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Old 9th October 2013, 02:16 AM   #21
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by Stefanoo View Post
I don't know if the motor is a high quality part or not....that is why I was asking to experts here.
On all my research I have done so far, hurst motors seem to be considered pretty low/average quality.
Speed stability is in the nature of an AC motor, provided the sine wave fed to it is stable. The problem with an AC is hum/mechanical noise.

Not sure what the sonic qualities of pulley vs belt, since I have never owned one, not lessrumble IMHO.
I am pretty sure that it should be more resolving on highly modulated passages.
Think about the amount of pressured imparted by the needle on highly modulated passages. The belt will automatically stretch out.
Provided the motor won't slow down, the platter will initially slow down and then belt will pull back thus accelerating the rotation and then it will settle down to the proper speed.
Now,in a complex recording, these hard passages will happen constantly and a frequency distortion will occur throughout.
Apparently frequency distortion is even worse than amplitude, as ear is more sensitive to tone and timing than it is to clipping.
This is the main reason why I am chasing after the rim drive solution.

My platter spins pretty nice and I noticed that noise is very related to the material and thickness used for the oring.
I will contact vpi to ask for a recommendation. For sure though...I can't imagine the pulley being quieter than a belt...just my two cents.
Hi,

A grip of real physics rather than simplistic marketing BS would help.

How accurate do think a cutting lathe can maintain speed cutting ?

In an ideal world your turntable drag dynamics = the cutting lathe
and you have perfect reproduction - at one speed - as if ever.

Your chasing emphemera that by definition is not really DIY.

You want a solution handed to you on a plate by some
expert who by fair means or fowl says it will be better.

rgds, sreten.
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Old 9th October 2013, 02:45 AM   #22
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The explanation I gave is physically accurate enough and put in simple terms, if you have a better one please let us all know!!!!
Beside the basic problem with the cutting process really doesn't matter.
Play by belt will just add the frequency distortion on top of the problem with the cutting, regardless!!
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Old 9th October 2013, 03:09 AM   #23
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by Stefanoo View Post
The explanation I gave is physically accurate enough
Hi,

No, its not remotely accurate regarding reality and drive systems.
It is implicitly inaccurate, implying a problem that does not exist.
(If you know anything about time constants in control theory.)
To be accurate you need to define the real physics of all systems.

rgds, sreten.
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Last edited by sreten; 9th October 2013 at 03:13 AM.
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Old 9th October 2013, 03:23 AM   #24
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I think you should shed more light for everybody because if I understand correctly you are saying that belt system will track speed better or at least equal to direct or idler drive!!! This is really new to me and to probably the rest of the world!!!!

Maybe even vpi doesn't know what they are doing since they went to direct drive for their most expensive tt they ever made!!!
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Old 9th October 2013, 04:18 PM   #25
dtut is offline dtut  United States
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Stefano,

The rim drive pulley and the belt drive pulley for your VPI have to be exactly the same size for what you are trying to do. The ratio of the driver to the driven has to be equal to keep the speed equal. Putting an O-ring on your belt drive pulley will make it bigger and make the platter turn too fast. When I tried O-rings on my direct rim drive, they didn't work well because they weren't precise enough and didn't stretch evenly so they weren't smooth. Most rim drives have a way of moving the rubber away from the rim so it doesn't get a flat spot. I think you will have a problem with that. The Hurst motor will work OK for a rim drive, but something with more torque would be better and with the O-ring tight between the rim and the pulley, you are probably putting a strain on the motor bearings.

I don't want to rain on your parade and I really encourage you to try rim drive turntables, but I strongly suggest getting a Lenco, Rek-O-Kut, Dual, Elac or some other relatively inexpensive rim drive, even a cheap Garrard or BSR, and studying them. Rim drives are great and can be simple, but they need to be well thought out and very precise.
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Old 9th October 2013, 04:31 PM   #26
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Thanks Doug.
What you are saying makes total sense to me. The thickness of the oring really affects both noise and rotation and if it is too thick it can put a strain on the motor shaft.
I have emailed VPI to ask for the right size. I talked to them over the phone and they asked me to write them so that Mike can give an exact answer on that.
Unfortunately he is retired so he comes in there every now and then.

Good side is that oring come in various thicknesses even in steps of 0.5mm.
I can just try different sizes and see which one works best.
I wonder if there is a recommended material since they comes in different flavors different hardness coefficient.

Getting a Garrard or other decent vintage table is nowadays not even convenient anymore.
Prices are unreasonable high and most of them are in a beaten condition.
Also I don't believe that they are necessary better than modern. I do think that their drive concept is better, but it doesn't make it necessary better overall.
All the springs the shafts for switches and thin cast platter, cheap bearing and noisy motor, cannot be in pair with a more modern solution.
This is just my two cents.
The only thing that they were doing right is that they were either direct or idler drives.
In order to make them extremely competitive I would have to redo plint, change platter, bearing, renew all spings, buttons and so on....this would be a huge project for me.
I am aiming for the simplest solution. Speed is not a problem as I am going to build a little two phase speed control if that was the main concern.
All it comes down is to find a proper oring to interface the platter and see if the system works or not.
However I did really appreciate your input and don't worry even if you made rain on my parade ahahahah.....
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Old 9th October 2013, 05:48 PM   #27
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Quote:
Originally Posted by Stefanoo View Post

Getting a Garrard or other decent vintage table is nowadays not even convenient anymore.
I have owned the 301 in both grease and oil and the 401. The idler sound is pretty impressive in drive and bass and for some reason cannot be emulated by belt drive. Otoh, the Garrards have lots of sonic issues which can only be resolved with a new bearing and possibly platter. Not to mention the looks definitely don't work for everyone. And there is that rumble issue too

The sound may, at least in part, be the result of a relatively light platter, high drag bearing and high torque motor. Not easy to replicate.

One thing i cannot quite understand with modern outside rim drives is how rim to platter pressure is adjusted in the absence of a spring. Rubber elasticity alone and rough positioning of the motor pod don't sound very convincing.

Last edited by analog_sa; 9th October 2013 at 05:52 PM.
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Old 9th October 2013, 08:48 PM   #28
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Originally Posted by analog_sa View Post
I have owned the 301 in both grease and oil and the 401. The idler sound is pretty impressive in drive and bass and for some reason cannot be emulated by belt drive. Otoh, the Garrards have lots of sonic issues which can only be resolved with a new bearing and possibly platter. Not to mention the looks definitely don't work for everyone. And there is that rumble issue too

The sound may, at least in part, be the result of a relatively light platter, high drag bearing and high torque motor. Not easy to replicate.

One thing i cannot quite understand with modern outside rim drives is how rim to platter pressure is adjusted in the absence of a spring. Rubber elasticity alone and rough positioning of the motor pod don't sound very convincing.
Man... you got ALL the points!!! You have read my mind....people say rave things about garrads, technics, Lencos etc...etc...but if you look at them...the platter is thin paper, not to mention plinth, bearing, spring mechanism everywhere.
The modern RIM drive, if you noticed, are external, in other words, you can adjust the distance to have proper contact.
In my case, motor is fixed with the platter, so the ORING will have to be precise not too close not too far.
Also Elasticity of the ring will play a role.
I just question how can this arrangement be quieter than a belt drive!

So if we all agree that the only positive thing on the vintage decks was the motor, the idea of using one of those to drive through a VHS tape the modern platter is not so silly.

Do you have any take on this?

My only concerns would be the vibration from the vintage deck could be passed onto the main TT through the tape....but at that point my take is that the overall noise measured on the platter of the technics for instance, is surely lower than noise measured directly out of the pulley of the motor.
If that is true, the coupling to the main platter will should be quieter with a vintage deck than with a direct motor.
Just my two cents if I was able to make some sense.
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Old 9th October 2013, 09:21 PM   #29
kevinkr is offline kevinkr  United States
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I guess I would ask pointedly whether you have ever heard a properly restored and plinthed 301/401 or TD-124? You are very quick to seize the opinions of others that seem to serve your viewpoint/current interest. Any one of these tables properly restored and in the right plinth will match or better the noise performance of the cutter used to make the record you are playing. They will give you sound no belt drive I have ever heard can match.

The main bearing in my TD-124 is a precision device maintaining tolerances of a couple of thousandths of an inch, and the platter is heavy - weighing over 10lbs. The only rumble I ever hear is cutter rumble. (Slate plinth, TD-124/II, Merrill-Scillia mat, Schick arm, Ortofon Royal N SPU)

I believed as you did once, but the table above turned out to be a bit of an epiphany for me. I also had an SME 20/2 with minor issues here at the time I could have bought, I kept the Thorens. (Personal preference)
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Old 9th October 2013, 10:41 PM   #30
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This is interesting! Unfortunately I have never heard one properly restored with slate plinth. I believe it sounds great.
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