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Bel Canto Furutech Ortofon Project
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FOR
THE RECORD: THE ROCK V MAX TOWNSHEND and PROFESSOR JACK DINSDALE Specification
BACKGROUND:
ANALOGUE RECORDING AND PLAYBACK The
Rock V Headshell, paddle, trough and cartridge when playing. Without
the trough, the headshell would have to rely for support on the
arm tube, and hence on the bearing which is over 20 cm away. Even
if the arm were damped at the bearing, a lot of vibration can
happen over those 20 cm and if the arm is wholly undamped there
is nothing to restrain it. What is more, the arm resonance at
around 10 Hz will be at best only loosely controlled. This means
that at the slightest provocation (such as any transient information
in the groove, from warps to cymbals) the arm will want to wave
to and fro at a frequency of 10 Hz in antiphase to the stylus.
Worse still, the large stylus excursion that this entails will
cause the generator assembly to approach the limits of its travel
where linearity is least good, and the output will be unduly distorted
and intermodulated with the 10 Hz signal. Against all these potential disasters, the trough is a uniquely effective and elegant safeguard. Its effect is to impart a 'viscous drag' on the arm, which is proportional to its speed of movement. So at low speeds, where the cartridge has to cope with tracking warps and changes in groove pitch, the drag is negligible; but at higher speeds the drag increases so that at frequencies of 20 Hz and over the arm is effectively locked into position. In the critical frequency band around 10 Hz where the arm tends to resonate, the drag has been adjusted (by suitable choice of oil viscosity and paddle dimensions) to damp the resonance "critically", reducing its effects to a negligible level. At the other end of the spectrum, the fact that the trough paddle is rigidly mounted very close to the cartridge by way of the double outrigger space frame assembly means that the cartridge is rigidly supported to a much higher frequency than it would be by the arm alone.
Frequency
Response and Rumble
Changing records is simple: the pickup is lifted from the record and the paddle is placed at the right hand end of the trough as shown in Fig 3.
Paddle in right hand end of trough. Much thought has gone into the design of the trough to make it as easy as possible to use and to prevent spillage of the trough fluid. Two conveniently positioned opening handles come naturally to hand. Silicone oil is basically harmless; it won't damage furnishings or clothing – it slowly seeps away. If it is spilled on polished wood, cleaning up is easy – remember that silicone oil is the basis of most modern furniture polishes! Full instructions for cleaning silicone oil from records are provided in the operating instructions. When records are being changed, the arm is parked so that the paddle rests in the right-hand end of the trough. When the arm is locked in the armrest, inevitable drips of fluid are caught in a small funnel fitted directly underneath the paddle as shown below
Clamp released, trough open, arm in armrest. Having thus proceeded from stylus to cartridge body to headshell, we come to the trough, which is fixed, by means of two very stiff pillars, to a heavy, rigid plinth. This plinth is made from a composite material (steel, acoustic damping and Herculite Plaster-of-Paris) chosen for strength, rigidity (stiffness) and damping; it has the lowest possible tendency to stretch, bend or resonate, as can be appreciated by tapping it. The plinth links three major components: the trough, the arm and the main bearing. The main bearing must support the platter as it rotates, without introducing any rumble or other vibration into the platter or plinth. To achieve this, The Rock V has a precision bearing using a hard steel ball against a polished case hardened shaft. The bearing support, like all other parts of the deck, is set into the plinth for rigidity, but is adjustable if necessary for azimuth setting. The platter is manufactured from high density polyethylene (HDPE) plastic mated to a disk of D Flex acoustic damping sheet which in turn rests upon a solid glass disk. HDPE was chosen because it has an acoustic impedance similar to that of the vinyl, from which records are made and is naturally homogeneous. Matching the impedance ensures that the sound wave that radiates outwards from the stylus is fully absorbed, without reflection, into the platter. Where there are reflections, due to the platter having a very hard surface (e.g. acrylic) or a very soft surface (e.g. felt) the sound becomes full slightly reverberant and blurred. This phenomenon is known as “vinyl ring”. It is an aberration not tolerated in The Rock V. The record is secured to the platter by means of a screw-down clamp with an adjustable raised centre section surrounding the centre spindle of the platter. This causes the record to be very slightly “belled”, giving close contact between platter and record and ensuring that any vibration of the record itself is properly conducted away into the bulk of the platter. The height of the washer may be adjusted to take account of records of differing thickness and degree of warp. With this arrangement, it is possible to flatten all but the most severely warped records. In the case of 180/200 gram pressings, the washer may be screwed right down below the record surface so as to not contact these usually very flat records. The record is restrained by the platter to within about O.1µm, and while we can't think of a way of measuring it, the results speak for themselves. A further feature of the centre washer is that it may be raised sufficiently so that a large-hole or doughnut 45 disk may be easily centred on the periphery of the adjusting ring. To prevent scratching the mirror stainless steel case, two clamp holders are provided, one on the left-hand side of the platter (for left handers) and one on the right hand side of the platter, to provide a convenient place to put the record clamp when changing records. Although the trough does the lion's share of the work in keeping the cartridge where it ought to be, the arm still has an important part to play. The ideal arm for use with The Rock V is the new Townshend Audio "Excalibur II", which includes a rigid space-frame outrigger and paddle to dip into the trough; however other arms may be used provided the double outrigger and paddle are fitted. Outwardly more conventional in appearance than the deck, The Excalibur II nevertheless represents the same degree of thought and attention to detail – a full description is given later in this paper. Fig. 3 shows how the arm base pillar is attached to a thick, non-resonant polycarbonate arm plate, itself screwed (with adjustment for setting overhang) to four mounting points set into the plinth. This completes the loop of firm supports for the cartridge, as shown in the diagram. Compare this with the conventional deck, where the cartridge is about as far from a firm support as possible. Drive to the platter is supplied via a circular flat belt by a synchronous motor. Voltage selection (220-240 or 110-120) is by way of a wire link in the motor compartment. The Rock V can be supplied for 50 Hz or 60 Hz working. The motor is switched on and off by an attractive push-button switch that lights blue with the Townshend Audio logo visible. The light is dimmed when the power is connected and the motor is off. Finally, just as no structure can be perfectly rigid, it cannot be completely immune to external vibration either. To reduce external structure-borne vibration from entering the enclosed sub-chassis by up to 40 dB, the Rock V incorporates a unique three-point suspension similar to that found in aerospace instrument mounts. The spring bellows-damped suspension is located as close as possible to the plane of the centre of gravity of the deck to provide optimum stability. Each suspension unit comprises a “soft” coil spring which is enclosed in a rubber concertina bellows sealed but for a very small (1mm dia) hole in one end. The spring rate is chosen to form a very high Q resonant system with a fundamental resonance of about 2Hz as shown in fig? as 0.05. where the resonant peak is high (amplification at 2Hz) but the isolation above a transmissibility of 1 (equivalent to 2Hz) is very high. If the springs were used alone, the isolation would be very effective, but the bounce resulting from a large external disturbance would be intolerable as the oscillation could last for minutes. The bellows/small hole arrangement however, acts as a viscous brake on the oscillation as the trapped air in the bellows must pass rapidly through the hole as the assembly moves. The friction loss as the air passes through the hole rapidly dissipates the spring/mass energy (C/Cc=2 above) and the suspended structure quickly settles down. When at rest, however, minute vibrations in the base structure will cause only a very small amount of air to pass through the hole which it will do without restriction, so there will be no damping, so that C/Cc = 0.05 or less will pertain. Thus we have the best of both worlds – maximum isolation with minimum oscillation. The three spring/bellows assemblies have threaded fittings that mate with threaded shafts to allow for fine level adjustment. When the turntable is sitting normally, this suspension is so effective that the sound from The Rock standing on a normal table or bookcase surface is only slightly affected when the surface is struck hard. When mounted on the Townshend Audio Seismic Sink Stand, the isolation and resulting in purity of reproduced sound is further enhanced. The underside of the suspension is attached to the turntable base which incorporates four adjustable feet at the periphery to allow levelling. For safety during transport, locking catches are provided, accessible when the platter is removed, to lock the sub-chassis securely down onto the thick steel base. The motor is attached to the turntable base via vibration isolating mounts, so that any vibration it generates is isolated from the sub-chassis. An extremely attractive, soundproof glass lid, with counterbalanced opening top and mechanically linked opening front is available as an optional extra. Now
you know why we have gone to such lengths to get the Rock's engineering
just right – and naturally, we have also given such a lovingly
crafted product looks to match its performance – but how
successful have we been? To say "very" would be both
facile and pointless. Instead, because the design of the deck
has been a rational process, based as far as possible on satisfying
known physical principles, we are able to point to specific areas
of improvement over other decks and also – who else does
this? – give reasons. The
trough also contributes largely to the unique sound. By reducing
the effects of arm resonances to virtually zero, as shown in Fig.
2, it ensures that the signal from the cartridge truly represents
the signal put on the record, neither more nor less, not modulated
by low frequency signals and not full of high frequency rattles.
It even aids the tracking of warps, contrary perhaps to instinct,
because undamped arms tracking warps will invariably resonate
badly, with severe ill effects. The maximum stylus excursion when
tracking warps is actually less with damping than without. Not
only does the trough improve the deck's sound, but the amplifier's
too; since the amplifier no longer has to deal with low frequency
garbage (either by filtering it out or by amplifying, depending
on the subsonic characteristics of the particular amplifier),
it can concentrate its efforts on amplifying the music signal.
Amplifiers, which pass subsonic frequencies, can cause undamped
decks to damage loudspeakers by their low frequency output –
remember that few loudspeakers and especially valve (tube) amplifiers
can handle much power at 10 Hz. It is a remarkable fact of audio reproduction that the ear interprets pitch instability, under certain conditions, as a lack of dynamic range. This is certainly true of "dynamic wow" - slowing under load -in a record deck. The heavy platter and high quality drive on The Rock reduce this effect markedly compared with conventional designs and the result is a considerable increase in perceived dynamics. Observation of the output power meter on an amplifier fed by a Rock reveals that comfortable listening levels are actually lower than normal; the absence of subjective compression of transients causes this. Listening to a Rock V, one comes to realise just how full of resonance-induced foibles is the output from other decks. Long-term listening is far less fatiguing than with other players (or, of course, with CD), a sure sign of reduced levels of spurious output. The ear generally does not detect low-level spurious signals directly – the brain filters them out automatically – but it lets let us know that it is doing so by becoming tired after a few minutes and starting to lose focus and concentration on the music. This effect does not happen at a live concert (of acoustic instruments, anyway) and it does not happen when listening to a good analogue recording via a Rock. The sound of a Rock, equipped with Excalibur and a good cartridge and played through high quality amplifiers – for example the Townshend amplification and Townshend Isolda cable into Townshend Glastonbury loudspeakers – is possibly the most natural, lifelike experience this side of a first-generation master tape. Even clicks and scratches are less audible on a Rock V. It has long been appreciated that most ticks and small scratches on records are equivalent to a single cycle of 10-15 kHz, in itself barely audible; and yet these same scratches throw most record playing systems into resonances which can last up to 50 times as long as the original tick, and are certainly very audible. In the Rock V, resonances right across the band are so well suppressed that for once we can approach closely the ideal of the inaudible tick. The effects are simply over so fast that the ear does not notice, and mildly 'clicky' records can become enjoyable once again. Townshend Audio is the only turntable manufacturer to advocate direct comparison of LP sound with that from open-reel tapes copied from the original master (as we regularly demonstrate at hi-fi shows). This test shows up in an instant the serious limitations in performance of conventional turntables – The Rock V stands close to master tape sound! If a turntable assembly cannot reproduce the master tape sound, it is inaccurate
Excalibur II arm with Townshend Audio “The Grail” cartridge. Compared with the obviously unique aspects of the Townshend Audio turntables, the Excalibur II arm similarly appears very unusual. Look at the peculiar features: the small paddle at the front, the way the headshell is attached to the arm tube, the length. In fact, Excalibur II reflects just the same design principles as The Rock V: Kinematic design and resonance control. Resonance control is an obvious requirement of any mechanical means of reproduction, since resonance implies added, spurious information in the output signal. Kinematic design demands the minimum number of mechanical restraints (e.g. three mounting feet rather than four), and that all the forces to pass through the centre-of-gravity. This principle, well established in precision machinery, reduces turning moments on parts of the system and improves stability, which is clearly beneficial in as precise a machine as a record player. So we find in the Excalibur II that everything possible is damped and that forces are arranged to act in or near to a plane co-incident with that of the record surface as it rests on the platter. The headshell is made from magnesium, a material with good self-damping properties and high specific stiffness (stiffness per density). The magnesium piece used is angled for high rigidity and includes a small paddle for use with the damping trough on Townshend Audio decks. For the utmost rigidity, space frame assembly is arranged to grip the paddle to couple the paddle as securely as possible to the cartridge. Cartridge mounting to the headshell is unusual in using tapped holes in the headshell. This is to ensure that cartridge offset angle is accurate (adjustment is then reduced to overhang only, easily done with the Townshend 'Elite Alignment Gauge') and has the additional virtue of making cartridge mounting easy and safe using socket screws from underneath. Viewed from above, a straight line joins stylus, paddle, arm tube and bearing, providing maximum resistance to twisting and bending under stress. The headshell is fixed to the arm by means of a scarfed joint, which offers not only very high torsional stiffness and strength close to the cartridge mounting position, but also a large area of contact with the arm. The joint is held with three high tensile pins and also glued. The arm tube uses thin-walled stainless steel as its basic material. Stainless steel is heavier than the more commonly used aluminium, but its specific stiffness is similar and it can be made into thin-walled tubing of larger overall diameter, which increases rigidity for a given mass. Importantly, its speed of transmitting sound is very high and it is this that determines the upper frequency limit at which the arm can be considered rigid. To increase this limit even further, the arm is significantly shorter than standard, a compromise with tracking error which nevertheless hardly increases tracking distortion. To further increase stiffness, the arm pipe is rigidly clamped by two high rigidity screw clamps to the lower short arm stub which has its centreline in the plane of the disk and the horizontal bearing axis. The inside of the arm is filled with a low density polyurethane foam which damps arm resonances and, in conjunction with the front-end damping, reduces arm-induced colorations to the barest minimum. Although the front-end damping trough considerably reduces the requirements of an arm, experience has shown that the entire arm, and especially the bearings, must still be of the highest possible quality (in other words, working without a trough places impossible demands on any arm, and especially on the bearings). The Excalibur II uses high grade, large diameter ball bearings. These are very strong; the horizontal bearings have a maximum working load of 0.3 tons. The point of using such bearings is to give maximum mechanical coupling between arm tube and arm mounting. Normally, bearings are lubricated with relatively light oil and tightened as far as possible without impeding movement, but this results in a mechanical coupling which is at best point-to-point and at worst highly temperature sensitive. In the Excalibur, the bearings are adjusted so that under normal conditions there is a very small amount of play detectable; this ensures that under extremes of temperature they will not start to seize, nor will friction vary with age. However, at signal frequencies (which is what counts), oil provides excellent coupling across the bearing, just as it does in the damping trough, ensuring that bearing rattle cannot occur. This arrangement also gives low bearing friction. In effect, the bearings "lift off” due to the oil running between the bearing surfaces by capillary action, eliminating metal-to-metal contact which in any bearing is the major source of bearing noise and wear. The dual counterweights at the rear of the arm are slung low to keep the centre-of-gravity close to the plane of the record surface and the mass as close as possible to the intersection of the bearing axes, thus keeping the moment-of-inertia and hence effective arm mass as low as possible. A wide range of cartridges may be correctly balanced, statically and dynamically, by means of these counterweights. Tracking force is applied by calibrated coil spring to ensure that the centre of gravity of the arm/cartridge assembly remains at the point of intersection of the vertical and horizontal axes. This is vital to ensure that the least amount of sound degradation is caused by external vibration. If the centre-of-gravity is not at the intersection of the bearing axies, translational vibration will cause a turning moment and hence a sound when the arm base is forced to translate due to external disturbance. Bias compensation is provided by a calibrated adjustable magnet mechanism which gives precise, friction free force for perfect bias operation. The arm bearing assembly may be raised or lowered and then securely locked in place to set the optimum vertical tracking angle (VTA). The
internal Excalibur arm wiring is by four bundles of ten-strand
ultra-thin Enhanced Deep Cryogenically Treated (EDCT) pure enamelled
copper wire terminated in the base of the arm with a gold-plated
5-pin DIN connector. The connection from the base socket is by
a gold plated 5-pin locking DIN plug wired with two EDCT small
diameter copper wire closely twisted pair for the two stereo channels,
both encased in two thin-walled PTFE tubes. Both cable assemblies
pass through large diameter ferrite radio frequency (RF) filters
at the amplifier end adjacent to the locking gold-plated phono
connectors. A single insulated trailing ground wire connects from
the DIN plug to a spade connector for the chassis earth. If you wish to use your own arm, then a double outrigger and paddle assembly is available to realise the full benefits of front-end damping.
Double
outrigger and paddle, One part of the outrigger is placed on the top of the headshell and the other part below, above the cartridge and the lot rigidly bolted together. The assembly must be arranged so the paddle, stylus and arm bearing intersection are in a straight line to reduce unwanted and unnecessary turning moments. Suitable arm-plates are available drilled for all common arms. Completing the partnership with a top flight moving coil cartridge and the purpose built TA732 Townshend Audio Phono stage feeding the Townshend Audio amplification and Glastonbury III speaker system produces a sound off vinyl that experienced critical listeners describe as astonishing. The lack of gramophone noise is the most striking aspect. There is no rumble, minute surface noise only noticeable during silent tracts at very high volume, and virtually no clicks. The music, however, is entrancing! Words cannot describe the aural experience – that’s a job for your ears! Townshend Audio has been developing high fidelity audio system components and accessories since the 1970s Accessories
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