Celestial Orbe

By Peter Comeau, Hi-Fi News & Record Review, May 1995

If your idea of heaven is analogue, Michell's new turntable will help to take you there.

The listeners accustomed to the comforts of Compact Disc may wonder why anyone should want to mess around with gently lowering a stylus onto potentially crackly grooves, when track selection is only a button push away. But for the seasoned enthusiast, the turntable carries a similar mystique to the steam engine. Everyone knows the modern alternative is more convenient, but somehow the magic is quite missing.

And know the vinyl enthusiast has another super-deck to drool over. Developed from the internationally famous GyroDec (but not replacing it), the Orbe is a massive and magnificent creation in black and perspex that will dominate your living room.

Gone are the famous Michell brass weigths, which both added inertia to the platter and lowered the centre of gravity. New is a twice decoupled case, ensuring super isolation from structural and motor vibration.

Construction

For those who are not familiar with the creations of John Michell, the basis of each of his turntables is precision engineering in both plastic and metal. Perspex is chosen for its fine machinability, excellent finish and self-damping properties as well as its visual elegance. Brass is used to add mass where necessary, bronze for smooth running bearing surfaces, and aluminium for casting and low mass parts.

Performance hinges around a high inertia platter lightly driven by an isolated motor assembly via a large, round-section belt. The platter is placed on an inverted bearing, chosen to lower the inertial mass below the pivot fulcrum and to even the side thrust on the bearing shaft. The bearing is a cunning assembly, designed to overcome nearly all conventional bearing problems. Machined in one operation from solid bronze to ensure accurate centring of inner bore and outer circumference, the bearing sleeve locates a screw-in stainless steel spindle which carries a centre machined cone to locate a hardened thrust ball. This machining method halves any alignment error to centre the ball accurately, reducing the precession of the ball in the bearing which Michell is sure is the main cause of rumble.

The heat-hardened bearing shaft is equally ingenious. Inverted bearings usually suffer from lack of lubrication. Here, in order to use a light machine oil and coat all bearing surfaces, a minute groove is spiralled up the inside of the bearing housing. As the bearing rotates on the shaft it forces oil up from a small reservoir at the base of the shaft. So efficient is this pumping action Michell found the platter was being forced up by hydraulic pressure in the prototype. Accordingly, an off-centre oil return bore is machined into the shaft to allow the oil to circulate.

Located on a flange on the spindle, and screwed down by a large diameter nut to prevent rocking modes, the platter is built up from carbon and vinyl damped acrylic. This is a large assembly rising 60 mm above the chassis, and hollowed out to place the mass at the main moment of inertia, while still being thick enough to avoid any bell-like resonance modes. The final portion of the spindle locates the record centre hole and has a two-start thread for the aluminium puck. The double helix avoids the possibility of cross-threading, and ensures only a few turns are necessary to tighten the puck on to the record label: so preparation for playing an LP is not the laborious ritual it is with some clamping systems. A thin domed washer under the record label forces the grooved area into contact with the acrylic platter surface. This effectively flattens out warped discs.

One further design aim was to balance the suspended chassis dynamically. Michell was not happy with the conventional asymmetric three spring support which is supposed to take care of differing arm weights by adjustment of the individual spring height. For a true 'bounce', dynamic balancing of the moments around the springs was considered essential. The springs are arranged at 120 degrees intervals with the arm mounting placed equidistant between two of them. Lead weights are fitted to the periphery of the chassis on the two sides opposing the arm mount, with all other empty space on the underside of the casting being filled with a damping compound.

Michell supplies mounting plates for a variety of arms, each of which is arranged to bring the total arm and plate weight up to 1 kg. In this way the force on each spring can always be equalised. Setting the deck up is thus simplified, though the dedicated enthusiast will still find room for fiddling and tweaking.

Setting up

Large slabs of perspex form the base and friction hinged dustcover, the former being fitted with three adjustable cone feet. Once levelled, the base is fitted with a sub-base which sits on three carbon-filled PTFE inserts, dimpled to locate screw spikes. This is adjusted by eye to give a nominal clearance of 2 mm all round. The idea here is to use double mass isolation on point supports to absorb vibration.

From the sub-base rise three shafts fitted with open-coil springs; the precision sand-cast sub-chassis is dropped over these, to locate on to turned aluminium supports fashioned to the large end of each spring. The springs are thus in tension rather than compression, to eliminate any induced noise that might arise from coils momentarily touching during vertical movement. Each spring is height-adjusted by all knurled collar at the top, and centred on its shaft by rotating the spring itself. This is the only fiddly bit, but at least you are working from the top of the turntable, rather than poking around underneath where you cannot see what you are doing.

Again adjustment by eye is the best method. After alignment the springs are covered by aluminium collars for visual appeal, though dedicated tweakers might want to leave these off until they are happy with the suspension arrangement.

Your choice of arm is then fitted to the mounting plate screwed down to the chassis via three spacers and machine screws. There is plenty of room for the arm lead to exit in a short coil, affixed by a 'hockey stick' of threaded steel which clamps the lead firmly to the main base. Adjustment of the length of lead making up the extra coil can damp any out of balance movement caused by the arm being an outrigger to the circular chassis.

Finally the motor is slotted down through a hole in the base, it being encapsulated in its own heavy plinth of solid brass. Its only contact with the turntable is via the belt and whatever the plinth is sitting on, so it pays to make sure the latter has a vibration path to the floor, preferably through a spiked support.

Motor drive comes from a separate power supply and crystal oscillator, deriving a split-phase 21 V sinewave to feed the Papst synchronous external rotor motor. The enthusiast has the choice of 33 and 45 rpm pulleys on the motor, or switchable 33/45rpm output from the crystal controlled oscillator.

Sound quality

Michell supplied an SME Series V arm, which is considered a good partnership, and we placed the Orbe in two systems. One used a Goldring Excel cartridge feeding a Musical Fidelity A-1000 and ATC SCM20T speakers. The other featured a Lyra Clavis via Tim de Paravicini's Head transformer and RIAA equaliser to an AVI 2000 pre-amp driving ATC SCM200 active speakers.

Ignoring for the moment the life and energy imparted to a system by good vinyl playback, the most difficult area for any turntable to conquer is the low frequency area below 200 Hz. Subject to a high degree of boost by RIAA equalisation, the bass performance is exposed more than any other aspect of vinyl replay. Yet it is this area which impresses most as soon as the stylus hits the black groove clamped to the Orbe.

Starting with the notoriously difficult double percussion and Moog bass pedals and guitar mix of Genesis Seconds Out live recording, I was struck by the clarity and separation of instruments and an extension to the lowest frequencies that had more in common with CD.

It is here that minute suspension adjustment imparts the greatest benefit. Realignment of the springs to achieve a perfect vertical bounce, the work of only a few minutes with the cosmetic covers off, yields a smoothly extended and highly detailed bass output capable of great power and physical impact.

As soon as the suspension is tweaked to maximise the clarity of low frequency transmission, the opposite end of the spectrum suddenly reveals a harmonic structure which escapes run-of-the-mill turntables. It was quite amazing how the slightest tap on cymbals showed up even while kick drum and bass guitar were in full flow.

Traversing side one of Seconds Out to its ridiculous tiny-diameter inner groove showed an unexpected security of stylus in groove. Despite dynamics being restricted by the cut to such a tight spiral, the sound remained open and untroubled by apparent distortion with the double drumming ending of 'Afterglow' portrayed in all its glory. As the record collection was raided for old favourites it became obvious that good stylus tracking was promoted by the Orbe, and surface noise reduced, too. While groove impediments still caused the usual noise this was lowered in level, appearing behind the music rather than interrupting it. Small clicks and pops, however, seemed to have disappeared on rock records, rendering a noiseless sound more akin to CD. They still showed up on classical records during quiet passages, of course, but still seemed subdued in level to the point where they could be ignored.

Classical listeners have deserted vinyl en masse for the relative audio security of CD, but there is still a place for the black disc when searching through older performances. Sir Adrian Boult's classic Vaughn Williams symphonies, for example, have not made it to the silver disc unscathed, with a highly doubtful re-mastering rendering the CD versions sounding disappointingly tired. Dropping the Sea Symphony onto the Orbe was a revelation. The secure tracking brought out the splendour of massed choral passages in Kingway Hall, while the soloists stood forward with tremendous presence and authority.

Similarly the massed voices of the Swedish Radio Choir in Ligeti's Lux Aeterna, under de direction of Eric Ericson, were separated beautifully, with only a trace of blurring of altos and sopranos as they broke forth from the underlying tension in a burst of light. In all case the stereo image was supremely stable, completely free of the speakers, and indicating a degree of perspective which stretched deep into the distance, but brought soloists forward into the room where close miking had been employed.

Playing around with mounting surfaces showed that the Orbe, for all its double isolation, was highly sensitive to supporting methods. The best results came, not surprisingly, with individual lightweight and spiked tables such as the traditional Sound Organisation unit, the worst from tall, multi-tier units holding other equipment such as amplifiers.

Investigating the vibrational characteristics of the Orbe showed this effect to be due to sub-chassis disturbance. The extra weight of arm plate and its counterbalance masses combined with the open coil springs realise a low springing frequency sub-chassis of 3.5Hz. While the system is well damped, an impulse shock will set the subchassis in motion for a few seconds before settling. The rocking modes of the taller stands were enough to jolt the subchassis into small vertical motions which were completely absent when the turntable was placed on an individual table.

Once the Orbe had been optimally aligned on its own table, all the life and energy of the performance burst out. Out of curiosity the puck, washer, and platter nut were removed and replaced by a thin felt mat, but this brought only a blurred and imprecise stereo image with much of the bass clarity reduced to an overall bloom.

The Orbe was easy to use, and the puck proved less of a hindrance than first thought. An on/off switch on the power supply is complemented by another on the motor housing, the latter proving more convenient for record changing. As the platter comes to rest a quick twist of the puck removes it. After centring the record on the marginally undersized spindle, the puck is then tightened down until all edges of the vinyl touch the platter. This may require a certain strength of wrist while holding both platter and record with the other hand, but one quickly comes to terms with the amount of pressure that needs to be applied.

Conclusion

Overall the Orbe seems to get the best out of every cartridge fitted while adding little character of its own. For once the clamping system and platter construction and drive method seem to manage the best compromise between clarity of sound and strong rhythmic performance. The realisation is exciting and vibrant, and the detail extraction enough to make you go through your whole record collection listening anew to old favourites. Add to this the low level of noise and you have a turntable to be proud of, and one whose precision engineering will keep it revolving long enough to see the vinyl revival pass into antiquity. Highly recommended.