3 Phase BLDC motor for turntable use?

galyons-

At this time, I have no plans to pursue this commercially. DIY would be difficult as it involves fine pitch SMT devices and software that is proprietary to our other PSUs.

I find it most interesting that VPI is rolling out some very expensive tables based on their earlier designs. The Titan which is a double decker version of the Avenger is still powered by the crappy Hurst motors and has a sticker price ~$48K. Almost every major table mfr with and entry in the $10K plus market offers a custom built high end motor with very sophisticated electronics to drive it. I wonder how a $50K table will be received when it uses a $30 motor and no controller?
 
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Calvin-

Per my earlier misunderstanding of another post, I do not wish to turn this thread into a DD vs BD discussion. There are people who do not prefer DD because of what they perceive as a coloration in the audio most likely due to the drive mechanism. FWIW, I am not one of them, I merely stated that the possibility exists.

Most of what you posted is accurate, but the output of all PLL systems "wobble" about their center frequency because of the loop filter response time. The wobble may be small, perhaps below the threshold of measuring equipment, but it exists because of the delay in the loop LPF. The frequency of the wobble should be centered around the natural frequency of the loop filter and the amplitude will depend on the loop BW and damping factor, the VCO conversion gain, the phase detector conversion gain & current drive of the phase detector/charge pump. There is also the element of the reference frequency that is not fully attenuated by the LPF causing FM in the VCO which can best be described as phase noise (analog jitter at the reference frequency) in the center frequency of the drive signal. Whether this shows up as speed instability is also a function of the platter mass and motor torque and is fairly complex to model.

The drive system I'm using does not use any feedback mechanism to create a stable signal for the motor. Is there an audible difference? Only each individual listener can answer that.
 
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galyons-

At this time, I have no plans to pursue this commercially. DIY would be difficult as it involves fine pitch SMT devices and software that is proprietary to our other PSUs.

That is most disappointing. I am no engineer, but my simple logic tells me you are researching something that would be a quantum improvement over the default Hurst motors.

I find it most interesting that VPI is rolling out some very expensive tables based on their earlier designs. The Titan which is a double decker version of the Avenger is still powered by the crappy Hurst motors and has a sticker price ~$48K. Almost every major table mfr with and entry in the $10K plus market offers a custom built high end motor with very sophisticated electronics to drive it. I wonder how a $50K table will be received when it uses a $30 motor and no controller?

I already shared my opinion on the Hurst motor. It works, but to get to high quality sound reproduction, one must spend quite a bit of $$$$ and effort to dampen the the motor's ills. Your fine products are prime examples of high value devices to clean up the intrinsic Hurst/synchronous motor issues.

Hard to fault VPI's commercial success. Especially given the digital onslaught that prompted the exit of so many from vinyl reproduction. For the most part, the controller has always been a separate device...PLC...SDS...ADS. Also SAMA's, flywheels, etc. to isolate and provide inertial consistency to the platter. Each of those products progressively isolated the motor from the stylus in the groove.

I have long drank the VPI Koolaid, and quite honestly, with little remorse. The ability to add upgrades to get to higher model performance/specifications has been the VPI strong suit. Not having deep pockets, this allowed me over two decades to go from entry level to near the previous TOTL in affordable incremental steps. Much of this was due to resale value of parts and pieces for those folks a bit behind me on the path.

I have had the opportunity to hear some of the newer VPI offerings and other brands in my system, (I mod/repair tube equipment and do turntable repairs, set-ups and tune-ups). The new VPI products do sound good. But there is not sufficient gain to motivate me to dump my TNT. IMO, and to my ears, that resale used price would not put me anywhere near where I am today in analog reproduction quality today.

Cheers,
Geary
 
Hard to fault VPI's commercial success. Especially given the digital onslaught that prompted the exit of so many from vinyl reproduction. For the most part, the controller has always been a separate device...PLC...SDS...ADS. Also SAMA's, flywheels, etc. to isolate and provide inertial consistency to the platter. Each of those products progressively isolated the motor from the stylus in the groove.

I agree that VPI has been very successful commercially, and kudos for their efforts during the CD boom. However, commercial success does not equal engineering success. The PLC was without a doubt the worst turntable motor controller ever conceived (see link below). Hard to believe that they ever released something so bad; harder yet to believe that still they promote it as one of their best designs. The SDS was a decent piece of engineering, but it was PLL based and suffers from all of the ills I outlined above. IMHO, it was also overpriced and underpowered. The ADS is interesting for a host of other reasons. Technically, it is inferior to the SDS and from early reviews this is borne out in the measurements. I recently had an interesting conversation on VPI's forum with the engineer that designed the ADS, and the gist of his position was that the measurements are irrelevant, the listening tests are all that matter. Perhaps. Then again, it could all be marketing, an area where VPI excels, at the expense of engineering.

The SAMA was a good idea, no bones with that. Their flywheel motor assemblies seem to have a following, though it is difficult to understand why. HW has posted (on their website) that the single motor flywheel has 62x the inertia of a 20lb aluminum platter. The math would indicate otherwise (~20% of the inertia of a 20lb platter, so off by a factor of ~300x), but so many swear by the positive effect that there must be something there worth investigating. Problem with this industry is nobody cares. Everybody eats it up like it is gospel, so why question it? Somewhere P.T. Barnum is smiling.
 
Hi Bill

If you do not mind where did you get the new motor from in US. I Google many ways no real success.

I read through the VPI website on the new controller for fun. You got to admit these guys know how to write copy.
I am having a hard time rapping my head around all analog feeding a motor sound so much better.

Thanks Tom
 
Look at Anaheim Automation or Teknic.

Regarding the ADS supply, I don't know how someone can make claims about motor operation and power supply design that contradict conventional understanding and basic Ohm's Law without explaining their rationale; whenever I present a logical argument, they run away and just say "listen to it". I'm beginning to think the "V" stands for Voodoo.
 
Look at Anaheim Automation or Teknic.

Regarding the ADS supply, I don't know how someone can make claims about motor operation and power supply design that contradict conventional understanding and basic Ohm's Law without explaining their rationale; whenever I present a logical argument, they run away and just say "listen to it". I'm beginning to think the "V" stands for Voodoo.

Commercial Voodoo it is.

Hans
 
Pyramid,
How fortunate that I've stumbled on your thread. I, too, have been experimenting with DC motors to drive turntables. Normal DC motors have speed stability issues over time, unless you create a PLL using hall sensors or rotary encoders. Brushless DC motors should give the best combination of relative ease of drive, speed control, and torque of DC with the lower noise and speed stability of AC motors.

However, I have had a problem with my experiments using this technology: the motors whine. In fact you can play a tune through a BLDC motor -- my BLDC controller helpfully(?) does this on startup.

So, I wonder, how do you minimize/control/prevent the whining from the motor? Is it just a controller issue?

Thanks,
JR
 
This is similar to what they use on model trains for a motor controller. It uses a low frequency (in the audio range) type of PWM in order to achieve slow speed rotation of the motor. Not what you want to use for turntable control. Trapezoidal commutation of a BLDC motor will produce cogging and the motor behaves as a DC motor (where speed is determined by the DC voltage) rather than an AC synch motor where speed is determined by frequency.
 
Excellent. Where can I find one that doesn't have these issues? Alternatively, would an arduino be able to supply a pwm signal with high enough frequency? This type of controller doesn't have hall effect sensor input because it uses back emf to determine rotor position. A controller that uses the hall effect sensors would be preferable because it's more precise.


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