Krell KPS-20i CD player Martin Colloms October 1995

Martin Colloms reviewed the KPS-20iL in October 1995 (Vol.18 No.10):

The High End is dead? Don't believe a word of it! The High End is alive and kicking—long live the High End! Larry Archibald had it right last January (Stereophile, Vol.18 No.1, p.274) when he said that a worldwide recession does not mean that the High End is in trouble.

It's always been true that fashionable entertainments—from video to computer games, multimedia computers to Home Theater—capture huge slices of disposable incomes. High-fidelity manufacturers may well eye such sales with envy and reminisce about audio's peak decade in the 1970s. Dream on, guys, we'll never see the like again! Nevertheless, high-quality audio survived the passing of the boom [Some might say it even grew out of it.—Ed.] and continues to maintain a healthy, long-term existence.

A number of major brands have now been with us for up to two decades and continue to prosper at the concentrated, specialist end of the market where high quality and constantly improving product performance maintain the industry's forward momentum. To name but a few, there's Spendor, KEF, Celestion, Tannoy, B&W, Naim, Linn, Arcam, Audiolab, Monitor Audio, Acoustic Energy, and Mordaunt-Short in the UK; and Krell, Audio Research, Conrad-Johnson/Sonographe, Mark Levinson, Apogee, Magnepan, Infinity, Threshold, PS Audio, Counterpoint, JBL, and Thiel in the US.

And that's not all. In general, the performance of these companies' products is getting better all the time. My numerical scores for perceived sound quality go back 15 years; they show a steady improvement in all areas of audio engineering save the glitch caused by the sound of early digital audio.

We don't need no steenkin' preamplifiers
The rate of progress in one area of reproduction sometimes outpaces that in another. At present, digital replay is racing ahead, followed by new (and rather costly) power amplifiers and some fine new loudspeakers. The state of the art in preamplifiers seems to be falling behind, however. Adding any preamplifier that I know of to a replay chain is guaranteed to significantly degrade the sound quality of the best-sounding sources (footnote 1). This point is particularly relevant to this review, as the $11,000 Krell KPS-20iL CD player includes a remote volume control feeding an output stage of true reference preamplifier quality.

The KPS-20iL is part of a series that includes the KPS-20t CD transport/digital switchbox (footnote 2) and the KPS-20i integrated CD player, recently reviewed in Stereophile by Robert Harley (April '95, Vol.18 No.4, p.201). If this product delivers what Krell claims for it, namely their best digital replay performance yet, then it may well help cause something of a revolution in high-end system-building. The system would be configured for one primary source, the digital CD player, and the preamp would be either omitted or relegated to a subsidiary function and normally positioned out of the signal path. A top-quality CD player connected directly to a power amplifier is likely to outperform any combination of CD source and preamplifier. This is down to shortening the signal path and the elimination of interconnect cable, sockets, and switches.

We don't need no steenkin' processors
I have long favored the concept of a unified, or one-box, CD player—particularly once the potential for sound-quality losses suffered by a digital audio signal transmitted over the S/PDIF interface were understood and quantified. Regardless of various palliatives—clock reconstruction, special sync procedure, and jitter reducer—the S/PDIF interface will always reduce quality. If you connect a transport's output directly to a local decoder board, correctly observing the timing- and data-matching protocols, then you can hear the sonic improvement. It's not trivial! The designer of a one-box CD player has an immediate quality advantage over that of a two-box player—if he or she does it right.

Digital done right?
Like the KPS-20i—"KPS" stands for "Krell Playback Series"—the KPS-20iL has five digital input options: coax 1 and 2, TosLink optical, AT&T (ST) optical, balanced AES/EBU XLR, as well as "CD," this the internal hot link to the inboard transport.

Aside from the baseplate, all the '20's panels are fabricated from heavy-gauge alloy plates and 5-, 6-, and 10mm-thick extensions. The assembled result feels very solid and inert, the whole supported in a second mechanical isolation system formed by the elastic conical diaphragm mounts for the feet, faced in foam rubber. Clearly, addressing vibration problems has been a key issue for the '20's designers.

The full range of facilities is spelled out on the front panel, including display "dim" (off), volume, and digital input. Unlike some models, a mislaid remote control does not leave you helpless. The handset is a chunky, anodized bar milled from solid alloy and clearly laid out and labeled. It also includes power control for compatible Krell power amplifiers.

Getting inside the '20 is easier than it looks. Removing the eight TORX bolts from the sides allows the whole top shell and cover system to be lifted away (take care first to detach the disc-illumination and motor-control cables). Build quality is excellent, with a well-thought-out and logical layout. The master, or motherboard, covers the whole lower deck area, carries the digital I/O, digital control system, and power supplies, and interfaces with the front-panel control and display sections. A subsidiary board is responsible for the slide motor control while the D/A decoder and analog sections are carried on another well-packed board on the right.

Power supplies and digital inputs are located on the left, with the fine-lamination R-core transformer to the front. This has independent bobbins for primary and secondary windings, to improve the broadband isolation. Multiple secondaries provide independence for the four main power supplies, and I was able to count upwards of 12 regulators for digital and analog sections.

AC power input is via a Coram filter-socket unit, to help the '20 conform with European EMC countermeasure regulations. The ground connection is used for the filtering process, and both the chassis and case are grounded. Good system-grounding practice is essential for the best results.

Dominating the center of the chassis is the custom Philips CDM9 Pro CD mechanism with its integral Mk.II servo board (footnote 3). This attaches to a black-anodized cover plate milled from solid, and firmly coupled to a subchassis block of solid brass weighing 4 lbs. The subchassis is isolated from vibration by four suspension points comprising precision cups molded from a selected visco-elastic polymer. The CDM9 mechanism is therefore accorded a foundation of great mass and rigidity essentially free of self-resonance, and well-decoupled mechanically and acoustically from the environment.

Krell's new high-force, star-shaped magnetic disc-clamp controls disc vibration, both by secure hub contact forces and by carefully tensioned contact to the disc edge at the clamp arm tips. The stabilizing function is achieved without slowing down the servo response of the hub drive. Krell's heavy sliding lid largely excludes both the external soundfield and ambient light. (The lid action is relatively slow, however, and the gears noisy.) Inside the disc chamber, 20 green LEDs illuminate the disc, this said to improve the signal/noise ratio of the data-sensing optical diodes.

When used as a CD player, the I2 data output from the transport "engine" is translated directly to the DPS-20's math section. A clean, local crystal oscillator, controlling both transport and DAC sections, confers a low-jitter performance.

The recovered 16-bit data are upsampled and digitally filtered at a 16x rate. The low-pass filtering, de-emphasis, and waveform reconstruction (interpolation) use proprietary Krell software operating at a 24-bit word length, implemented in a Motorola 56002 DSP chip, this featuring 56-bit internal precision and clocked at a high 66MHz. The filtered and interpolated digital data feed an array of four Burr-Brown PCM63PK "Colinear" DAC chips. These well-respected 20-bit devices are operated differentially to maximize linearity, resulting in near-zero error when operating on the 16-bit CD data. All the possible fine-tuned calibrations for these DACs are implemented in the KPS-20iL.

Selected high–slew-rate IC amplifiers—the Precision Monolithics PMI 2131—are used for I/V conversion, their outputs feeding four discrete, medium-power, class-A, push-pull amplifiers—symmetrical and DC-coupled in classic Krell style. These amplifiers cover plus and minus polarities for the balanced outputs for the two channels. The positive-phase signals are also fed to the normal single-ended output sockets, meaning that only in full balanced mode will the Krell's maximum performance be achieved. Failsafe relay muting is present at the outputs.

The "L" version is differentiated from the KPS-20i by its uprated output stage. This is essentially the same topology, but run at a higher bias current with bigger transistors. A FET-switched attenuator array is used as a fully balanced level control, activated by the remote control using in-house software codes. The 'L's volume control and output stage are similar to those of the well-received KRC-2 preamplifier (reviewed by me in the June 1994 Stereophile, Vol.17 No.6, p.113).

When the player is driven by an external digital source, the initial acquisition is by the popular Crystal Semiconductor CS8411 chip, though its clock-recovery circuitry is augmented by Krell's proprietary jitter-reduction module. This is specified as reducing jitter to typically 50 picoseconds. If specified as an option on purchase, the 'iL may also have Krell's "Sync" option fitted. When used as a transport to drive a Krell Reference 64 decoder, the 'iL outputs a 2.824MHz clock signal derived from the 11.289MHz master transport oscillator to minimize S/PDIF interface jitter.

All in all, the KPS-20iL is well-built and -executed, reflecting the increasing skill and sophistication of specialist-audio houses.

Krell HDCD
Krell initially played a waiting game with HDCD. Like other manufacturers using custom digital filter software operating on a DSP chip, the implementation of HDCD is impossible without Pacific Microsonics releasing the source code. Using the Pacific Microsonics PMD-100 chip for HDCD replay would negate Krell's investment in custom digital filtering and interpolation.

Krell therefore chose an HDCD-option route for the KPS-20i and 'iL. (This may also be retrofitted to the Reference 64 decoder.) When the option is fitted and an HDCD-encoded CD is being played, the PDM-100 filter decoder takes over from the Krell DSP filter. Non–HDCD-encoded discs continue to be filtered by the Krell software. Though the HDCD option adds to the price of the KPS-20i and 'iL, in Krell's view it offers the best of both worlds.

Initial impressions
The KPS-20iL sounded fine straight out of the box. My first impressions were very positive. I generally find that if a component is really good, then it will tell you that straight away, fresh and raw from the production line. Nonetheless, the KPS-20iL did show the customary benefits resulting from an extended burn-in. While the qualities of dynamic power, clarity, and bass precision were present at the outset, a week or so's use brought about a number of improvements. The sound was now finer-grained, with more musically balanced timbres. Stereo perspectives and transparency also improved.

You don't have to mess with fine-tuning to get good sound out of '20iL, but for those who want the very best, it's certainly worthwhile. It's at this point that audio reproduction can take on magical properties, with the listener's increased emotional involvement in the reproduced sound transcending the usual earthbound engineering limitations.

A dedicated AC line delivered quieter backgrounds, deeper silences, purer treble, and increased image depth. A specialist audio component table improved rhythm and dynamic range, enhanced tune playing in the bass, and lent the sound a greater sense of ease. Depending on the support used, Harmonix feet were also effective. However, the integral suspension of the '20 was quite effective, and I found the improvement with special feet not to be as great—for example, as with the Accuphase DP-70V.

I also found experimenting with cables worthwhile; doing so allowed subtleties of tonality and inner balance to be optimized. (Note, however, that the specific cables found to be "best" will depend on the context of a particular loudspeaker and room combination.) I also found that turning the display off gave an additional, worthwhile gain in clarity. My final rating and comments reflect this condition.

Sound quality
There's no need to beat around the bush. Optimally placed and cabled, broken-in, and used without a preamplifier, the KPS-20iL delivered the best digital playback I've ever heard. This Krell lives and breathes High End, giving renewed hope for the long-term future of digital audio, and setting new standards for digital replay.

The margin of superiority the Krell offered wasn't subtle. It was supremely confident, capable, powerful, and communicative. When I inserted the KPS-20iL into my system, it kicked in like an audiophile thoroughbred should!

That fantastic bass continued to satisfy over hours of listening. Quite unexpected levels of bass detail and articulation were retrieved from recordings I had passed over in recent years in favor of more impressive newcomers. Led Zeppelin's reissue CDs were a case in point, as were those of Dylan with the Band and Little Feat. It's hard to convey just how crisp, impactful, and deep the Krell bass was when compared with known references; the difference was not subtle!

Although the '20i offered a marvelous transparency, its balance shaded toward brightness. The "L" preserved that vital transparency while managing to bring the mid- and treble regions into a more neutral balance. As a result, system-matching is no longer so critical to getting a natural sound.

Well-recorded vocals had presence, superb clarity, and crisp diction without excessive sibilance, breathiness, or grit. Through the treble, the Krell sounded consistently open and airy, sparkling, focused, and essentially grainless—particularly when the unit was properly positioned and supported.

Stereo focus was first-rate, maintained over a wide frontal spread reaching back into the soundstage. Depth resolution was also extremely good, of crystalline clarity, with the player presenting finely layered perspectives.

Resolution of detail at high and low signal levels was consistently high, with no loss of clarity during highly complex musical passages. Dynamics were excellent, fast transients showing almost explosive attack. The punchy bass helped to communicate an involving upbeat quality.

Lesser CD players sounded slow, dulled, and compressed by comparison. Extended listening served only to reinforce my view that here was a true reference.

Taking into consideration the deletion of the preamplifier, the sound of the Krell '20iL in a top-class system was thrilling. High-caliber power amplifiers, such as the Krell KSA-300S, will serve it well; but such is the intrinsic quality of the 'iL that super-fi amplifiers—the balanced Audio Research D150SE, for example, or the unbalanced Conrad-Johnson Premier 8—that they will bring immediate rewards. Note that the Krell sounded similarly fine used via its balanced or unbalanced outputs.

For me, the KPS-20iL sounded at its very best with a Krell KAS-2. No doubt the mighty KAS itself would also suit very well. With the KAS-2, the bass was simply stunning—the '20iL seemed fully capable of exploring the known limits of these reference-class monoblocks. It produced highly focused, panoramic soundstages, while stage depth was excellent, with superb clarity and detail audible throughout the range.

As far as I'm concerned, the Krell KPS-20iL is the world's best one-box CD player. Krell rightly claims essentially zero jitter for the digital-domain join between transport and DAC (this is true for all well-implemented one-box players), and you can really hear the resulting performance edge over two-box players when so clearly expressed in a design such as this. With a single bound, the Krell KPS-20iL has leapt ahead of the competition, dismissing any notion of an auxiliary preamp or control unit—which, by definition, must, and in reality does, significantly impair sound quality.

Incredibly, the L version of this player improves upon the 'i. Its tonal balance is more neutral, its midrange sounds more natural, and its grip in the bass firmer still.

Summarizing some general thoughts, the KPS-20iL sets a high standard as an independent D/A processor—more than good enough for virtually any transport, DAT, or other digital source. I would unhesitatingly place the KPS-20iL, as a transport, in the reference class. It will drive any power amplifier in both normal and balanced modes. Its test and technical specifications are state-of-the-art, while both finish and build quality are excellent.

I was greatly impressed by the KPS-20iL—for its outright sound quality and its all-round compatibility. In my opinion, there is no better CD replay sound presently available, HDCD or not (and in any case, you can fit the Krell with the HDCD option card with no loss in fidelity).

While Krell is certainly not giving this player away, in terms of sound quality for the dollar the KPS-20iL represents a superb deal. For now, there's no point in spending any more on CD replay.

Footnote 1: I recently met this problem head-on when attempting to assess the Krell KAS-2 reference monoblock amplifiers. I knew that they were good, but I couldn't appreciate just how good until I put aside the several balanced preamplifiers available for test. Direct connection to new-generation one-box CD players like the KPS-20iL and the Wadia 16 was the answer. The KAS-2 immediately shifted up a gear or two and really began to show its paces, freed from the sonic shackles imposed by a conventional preamplifier.

Footnote 2: The "t" is currently Krell's best transport, intended for use with the top-of-the-line Reference 64 decoder until a new version of the earlier MD10T becomes available.

Footnote 3: Krell has improved the system and servo operation for the CDM9 laser transport by using in-house software. Their aim has been to improve the quality of eye-pattern recovery—the actual FM data signal read off the disc. With the new software, better control of torque and overshoot is also said to be achieved for the disc hub motor.

Krell Industries
45 Connair Rd.
P.O. Box 0533
Orange, CT 06477-0533
(203) 799-9954
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