Turntables DD vs BD vs Idler

[murray johnson]

Some rambling thoughts...

As the mass of a platter rises, inevitably so will the likelihood of bearing noise. They have to go hand in hand. Magnetic levitation may help if it can be implemented without lumps & bumps in the field although I'd still be happier to keep a slight mechanical ground path in the bearing.

The only source of constant speed in a turntable is the motor. "Removing the motor from the equation" by any form of decoupling diminishes the chance that the record can be rotated at a constant speed past the stylus. Whether this is achieved by mounting the motor in a compliant (at audio frequencies) material or by decoupling thesuspended mass with springs and a compliant belt the effect is the same. Yes there may be improvedsignal/noise but somehow a believable sense of progression can belost.

Using a high mass platter (particularly with an external flywheel) and a thread or tape drive gives the record's movement past the stylus some chance of following the motor. However, a high mass deck will usually be solid andits performance will be affected by what supports it, as the stylus not just reading the groove but the structure supporting it too.

A motor is still a transducer. It will try to follow any hash or noise in the power supply that feeds it not just the dc or ac supply it gets. It always amuses me to read the NAS website about the benefits of heavy platters smoothing out speed fluctuations and then alongside that a recommendation for the 'wave mechanic' power supply.Despite the great mass, the platter is still sensitive to fluctuations in the motor's pull!

For anyone interested here's an example of perhaps the most extreme high mass TT I've read about http://www.aca.gr/paper37.htm

Of course speed constancy isn't everything. CD hasperfect pitch stability but might be said to be flawed elsewhere. It does help, but with good engineering comparable levels of wow & flutter can be achieved by either method. The Continuum turntable is belt driven and yet produces (apparently) some of the most constant speedmeasurements yet recorded.

My preference for DD turntables derives more from the elegance of the solution (if done well) and the possibility of keeping the thing to a manageable size. One of the best turntables I've ever heard was the belt driven, high mass, Morsiani which has a similarly powerful & calm (no sense of a record playing) presentation that the better DD's have. Doubtless the big Micro's also had this quality.

Having owned a couple of idler driven Garrards in the past (and having heard several others) I'm not convinced they, however well sorted, quite reach the same heights although it would be interesting to hear a modern take on the approach with new materials and better motor technology/control applied. They certainly can be made to sound more expressive than the more common Vilchur based suspended subchassis designs that have been so prevalent during the last 30 years.

[Uncle Ants]

SergeAuckland wrote:

That's quite right, a record on a platter weighting many kilos is unlikely to suffer from dynamic wow caused by modulation. And I'm not saying that belt drives are incapable of good performance, equivalent to DD and ID, and they do have the advantage that motor cogging noise is isolated.

Most belt drive decks don't have sophisticated motor controls though to be fair, becasue they dont need them. Well those with AC synchronous motors anyway (which is most of them). A regenerating power supply is about as sophisicated as they get and that in effect is just better, cleanerAC, nothing to do with speed control or correction. An ACsynchronous motor driving a heavy platter with abelt is pretty elegant and very simple solution. You don't even need a lot of torque, as the NAS designs attest.

The sort of micro speed changes you geton a feedback driven DC setup would presumably just get soaked up by the belt if you had a heavy platter, unless you used a very very light platter and a none too stretchy belt (the Funk Firm take this approach).

[kingsxfan]

i_should_coco wrote:

I which case, why in practice do most direct drives give a much more subjectively pitch stable presentation than even belt drives with high mass platters? I agree with Serge that belt drive originally came about to allow the use of cheap noisy motors by adding a measure of de-coupling. Following the KISS principle, IMO DD *is* the most elegent solution form an engineering point of view as it's the simplest - the motor is directly connected to the platter. Adding a floppy belt which is subject to age and inconsistency complicates the system and introduces scope for more things to go wrong.

Silent operation is a pre-requisite with both MC and MM - the types of cartridge is irrelevant to mechanical noise from the TT. DDs like the Technics and EMT are quieter than most belt drives, so motor noise is not an issue in practice. Cogging is also not an issue, I seem to recall a post my Mark Kelly on Audio Asylum with calculations, and the effect is absolutely miniscule.

I'm not saying MM wouldn't beaffected. I would say more so with a moving coil in terms of extracting the minuti.What's the point of having all that extra transducing capabilityif its written off with rumble?MM generally are not going to be 'spoiled' as much as anMC on a deck thats sufferswith a few design compromises here and there.

[kingsxfan]

murray johnson wrote:

Some rambling thoughts...

As the mass of a platter rises, inevitably so will the likelihood of bearing noise. They have to go hand in hand. Magnetic levitation may help if it can be implemented without lumps & bumps in the field although I'd still be happier to keep a slight mechanical ground path in the bearing.

The only source of constant speed in a turntable is the motor. "Removing the motor from the equation" by any form of decoupling diminishes the chance that the record can be rotated at a constant speed past the stylus. Whether this is achieved by mounting the motor in a compliant (at audio frequencies) material or by decoupling thesuspended mass with springs and a compliant belt the effect is the same. Yes there may be improvedsignal/noise but somehow a believable sense of progression can belost.

Using a high mass platter (particularly with an external flywheel) and a thread or tape drive gives the record's movement past the stylus some chance of following the motor. However, a high mass deck will usually be solid andits performance will be affected by what supports it, as the stylus not just reading the groove but the structure supporting it too.

A motor is still a transducer. It will try to follow any hash or noise in the power supply that feeds it not just the dc or ac supply it gets. It always amuses me to read the NAS website about the benefits of heavy platters smoothing out speed fluctuations and then alongside that a recommendation for the 'wave mechanic' power supply.Despite the great mass, the platter is still sensitive to fluctuations in the motor's pull!

For anyone interested here's an example of perhaps the most extreme high mass TT I've read about http://www.aca.gr/paper37.htm

Of course speed constancy isn't everything. CD hasperfect pitch stability but might be said to be flawed elsewhere. It does help, but with good engineering comparable levels of wow & flutter can be achieved by either method. The Continuum turntable is belt driven and yet produces (apparently) some of the most constant speedmeasurements yet recorded.

My preference for DD turntables derives more from the elegance of the solution (if done well) and the possibility of keeping the thing to a manageable size. One of the best turntables I've ever heard was the belt driven, high mass, Morsiani which has a similarly powerful & calm (no sense of a record playing) presentation that the better DD's have. Doubtless the big Micro's also had this quality.

Having owned a couple of idler driven Garrards in the past (and having heard several others) I'm not convinced they, however well sorted, quite reach the same heights although it would be interesting to hear a modern take on the approach with new materials and better motor technology/control applied. They certainly can be made to sound more expressive than the more common Vilchur based suspended subchassis designs that have been so prevalent during the last 30 years.

My post of the day, great stuff.

[i_should_coco]

kingsxfan wrote:

i_should_coco wrote:

I which case, why in practice do most direct drives give a much more subjectively pitch stable presentation than even belt drives with high mass platters? I agree with Serge that belt drive originally came about to allow the use of cheap noisy motors by adding a measure of de-coupling. Following the KISS principle, IMO DD *is* the most elegent solution form an engineering point of view as it's the simplest - the motor is directly connected to the platter. Adding a floppy belt which is subject to age and inconsistency complicates the system and introduces scope for more things to go wrong.

Silent operation is a pre-requisite with both MC and MM - the types of cartridge is irrelevant to mechanical noise from the TT. DDs like the Technics and EMT are quieter than most belt drives, so motor noise is not an issue in practice. Cogging is also not an issue, I seem to recall a post my Mark Kelly on Audio Asylum with calculations, and the effect is absolutely miniscule.

I'm not saying MM wouldn't beaffected. I would say more so with a moving coil in terms of extracting the minuti.What's the point of having all that extra transducing capabilityif its written off with rumble?MM generally are not going to be 'spoiled' as much as anMC on a deck thats sufferswith a few design compromises here and there.

I don't see how MC & MM differ? Just because one has a lower output does not make it more or less sensitive to noise, if that's what you're getting at. MC doesn't fundamentally have any more resolution than MM, they're just two different ways of implementing a transducer.

[Uncle Ants]

murray johnson wrote:

A motor is still a transducer. It will try to follow any hash or noise in the power supply that feeds it not just the dc or ac supply it gets. It always amuses me to read the NAS website about the benefits of heavy platters smoothing out speed fluctuations and then alongside that a recommendation for the 'wave mechanic' power supply.Despite the great mass, the platter is still sensitive to fluctuations in the motor's pull!

Hmm, strictly speaking the NAS site won't say that because NAS don't have a site ... they don't even have email . If that's what, whatever site says the wave mechanic does, I think it may bemisleading, given that their are no noticable speed fluctuations without such a controller. The Wave Mechanic is a mains regenerator, so it will smooth out the sort of long termspeed fluctuations you get over time as the mains drifts above and below 50Hz ie. it means the motor gets a spot on 50Hz rather than the 49.8 to 50.2Hz or whatever it is the real mains may be doing, but that's all - it has no mechanism for addressing very short term speed changes if there are any (which I doubt given the design).

So far as I'm aware all it does and will ever really do is fix the frequency at 50Hz dead and clean up the messy mains sine wave and as a result any noise induced in the motor because of it.

[murray johnson]

The mains supply can contain all sorts of high frequency hash which an ac motor will try to follow as well as the fundamental 50 Hz. A supply that re-generates a pure 50 Hz sine wave should remove this hash and the 'juddery' pull of the motor following it. A clean supply will give a calmer presentation. I doubt very much that the slower frequency variations that occur over the course of a day would be significant enough to be audible to anyone, but the removal of hash will be (even via a rubber belt and heavy flywheel)

[i_should_coco]

But surely if mass is a solution, then this hash, etc. should not be audible?

[SergeAuckland]

kingsxfan wrote:

JCL wrote:

I don't see how DD can be seen as the "best engineering solution". I would think the fundamental design criteria for a turntable would be to isolate the extremely delicate stylus/record interface from bearing and motor vibration. Removing the motor from the equation is almost essential if you're going all-out IMO.

It isn't, its a solution but not the out-and-outbest one. In studio applications of yore, fast starts post cue are essential, a DD would be the only realistic choice in this environment. Enter various EMT/SP10 incarnations!

Although EMT and others had rim-drive turntables long before DD was possible. They used a more sophisticated version of the slip-mat, a slip platter, to provide the "instant" start.

As to "going all-out" it rather depends what your criteria are;- For isolation,a sprung sub-chassis turntable,of the SME or Vilchur types will provide the best performance. For speed stability, a very high-mass platter either belt or DD will bebest, but the high mass will make isolation more difficult, or at least expensive (Lumley Stratosphere?)

For fast-start DD is the most practical solution, and I would argue that for consistency and reliability also as there's very little to go wrong.

So it all depends what you want: For me, DD is the best compromise, others may well take a different view.

S.

[Uncle Ants]

murray johnson wrote:

The mains supply can contain all sorts of high frequency hash which an ac motor will try to follow as well as the fundamental 50 Hz. A supply that re-generates a pure 50 Hz sine wave should remove this hash and the 'juddery' pull of the motor following it. A clean supply will give a calmer presentation. I doubt very much that the slower frequency variations that occur over the course of a day would be significant enough to be audible to anyone, but the removal of hash will be (even via a rubber belt and heavy flywheel)

Quite. Which is what it does (or should). Any claim that it smooths out speed fluctuations sounds to me like a marketing man's misunderstanding of what it actually does. Tom Fletcher is pretty precise about what he says anddoesn't have a marketing man. You are right in that I doubt anyone will notice the difference between a motor being fed 49.8Hz and one being fed 50Hz, but there are enough audiophiles who care about it

I haven't ever used a Wave Mechanic on my NAS but have and do use a Heed Orbit 2 which is in effect the same sort of thing. The calmer presentation effect was evident in my last house but not this one (the mains here may well be cleaner). Speed stability is unaffected with it in or out. The main reason for using it tbh is push button speed control. Paula plays a lot of 45s and hates moving the belt on the pulley ...which is actually why I bought it.

[murray johnson]

my point exactly

[Uncle Ants]

i_should_coco wrote:

But surely if mass is a solution, then this hash, etc. should not be audible?

Mass is the "solution" to speed stability on belt drive, the belt drive itself is the "solution" to nosiy motors. It shouldn't be overstated, we are talking about a very subtle effect which may or may not happen depending on how messy your mains is.

[i_should_coco]

Uncle Ants wrote:

i_should_coco wrote:

But surely if mass is a solution, then this hash, etc. should not be audible?

Mass is the "solution" to speed stability on belt drive, the belt drive itself is the "solution" to nosiy motors. It shouldn't be overstated, we are talking about a very subtle effect which may or may not happen depending on how messy your mains is.

Ok, but if high-mass platters are an effective solution to dynamic wow, as stated above, then they should also work to prevent the micro-variations is speed due to crap on the mains.

The fact the these AC re-generating PSUs work (and they do), indicates that actually high mass does *not* in fact do this, or not well enough so that it's inaudible.

[Uncle Ants]

i_should_coco wrote:

Ok, but if high-mass platters are an effective solution to dynamic wow, as stated above, then they should also work to prevent the micro-variations is speed due to crap on the mains.

The fact the these AC re-generating PSUs work (and they do), indicates that actually high mass does *not* in fact do this, or not well enough so that it's inaudible.

Edit - crap on the mains doesn't cause microvariations in speed with a high mass platter, crap on the mains can cause motor noise.

There's no such thing as the perfect deck y'know Like I said its very subtle and mains regenerators needn't be expensive. The purpose built one for Pro-Ject decks for example is about £80. Ideally it would be included as part of the price of the deck, but they are almost always an optional extra, it keeps the price down and also because even without one a decent belt drive deck will give 98% (can we make figures up out of the air in this section - obviously it also depends how well the motor is siolated from the plinth) of their performance without a controller at all, unlike say a DC driven deck where its essential.

[i_should_coco]

Uncle Ants wrote:

i_should_coco wrote:

Ok, but if high-mass platters are an effective solution to dynamic wow, as stated above, then they should also work to prevent the micro-variations is speed due to crap on the mains.

The fact the these AC re-generating PSUs work (and they do), indicates that actually high mass does *not* in fact do this, or not well enough so that it's inaudible.

Edit - crap on the mains doesn't cause microvariations in speed.

There's no such thing as the perfect deck y'know Like I said its very subtle and mains regenerators needn't be expensive. The purpose built one for Pro-Ject decks for example is about £80. Ideally it would be included as part of the price of the deck, but they are almost always an optional extra, it keeps the price down and also because even without one a decent belt drive deck will give 98% (can we make figures up out of the air in this section - obviously it also depends how well the motor is siolated from the plinth) of their performance without a controller at all, unlike say a DC driven deck where its essential.

If crap doesn't cause variations in speed, then what does it cause? Noise is effectively variations in speed...

[Uncle Ants]

i_should_coco wrote:

If crap doesn't cause variations in speed, then what does it cause? Noise is effectively variations in speed...

the mass of the platter smooths it out ... is this getting circular??

[i_should_coco]

Uncle Ants wrote:

i_should_coco wrote:

If crap doesn't cause variations in speed, then what does it cause? Noise is effectively variations in speed...

the mass of the platter smooths it out ... is this getting circular??

That's my point. It doesn't, or the power supply would be inaudible.

[Uncle Ants]

i_should_coco wrote:

Uncle Ants wrote:

i_should_coco wrote:

If crap doesn't cause variations in speed, then what does it cause? Noise is effectively variations in speed...

the mass of the platter smooths it out ... is this getting circular??

That's my point. It doesn't, or the power supply would be inaudible.

Nobody said it was perfect

Actually - are you right though. Are motor vibrations the same thing as speed fluctuations? That's a genuine question.

[Uncle Ants]

I mean yes I could see that a motor vibration might well be micro speed fluctuations - but if the mass of the platter smooths those out its speed stable - that's the theory. If we assume the platter was speed stable despite hash causing some motor vibrations it will to some smaller or larger extent get transmitted down the belt and into the platter as a vibration - a noise.

The platter might well then be speed stable but still motor noise might be audible, wouldn't it?

[i_should_coco]

Uncle Ants wrote:

i_should_coco wrote:

Uncle Ants wrote:

i_should_coco wrote:

If crap doesn't cause variations in speed, then what does it cause? Noise is effectively variations in speed...

the mass of the platter smooths it out ... is this getting circular??

That's my point. It doesn't, or the power supply would be inaudible.

Nobody said it was perfect

Actually - are you right though. Are motor vibrations the same thing as speed fluctuations? That's a genuine question.

No, agreed, no system is perfect! I am interested in the compromises and problems with each system, though. DD has it's on problems, e.g. servo design and the possibility of hunting and whether it is in fact possible to design a servo that does not do this - a servo requires an error for it to operate, so I'm not 100% sure.

My thinking is that the component of the vibration that is transmitted longitudinally along the belt should appear as speed variation (of course this *is* damped by the belt and platter mass). The lateral component (at 90 degrees) would seem to have less effect.