Refent Audio ultimate turntable

All REFENT AUDIO sculptures except GRAMOPHONE UNIT have the rectangular shape. That makes possible to combine those components creative and to form and place the complete sculpture in area of own wishes and taste directions. Those sculptures are 50cm wide and deep, and 15cm high, to make it possible to be noticed as a special art design object in your space. It makes the look and feeling  like  one Bauhaus-Art-Sculpture from the Twenties in front of you. No product has visible display. The massiv alloy buttons have also this massiv-retro-touch-feeling. All products are hand made with the most nice special old times aspects.

What should an excellent turntable do?

1. The platter should rotate constantly with the chosen speed without any variations due to different load during play back.
2. The turntable should be as immune as possible to any disturbance coming from outside.
These disturbances are:
A. Borne noise:
These are all disturbances which reach the turntable by material contact from outside. Examples are a vibrating floor, due to the music played, whose vibrations are transferred by the stand the turntable is placed on. Or any other vibrations reaching the mounting area of the turntable, like footsteps or other vibrations.
B. Airborne sound:
This is any kind of energy which is transferred by the moving of the air inside the listening environment. The most significant source is the music played. “Sound” is a variation of air pressure, which is also a force, that can interact with the reproduction of the tiny information in the grooves. Worst case is feedback, which is a high wheezing sound.
C. Electromagnetic interference:
The cause can be a transformer placed nearby, HF-emissions from a handy or the magnetic field of a magnetic bearing.
3. Disturbances that are produced by playing a record:
A. Any kind of noise generated by rotating the platter, as noise from the driving motor or the bearing of the motor.
B. Any kind of noise generated by the bearing of the platter.
C. Vibrations, which are generated by the play back procedure. Just listen to a record played, with the speakers switched of. You can hear some of the music, just by the mechanical process of tracking a record. That is quite some energy, which shouldn’t cause any resonances or reflections. This energy must be channelled to a place, where it can do no harm – the mounting surface of the record player and finally the floor.

How we solved this duties:
To get a constant speed from the driving motor, we use a quartz- driven PLL. To explain this: A quartz gives a stable and constant frequency, accurate to 0,0001%. In the motor we have a hall-generator, which gives 200 pulses per revolution. Now the frequency of the quartz is divided, till it´s also 200 impulses for the given time of one revolution. Than both pulses are compared and the speed of the motor is regulated, that there is no difference. Execution of such a PLL not easy, because the reaction time is critical, that there is no cough or low frequency variation of the speed.
We did some measurements of speed accuracy of the motoron our HP 5371A counter, feed by an optical encoder, which was mounted to the platter. You see the distribution of 1000 measurements taken.
The deviation is from left to right of the display window: -0.001% to + 0.002%
This big pulley has some advantages:
Platter speeds are 33 1/3 or 45 revolutions per minute. This equals a frequency of: 0,55 Hz (33 1/3rpm) 0r 0,75 Hz (45rpm). In case the pulley has a diameter of 1,5 cm, like commonly used, so we got a frequency of the pulley of 11,1 Hz (33 1/3rpm) or 15 Hz (45rpm) Whatever rotates makes some noise and also the related harmonics of the fundamental frequency. For 33 1/3 platter speed, the 2nd to 10th harmonic are in the area of 22,2 Hz to 111 Hz, which is well in the audible area.

Our Pulley has a diameter of 16cm. By this diameter results a frequency of the pulley of 1,1 Hz (33 1/3rpm) or 1,5 Hz (45rpm). All the harmonics up to the 10th are well below the audible area. 

Our Pulley has a weight of 1,6 kg. So the pulley also operates in the way of a fly-wheel. By the inertia, the drive of the platter has much less variations, than one with a smaller pulley.
The bigger diameter of our pulley also has another advantage: A standard pulley of 1,5 cm diameter only has a contact area between pulley and belt of about 1,6 cm, while with our pulley the contact area is 16,75 cm. This much bigger area of contact means much less slippage of the belt equals higher torque. We accomplish torque-values of an idler drive turntable, without the disadvantages of an idler drive (noise). By having so much contact area and torque, we don´t need a high tension of the driving belt, which results in less disturbances from the motor transmitted and also less horizontal force on the bearing.

All parts of the pulley and motor housing are optimized for minimum resonance and high internal damping. The motor is fed by an external DC power supply. Optional available is a battery power supply with internal automatic charger. 

Just to show what we mean by optimizing the resonance behaviour:

After some damping measures were taken, the resonance is down a bit, but not satisfying. Some more damping measures finally gave a satisfying result – no resonance, no more ringing:
We use an air bearing, normally used in highest precision laser applications. The concentricity is 0.1 micron. The camp takes both horizontally and vertically. Thus, no running noise by the rotational movement can be expected. Also the air bearing is maintenance free and has no wear.
The air bearing is designed to hold a load of 160 kg. a force horizontally to the axis of 25 kg is allowed. The tension of our string is less than 1 kg. So the air bearing is intentionally oversized about 10 times.
If we now simply would mount this air bearing, the platter could rotate perfectly and without noises and friction. However, would we have the vibration energy generated by tracking the grooves in the platter without any way to be dissipated. This would affect the quality of the play back in a very negative way.

For this reason, we have constructed an axis with a very low adjustable ground pressure over a ceramic ball and a Teflon mirror which can lead the generated vibrations to the tripod and sub chassis. The overall design of this is a world first in this form.
The platter created by us consists of two components: the support platter to which the air bearing is secured and which is driven by the belt. This support plate is made of aluminum and other metals to gain the necessary weight and inertia. That compound platter is optimized to be free of any resonances and reflections.
On this support plate is, decoupled with spikes the playback platter made of POM, which has been proven for its good sound characteristics already widely. The spikes, made of brass and additional weights, also made of brass help to avoid any resonances.

In “normal” drives the bearing axis is usually also the pin on which the record is fixed. This way any noise from the bearing then is transferred directly to the record! 

By the division of the platter, we have this problem completely eliminated.

Also another problem is eliminated: A heavy platter is needed for high inertia, to keep the speed of rotation constant. But in a heavy platter, a lot of energy generated by the vibrations of play back can be stored. This energy is also partly and without control reflected to the record. This effect is frequently heard as a loss of dynamics.
Light weight platters, as used in direct drive turntables or idler drive turntables have a widely spread reputation for sounding more dynamic, cause the lighter platters store less energy. By our construction we gained the advantages of both principles without the disadvantages of them!
Tone-arm base:
This component is usually constructed with conventional products exclusively according to visual criteria. It is this component that is really significant for perfect reproduction. It is crucial that the base fixes the arm completely locally stable relative to the turntable. But to avoid vibrations from motor and bearing to reach the tone arm there also should be some way of decoupling. In addition, the vibration energy generated by the reproduction process must still be discharged in a single and exactly defined way via tone arm and tone arm base.

To meet these requirements, we have designed a new tone arm base: The tone arm itself is fixed on a brass plate with eccentric bore in order to adjust the effective length accurately. (Brass plates for tone arms 9-12 inches in length are custom designed). More than 12 inches bases on request.

This brass plate is suspended on three Kevlar strings in the tube-shaped tone arm base In addition, below the brass plate a substantial counterweight is attached to keep the tone arm in a balanced horizontal position.

In principle, this suspension acts as spikes normally used to work in a horizontal direction: from the tone arm vibration energy can flow through the brass mounting plate and Kevlar strings to the sub-chassis. Interference from the sub-chassis may be transferred only very slightly to the mounting plate.

The complete tone arm base can be exchanged quickly for change of tone arms. All adjustment parameters are not affected by the change. A structure with two tone arms is not possible, since this would contradict the concept of a well-defined single path energy flow. Change of the tone arm can be done in one minute, without changing any adjustment parameters. Thus, a set arm is replaced by another in no time.
Sub chassis:
Our sub-chassis consists of two parts:
Once the tripod: On this the platter bearing and the tone arm base is mounted. The plate which supports these two components is made of different metals, which attenuate each other in their resonance frequencies. The other two arms are made of POM and carbon to ensure a secure footing. Only under the metallic support plate is a brass spike mounted, in order to guarantee a defined energy transfer path. The other two spikes are made of POM and thus acoustically insulating.

This tripod stands on a massive 6-pointed star, which is decoupled with air bearings and pillars of the installation area.

Overall, all parts are made as small as possible in order to provide a low impact surface for airborne sound.

The sub chassis is equipped with a purely mechanical self-adjustment. In this type of building an absolutely unique achievement in building turntables.
Dimensions: 86 cm width 73 cm depth 39 cm height
530 mm wide x 830 mm deep x 460 mm height Air Bearing
String driven turntable
Round supply (according to the engine can) with a diameter of 300 mm and 228 mm height
Battery power supply with battery charger for 230 V AC / 115 V AC12V 14Ah batteries with additional filter to suppress the chemical inducted noise of the batteries
Speeds: 33 1/3 U / min and 45 U / min Accuracy 0.01%
Total weight: 125 kg
Usable tone-arm:

9-12 inch length, mounting plates are manufactured to customer specifications
Stabilization: outer ring holds the record at the edge. Self adjusting dampers and an unique system, normally only used for stands of microscopes. The stability of course is only achieved by use of a huge counterweight with high resonance absorbing abilities
Other surfaces are practically feasible in every design due to the so far worldwide unique coating technology:

– Pure Gold, Silver, Diamonds, carbon, wood finish, stone look, self-chosen motifs, stealth, camouflage, and much more.
– Rack acoustically and visually optimized to drive.
– EMV-shielding chamber for the complete turntable, to avoid any HF-interference.
We produce our products very specially and individually for every music and art sophisticated enthusiast. It takes about 8 to 10 weeks after the finished contract