Oracle Delphi turntable TJN & Delphi Mk.IV part 2

Solution: contact Graham Engineering. Bob Graham modified Oracle's SME mounting plate (which uses the same cutout as his arm) by providing additional threaded holes in the bottom of the plate to accept the arm mounting bolts. He also furnished the longer arm bolts needed to reach these threaded holes. Now both halves of the plate could be fastened to the subchassis first, following which the arm could be mounted on the top plate. (Oracle is now able to provide mounting plates suitable for the Graham arm.) I should also make one other note concerning the Graham arm on the Oracle. Those who like to tweak VTA for every recording will love the Graham's calibrated scale, but may wish for a bit more available downward adjustment range in the arm on the Oracle. It's possible to set most cartridges with their back ends just below the level point, but not by much.

While the Oracle's detachable arm-mounting plates make arm-swapping relatively easy, the nature of the mounting plate and the way in which it's fastened to the subchassis (round, in a round holder) means that precise and repeatable alignment of the arm is not simple. Rotating the mounting plate in its bracket even slightly while it is being set up will change the stylus to pivot-mounting distance—except in that rare case where the arm is mounted dead-center on the plate. Turntables which provide for rapid and precise alignment of the arm mounting base or plate on the turntable are better suited to frequent arm swaps than is the Oracle. For most users, this will not be an important consideration.

The Delphi Mk.IV has a new motor made in Germany for Oracle. Previous versions of the Delphi used a low-torque DC motor; the new motor is a high-torque, low-voltage AC design driven by an 18V DC external power supply. Internal circuitry itself—located on the turntable base-plate—generates the appropriate AC signal to drive the motor. The silence of the latter, aided by its housing, damper, and mounting sleeves, makes the Delphi Mk.IV the most environmentally quiet turntable I have ever encountered: quieter than any SOTA or VPI I've ever used. Not obviously quieter through the system, but quieter with respect to noise emanating directly from the motor and other moving parts of the system. This is an important consideration if you have a small listening room and/or must sit (or choose to sit) quite close to the turntable.

The speed-control adjustments are located on the bottom front of the thick black plexiglass baseplate which forms the structural support for the turntable. They are very inconveniently located, as they are inaccessible when the turntable is mounted on a flat surface; the entire assembly must be pulled forward several inches, where it balances precariously over the front of the turntable stand as you fiddle with the inset, screwdriver-adjustable controls. The instructions indicate the presence of an additional speed control on the side of the front-and-center switch panel, but this control has apparently been deleted in the Mk.IV; at least it did not exist in our sample. In partial compensation, Oracle does provide a large, easy-to-read strobe disc.

The three suspension pillars of the Delphi Mk.IV are actually quite complex, spring-based assemblies with 13 different component parts. Suspension tuning is set at 3.5Hz. These assemblies have undergone continuous refinement since the initial Delphi. The Mk.IV has been revised to simplify setup (except for certain reviewers—see further on). The suspension is well damped with Sorbothane dampers; oscillations from floor movement die out quite rapidly.

While the ability of a turntable's suspension to isolate the record and tonearm from floor-borne vibration will always depend on environmental factors which will vary from installation to installation, the Oracle did an excellent job in my situation. Seated atop a solid support (in this case an early-model Lead Balloon) on a reasonably solid suspended floor, it would only skip when subjected to violent jumping up and down in its immediate vicinity. The same rather extreme disturbances elsewhere in the room failed to rattle it; neither did normal foot traffic, including approaching it to change the record.

Other improvements to the Delphi in its Mk.IV guise include a new bearing and bearing mounting, and in-house machining of parts, claimed to improve fit and finish. Whatever your definition of excellent build quality, the Delphi Mk.IV has it. All parts are superbly made and put together, with but one exception: the trueness of the platter itself. The Delphi Mk.IV has been in my system for over ten months—the unusually lengthy time due to waiting for associated equipment which I wished to use with it, and compare it to. When I first received the unit, I noted no problems with warpage in the platter itself, and gave it little thought thereafter. Then, in the final stages of auditioning before submitting the review, I noted that, viewed on-edge, the platter displayed a very small degree of warpage. It was barely worth mentioning, and caused no sonic problems whatsoever that I could determine. But the Oracle is, after all, a rather expensive turntable, and this minor flaw cannot be ignored. Since, to the best of my knowledge, the platter was perfectly flat as received, I surmise (and it is only a surmise) that the heavy composite material which makes up much of the platter sagged slightly over time under its own weight.

A less significant problem is the tendency of the plexiglass baseboard to accumulate fine, almost invisible hairline scratches. These should polish out with a good plastic cleaner, though the one that I tried (Meguiar's Mirror Glaze 10 Professional Plastic Polish) did not remove them.

Owners of earlier versions of the Delphi should know that upgrades to Mk.IV status are available. They are not cheap—$795 with all of the recommended pieces except for the Turbo power supply, which will up the total cost to about $1245 [in 1991—Ed].

I've said it before but it bears repeating. Any dealer selling high-end turntables should be able to set up those turntables for his or her customers. The Delphi Mk.IV is no exception. Still, in the real world there will no doubt be situations where you, the user, will either perform the initial setup or wish to tweak a dealer's work. While the Oracle's setup instructions are reasonably complete (with photographs), it's no simple procedure if your talent in things mechanical barely extends to flipping your preamp's selector switch and adjusting the volume control. The most involved part of the setup involves the suspension springs, a mechanical operation which consists of preliminary adjustment of each spring, following which the subchassis is dropped into place (figuratively speaking, of course) and its level relative to the baseplate checked using a furnished gauge. It is then apparently possible to zero-in on the right settings of the springs without having to remove the subchassis again—something yours truly didn't realize until he'd finished the entire setup by removing the entire subchassis to make each incremental adjustment!. This was, it must be said, more than a bit tedious—and apparently unnecessary.

I only encountered three other problems in setup (in addition to mounting the Graham arm and my own creative method of setting the suspension springs), two of them minor, the other a royal pain. First, the pain. The drive-belt runs between the motor pulley and a ridge machined in the underside of the (one-piece) platter. You have to first put the belt around this ridge under the platter, then hold it free on one side while you insert the spindle shaft into the bearing; then, as you slide the spindle down, simultaneously slip the free end of the belt over the motor pulley without its other end slipping off the under-platter ridge. It's as difficult as it sounds, and I must have played around with it dozens of times before it finally held without falling off, either immediately or as soon as the motor was started.

And care must be exercised to avoid transferring oil from the spindle shaft to the belt while performing this operation. In addition, if you don't get the belt on the right part of the pulley (which becomes hard to see just as you get to the point where you need to see it), the platter will rotate madly at what seems to be about 200rpm. And even after I thought I had the belt seated properly, it came off for no apparent reason a couple of months later. This time I got it back faster—I must have been getting good at it—and it has functioned normally for several months since that time.

The first of the less significant setup problems involved the sleeves that fit over the support pillars below the spring-loaded supports. If these are not adjusted to sit in a precisely vertical position, they'll rub against the subchassis, partially short-circuiting the suspension. It's an easy problem to solve, but if you hear scraping after setup as you move the subchassis up and down and everything else looks OK, you should check these lower sleeves for clearance. The second problem was a tendency for oil to leak out of (or perhaps overflow from) the bearing well during the first few weeks of service. The solution to this is to put something under the turntable if the surface on which it sits is one you don't want to christen with a sprinkling of oil.

Oracle SME 345 tonearm
Oracle also sent along a sample of their 345 tonearm to use with the Delphi Mk.IV. This is basically a special version of the SME 309, made specifically for Oracle. It has the detachable headshell of the 309, the bearings of the SME IV, and the arm lead from the SME V—thus the designation 345. It retails for $1595 in its standard, silver version, and $1795 in black and gold.

The Delphi Mk.IV has been in my system for a number of months now, and has been put to use with a wide range of associated equipment. More often than not, however, it's been connected to the Rowland Consonance preamplifier, the latter driving either the Rowland Model One (stereo) or Threshold SA/12e (monoblock) power amplifiers. The loudspeakers in question were, most often, the Apogee Stages. Similarly, interconnects, while varied, were usually Cardas Hexlink (balanced) from preamplifier to power amplifier. The lead from tonearm to preamp was, in all cases, the SME V tonearm lead. The latter was also used with the Graham tonearm in the system. Though the latter has its own tonearm plug and adapter box (for using your choice of interconnects), I chose to use the SME lead to minimize the variables when changing to the Graham arm from the SME.

Oracle Audio Technologies
6136 Blvd. Bertrand Fabi, Suite 101
Sherbrooke, Quebec, J1N 2P3
(819) 864-0480
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