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Turntable Design
Thoughts on Turntable Design by George Merrill
This paper covers the self-generation and internal coupling of energy. The turntable must cope with four types of energy:
One
Self-generation and internal coupling of energy produced by the motor, drive system, platter support bearing and tonearm.
Three
Airborne energy contained within the operating environment.
Two
Mechanically coupled energy that enters the support feet.
Four
Energy generated by the stylus to groove contact during tracing (playing of the record).
"Energy Management Design""Tonearm Release Energy" is one of the major determining factor of sonic performance.
This term "tonearm release energy" was coined during the development of the AR modifications (1976). Release energy is produced by the tracing of the record groove. The stylus only moves microns. A very small amount of energy intrusion will diminish low-level information and cloud sonic quality. The start of the energy chain is within the cartridge body. This energy is equal and opposite of the stylus movement. The energy is then fed from the cartridge to the tonearm. Many cartridge and tonearm manufacturers now design their product with materials and form to minimize the body-induced resonances produced by this energy. The final step is when the energy is released into the arm mounting platform. What happens at this step is the true test of the design. The energy must be dissipated and not reflecting back into the tonearm.
The Energy Management design principles are incorporated in all the Merrill product designes. In the design of the AR subchassis and Heirloom the arm mounting platform is a nonremovable part of the sub-chassis allowing coupling the released energy to a large homogeneous dissipating area. This area was many times larger than that of any turntable produced at that point in time and probably most now. This is one of the main reasons for the sonic integrity and cult status of these products. The PolyTable utlizes the same principal.
The Energy Management design principles are incorporated in all the Merrill product designes. In the design of the AR subchassis and Heirloom the arm mounting platform is a nonremovable part of the sub-chassis allowing coupling the released energy to a large homogeneous dissipating area. This area was many times larger than that of any turntable produced at that point in time and probably most now. This is one of the main reasons for the sonic integrity and cult status of these products. The PolyTable utlizes the same principal.
The Spindle Bearing
The design of a high-quality spindle bearing is very simple. The lowest noise is achieved from an Oil Well design. (Test it with the stethoscope) The oil creates a dead quiet isolation film between the shaft and the bearing. Belt tension load on a properly designed oil well turntable spindle bearing is of no consequence. A 7000 horsepower dragster engine uses an oil film to separate the connecting rods from the crankshaft. This surface is about one inch wide, smaller in width than the length of a typical turntable bearing. The turntable bearing is placed under a few pounds of load.
The Drive System
The only drive system that will ensure low noise intrusion uses a single elastic belt and a single isolated motor (The more motors or idler pulley bearings, the more noise intrusion). A properly chosen belt as to the size, type, elasticity and free air length becomes a low pass filter. This filtering action helps eliminate higher frequency information from entering the platter and smoothes the motor impulses. Remember, it only takes a very small amount of energy to cloud the input from the stylus to the cartridge signal generator.
A synchronous motor (synchronous motors are frequency locked, not feedback locked) of just enough torque (small motors equal low noise- large motors add more noise) is my choice. Some say much torque is necessary to overcome groove loading. Groove loading will, to a very minuscule degree, reduce the speed. Most any quality turntable with a heavy platter will have enough inertia to keep the micro speed changed invoked by signal modulation groove loading to a level completely undetectable.
The direct-drive motor: The name indicates the absence of isolation from the motor to the platter. Direct drive turntable motors can exhibit cogging the amount of this cogging is determined by the pole number and the inertia (weight) of the platter. Hunting can be a problem if the feedback servo is lacking in definition.Direct drive motors do not use an oil well bearing.
The rim drive (idler) is plagued with problems. The reason it came into existence is; in the past, motors with torque enough to rotate the platter were of the induction type and operated at high speed (1800 rpm). The Idler drive allowed enough speed reduction (16-33-45-78 rpm platter speed) and made for a compact design. More bearings and a hard drive wheel that generates and transmits noise are a real detriment to sound quality. Some early turntable manufacturers added a belt to the equation ( Thorens TD124) to tame the motor noise presented to the platter. But this did not eliminate the rolling wheel and second shaft bearing noise.
The test to verify if motor-induced noise plays a role is simple. Useing a synchronous motor belt-drive turntable. The motor is first powered directly by the AC supply line. After listening, the direct AC supply line is subistuted with a motor drive supply (DMD) that generates an internal sign wave, thus isolating the motor from the AC line noise. The difference is stunningly apparent because eliminating any type of noise transmitted from the motor through the belt then into the record support platter always improves the sound.
A synchronous motor (synchronous motors are frequency locked, not feedback locked) of just enough torque (small motors equal low noise- large motors add more noise) is my choice. Some say much torque is necessary to overcome groove loading. Groove loading will, to a very minuscule degree, reduce the speed. Most any quality turntable with a heavy platter will have enough inertia to keep the micro speed changed invoked by signal modulation groove loading to a level completely undetectable.
The direct-drive motor: The name indicates the absence of isolation from the motor to the platter. Direct drive turntable motors can exhibit cogging the amount of this cogging is determined by the pole number and the inertia (weight) of the platter. Hunting can be a problem if the feedback servo is lacking in definition.Direct drive motors do not use an oil well bearing.
The rim drive (idler) is plagued with problems. The reason it came into existence is; in the past, motors with torque enough to rotate the platter were of the induction type and operated at high speed (1800 rpm). The Idler drive allowed enough speed reduction (16-33-45-78 rpm platter speed) and made for a compact design. More bearings and a hard drive wheel that generates and transmits noise are a real detriment to sound quality. Some early turntable manufacturers added a belt to the equation ( Thorens TD124) to tame the motor noise presented to the platter. But this did not eliminate the rolling wheel and second shaft bearing noise.
The test to verify if motor-induced noise plays a role is simple. Useing a synchronous motor belt-drive turntable. The motor is first powered directly by the AC supply line. After listening, the direct AC supply line is subistuted with a motor drive supply (DMD) that generates an internal sign wave, thus isolating the motor from the AC line noise. The difference is stunningly apparent because eliminating any type of noise transmitted from the motor through the belt then into the record support platter always improves the sound.
My Secrets to Turntable design
By George Merrill
The Turntable system ( turntable/ arm/ cartridge) copes with 4 types of energy intrusion, as stated in Thoughts on Turntable Design.
In order to design the AR modifications and the Merrill Turntables I designed and constructed a device I called the Vibration Intrusion Table along with a vibration pickup transducer. The operating frequency is from .1 HZ to 100 K HZ. The VIT allowed me to analyze important design points. Testing the ability of a turntable to effectively decrease the mechanical input from the platform supporting the turntable. The intrusion of airborne acoustic energy. Testing the different parts within the turntable for resonance frequency and top.
As a side note, the results from tests of mechanical intrusion lead to the design of the Stable Table support stands and the Energy Absorption Plate (EAP). These products were manufactured over 35 years ago.
This brings me to the first point of the paper. Which type of turntable, suspended or non-suspended, is better at isolating energy from both airborne and mechanical intrusion from the support platform. The tests prove a conventional suspended turntable is generally better. The (springs Heirloom) (Rubber elastomer Merrill-Willians) (Sorbothane Isolation Pucks PolyTable Signature) allow good isolation from mechanical input vibrations. If properly designed, the sub-chassis will act as a tuned low pass filter. In order for the filter to perform effectively, the total mechanism resting on the suspention must have a balance between weight and self-resonance. For instance, most effective suspended designs have a less bulky platter. Thus allowing for a more supple suspension, lighter springs allow less energy intrusion into the sub-chassis. The suspended turntable can be designed to control energy to very good degree. This is the reason the old AR was such a good design and to this day still a highly regarded product.
There are three major drawbacks to the spring-suspended turntable.
In order to design the AR modifications and the Merrill Turntables I designed and constructed a device I called the Vibration Intrusion Table along with a vibration pickup transducer. The operating frequency is from .1 HZ to 100 K HZ. The VIT allowed me to analyze important design points. Testing the ability of a turntable to effectively decrease the mechanical input from the platform supporting the turntable. The intrusion of airborne acoustic energy. Testing the different parts within the turntable for resonance frequency and top.
As a side note, the results from tests of mechanical intrusion lead to the design of the Stable Table support stands and the Energy Absorption Plate (EAP). These products were manufactured over 35 years ago.
This brings me to the first point of the paper. Which type of turntable, suspended or non-suspended, is better at isolating energy from both airborne and mechanical intrusion from the support platform. The tests prove a conventional suspended turntable is generally better. The (springs Heirloom) (Rubber elastomer Merrill-Willians) (Sorbothane Isolation Pucks PolyTable Signature) allow good isolation from mechanical input vibrations. If properly designed, the sub-chassis will act as a tuned low pass filter. In order for the filter to perform effectively, the total mechanism resting on the suspention must have a balance between weight and self-resonance. For instance, most effective suspended designs have a less bulky platter. Thus allowing for a more supple suspension, lighter springs allow less energy intrusion into the sub-chassis. The suspended turntable can be designed to control energy to very good degree. This is the reason the old AR was such a good design and to this day still a highly regarded product.
There are three major drawbacks to the spring-suspended turntable.
One
The low resonant point (3-6 HZ) of the system is subject to footfall problems. A stable platform is necessary. Not a major problem with the M-W or PolyTable Signature.
Two
The tonearm is energy connected to the platter bearing. This can be a major deterrent to energy management if not designed properly.
Three
The motor is decoupled from the platter and sub-chassis. This can cause a torque recoil problem ( not a problem with the PolyTable or Merrill- Williaams). To overcome this problem with the design of the Merrill Heirloom, I developed the constant resonant tuning system for the Heirloom sub-chassis. This allowed the sub-chassis to have the constant energy input band when using any tonearm and afford inertia to stabilize the sub-chassis from torque recoil.
Most non-suspended turntables rely on mass to lower the intrusion of energy. The problems are: Most of these non-suspended turntables are manufactured using materials in the energy conduction path that conduct energy to a high degree (metal, glass and wood). Energy moves freely within the mechanics of the turntable. There is not a filter within the turntable to act as a barrier to mechanical intrusion. Some try to achieve this with feet. The feet will help, but due to the stiffness necessary to support the total weight of the turntable, they are not a totally effective filter.
The Merrill- Williams R.E.A.L.
The M-W utilizes a 14 lb rubber elastomer to isolate and absorb energy.All of the parts motor, platter bearing, support feet and tonearm mounting are suspended in a rubber isolation barrier. These operating parts are totally isolated and completely energy damped. Their is NO metal, glass or wood in the energy conduction path. A outer skeleton is used to contain the elastomer. The design is so radically new that a 18 point USA patent #8,406,112B2 was granted.To understand why it works so well try this experiment, use a bar of metal and a stethoscope. Strike one end while listen to the other. Energy moves freely. Try it with rubber. No transmission.The other problem that was eliminated by mounting the motor in the same rubber elastomer as the spindle bearing eliminating torque recoil.
The Most Dramatic improvement in turntable design in 30 yearsNot in production at this time.