Krell KPS-25S (1998)
One box, twenty thousand dollars, and every argument Krell ever won about separates, settled in a single chassis.
Overview
Krell took its best CD transport, its best digital-to-analog converter, and its best preamp and put them in one component. That is the KPS 25s, which the company called a "Playback System." Audio (January 1999, p.79) said the courage came from bucking the high end's long tradition of separates, and the vision came from making the whole thing upgradable to handle any foreseeable CD or DVD-audio format. At $20,000, the magazine observed, it had to be not merely very good but superb.
The transport is a top-loader built around a JVC EXU-901A mechanism, with a high-power neodymium-magnet direct-drive motor on an oversized drive shaft. A low-mass metal disc clamp isolates and damps the disc. A belt-driven laser carriage and viscous-damped suspension keep data transfers error-free. You drop the disc onto the spindle by hand, and Krell doesn't hide that: a clear acrylic lid shows off the visible clamp, and an LCD shutter fogs the lid opaque during playback to keep light off the disc.
The oversampling algorithm is written by Krell and drives dual 80-MHz Motorola DSP engines. These feed twin dual-converter DAC circuits, intended to boost processing power and cancel common-mode distortion. UltraAnalog built the DAC boards to Krell's spec, and they run 16-times oversampling. A master oscillator and clocking system syncs the digital stages for jitter-free timing. A Pacific Microsonics PMD-100 chip handles HDCD decoding, with an LED on the front panel to tell you when it's working.
The analog side is where Krell's fingerprints are deepest. The sections are direct-coupled, complementary circuits using the company's patented Current Mode topology. That means paralleled small-signal transistors running in Class A rather than comparatively sluggish power transistors, amplifying current rather than voltage. The claimed payoff is lower distortion, wider bandwidth, and low noise with only modest feedback for stability. The volume control is digitally controlled but operates in the analog domain, with more than 65,000 adjustment steps. Current Mode also underpins CAST (Current Audio Signal Transmission), Krell's four-pin bayonet connector scheme meant to shrug off cable reactance even over long runs. The KPS 25s was the first component to carry it.
Connectivity is generous. There are five digital inputs and five digital outputs - one AES/EBU, two coaxial, two Toslink - enough to hang more than one digital recorder off the thing. Analog connections run to five input pairs (one balanced, four unbalanced) and six output pairs: two balanced XLR, three unbalanced RCA, and the CAST pair. Add terminals for slaving Krell Full Balanced amplifiers on and off, 12-volt triggers for KAV amps and other home-theater gear, and an RC-5 input for whole-house control systems, and the total lands at ten inputs and eleven outputs.
The preamp section has per-input sensitivity adjustments, so switching sources doesn't produce a jump in volume. Combined with programmable gain on the volume control, it lets an owner match the control's range to the amplifiers and speakers in the system. The full travel of the dial becomes usable, and finer adjustments become possible. Balance can be set in 0.5-dB steps, finer than the 1-dB steps on some other Krells. Two remotes ship with the unit: a small one about the size of a cigarette pack for casual use, and a 50-button tabletop controller that reaches virtually every adjustment.
Krell also made the modular input receiver and DAC circuitry upgradable, along with the transport mechanism. Audio (January 1999, p.79) read that as the visionary half of the design. The CD section covers the usual track-access and repeat functions, including A/B looping between two points in a track or across several tracks, with LEDs showing HDCD decode status and transport/DAC sync.
On sound, the same review (p.81) was unreserved. It reported never having heard a CD-driven front end deliver such bass quality, and suggested that anyone with speakers capable of flat, high-power reproduction down to 30 Hz or below really ought to hear it. The midrange was called appropriately neutral. The treble was clean enough that the sheer quantity of upper-octave information takes time to register. The dynamics, while not as "live" as the very best tube equipment, tracked major shifts in musical energy and delivered immense subtle transient detail in soft passages. Bass depth, definition, and power were described as extraordinary yet realistic. Artificial reverb and multitracked vocals sounded as unreal as the recording, but genuine depth in the source came through.
That review ran as an Auricle feature in the January 1999 issue, with Anthony H. Cordesman on the byline and the KPS 25s sharing the cover with a Marantz DR700 CD recorder. Cordesman's verdict was that the KPS 25s was what audio is all about, and that even listeners who could never afford one should hear it to recalibrate their standards. The integrated approach, he argued, let Krell minimize interface problems between transport, converter, and preamp, avoid level-matching headaches, and voice the whole chain consistently.
Anyone buying one today gets a late-nineties unit with a laser mechanism, a belt-driven carriage, and a fair amount of proprietary digital hardware inside. The upgradable modular design that looked forward-thinking in 1998 is also the reason service documentation and module availability matter more than usual. The CAST output is only useful with a Krell amplifier that has a matching input, though the balanced and unbalanced outputs cover everything else. The acrylic lid and LCD shutter will look as good or as bad as the previous owner left them.
What the KPS 25s represents, more than any single specification, is a moment when a company with a serious separates pedigree decided the future was integration — and priced the conviction accordingly. Whether that reads as courage or hubris depends on your rack. The review record, at least, came down firmly on the side of the former.
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