Motor for turntable

Hi all,

I have started fiddling around with my VPI classic 3 + SDS.
I don't have extensive experience on motors so my apologies in advance.

The VPI uses hurst 300RPM AC motor. The outer edge of the pulley of the motor is only 3mm away from the outer edge of the platter, which makes it for an easy modification to have the pulley come in contact with the platter for RIM drive.
Pulley has a diameter of 50mm and I found that it is easy to find a proper O-Ring that will fit the application.

Nevertheless I have the issue that platter with such a pulley will spin at 45RPM and to adjust it down to 33 1/3 RPM, the SDS would have to go down to 45Hz.
Unfortunately minimum frequency for SDS is 52Hz which is a no go. Also I don't know if the motor would still operate properly at such a low frequency anyway.


My question is: is this motor suitable for Rim drive?
Can any expert here please recommend me a top quality AC motor that I can use to replace my original Hurst (no cost object) using 50mm pulley?
Or maybe for this application another type of motor i.e. DC or EC be more suitable?
For AC motors I also have read that best solution is having two sine waves with phase control, such as mark Kelly controller.
Unfortunately it seems that this controller is no longer available. Is there anything similar to this available for purchase?

Thank you all for the attention paid.
 
so basically just swapping phases on the motor reverse rotation?
For initial torque, I can always start up the platter with one finger.
Does it take more torque with direct contact than with belt? If motor is the same as now, and it is capable of starting platter without any difficulties when used with belt, will it struggle if used as RIM drive?

I would like to upgrade my motor, if any expert here could could comment on a top end synchronous motor (if suitable for the application) or some other type of suitable motor and control for RIM drive, I would really appreciate it.
 
Stefano,

I built something similar, but if you want to try it, I recommend leaving the VPI as it is and finding another TT or some used parts to experiment with.

http://www.diyaudio.com/forums/analogue-source/240222-no-idler-rim-drive-tt.html

I enjoyed this project and like the way it sounds. If you use some basic inexpensive parts, you can work out the design and then decide if upgrades will help.
 
Thank you Dtut...appreciate your contribution!
At this time I would like to use my VPI as I am really pleased with it and the look of it.
I just want to upgrade it to a RIM drive using same pulley same assembly. Just replacing motor underneath and using a proper O-Ring. I found that pulley is 50mm and outer edge of it is about 2.5mm-ish away from outer edge of the platter.
I am assuming that a 48-49mm O-Ring 3mm, 3.5mm diameter will do the job.
The point is that, the motor I have like somebody outlined here won't have enough torque, but I can always push the platter at start up.
But will this affect speed stability? Do I need an higher torque? Can anybody point out a better AC motor?
I would drive it with a two phase adjustable angle adjustable voltage and frequency (look at this simple idea The Altmann DIY Turntable .)

I read that if phase is properly tweaked mechanical noise goes down significantly making an AC motor very suitable given its natural speed stability (if generator is stable) and low noise if phase are tweaked.
I hope that some experts here will comment on the motor.
 
On an AC motor you have three or four wires providing the supply to two coils.
There is a capacitor between two wires, just apply the AC supply to the other side of the capacitor to reverse the rotation and leave open the wire where the supply was before.
Leave the wire (or the two wires connected together) at the other side of the power supply.

Generaly the idler drive turntables have bigger motors than the belt drive turntables, I suppose it is for the need of torque. But you are right you can start the turntable by hands.
 
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I don't get it!
My motor comes with 4 wires. There are two blue wires one red and one black.
The datasheet says to connect capacitor between red and black wires.
Supply between Blue and Red for CW rotation, Black and Blued otherwise for a CCW rotation.
I don't understand how to apply your concept. Did you mean to take cap off and power up just one side of it?
My plan was to get a little power amplifier with step up transformers, connect it to the output of my soundcard and generate two independent sinewaves and control amplitude and phase.
 
The two blue wires are connected both to one wire (neutral for example) of the mains.
There is a capacitor between red and black.
For CW connect the other wire (line) of the mains to the red wire, for CCW connect to the black.

Of course if you use a two phase inverter or another power supply you must remove the capacitor and drive the two coils separately.
 
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gotcha!
The problem with the capacitor is that if I want to go down in frequency, say 42 Hz to get to 33 1/3 RMP, the size of the cap has to be different from the regular 60Hz recommended by the manufacturer.
This is what I was told by Hurst. With the 2 phase sine wave generator, I don't need capacitor so no problem with that.

Isn't there any better AC motor than the Hurst I am currently using?
Still waiting on some expert here to pour out some good advice :xeye:
:cool:
 
Little update, I have bought few orings at the store tonight.
Unfortunately, they were all too thick though.
As a result, the motor would just stall running out of torque unable to turn the platter even if I would try to push it.
Confirmed by me trying to turn the platter and it turned out to be pretty hard.
So I trimmed the oring out with snippers to make it thinner.
Result was that the platter spinner properly at that point. The method seemed to work well, in regard to speed regulation, much better than belt.
Nevertheless there was an audible noise when platter spins and my guess is that it's not the motor but rather the irregular oring causing irregular rubbing noise.
Also, is there any recommendation as far as what material to use for oring?
 
I have started fiddling around with my VPI classic 3 + SDS.

Hi,

You want an experts opinion ? After spending $6K on a turntable
you have got more money than sense thinking you can improve it.
If you can then you've spent $6K on a very poorly designed turntable.

rgds, sreten.

FWIW you should be able to interject a precision tensioned rubber wheel
between the motor and the rim solving all of your imagine problems,
for one speed at least, but I doubt it will work better than it does.
 
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Your input makes little sense. I could kind of see your point somehow.
However, if you have noticed the motor is not a top quality part. I haven't received yet an advice on that. Does it mean that no better motor than ac hurst exists?
Also all vpi tables but the classic have access to the rim drive upgrade.
If you research, many people have benefited from either single the rim drive or a Teres direct drive.
Research and you will see it for your self.
Does it mean that many tables are poorly designed? Well I don't think so. I just think that a rim drive is a viable SURE upgrade. I also have a linear air bearing tone arm, does it still mean that the table is poorly designed? :eek: :eek: :eek:
 
I have to agree with sreten on the motor. I use the same one and even though I use a non standard lead filled acrylic platter and have to hand start it sometimes, I can detect no speed issues compared to my other SOTA star table. I might even say maybe slightly even better, but thats a tough one.

I would like to know what it is about a physical contact rim drive concept that people are so interested in. Is there some documentation that shows more speed stability or lower rumble ( having trouble on that one) that moves people in this direction?

Regards
Dacid
 
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.
 
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