Pierre Lurne: Audiomeca's Turntable Designer Page 3
The Audiomeca J1 is one of the more elegant turntable designs I have seen, being constructed from a black methacrylic sheet. In common with the Oracle, it dispenses with the traditional box construction for the plinth.
"Most turntable bases are like the sounding box of a guitar: we use two U-shaped forms that fit together without resulting in any box resonance. Inside, there is a subchassis, again fabricated from a three-layer sandwich of methacrylate and lead to optimally disperse vibrations from the bearing, sitting on a three-point suspension. You can adjust the springs from the top."
Had Pierre taken the same care with the subchassis that its center of motion is the same as the center of mass?
"Yes, the center of gravity is always in the same place. Let me explain the problems of spring suspension. Some designers hang the subchassis from the springs, and say that this is better: if the subchassis is hanging, then the restoring force will be back toward its natural position of rest. They are right if the springs are long and very thin, but if you use large springs, this is not so good. The Audiomeca J1 is the proof. The mass of the subchassis and platter is centralized between the springs, and when everything is set up correctly and balanced correctly, and the tonearm is balanced with the appropriate counterweight, you can push the subchassis, and the response up and down is quite correct. It just bounces vertically."
The drive system of the J1 appears to be unique, for the belt doesn't just rotate around the motor pulley and the subplatter; there is also an idler pulley on the opposite side of the platter. The only thing like it that I have seen is the two-motor arrangement featured by the Alphason Sonata.
"If you have no counter-pulley, the belt will pull the platter toward the motor, resulting in wear. If you use a counter-pulley on the other side of the platter from the motor, the platter is in balance. This has been a feature of my turntables through the years since the Minimum."
Pierre showed how the motor itself is quite independent of the rest of the turntable. It is locked for transport, but when the J1 is set up, the motor, coupled to a 3kg block of lead to absorb vibration, sits on three Delrina high-density grade of nylonfeet that protrude through the U-section base to couple directly to the support; it has no contact with the base at all.
"The motor and its big lead block are twice decoupled because we try to create an artificial ground. Vibrations should be removed from the turntable system so that the stylus/groove relationship is as undisturbed as possible. I take the motor vibrations to the lead and try to earth them essentially out of the system. The counter-pulley offers a similar kind of advantage because it is also decoupled from the turntable base. In the accessory pack supplied with the turntable, there is a threaded spike which screws in to the base of the turntable underneath the counter-pulley to touch the surface that the turntable is sitting on. This takes any vibration from the belt, vibration from the bearing, and so forth, and in effect takes it to ground.
"The motor itself is a dual AC type, but rather than relying on the stability and purity of the mains frequency, what's presented to the motor is a synthesized sinewave based on a clock pulse generator, similar to what Linn is doing with their Valhalla board. To specify direction, this is then flipped by a capacitor right at the end to give two out-of-phase signals to the two different sections of the motor. You also get the smoothing effect of multiple poles, and can change the speed by varying the frequency to drive the motor. There is both a coarse and a fine speed adjustment. I chose this solution because I have used it for many years. But, of course, this is only one point among many that contribute to a good turntable design. You can actually make a very good turntable with any system of motor, even with the old idler-wheel drive, but it's more difficult then, of course.
"I also machine the Delrin motor-pulley after it's been mounted on the motor. If you machine the motor pulley separately from the motor, you have a problem with eccentric rotation. We put the pulley on the motor, and we finish the machining of the pulley with the motor turning so that the pulley becomes absolutely round."
The J1 can be fitted with any tonearm, not just the parallel-tracking Audiomeca SL5 (a derivative of the Goldmund T5). As well as supplying dedicated armboards, Audiomeca supplies counterweights to adjust the mass of the subchassis to correspond with that of the arm so that the three springs can be adjusted to give a good balance with any arm. Stereophile will report on the success of the various design philosophies outlined by Pierre when we receive a J1 for review. Before returning to my hotel room in New Haven, I concluded our conversation by asking Pierre what he felt to be the future of the analog turntable.
"I think nobody knows. At any time, you can always find people against and for anything. But think of the millions and millions of records in the world. There's a significant group of people out there who still buy LP records or have very valuable record collections, who are very interested in finding ways to play those records at a higher and higher quality level. Phonographyanalogmay no longer be a great business, no. But it will be a parallel business, and there will always be a niche for a good analog turntable."
I asked what were the areas where he saw the analog disc still scoring over digital
"I can speak on that subject for hours. This subject is so complicated that I'm sure nobody exists on earth today with a complete view of the problem. I like compact disc very much because it is good for the music. To many people, who bought in the past a horrible turntable in the discount shop, now that they have a compact disc player, they have better music. This is the good side of CD, but I am not absolutely convinced of any real advantage in absolute terms for two principal reasons.
"The first one is that CD players are made by giant companies who also make turntables. And they cannot cut off the limb on which they sit? Initially CD was bad, and it was stupid to sell CD. But if the quality of CD was higher than analog, it would also be stupid because they would kill off the analog too fast. The only solution is to have a similar quality from both media. This is the only way to have a business going on.
"Secondly, on the technical side, the analog system can be improved more and more and more. This cannot be said for CD players. One of my hobbies is philosophy. Your ear, and everything in nature, works like analog, with low, low levels of degradation at very low levels. But CD is the opposite, with low-level information having very high levels of distortion. This is contrary to nature; a problem of philosophy.
"Maybe CD players really are better! But the problem is here. And one day if the sales are to increase further, they will need to find a solution to this problem."