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Old 7th October 2013, 02:57 AM   #1
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Default 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.
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Old 7th October 2013, 03:03 AM   #2
kevinkr is offline kevinkr  United States
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Why not get a good idler drive like the TD-124, Garrard 301/401 or a Lenco?

I run two TD-124 on slate plinths and am planning to refurbish a 401 I got recently. (Belt and DD for 30+ yrs, no going back now)
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Old 7th October 2013, 03:24 AM   #3
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I thought of that but after much research, I found there is no heaven unfortunately.
Their bearing and platter are not up to date to the best available nowadays.
Plinth needs to be upgraded as well....just too much work for me

I would like to maximize my VPI

I found this other thread interesting too.
DD belt drive platter via VHS tape
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Old 7th October 2013, 04:17 AM   #4
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Which I just realized that for RIM drive I need motor to spin counterclockwise
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Old 7th October 2013, 06:11 AM   #5
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That is not a problem, you only need to swap the capacitor on the AC motor.
But that kind of motors don't have enough torque to start a platter that way.

Last edited by Arch Stanton; 7th October 2013 at 06:14 AM.
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Old 7th October 2013, 02:41 PM   #6
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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.
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Old 7th October 2013, 04:29 PM   #7
dtut is offline dtut  United States
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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.

No Idler Rim Drive TT

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.
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Old 7th October 2013, 04:43 PM   #8
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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.
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Old 7th October 2013, 06:23 PM   #9
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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.

Last edited by Arch Stanton; 7th October 2013 at 06:25 PM.
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Old 7th October 2013, 08:19 PM   #10
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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.
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