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I suspect we might end up going round in circles on this one again... I was just mentioning the convo I had with dave.
if he continues to avoid comment on the forum I expect dave will provide some info on his website in due course
my own personal untrained logic tells me that a greater massed platter would be less suseptable to minor changes in speed caused by the contact of the needle in the groove... But then what the eff do I know?! :)
Hamish,
The problem occurs much earlier than that as soon as the motor has to deal with the extra weight of the new platter.
You may be right though, and if you are, then it would be great news. However, I'm afraid that Dave's 'word of mouth' is simply not enough on this, at least not for me anyway.
And of course his current refusal to comment here is doing nothing whatsoever to clarify the situation and/or help matters :rolleyes:
Anyway, the least said about that the better!
Marco.
Yes as has been discussed al length, it's perhaps advisable for all partys if that particular angle on this subject is avoided!
Dare I once agian utter the words "it's his perogative" :)
Yes, and it's also our prerogative to challenge him and/or his assertions, even if he doesn't reply! ;)
Just to reiterate and make it absolutely clear: this is not about a squabble between Dave and me; it's about getting to the nitty-gritty of whether the new platter offers an all-round sonic improvement, with no trade-offs - or not, as the case may be. And I intend to be thorough and get to the bottom of it for everyone's benefit :)
One further thought I'd add regarding your assertion earlier:
...Is that the ability of the high-mass platter to even-out stylus drag is a misunderstanding of the circuit, IMHO, as the torque does that.Quote:
my own personal untrained logic tells me that a greater massed platter would be less suseptable to minor changes in speed caused by the contact of the needle in the groove...
The control circuitry and feedback loop do not exist to counter the drag of the stylus; they exist to counter the inherent speed inaccuracies within the drive system.
It's the new platter's effect on the ability of the control circuitry to do its job properly and maintain the drive system's speed accuracy that others and I here are concerned about.
Marco.
Make your mind up mate
or am I just very confused?Quote:
Quote:
How will the new heavier platter affect the motor and therefore its control circuitry's ability to cope and still be able to adjust and change "INSTANTLY" to the very small but infinite changes needed to counteract the ever-varying different and complex loading that is a fact of needle and record groove contact?
Lol - it was Anthony who wrote that, not me. I agree with him, although he's said what I'm getting at in a slightly different way.
Marco.
Ok... Here is how I see it... This FYI is me speaking, not dave...
Tie a tenis ball to 3 foot of string and swing it round next to you, after it is up to speed, adjusting the speed it is spinning is easy, and if fact retaining the speed it is spinning is also easy it can be done with just a very slight flick of the rist.. In fact after a point you hardly realise it is you spinning it...
Now take a ball 5 times heavier and do the same... Getting it up to speed is gonna be hard work, but once it is up to speed it will still only take that slight flick of the rist to keep that momentum going and indeed to adjust the speed....
Does the same not apply?
I have been involved in turntable design and motor control for very many years (far too many, enough in fact to remind me I am now old, retired and decrepit and with too few days left ahead of me!).
There seems (to me at least) after reading with much amusement that there is a load of nonsense being written about new bearings and platters available from third party sources for a certain model of turntable. I wonder what drives this sudden appearence of third party so-called upgrades (apart from commercial desire, my controversial opinion only of course)?
During the early days I was privelege to certain information and had contact with certain designers. Most if not all this information is still privileged and confidential. However some facts are in the open domain and therefore may I be so as to offer the following from ancient notes and thoughts that may (or may not!) be of possible assistance as to why certain components were chosen for production in the first place and have stood the test of time.
I have highlighted in bold some of the points I feel should be taken into consideration when thinking about messing about with a tried and tested design.
Principle Aims:
1) provide turntable drive by means of electronic commutation motor control
2) provide smooth rotation
3) provide very low levels of vibration
4) provide self-starting DC powered turntable
5) provide long-term operational reliability and function
6) provide electronic turntable speed control
Torque and noise:
Torque is produced between the rotor and the stator windings, this will vary periodically depending upon the relative rotational position of rotor and stator. This is due to the varying value of the inter linking magnetic flux in the stator windings induced by the changing relative angular rotor position. With the rotor rotating at constant speed the angle between rotor and stator winding varies at a constant rate and the resulting torque varies periodically with time.
With rotor of "P" poles, commutation rate of "Z" the dominant angular period is given by 2/PZ revolutions.
The resulting ripple frequency is given by PZ/2xN/Hz where "N" is the rotor speed in rpm.
It is this inherent ripple torque that produces periodical speed deviation in the turntable. This ripple torque manifests itself as noise. This may also be referred to as "flutter".
This turntable flutter may be reduced by increasing the number of motor poles resulting in a higher commutation rate and in inverse proportion a decrease in ripple torque frequency. An increase in the number of poles does not reduce the ripple torque amplitude.
Flutter may also be reduced by increasing the moment of inertia of the turntable. However any increase in moment of inertia will reach a practical limit due to the fact that the acceleration time to bring the turntable to a predetermined speed will be prolonged.
For example two turntables with the same style motor may be compared. Example one has the turntable moment of inertia increased by a factor of ten and results in a flutter level of 0.1%. Example two has the number of poles increased by a factor of three and results in a flutter level of 0.1%
Practical design balance may be reached by combining the reduction of moment of inertia in example one and the increase in number of poles in example two.
Further there is a relationship between the number of poles and the frequency of the voltage induced by leakage flux as a result of the rotor mechanism. Increasing the number of poles will result in increased amplitude of the induced voltages. The included voltage amplitude is in proportion to the frequency.
Further improvements in flutter and noise levels may be achieved by the correct balance of chassis moment of inertia, number of motor poles and turntable moment of inertia.
Motor and Chassis:
The main motor support frame when fixed solidly produces no twisting vibration. When the main motor support frame is incorporated into the chassis a torsional vibration will be produced around the axis of the turntable. This results in noise with a similar footprint to the record medium background noise.
Although the dominant ripple torque noise frequency is below the audible noise frequency region this noise contains a multitude of harmonic frequency components.
It has been shown that in an electronically commutated direct drive motor the twisting effect produced in the chassis due to the axial torsional vibration can be reduced to a low noise level by increasing the effective moment of inertia of the chassis not by increasing weight or hardness of the chassis material, turntable platter or spindle shaft.
Design Tests:
It has also been shown that it is more important to optimise chassis design and material than alter the previously defined design parameters of the platter. This follows on from previous flutter tests and is due to the practical limit for optimum platter inertia already being reached and incorporated in the final design of the turntable .
Further tests have shown that peak instantaneous dynamic motor load change demand resulting from increased drag due to demanding groove modulation/stylus interface is affected by final choice of platter moment of inertia.
During tests to determine final platter moment of inertia is has been shown that a heavier platter produced slower motor loop feedback control response to motor load demand whilst a lighter platter produced faster motor loop feedback control response to motor load demand.
May your days be long and peaceful, Dale
I guess Dale hits the nail on the head with these 2 statements
1
"During tests to determine final platter moment of inertia is has been shown that a heavier platter produced slower motor loop feedback control response to motor load demand whilst a lighter platter produced faster motor loop feedback control response to motor load demand" Is the motor able to deal with these new demands
2
"It has been shown that in an electronically commutated direct drive motor the twisting effect produced in the chassis due to the axial torsional vibration can be reduced to a low noise level by increasing the effective moment of inertia of the chassis not by increasing weight or hardness of the chassis material, turntable platter or spindle shaft" This suggest that the bigger improvement in sound might come from the chassis
So what we *could* assume then, is that the existing platter is fine with the regulator and external supply fitted and the MN bearing may improve things by being quieter and better engineered. Adding a heavier platter to this mix may upset the servo balance and make it worse, yet drastically improving the plinth system (making it more solid, massier and more inert) may make things better as a mass-sink for the motor system...
Perhaps all that's needed is a perspex or acrylic top platter of some sort, with the tonearm mounting plates increased in thickness accordingly (and adding mass as a by-product)..