Krell KPS-20i CD player
A CD player offers the potential of giving a similar sound quality for less than the price of a transport and outboard processor combination: with only one chassis, packing carton, power cord, and other items, a CD player costs less to build than a comparable pair of separates. More importantly, putting a CD transport and digital processor together in the same box is a huge benefit when trying to achieve low clock-jitter. In a well-designed outboard digital processor, most of the clock jitter is introduced by the interface between the transport and processor. The S/PDIF or AES/EBU interfaces are inherently flawed methods of transmitting digital audio. A CD player has no S/PDIF or AES/EBU interface, thus offering the potential for lower jitter. Krell has taken this idea a step further in the KPS-20i by using a single master clock for the transport and digital-processor sectionsthe processor is slaved to the transport's clock.
The KPS-20i's styling is something a futurist may envision a music playback system to look like. The unit is sleek, looks high-tech, and gives the feeling that it's built like a tank. These impressions are reinforced by pushing the front-panel "Open" button, which causes a motorized cover to slide back, revealing the top-loading Philips transport mechanism.
The front panel is packed with buttons for controlling the transport and selecting external digital sources. A direct-access keypad (which allows you to enter a track number directly) greatly adds to the front-panel button density. In addition to the usual transport controls, the KPS-20i has some unusual features. An index forward/backward control lets you search index points on a disc. Krell's Disc Management System can remember which tracks you've skipped on a disc, then skip those tracks (if so instructed) the next time you play the disca feature similar to Philips's Favorite Track Selection (FTS). The transport control section also provides an AB loop, shuffle play, repeat track, repeat disc, introduction play, and direct time access. Two LED displays indicating the track number and elapsed/remaining time can be turned off from the front panel or remote control.
All these transport control functions are duplicated on the large, machined remote control, which will also control Krell remote-controlled preamplifiers and power amplifiers.
The rear panel is as packed with input and output jacks as the front panel is filled with buttons. Analog output is via a pair of XLR jacks, and single-ended output is from RCAs. Digital inputs include two coaxial on RCA jacks, AES/EBU, ST-Type optical, and TosLink. One digital output (an RCA jack) is included as standard. If you want more digital outputs, the KPS-20i can be ordered (or retrofitted) with ST-Type, TosLink, and Time Sync optical outputs. When using the KPS-20i as a transport to drive a Krell processor, this optional output board must be present to use the "Time Sync" function, which locks the processor and transport to the same clock via a separate link. A front-panel LED marked "Sync" illuminates to indicate when the transport and processor are locked to the same clock. This LED also illuminates whenever the KPS-20i is playing a CD: because the transport and processor are in the same chassis, they're automatically driven by the same clock.
A pair of rear-panel jacks is included to provide intelligent communication between different Krell products in the future. A rear-panel power switch turns the unit on and off; the power switch on the front panel controls only the transport section. By leaving the rear power-switch on, the KPS-20i is always warmed up.
The KPS-20i is also available as the KPS-20iL, a remote-controlled line-stage preamplifier that uses a resistor-ladder volume attenuator and relays, and adds $2000 to the pricenot much more than you'd spend for a good pair of interconnects between a processor and a line-stage preamplifier.
Another member of the KPS family, the KPS-30i, uses the same custom digital filtering, DACs, and analog output stage as the KPS-20i, but costs only half as much as the latter: $4500. The only difference is the transport mechanism, power supply, and metalwork.
Inside, the KPS-20i is packed with electronics, with a heavy emphasis on the power supply and analog output stage. The supply is fed from a large (100VA) transformer, and features 11 separate regulation stages. Of these, the ±18V analog supply and the DAC supplies use cascaded regulation (the output of one regulator is re-regulated by another regulator). These circuits use a combination of discrete devices and three-pin chips. The heatsinks for this massive supply are bolted to the chassis, thereby converting the entire unit into a huge heat dissipator. As with other Krell components, the KPS-20i runs very hotparticularly the left-hand side, where the heatsinks are bolted to the chassis. The main filter caps are very large electrolytics, and many small distributed electrolytics (which are bypassed with film types) are located next to the circuits they supply.
The digital input receiver, the ubiquitous Crystal CS8412, is used only when the KPS-20i is decoding the signal from an external digital source. When used as a CD player, the KPS-20i needs no input receiver, and doesn't suffer from S/PDIF interface-induced jitter.
This is a good time to point out a fundamental limitation of outboard jitter attenuators: After creating a low-jitter signal internally, they must then output that signal through an S/PDIF interface, which adds jitter. A CD player, which has no need for the S/PDIF interface or clock-recovery circuits, doesn't suffer from this problem.
Krell has long been an advocate of custom, software-based digital filtering rather than relying on off-the-shelf digital filter chips. In a software-based filter, the digital filtering is performed by general-purpose Digital Signal Processing (DSP) chips, which are run by instructions (the software) contained in a memory chip. The designer can change the processor's sound simply by changing the software code. In addition, higher oversampling rates can be created in the custom filter. In the KPS-20i, a single Motorola DSP56002 chip performs the digital filtering, running at a 16x-oversampling rate. Most digital filters run at 8x-oversampling.