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Krell FPB 400cx Stereo Power Amplifier Print E-mail
Tuesday, 01 April 2003
Article Index
Krell FPB 400cx Stereo Power Amplifier
Page 2
ImageMovie buffs may remember the name Krell from the movie "Forbidden Planet," where the Krell were the most powerful race of an alien civilization. Krell Industries, manufacturer of some the world’s most exotic AV equipment, named its company after this superior species. Like Morbius, another “Forbidden Planet” character who sat in front of the Krell’s computer terminal trying to understand their science, I sit in front of Krell’s amplifier, learning about its science.

The amplifier I’m talking about is the Krell FPB (Full Power Balanced) 400cx, Krell’s latest “mid-priced” offering in the FPB stereo amplifier line-up, priced at $10,500. The 400cx is rated at 400 watts per channel into eight ohms, 800 watts in four ohms and 1600 watts into two ohms. Upon unboxing the Krell FPB 400cx, I was immediately struck by its build quality. Weighing in at 110 pounds and measuring 19 inches wide, 10.3 inches tall and 19.7 inches deep, this doesn’t exactly make it an easy amplifier to haul around - I hoped that what my back didn’t like, my ears would love. The 400cx’s large black anodized face and three small blue LEDs give the amplifier a very appealing, distinguished appearance. The front panel also has an infrared sensor for remote operation and interaction with other Krell products. The rear panel has two pairs of speaker binding posts per channel for bi-wire applications. These can be easily thumb-tightened, but they will not accept bare wire, banana plugs or pins - only spade lugs will work. It also offers both single-ended and balanced connections, as well as the proprietary Krell CAST inputs, which I’ll cover later in this review. The rear panel also includes the remote control Krell Link to turn the amplifier on and off, a very substantial non-detachable power cord, as well as a power breaker switch and a pair of handles to carry the beast around.
I placed the Krell FPB 400cx on the bottom of my rack and connected it to my Krell HTS 7.1 via the balanced inputs with my reference Cardas Golden Cross XLR interconnects. I made the speaker connections using the Cardas Golden Cross bi-wire speaker cables to my Martin Logan Prodigies. I’ve found the Cardas Golden Cross cables are a great value and work exceptionally well in my system. My Arcam DV-27 was used for both the audio and video source of my evaluation and the analog outputs were used for CD playback, while the DACs in the Krell HTS 7.1 were used for all movie watching.

The FPB 400cx is a Full Powered Balanced X Series Stereo Amplifier, which is what Krell calls their latest iteration in circuit design. The latest X Series Amplifiers use the Krell Sustained Plateau Bias III microprocessor control system that maintains Class A operation regardless of music or movie demands. Class A bias is the most accurate method used to amplify musical signals, but has it’s engineering challenges. Class A operation means that all transistors in the amplifier draw current all the time. However, the large current consumption gives us one of the benefits of Class A operation, namely a distortion that is low and kind to our hearing. It’s a design that’s neither cheap nor easy to engineer, but has obvious advantages. As I mentioned earlier in the review, the FPB 400cx has its own proprietary output design, called CAST Technology (Current Audio Signal Transmission), or in this case, CAST II Technology, Krell’s latest update. Krell claims the CAST II system improves every performance area, including speed, precision, dynamic range, depth and width of the soundstage, transient impact, tonal balance, harmonic distortion, and more. Unfortunately, I’m not able to confirm this, because my reference preamp, the Krell HTS 7.1, doesn’t include CAST outputs. With all the benefits that Krell claims CAST II technology delivers, it seems to me it would be a feature they’d want to include in their best and latest A/V processor, or at least create a Class A Series A/V processor that includes CAST technology. I’m always skeptical when a manufacturer makes claims of superior technological or sonic advantages of any type, whether it is Class A, Class AB, Zero-Feedback, Single-Ended Triode, or anything else for that matter. My thought is that it is implementation that rules the sonic world, rather than claims about technology.


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