You would like a Voyd/AN TT then. I had a 3 motor Voyd with Acrylic platter before the Yamaha and it was very dynamic and involving...but also perhaps a bit noisy and "dirty". I had Helius Cyalene arm on that one and split phase PSU.
A Direct Comparison: Technics SP10 Mk3 and SME Model 30/12A
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You would like a Voyd/AN TT then. I had a 3 motor Voyd with Acrylic platter before the Yamaha and it was very dynamic and involving...but also perhaps a bit noisy and "dirty". I had Helius Cyalene arm on that one and split phase PSU.
His speakers are the enormous Focal Grande Utopia EM and he recently has been using the Audio Research Ref 250's - neither of them suggests a warm, forgiving environment.
I spoke to the guyser, who is the person at whose place I heard the sp10mk2 and started my conversation with Peter. He was involved in the design and build of this Voyd back in the days and later worked for Peter Qvotrup. He said he tried the SME V and got similar results to what Peter described, and now he is using the Groovemaster with the Etsuro Urushi which I heard. He said with this combo, as well as the FR arm and the FR carts, this problem went away, so SME V is not working with the technics on his double layered slate plinth. He also said the arm rigidity matters and he uses plywood arms so that he can swap, he tried aluminium before and did not work well.
Why should a cored DD motor have more potential for cogging and torque ripple issues than a coreless design? We are addressing a motor spinning at less than one revolution per second, not a high speed turbine!
It certainly tells him what he heard. You can’t ask for a better real world comparison than that. Putting system matching into the equation just gonna drag the thread into different subjects.
Tang
It matters more at low speed than at high speed actually. A cored motor has iron poled stators, which attract and repel the rotor and result in acceleration and deceleration throughout a rotation.
"Cogging torque of electrical motors is the torque due to the interaction between the permanent magnets of the rotor and the stator slots of a Permanent Magnet (PM) machine" "Cogging torque is an undesirable component for the operation of such a motor. It is especially prominent at lower speeds, with the symptom of jerkiness. Cogging torque results in torque as well as speed ripple; however, at high speed the motor moment of inertia filters out the effect of cogging torque."
A coreless motor does not have poles and therefore it has no cogging:
"What are the main advantages of this kind of motor?
•Dramatically improved acceleration and deceleration because, the iron core in usual rotors contributes to 90% of the rotor inertia. By removing this iron core, we can improve the acceleration & deceleration by an order of magnitude.
•Reduced hysteresis losses in the iron core. In a normal DC motor’s core, because the magnetic field is switching direction continuously, there are hysteresis losses. Coreless motors have significantly reduced hysteresis losses.
•No cogging. In normal DC motors, when the motor is off, and when you try rotating the motor shaft, you experience a slight resistance in motion, because the rotor is attracted by the stator. You also notice ups & downs in this resistance to motion. This is completely absent in coreless motors!! As a result of this coreless motors start rotating even at very low voltages, unlike normal motors which need a minimum voltage to start rotating. This makes these motors very well suited for control systems as they are very linear systems.
•Low ripples in torque, during operation, resulting in smoother motion.
•Possibly lower viscous losses (because of the very smooth rotor shape)
"
That could be...there have been reports that the SME arms are not so compatible with all kinds of TTs.
You are quoting Wikipedia on the definition of cogging torque, that applies to general electric motors and generalizing on the problems of general purpose brushed motors. A brushless cored motor, such as used in DD turntable, can easily be cog free - it depends on the controller. People used to stop the platter and then slowly move it to show the cogging - a ridiculous experience, as the control systems responsible for uniform torque only work at the operational speeds.
And yes, I know since long the numerous advantages of coreless motors, I do not need google searching. My question is weather they are really relevant and indispensable to DD turntables. IMHO they are only one more possibility.
Btw Perart1 who in the 80s used to own a Spundlabds system and then a Cello system and whose place Roy Gregory used to use as a reference room, owned both the Goldmund Studio and the Reference. He was an expert here on setting up the T3f and said that the Studio was extremely close to the Reference in SQ. He is probably reading this so he can add. But the point is the cost difference between them is huge, the SQ is not.
Cogging is a function of a motor having an iron core and not whether it is brushless or not. I chose the Wikipedia definition because it is simple and still accurate.
A brushless DC motor, which is really an AC motor, will be pretty smooth with sinusoidal commutation but still will cog at low speeds. At higher speeds they make good motors for belt or maybe rim drives because they are smoother than a normal AC motor and more speed stable than a brushed DC motor (they still need feedback control). Also they have good torque...a coreless motors main weakness.
As to necessity, most of the top Japanese DD TT makers at the end went this direction. i think a lot of tape decks are also having motors of this type. To my knowledge only Kenwood though had a coreless and slotless motor in their TTs.
Interestingly, the Caliburn, although belt drive also used a coreless/slotless motor. It was very expensive and I think the Rockport DD had a similar kind of motor.
What the Japanese did then you only find now only in ultra high end today.
So, it seems that when one decides to invest in a great motor (the literal heart of a TT) that often a good result comes out.
Marc - well put... and I suspect unconscious / subconscious elements of cognition ...shape / influence our perception
BMCG, thanks.
I do think I may be right, and I’m guilty of it myself.
I’ve often thought I ought to start a thread entitled “my £70k sound system...and the £150k tone control spent via room, power, cables, supports”.
Or “how I fell in love with a tt or dac...and spent many multiples of the amount making sure it was complemented well”.
I do think I may be right, and I’m guilty of it myself.
I’ve often thought I ought to start a thread entitled “my £70k sound system...and the £150k tone control spent via room, power, cables, supports”.
Or “how I fell in love with a tt or dac...and spent many multiples of the amount making sure it was complemented well”.
It makes sense that the SME 30/12 with 12 inch arm and lower compliance cartridge would sound smoother than 30/2. That's kind of what you go for with a 12 inch arm.
The brighter sound of the 30/2 seemed to be a taste of Alistair-Aikman. I have not been a fan of the 30/2 screwing clamping system, which is designed to bend the edges of the record down so that the periphery has the heaviest contact and the center is elevated on a washer. Records have different thicknesses and stiffness, from potato chip to heavy and unyielding, so the screw down system can fracture center holes and does not have a uniform result on all records, though the tendency of the screw down clamping system is to move the resonance toward the upper midrange and give the bright sound that some critics note in the SME 30/2.
Since using a heavy passive clamp and a mat, the same 30/2 now has a much more mellifluous sound without losing detail. It sounds more like the classic mass loaded turntable.
The brighter sound of the 30/2 seemed to be a taste of Alistair-Aikman. I have not been a fan of the 30/2 screwing clamping system, which is designed to bend the edges of the record down so that the periphery has the heaviest contact and the center is elevated on a washer. Records have different thicknesses and stiffness, from potato chip to heavy and unyielding, so the screw down system can fracture center holes and does not have a uniform result on all records, though the tendency of the screw down clamping system is to move the resonance toward the upper midrange and give the bright sound that some critics note in the SME 30/2.
Since using a heavy passive clamp and a mat, the same 30/2 now has a much more mellifluous sound without losing detail. It sounds more like the classic mass loaded turntable.
I have not heard David's system in a long time. There have been changes with cables and upgrades from the manufacturer. My overall impression is one of inconsistency. It has sounded very good, extended and well balanced. But it has also sounded very aggressive or restricted. I could say the same thing about any of the regular systems I hear: Madfloyd, Ack, Al M. It depends on what gear is in at the time, and in some cases, whether the latest mod is working. David's system has had authority, good bass, mid bass and lower mids, but they have also sounded bloated at times. Again, it depends. I have also heard good top end, but also a slightly glassy or mechanical sound. I can not speak to resolution on tuttis. I think David would admit that the system is a bit unsettled and a work in progress. It has demonstrated its potential but I have not heard it lately.
David should answer your question, or perhaps Al M. because they have both heard it more recently.
Sorry, you are overlooking the issue and most people mix different aspects relevant to motor performance. Cogging as referred in the wikipedia is a consequence of the variable magnetic field driving the magnetic stator non uniformly. This magnetic field is created varying the currents in the coils of motor in a way that the moving field ahead of the stator looks constant. This field is created by the vectorial sum of the fields created by each set of coils. Since long manufacturers know how to overcome this situation using optimized geometries of the core and optimized driving of the coils. Nowadays even step motors can be driven at low speeds with uniform torque using digital controllers. Twenty years ago I used a brushless 5 phase motor driven by synthesized waveforms that was extremely smooth down to one revolution per minute.
The other "cogging" people often refer is that due to the need to perform correction of speed - manufacturers claim to use algorithms to perform this correction in non audible way independently of having a core or being coreless.
The physics of electrical motors is the same for motors with a core or coreless. Hysteresis of core motors is not relevant for low power, low speed motors. But surely different approaches must be considered for the drivers.
People should remember the famous VMS66 and VMS70 Newmann lathes, that cut most of their precious Decca's recordings, used a Technics direct drive motor with large cores ...
In the end, the real judge in this hobby is our preference.
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The arm mounting material seems to affect the performance of different tonearms in different ways. I'm not sure there'd be one perfect material used for mounting the arm that would give optimum performance with all arms or all plinth/chassis designs.
With regard to DD motor systems I'm not convinced that maximum torque & heavy/active electronic control is the answer either.
What we need is a falling weight system that will run for 25+ minutes & no cogging etc to worry about!
What does "non-audible" minimization of cogging mean to you? If we can hear down to picoseconds in jitter, what makes you think residual micro speed fluctuations in analog are not audible?
Don't start adding alternative definitions to something that is clearly defined. Yes, there are tricks that can be done with electrical commutation to minimize the effects but the reality is physics and attraction/repulsion from the poles of an iron core motor causes torque and speed variation. The physics is not exactly the same between a core and coreless motor.
Your motor example might have felt smooth but if it was a cored motor it still had cogging.
"Absence of cogging (torque ripple) is another benefit critical for many applications.* In a conventional cored motor the rotor has a tendency to assume a certain position due to the uneven reluctance of the slot wound laminated iron rotor. Because the ironless motors have no core, the torque is more evenly distributed during any position of the rotor. The rotor can be positioned more accurately and the motion at low speed is much smoother."
"These factors bring some distinct advantages over a conventional iron core motor.
No cogging torque and smooth rotation even at low speeds
Low vibration and low noise operation
Linear speed/torque characteristic’s so the motor speed and torque is easily controlled
Efficiency. The motors are highly efficient at 90%. The motor does not have to break down the magnetic fields. The winding can almost fill the air gap between the magnet and its magnetic return
As the motors don’t have an iron core, the coil and the magnetic field of the stator is not affected by saturation effects in the magnetic field. This means stronger, more powerful magnets can be used. Many of the ironless rotor motors are using rare earth magnets to maximise performance and size
The motor winding has a very low inertia as there is no iron core to accelerate. The motor can accelerate and decelerate to full speed in milliseconds, offering very high speed performance."
THese are from current news articles and motor vendors, which make both types of motor, and show clearly that the advantages of which I speak are not some fantasy imagined. Compensate all you want but to truly eliminate cogging and torque ripple the motor has to be coreless.
