Alternative platters ?

No disrespect meant; but, all the hoopla over the Techy not spinning correctly at 45 rpm is based primarily on a specimen that had been tinkered with???

The 1200 motor is essentially the same as used in the 150Mk2, 1300/1400/1500Mk2, M1a, M2 & M3 and all of the platters on these decks are heavier than the 1200's and balanced. It seems to me the motor is overspec'd for the job, if anything. In addition I use a 454g record weight on top of that. I have no problems running 45 rpm. Granted the MN platter is certainly heavier; however, I do believe I've read that Richard from Vantage himself has offered/done upgrades to the stock platter with more aluminum on the bottom side not to mention Inspire's use of a heavier platter on the Monarch. I also don't recall ever reading posts here when the MN platter first had it's go around that anyone's deck had a problem spinning at 45 rpm. So, what gives here guys? Was this problem ever documented by watching a strobe, flutter tests? I could be wrong; but, this does seem strange that said issue has appeared this late in the game. If I missed such posts back in the day, I unreservedly apologize.

Can those still using a heavy platter (MN or Vantage upgraded) on a 1200, or an owner of the Inspire Monarch weigh in here, please??

QUOTE=chris@panteg;497388]The platter on an SP10 MK 3 weighs 10 kg , the motor and control circuitry is a different ball game to the 1200 of course .

I tried to point out some time ago that a high mass platter doesn't work on a 1200 , the compensation circuitry is set in stone .[/QUOTE]


Martin T has commented that he heard hunting when using a “high mass platter”.
Similarly Marco has observed negative effects that he ascribes to “platter mass”.

Well for my part all I have to say is that where DDs are concerned, “High mass platters” don’t in fact do this or that.
Because mass, per se, is irrelevant. Platter mass is static and sits on the bearing. For a heavy platter the bearing might then scream: “I’m not bloody Hercules” but that’s all.

You may have noticed, but when we feed energy into our decks, the platters start to rotate and this changes everything; now we have inertia. It is this that matters because its value is non-linear. Inertial values increase by the square of the increasing distance from the centre of rotation.

We can have a very heavy (massive) platter with its mass close to the centre and it will have a "low" inertial value.
Or a low mass platter with material concentrated at the edge and the inertia can be higher than the case above.
Or they can be balanced to the give same inertial value, when despite our scales telling us they are totally different, as far as the electronics are concerned, they are one and the same!

From our point of view, because we are listening (measuring?) to the mechanical interactions of both constructs, these two designs are again deemed to be different.

So, what we are left with is the fact that in DDs the system has to be optimised to match the power available to the inertial load. If the value goes outside of the loop constants, (high or low) then instability can set in, and hunting can be detected.

In developing professional versions of our platter for as fast a startup as possible for a particular client, we reached a point where servo lock was lost and hunting occurred - quite impressive.
The best solution for recovery we found was mechanical and not electronic.

The Technics engineers optimised the 1200's R-C values for the (maximum) power available from the motor and matched it to the platter(‘s inertia).
Tinkering with the values will not yield improvements as drawing any more power from the coil winding will only shorten the motor’s life – I’d say blowing up fits into that condition.
For this reason, one can argue the design is indeed set in stone.

if you want more power, then an SP10 is a pretty good place to start...

In developing our platters, therefore, we have always stuck within the designs constraints, both with our original Type I and now also with Type II. They are two totally different animals, so you can have you cake and eat it. I say this only because of previous comments regarding the deleterious effects of "mass".

As a relevant adjunct to this post, I'll tell you why belt drives are attractive: As the motors operate at much higher speeds and produce many times more error pulses per platter revolution.
This then permits for much smaller and hence less intrusive correction to take place.
With DDs the correction has to be applied with great finesse lest it be heard. And with 1200 I think we already know the answer!

That apart, in truth, there is no real difference between the two philosophies. The only difference is that we have designs fixed and this prevents us from exploring. We are then left saying that a belt drive DOES this and a DD DOES that. To my mind, both work.

Arthur

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Originally Posted by Arkless Electronics

Like many phono stages it doesn't have a MM stage to remove... units which have a separate internal head amp for MC are in the minority. In the case of the Arkless 640p and many others there is no more in the signal path when switched to MC than there is on MM. Only the value of 1 resistor is changed in order to give higher gain for MC.

The Paradise is different again.... The only other phono stage I know of which works in a similar manner is the Pink Triangle "The Pip". It is much more involved to make it into a MM stage but it can be done.... making it switchable is not possible. It involves a major redesign! (I don't know if the pip is switchable...).
I'm hoping to have a MC only phono stage of my own which works on the same principle available before too long ;) It's a very interesting principle on which this technology is based.. zero feedback and virtually impossible to overload. I'm quite excited about the possibilities of this way of doing things.. just wish I didn't have to do mundane stuff to make a living and then it would be ready a lot sooner :doh: I can see possibilities (thinking out loud now) for line stages.... and more to the point, power amps, built with this technology. The later is not possible to do cheaply though!

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"This technology" I assume refers to transconductance gain stages. Pip is effectively modules, active line, riaa (mm) in this threads speak, and mc which is further gain. There are at least 4 variants I am aware of in that basic circuit (pip 2 variants also had power supply options). However because the regulation is applied at each stage independantly and integrated with the transconductance circuit, in addition to low distortion zero feedback the noise on the power rails effectively doesn't reflect in the signal path. Switching in pip 1 and 2 is achieved by custom built 16 pin dil headers which set the load and where necessary bridge in the additional gain. Whilst I have the schematics this stuff is in published magazine articles. Pip2 headers whilst identical in appearance to pip1 are configured differently - one of the reasons I asked paul stewart which pip he was comparing to his "superior" successors. Extending the principle (concept?) to power amps is the next idea, but as you note jez there is the bother of going beyond concept and successfully implementing it. That bit was way over my head :mental:

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Originally Posted by Mike_New

Hey Folks,
Dave B really is correct when he says that all this SUT and phono amp talk is off topic.
A SUT or amplifier or surely speakers can hardly effect the characteristics of a humbl platter.

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Hi Mike,

It's acceptable thread drift (in the AoS tradition), where discussions will sometimes extrapolate into other areas, running concurrently with the original thread topic. As long as all comments remain constructive and no-one 'thread craps', by denigrating any of the products or turntable modifying methodologies mentioned here, then there is no problem :)

Marco.

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Originally Posted by FunkArt

You may have noticed, but when we feed energy into our decks, the platters start to rotate and this changes everything; now we have inertia. It is this that matters because its value is non-linear. Inertial values increase by the square of the increasing distance from the centre of rotation.

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Agreed, I did mention momentum further up the thread. Using mass simplistically in place of momentum, you'd have to have a very unusual design of platter to be high mass but low momentum.

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Originally Posted by MartinT

Agreed, I did mention momentum further up the thread. Using mass simplistically in place of momentum, you'd have to have a very unusual design of platter to be high mass but low momentum.

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What effect would plonking a heavy record weight of high mass have?

Indeed, Martin...

Arthur, I hear what you're saying, but surely mass acts as the catalyst for the knock-on effect on inertia? Therefore, the existence of too much mass is the root cause of the problem.

Therefore, in the case of aftermarket platters for the Technics, any new design should not have any more mass (be heavier) than the stock platter, as otherwise one encounters the problems being described here in relation to 'hunting', and consequently audible 'warbling' on playback.

Marco.

I think Arthur's point is that mass defines the platter as a whole. The value of inertia is dependent on where how that mass is spread across the width of the platter.
So just talking about mass alone is meaningless unless you consider it in conjunction with it's position.

.....and he would be correct!

Think about a seesaw.
Put a fat kid and a skinny kid on it. The fat kid near the middle and the skinny one near the other end. This gives the skinny kid greater downward inertia.
Now move him in to the same relative distance as the fat kid. The fat kid now has greater downward inertia.

Now move him back a bit and they balance, so they have the same downward inertia (in this case, zero)

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Originally Posted by Marco

Indeed, Martin...

Arthur, I hear what you're saying, but surely mass acts as the catalyst for the knock-on effect on inertia? Therefore, the existence of too much mass is the root cause of the problem.

Therefore, in the case of aftermarket platters for the Technics, any new design should not have any more mass (be heavier) than the stock platter, as otherwise one encounters the problems being described here in relation to 'hunting', and consequently audible 'warbling' on playback.

Marco.

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What happens when you plonk a heavy record weight (high mass) on a technics deck? (2nd time of asking) (ps you'll like the answer);)