the felt version of the clamp for many years on my Rockport Sirius. The Rockport incorporates a vacuum hold-down and a damping layer on top of the stainless steel platter, so any positive effects in the sound that would have resulted from the clamp either flattening or damping the record are eliminated. Nonetheless, the clamp still had a positive effect on the sound. While the effect was less pronounced than on the Linn, it was still clearly audible as a reduction in the noise floor, a slight increase in definition and low-level resolution, better focus, and an increase in depth. More importantly, it further decreases a slight tendency toward leanness in the midbass through the lower mids. On the Rockport, the nude clamp clearly has better leading edge definition and better resolution of low-level detail but at the expense of a bit of hardness on some recordings. Like my friend, I found that my preference was determined by the recording; however, for the most part, the version of the clamp with the felt suited my tastes better.
Over the Memorial Day weekend, I went to Albert Porter’s place, and we spent many hours comparing a variety of clamps on his modified Technics SP-10 Mk. 3. Although a number of well known clamps were tested, the two that were clearly head and shoulders above the rest were the Pierre Lurne and the Walker. Both shared certain similarities in design, with the Walker being significantly heavier. While the Walker clearly excelled in bass impact and tightness, the Lurne sounded more natural and was my preference in all other areas. The Lurne was particularly outstanding on male and female voices as well as stringed instruments and was more dimensional. I should point out that both clamps were excellent. All other clamps that we tried were a very distant third.
Comment from Pierre Lurne:
To my opinion your article is very good and you explained things quite clearly. I share almost everything with you and particularly I love your second chapter which starts by ‘The clamp is also designed to address another problem etc…’ This is exactly so !
As for the sixth chapter, starting by ‘over the course…’, I should say that it is always the same problem with improvements, let’s call it the other side of the Hi-Fi quest: As quality improves progressively, new problems come up which were hidden in the mud until then. Sometimes the price to pay seems heavy. I believe you went through that kind of reflection hundred times yourself.
As regard to the turntables you used, I think the SP-10 is not seriously designed enough. Japanese have always been very weak with their turntables. I still wonder why they seem to be not interested by the source and its philosophical importance, “all what is lost at the Source is lost forever”. Many great and famous Japanese Audio systems work with incredible speakers and amps, all driven by a weak turntable. This remains beyond my understanding.
You naturally mentioned your lovely Rockport. No doubt it is one of the handful of great Analogue front-ends. You love it and you are right to love it. Be sure I do respect that piece of work myself. The point which is scratching my head is that I know it belongs to, let’s say, the old generation, and that vacuum is debatable. As good as it could be, and even if vacuum hold were not a question, the platter and bearing for instance, are not designed at their best and this point is more important that vacuum or no vacuum. A Turntable is a sum of hundred parameters of various importance. The ultimate point is to make the right combination, the happy wedding. If you have read my article ‘Platter design’, you know there is only one way to design a platter and why. A funny conclusion, isn’t it ? This is not a “Pierre ’s idea”, this is merely physics. Which cannot be sufficient alone, I admit, but we’ve been through those questions before.
Caution : The ‘felt’ version is deleted. The ‘nude clamp’ (all metacrylate) replaces it though I see nothing wrong to produce the felt version again after having read your article! It would be so simple, why not. My personal opinion is that the felt one was alright and the nude one is just a little bit better.
You did not mention the built-in piece of lead. Lead has fantastic characteristics for us and I know it quite well after 40 years.
Enough with my comments…
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