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TTWeights GEM Turntable Review

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Larry is a long-time fan of direct-coupled turntables, and he wanted his table to emulate what was good in the vintage tables – i.e., some of the basic design elements, and improve upon that which was not – in particular, materials (by using all NADCAP Aircraft grade aluminum, 303 stainless/304BL Stainless/Brass/Carbon Fiber/Cobalt/Oilite) and tolerances (all CNC machined to MIL-STD tolerances). TTWeights currently manufactures two models, the smaller GEM which is the subject of this review, and the larger MOMENTUS. The two models are similar in design, differing mostly in scale. Each is available with various upgrade options. An intriguing feature of both the GEM and MOMENTUS is that they can be used as either rim-drives or belt-drives. They use a directly driven platter for, as Larry describes it, “absolute pitch control.” LD explains that he opted for rim drive rather than “true direct drive” for two reasons: First, because in a direct drive the motor is also a bearing, and second, because in a true direct drive the motor runs at a very low speed (i.e., 33 rpm) whereas with the rim drive it run at 660 rpm which he feels provides far greater resolution, and thus musical detail.

The GEM (and the MOMENTUS as well) is a fully modular design, in that the motor, arm pod(s), and controller are external to (i.e., decoupled from) the ‘table itself. The lack of an enclosure, the metallic elements, and the three footers lend a somewhat futuristic appearance to the GEM, which reminds me of a lunar-earth module. The GEM is a prime example of form follows function, an approach which appeals to my sensibilities.

The GEM’s plinth consists of 1 5/8” slab of solid aged oak, through which the massive bearing housing passes. Oak is used for its rigidity and resonance control. The plinth is supported at each of its three corners by height-adjustable footers, which TTWeights refers to as TTSoundPoints and Base Discs. The bearing may be thought of as the heart and soul of a turntable; its role is to allow smooth, low-friction rotation of the platter, without any “chatter” from asymmetric forces – for example, a belt being pulled from one side, or the cogging of a motor. The GEM uses a large bearing of 1.25 inch in length and 0.500 inch in diameter, manufactured from pure cobalt (the GEM Platinum uses a carbide bearing with an additional dampening bearing well to further reduce rotational noise) for maximum rigidity and accuracy. The bearing main housing is MIC 6 Aluminum high dampening tooling material, used in machining fixtures to absorb vibration. The bearing is Oilite, a self lubricating material in which oil is impregnated in the material. It is used in critical aircraft applications where lubrication can be a problem, provides the most non-wearing surface possible, and is machined to +/-.00005 true roundness.

The GEM’s platter assembly comprises five decoupled layers; from top to bottom they are :

· .030-inch aircraft fine woven carbon fiber

· 1/8-inch stainless alloy

· a second 1/8-inch stainless

· 1/8-inch Acetal

· 1.25-inch of 6061 aluminum (base platter)

The above components are laminated, pressed together, then finally machined. The 13.5-inch acetal ring is attached to the aluminum base platter; the ring’s contact with the drive wheel constitutes a 6th decoupling interface.

The GEM’s motor – which TTWeights terms the “heartbeat’ – is a brushless DC design, encased in a nearly 20-pound carbon steel housing. It has its own 24-volt power supply that provides 24 +/-.01 volts at all times regardless of line voltage. The motor base is a 6mm diameter Delrin with silicone locking ring, designed to provide zero movement by virtue of the weight and vacuum created under the motor. I can attest that the motor is remarkably free of vibration, and does not move during operation. The motor specs are as follows:

· Motor actual size is 3.15 x 4.0 inches depth, weighing 6 pounds

· Mounted internally in an in-house designed solid CNC machined 13.8 lb steel motor housing, to provide vibration free operation

· Motor mounting cap 304BL Stainless Steel

· Motor base 6.0mm diameter delring with silicone locking O-ring that prevents movement by the weight and vacuum created under motor

· Motor height approximately 6 x 4 inches (varies by table type)

· Bushless speed control system that uses .054 degree increments (6600 steps per revolution of the motor; the motor runs at 660 rpm, thus the actual steps per platter revolution is 4,400,000 steps at 33.33 rpm)

· Programmed to run at 1/15 horsepower (10% of its available power, to assure super smooth operation of rated power) and torque of 18.1 oz-in2 (100 x the torque of a Technics SP-10)

Though LD favors rim-drive operation, he recognized some customers favor the quieter operation of belt drives. A remarkable feature of the GEM (and the MOMENTUS) is that they can operated either as rim- or belt-drives!

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