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'Number9' TT AC motor controller web site finally up

Steve, i used a Rega 24v motor with a dual mono, voltage, frequency and phase adjustable USB interface controlled TT-psu for a couple of years before replacing it with a DC unit. I'm a believer regarding the benefits of accurate correction of motor drive. You unit appears to offers twin motor drive and phase per selected speed beyond what I used previously.

The biggest noise issue in AC motors seems to me, and others who've looked at FM demod's, cogging, accurate adjustment of phase and lowest possible drive voltage can help ameliorate it. Lots of supplies offer these adjustments.

A unit with intra revolution speed sampling could be used to synthesise adjusted drive sinewaves that include a modicum of cogging compensation- irrespective of platter mass and rubber band.

Let's be honest though, there's a reason for DC motors and shaded pole Ac motors...
 
sq225917- You should see what happens when you use a 3 phase AC synch motor (aka BLDC) and the right controller (variable frequency/voltage/phase sinewave drive). Zero cogging, 3x-4x more torque than a comparable AC synch (or DC) motor, 100:1 speed control (think 1 RPM-100 RPM platter speed with the same pulley, no burn out on the belt & no loss of torque at the high speeds) and the ease of speed control determined solely by the frequency, so there is no droop in speed vs torque or temp that you get with a DC motor. Also, no brushes to wear out (or create arcing and/or mechanical noise) and precision ball bearings that don't wear out with age like the sintered bronze bearings in the Hurst motors.

http://www.diyaudio.com/forums/anal...phase-bldc-motor-turntable-9.html#post5050841

AC induction and DC motors are more difficult to control the speed accurately than AC synch motors as they both have a negative torque-speed slope. AC induction are also very inefficient.
 
sq225917 said:
The biggest noise issue in AC motors seems to me, and others who've looked at ... and lowest possible drive voltage can help ameliorate it.
Click to expand...

Sure it can, Simon - hence how the Lingo functions. But the experiments we have done with just one 24v AC motor on my 'SkeletaLinn', with Steve's motor controller:
  • having got the optimum phase angle (<90deg!)
  • which delivers minimal motor vibration
  • which allows you to increase the voltage fed to the motor without getting any noticable increase in motor vibration
  • showed that 32v delivers a much more dynamic presentation of the music than 24v did! :)
My reading of this is that higher voltage delivers higher drive potential - I call it torque - and when you have 2 motors driving the inner platter ... you get even more of the same! :D


Andy
 
Torque delivery is proportional to load. Torque is generated during start up as the inertia of the platter is overcome but once up to speed torque drops almost to zero - generated only by losses in the motors own bearing and that of the platter. Increasing the potential maximum torque of the motor is something of a red herring as this will mean that platter gets up to speed quicker but actual running torque is almost identical because of the low load presented.
 
YNWOAN said:
Torque delivery is proportional to load. Torque is generated during start up as the inertia of the platter is overcome but once up to speed torque drops almost to zero - generated only by losses in the motors own bearing and that of the platter. Increasing the potential maximum torque of the motor is something of a red herring as this will mean that platter gets up to speed quicker but actual running torque is almost identical because of the low load presented.
Click to expand...

Sure, that's theory, Mark.

Perhaps I should not have mentioned the word 'torque'? My experiments showed that as I increased the voltage fed to the motor from 24v to 32v (the maximum possible on the prototype) ... the SQ improved. But of course this is only possible when you have achieved the optimal phase angle.

I suggest this is something that needs to be experienced with your ears - not theorised about.

Andy
 
YNWOAN said:
With regard to my comments on torque it's not just theory, that is how motors work.
Click to expand...

Mark, I am sure you are correct (in terms of torque).

All I'm saying is that the difference in the SQ that you hear as you wind up the motor voltage ... is clear. But I have absolutely no idea what artefact you would need to measure, to correlate with this 'heard' SQ improvement.

Andy
 
With regard to your set up Andy increased voltage might increase torque, but only if there's some 'fighting' between yours motors.

Have you ever marked your pulleys and checked sync before and after playing to check if one motor pulls the other a little.
 
sq225917 said:
With regard to your set up Andy increased voltage might increase torque, but only if there's some 'fighting' between yours motors.

Have you ever marked your pulleys and checked sync before and after playing to check if one motor pulls the other a little.
Click to expand...

Let me say again, I should not have used the word 'torque' - so please don't focus on it. The fact is - SQ increases as the motor voltage rises!

Are my motors in sync ... or are they fighting each other? I think they're in sync as what I did was:
  • use a strobe & strobe-disc to get the Hz required to get the correct speed using the 1st motor alone
  • then do the same for the 2nd motor alone
  • then input the "relativity number" into the speed controller - eg. 0.996. This adjusts the Hz output to the 2nd motor, relative to the 1st, so that both motor circuits are outputting the right no. of Hz to produce the correct speed. (The speed variation is due to production variations in the motor and, since they are hand-machined, the pulleys.)
  • then enter a 45 deg phase lag between the 2 motor circuits, so the motors apply their drive to the inner platter at slightly different times.
On the SkeletaLinn, it is very easy to see whether the 2 motors are driving the inner-platter in sync ... or are 'fighting' each other - as, if they're trying to drive the inner platter at different speeds, this causes the skeletal chassis to shake. You can easily see this shaking because the bias-weight buckets on the 2 arms are jiggling around. When the "relativity number" is correct - and the 2 motors are each driving the sub-platter at the same speed - the bias buckets hang without jiggling around.

Andy
 
Andy, You'll be pleased to know that on the current version of the controller I have largely automated the tedious process of setting up the tracking speed differential variable. You'll still have to swap the belts in and out, but the controller will do the rest.
 
Steve#9 said:
Andy, You'll be pleased to know that on the current version of the controller I have largely automated the tedious process of setting up the tracking speed differential variable. You'll still have to swap the belts in and out, but the controller will do the rest.
Click to expand...

Excellent! :)

Andy
 
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