![]() ![]() ![]() In fact, the Solo 575 is unusually powerful for a class-A amp, outputting a claimed 575W RMS into 8 ohms or 900W into 4 ohms, yet weighing only 70 lbs and having no external heatsinks. The subject of this review, the Solo 575 ($22,500/pair), is their most powerful iBias monoblock. Krell uses iBias in a broad range of models: monoblocks, as well as amplifiers of two, three, five, and seven channels. Krell's iBias circuit is said to monitor the amplifier's output current, which the company claims is a far more precise and efficient arrangement because it measures the real-time demands of the specific speaker to which the amp is connected. iBias is conceptually similar to the sliding-bias or tracking-bias amps of the pastNelson Pass's Threshold 800A of the 1970s might have been the firstin which input signal was monitored, and that information was used to adjust the bias voltage, all based on an assumed speaker load. And I would guess that Krell isn't willing or able to invest in a separate line of mono or stereo class-A amps designed only for audiophiles.Ī class-A amp that would be sensible for use in a multichannel system would have to produce a prodigious amount of power, be of practical size, consume little power at idle, and run relatively cool, eliminating the need for massive heatsinks Krell's recently developed iBias technology (patent pending) appears to fulfill those requirements. While class-A amplifiers figure prominently in Krell Industries' genome, the company has steered clear of them for a whilepresumably for the disadvantages described above, and because those disadvantages make traditional class-A amplifiers impractical for home-theater-friendly, high-powered, multichannel systems. And that, say class-A fans, is the source of the breed's magical sound, which is often described as smooth, rich, and coherent from top to bottom. These disadvantages are the results of class-A's advantages: When output devices are biased for class-A operation, the crossover distortion normally generated as the signal swings from positive to negative and back is eliminated. And these days, energy inefficiency is out of fashion. This is why class-A amps tend to produce relatively low power, and tend to be heavy and expensive to buy and run. They're inherently inefficient because their output devices conduct full current at all times, and much of that current is dissipated as heatrequiring, in the case of class-A solid-state amplifiers, massive heatsinks. ![]() Class-A amplifiers have a well-deserved reputation for being power guzzlers that run hot enough to burn fingers. ![]()
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