Linn Karik/Numerik CD player Page 3

The Numerik
The Numerik is similarly forward-thinking in design. The unit uses a brand-new chip set not yet seen in any other D/A converter.

The digital filter is an 8x-oversampling unit from Burr-Brown, the DF1700. This linear-phase filter has 20-bit word output and 25-bit internal word length. I haven't seen this filter used before; most converters use the NPC or Sony digital filters.

D/A conversion is handled by dual Burr-Brown PCM63P DACs, another brand-new part. This 20-bit monolithic DAC, called a "Sign-Magnitude" converter, has some impressive performance specifications. I saw one of the PCM63P's designers give a technical paper on the part at the 1990 Los Angeles AES convention. The DAC has excellent low-level linearity and doesn't need MSB trimming. This is a result of a neat trick: the zero crossing point where all bits toggle (the 19 LSBs turn off and the MSB turns on, or vice versa) is shifted to a much higher level, moving the zero crossing glitch away from low-level signals. This technique is described in more detail in my review of the Museatex DCC in Vol.13 No.11. In that product, the same goal was achieved by conventional DACs and proprietary circuitry. The PCM63P incorporates these techniques within a monolithic part. Linn chose the PCM63P after listening to over a dozen DACs. Incidentally, the PCM63Ps used in the Numerik are the highest grade available, then selected by Linn for lowest switching noise.

A Philips SAA7273 S/PDIF input receiver was chosen over the more popular Yamaha chip. When the Numerik's sync cable drives the Karik, the clock recovery portion of this chip is unused. Without this sync cable, the 7273 can function normally. The input receiver and the 8x-oversampling digital filter are shielded by a pair of flat metal cans.

The power supply features a large toroidal transformer, dual full-wave bridge rectifiers, and generous filter capacitors. The ±15V analog rails are supplied from separate transformer windings and a dedicated full-wave bridge rectifier. Like the Karik, each rail of each stage is buffered with an emitter follower. Four trim pots adjust the reference voltages to the DACs.

Current to voltage conversion (I/V) is performed by the popular AD846 op-amp from Analog Devices. The analog output stage is all discrete, with 1% metal-film resistors and 1% polystyrene and polypropylene caps. These caps, found in all Linn products, are hermetically sealed to maintain their characteristics over long periods of time. The output filter is a fifth-order Bessel type, and de-emphasis is passive, switched in by JFETs.

All the circuitry is contained on a single printed circuit board, with maximum physical separation between digital and analog sections. Further reducing RF contamination, the digital signals have been band-limited to reduce their RF radiation. In addition, critical pcb traces are shielded from noise, and the master oscillator is low-noise and isolated by RF shielding. There was obviously much thought put into the Numerik's design, especially in keeping RF noise out of the analog sections.

Construction and parts quality were high, but there were a few "Band-Aids" (additional components soldered on after the board layout was finished) around the digital filter.

The music
I auditioned the Linn CD player with three different pairs of loudspeakers that made their ways through my listening room over the past weeks: the Monitor Audio Studio 20 reviewed last month, the Apogee Centaur Minor reviewed in this issue, and my reference system, the Hales System Two Signatures augmented by a Muse Model 18 subwoofer. VTL 225W monoblocks were the primary amplifiers—a Jeff Rowland Model One saw brief action—and an Audio Research LS2 line-stage preamplifier provided gain and switching control. Interconnects were Straight Wire Maestro and loudspeaker cable was Symo, AudioQuest Dragon/Clear, or Sterling/midnight bi-wired sets. AC power to the processors was conditioned by a Tice Power Block and Titan.

I put the Linn CD player up against some very tough competition—the Theta Data Universal Transport driving the Audio Research DAC1-20. Both the Data and DAC1-20 are, in my opinion, some of the best digital playback products yet designed. Coincidentally, they are about the same price as the Linn CD player ($5900 vs $5590). During Linn's visit, they encouraged me to compare their player to any combination of processor and transport I wanted, regardless of price. Thus the Data/DAC1-20 seemed an appropriate reference.

In addition to long-term "single presentation" listening, the Linn was compared with other digital processors. Some of these included the new Theta DS Pro Basic II, Kinergetics KCD-55 Ultra, Deltec PDM Two, Meridian 203, and that long-term reference, the Wadia 2000. Levels were matched between processors to 0.1dB at 1kHz.

Although the Linn CD Player comprises the Karik transport and Numerik converter, I decided to treat them as a single product. While audiophiles can buy them separately, I doubt many will. The two units form a musically synergistic combination, partially as a result of the separate sync connection described in the Sidebar. Further, Linn owners tend to buy into the Linn philosophy and are less inclined to mix'n'match with non-Linn components. Those wanting to own the Linn CD Player can buy the Numerik for use with their existing transport or CD player and buy the Karik as finances permit.

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