Krell, the iconic amplifier manufacturer, has recently introduced their no-holds-barred integrated amplifier, the Fully Balanced Integrated Amplifier (commonly referred to simply as "FBI"). The FBI is designed to be a serious world-class audiophile piece. One look at this $16,500, 104-pound piece of equipment and you will have no doubt that it is not to be taken lightly.

The FBI design is comprised of separate amplifier and preamplifier sections, each designed for maximum performance and synergy. The amplifier portion of the FBI is based on the popular FPB 300cx stereo amplifier. The Full Powered Balance (FPB) series of amplifiers features completely discrete, fully-balanced, dual differential single-channel and stereo amplifiers.  While the smaller KAV-400xi features Class-A circuit topology up to its driver stage, the FBI features Class-A topology throughout.

As its name implies, in addition to being Class-A, the FBI also features a fully balanced design and actually goes one step further. The FBI has a dual differential design throughout the entire signal path. This push-pull design effectively doubles the number of amplification components while providing greatly increased control over the signal. The FBI is rated at 300 watts per channel into eight ohms, 600 watts into four ohms and 1200 watts into two ohms.

The chassis, made out of half-inch-thick anodized aluminum, measures 17.3 inches wide by 10.3 inches high and 20.5 inches deep. The industrial design of the FBI follows Krell's new Evolution series, with the front panel made of brushed silver aluminum and the center of the panel featuring a vertical strip of highly polished convex aluminum. In the top center of the front panel is an LED window that displays the volume, balance, etc., and an IR sensor. Smack dab in the middle of the panel is a machined metal volume knob that appears to have come from the Evolution line and would feel at home on the most expensive pieces of equipment.  Moving away from the center panel on each side are three buttons in a vertical line, then stout vertical handles. The sides are heavily finned for dispersing the heat generated by the large number of output devices and Class-A topology. The rear panel features another set of handles, which is welcome on this heavy unit. Eight large binding posts allow for easy bi-wiring.  Line-level audio connections include three pairs of single-ended inputs, a single-ended tape loop, one pair of balanced inputs, a pair of CAST inputs and a preamplifier output. Other connections include an IEC power plug, a power switch, 12-volt trigger input and output, and an RC-5 input.

The Krell FBI incorporates other proprietary technologies, such as Sustain Plateau Bias and Krell Current Mode technology. The Sustain Plateau Bias circuit constantly reviews the input signal and adjusts the amount of current that the transistors conduct accordingly to minimize wasted current while maintaining the benefits of the Class-A design. Krell's Current Mode design uses manipulated current, rather than voltage, to conduct the signal. This is said to protect the integrity of the signal and minimize the effects of cables on the signal. This design is maximized with the use of a Krell CAST system source, connected to the FBI through the CAST input. This is alleged to allow the components to act as one unified circuit.

High Points
• The FBI is built like a proverbial tank and exhibits Krell's pleasing new aesthetics, derived from their Evolution line.
• The provided amplification easily drove the heaviest and most difficult loads while maintaining complete control.
• The FBI is flexible, as it can accommodate single-ended, balanced or CAST sources and is capable of being integrated into a home theater.
• The Krell FBI is quite simply the best integrated amplifier I have heard. Honestly, it's the best integrated amp ever made.

Low Points
• I would like to see more inputs, particularly balanced inputs, so that it can be used in larger, more complex systems.
• The remote is not up to the aesthetic level of the FBI itself and, at this price, you shouldn't have to invest in an additional remote from a third party.

Conclusion
Krell's Fully Balanced Integrated is the best integrated amplifier I have heard. Those who were previously unable to use integrated amplifiers because of difficult-to-drive speakers no longer have to worry. This integrated amp has the power and finesse to drive the most difficult of loads.

In addition to having the power of a large, free-standing amplifier, the Krell FBI also delivers audiophile quality. The sound is detailed, clean and slightly warm in the midrange. Soundstaging is well-defined and the individual sonic images have an appropriate sense of weight and presence. The FBI does a good job of getting the music signal amplified and controlling the speaker load, without harming the signal itself.