VPI HW-40 Direct Drive VPI HW-40 (1).pdf

Designing VPI's Next Generation Direct Drive Motor Technology

Harry Weisfeld's 2012 CLASSIC DIRECT direct drive turntable was an
outstanding technical achievement, earning Stereophile Magazine's
Class A+ rating. This award-winning table was loosely based on the VPI
Classic Series table technology and included a thick aluminum plinth
and armboard and an inverted platter bearing riding on a PEEK thrust
disc. Combined with a cutting-edge BLDC direct drive motor, the
CLASSIC DIRECT was created. The Classic Direct provided a stable,
solid foundation for the music, allowing the listener to hear deeply
into the recorded grooves to the treasures buried with-in!

Designing a new turntable to celebrate VPI's 40th anniversary provided
VPI an opportunity to update the direct drive motor technology to
incorporate advances in motion control and materials technologies.

The 40th Anniversary project:

As the starting point we re-evaluated the CLASSIC DIRECT’s motor
design. While still an awesome motor, our assessment found it to be
overly complicated, difficult and expensive to manufacture, requiring
custom written motor control software and no ability to fine tune or
scale the technology into other models.

Surveying current available motion control technology, it was apparent
that advances had been made in not only the available drive
electronics, but also in materials and software control. The demands
of mainstream industries involved in robotics, manufacturing,
machining, inspection, etc. had been driving the motion control
industry for higher precision, speed, reliability and affordability,
providing a wide range of technologies to evaluate.

Starting with the Motor Components

The first decision made was to retain the 2012 motor components
and re-engineer the motor housing and platter. The rotor and
Stator components being still available from our American vendor.
These component parts are one of their most popular models due to
its size, high torque and smooth cog-less motion.

CLASSIC DIRECT/HW-40 motor stator coils are constructed of solid
copper, square cross section wire embedded in a hi-temperature
composite material for increased vibration damping. The stator's
tubular construction also resists the flexing under load that
affects substrate base coil designs. This construction also
provides excellent cooling and near-optimal interaction of the
electromagnetic conductors within the magnetic circuit. The
unique iron-less coil assembly avoids the use of magnetic
materials in its construction. The stator coils also feature a
overlapping V-shaped coil construction, these features smooth the
rotational transition from pole to pole, eliminating the cogging

that accompanies simpler direct-drive motor designs.

Additionally, the rotor magnets are shaped to smooth the Back EMF
(electromotive force) from the stator as the they transition from
pole to pole. This feature eases the demands on the motor drive
circuitry and power supplies. Combined, these elements of the
thin-gap motor components produce an unprecedented rotational
smoothness and virtually unmeasurable wow-and-flutter.

Motor Design Improvements

Because we were retaining the original BLDC motor components
discussed above, we next focused on the mechanical design of the
new motor. Working with engineers at our long-term machine shops
and learning from Harry's experiences with the 2012 design, the
first step was to design the massive can-style housing to support
the stator assembly and machine it from a solid billet of T6061
aluminum. Its design was optimized to create a solid platform to
support the stator and act as a vibration sink, effectively
absorbing motor vibrations into the 1/2" thick MDF-damped
aluminum plinth through a solid 5-point mounting.

The rotor/magnet assembly is pressed into the aluminum platter
support hub; this, too, is milled from a solid billet. The hub
housing provides mass damping, absorbing and dissipating drive
vibrations into its mass. The platter was engineered to securely
mate to the hub, improving its damping while still allowing its
easy removal for shipping.

The rotor hub is precision machined to hold the 100mm rotary
encoder system that provides ‘2500 timing counts per revolution
of position’ feedback to the servo amplifier. At 33RPM, this
provides 1423 counts/sec of extrapolated resolution contributing
to the tables’ extremely low wow and flutter and exceptional
speed accuracy.

Servo Drive Electronics and Motor Control Software.

The need to precisely control mechanical movements in smooth
precise motions has helped the motion control industry create
hardware and software far advanced from their 2012 equivalent.

The 2012 version of the direct drive motor was a bit under­driven, with low torque and a very slow ramp-up to speed.
Driving it harder resulted in an objectional rise in servo noise.

The motor drive electronics for the 2019 HW-40 are being sourced
from one of the leading companies in the industry. Established in
1990, they now have locations and manufacturing plants worldwide.

Historically, VPI tables have shown increasing improvement in the
foundation and purity of music as the torque has increased. This
evolution has involved utilizing massive platters, multiple

belts, flywheels, dual flywheels, dual motors through rim drive
models.

The focus for the evolution of the HW-40 motor was to increase
the running torque and improve speed stability without affecting
the silent noise floor that VPI turntables are renowned for.

A design challenge stemmed from using a motor that is more
powerful and efficient running at 2-3K RPMs and running it at 33
RPM. Adding the mass and inertia of a 27lb platter, it became a
challenging feat to manage the drive signal to obtain our torque
and speed stability goals while maintaining low drive noise.

Working closely with motor control engineers while
monitoring/listening to the motor noise using an unmodulated
disc, we were able to fine tune the motor drive for high torque
and silent operation. Listening to the HW-40 allows the listener
to hear the success of our efforts.

Electronics Layout and Construction.

Considerable effort was put into the physical layout of the HW-

40. Stable operation, low electrical noise, ease of assembly and
servicing as well as long-term reliability were the goals.

HW-40 Isolation

Very high on our design checklist list for the HW-40 was the
physical isolation the table, with two specific priorities to
address. First, obviously, was to provide a high level of
isolation to structural borne and airborne vibration. Second was
to cleanly integrate the isolation into the look of the table.

Towards this end VPI performed a lot of development work
evaluating the technology and materials available. After
evaluating dozens of prototypes and an endless supply of damping
materials, the table isolation was finalized. The HW-40 is the
first VPI table to benefit from these efforts.

Through a combination of reinforced composite absorption pads
coupled with low durometer horizontal isolators and their
mounting assemblies, the HW 40 suspension interacts with the mass
of the table to provide excellent broadband isolation in both the
vertical and horizontal axes.

The Elastomeric composite pads provide high energy absorption
with less than 10% compression set. There are no plasticizers to
interact with cabinet surfaces. The combination and execution of
the design elements guarantee consistent long-term performance of
the isolation system.

The sonic results are heard as an improved sense of focus and
articulation in the bass that extends well into the lower
midrange.

Check out this Facebook link to see the isolation in action.

The Bottle Challenge on Facebook:
https://www.facebook.com/vpiindustries/videos/vb.313369810917/335
742833641928/?type=2&theater

In summary,

VPI’s efforts to create the next generation direct drive table
have been well worth the time, effort and money invested in this
project. We have created an extra powerful, yet ultra-quiet

direct-drive motor, resulting in unprecedented rotational
smoothness and relatively unmeasurable wow-and-flutter.

The isolation system that grew out of our research is also first
class and provides cutting edge isolation performance.

With the combination of 40 years of global award-winning table
design, the inclusion of the new 3D Gimbal Fat-Boy tonearm, our

new state of the art direct drive technology, and an isolation
system that lowers all noise levels, VPI has created a turntable
that truly demonstrates what is possible from vinyl playback
technology in 2019: the VPI 40th Anniversary HW-40!

Michael Bettinger, February 2019