Acutus Design

The uncompromising approach to design, from concept and choice of materials to finish and execution has produced a turntable that sets new standards in vinyl replay. Rather than looking at existing designs for inspiration, to embellish or re-engineer we started from a clean sheet, not only going back to first principles but using an "outsight" principle of design for each component. A jigsaw of parts, each essential to form the final pictorial transparency that is the music you hear, and not the equipment you play.

The purpose of the turntable is to support a pick-up arm and cartridge, spin a record at a constant speed, isolating the stylus interface from unwanted energy originating from the stylus itself, drive motor and outside world, which causes loss of information and distortion. For explanation, turntables can be divided into three major elements; 1.platter/arm/subchassis loop, which must be a rigid system, transmitting any vibration near the stylus to the subchassis; 2.main chassis/suspension which isolates it from the outside world. 3.The motor which supplies the power to rotate, free from vibration and instability.

The stylus, as it traces the groove will make the record vibrate and uncontrolled will cause loss of information and distortion. Current remedies include acrylic platters or various mats. Acrylic platters, whilst offering impedance matching, have the same frequency characteristics as records, hence will be excited by the resonating LP becoming one large vibrating mass. The stylus reads this vibration, producing a sonic signature common to all acrylic-based turntables. Mats in contrast allow the record to vibrate locally or at selected nodal points. This produces instability as the stylus traces the groove leading to loss of information and distortion.

Rejecting compromise, research into polymer engineering and clamping evolved our unique "energy transmission" system. The aim; record stability, freedom of vibration at the stylus.

Using our bonded polymer surface for the mat, which is designed to reflect angular energy and decelerate vertical energy, the record is clamped uniquely, directly to the main bearing, which is raised at the centre. The act of clamping makes the record more rigid, aiding its energy transmission properties. Flattening the record to the polymer surface provides a stable groove to be traced.

The result; a record free of resonant feedback allowing more information retrieval, lower noise floor, focused sound and pin-point soundstaging.

The energy created by the stylus enters the main bearing, designed to pass energy to the subchassis one-way, much like an electrical diode. As the energy produced is equal and opposite, vibration enters the pick-up arm and is ideally transmitted to the subchassis mounting. The bearing is inverted for several reasons; crucially the point of contact is only 4mm from the record aiding rapid energy transfer. A high centre of gravity to give stability and reduced noise. The point contact, made from a sapphire cup jewel and tungsten carbide ball rotates concentrically. Commonly used bearings running on flat plates allow lateral platter movement causing loss of information. The supporting shaft is 16mm diameter through hardened stainless steel, tapered to the top. This prevents standing waves and creates the diode effect, friction fitted to the subchassis increasing rigidity.

One piece complex aluminium casting forms the subchassis. Most designs emphasise rigidity and damping, a contradiction as the more rigid an object the less it will damp. Take a flat sheet of paper, not very rigid until its folded, strength increasing more than 10 times. Any movement of the pick-up arm relative to the platter results in lost information, hence the link between arm mounting and bearing has to be the most rigid. For this reason no arm boards are used, the mounting integral with the casting. Three folds in the casting provide massive strength in this crucial area.

Assuming that infinite rigidity is impossible this design puts strength were its required and uses weakness to dissipate energy rapidly. The next in importance, the suspension points, are located on the end of shallow folds, with no strength being added to the flat panels between. These flat sections are less rigid and dissipate energy rapidly without loss of information. The irregular grain size and pattern of the material dissipates energy more effectively than extruded or rolled material and the paint finish applied has been developed to assist energy release by controlling material skin tension. Again, with no parallel edges, standing waves are eliminated. The platter/arm/ bearing loop is complete. Also free standing of the suspension enables easy, accurate cartridge alignment. This "loop" must now be isolated from external disturbance, a major cause of distortion, especially in the frequency extremes.

Isolation of the "loop" is essential, otherwise structural energy reaches the stylus leading to distortion. Traditional isolation techniques include springs, airbags, rubber, spikes or nothing, relying on sheer mass. None to our knowledge work, confirmed by putting the turntable on different structures. If the sound changes, the loop is not isolated and loss of information and distortion occurs. Rubber, spikes or mass loading act as filters, usually just shifting the problem to get a sonic change. Springs however are isolators above a certain frequency, therefore the lower the frequency the greater the isolation. Existing designs use three or more spring points to suspend the loop, but all suffer the problem of instability and erratic, uncontrolled movement caused by differential spring loadings, a result of uneven mass distribution of the loop. Uncontrolled suspension also causes most of the problems associated with speed instability in belt drive designs when the distance between platter and pulley changes. There is a tendency for the subchassis to try and rotate around the bearing causing both wow and distortion.

Again rejecting compromise to develop our unique frequency adjustable suspension. Using three extension springs giving low centres of gravity and stability, each spring is equally adjusted regardless of load. When the "loop" is level to the supporting base all springs react equally giving perfect stable vertical movement. High platter mass allows a low 2Hz suspension setting within compact dimensions. Especially designed spring termination prevents subchassis rotation. Achieving perfect vertical isolation however highlights other problems. Rocking modes as the "loop" tries to topple over, pulling of the drive belt and external movement. Lateral damping rings in line with the drive belt and stiffer than the vertical provides a perfect solution. Rocking modes are rapidly damped and energy transferred to vertical motion, also damped by the rings lateral tension. Being parallel to the drive belt stops rocking and allows maximum delivery of motor torque.

Traditionally motors driving turntables have been low powered AC synchronous devices driving high mass platters. More recently DC and multiple motors have been used, trying to achieve speed stability through rotational inertia of the platter. Motor noise transmitted to the "loop" and cogging, all problems to be solved. During playback the platter is subject to varying stylus drag which, despite the flywheel effect puts load on a weak motor, loosing synchronicity, massively increasing vibration.

Contradicting current trends an extremely powerful singular AC synchronous motor is used to drive the 10Kg platter. In contrast to other designs, the motor controls platter speed. The motor output of 130mN-ten times the power of conventional units-is completely rebuilt to reduce vibration and noise to exceptionally low levels. Powered by a state-of-the-art, split-phase quartz-locked purposed designed power supply keeps motor speed precisely constant. Using a round section belt without retaining groove ensures no speed variation, even with the suspension oscillating. The high mass of the platter in conjunction with belt compliance eliminates any cogging present.

With all our designs we look for improvements were it's possible. The lack of changes over the years, especially in comparison to other designs, clearly shows we spent the time doing it right first time. Time well spent then offers you time well spent listening now.