Krell CMT, what is it? - diyAudio
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Old 31st May 2007, 03:18 PM   #1
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Default Krell CMT, what is it?

Krell uses current instead of voltage for signal transfer.

CAST uses Krell's Current Mode Technology (CMT) to transmit the signal as current rather than voltage. Normally, you'd want a system's preamp output to be low and the power amplifier's impedance to be high, but that creates a situation in which the interconnect's impedance could affect—even distort—the signal voltage operating the amplifier. CAST, says Krell, transfers current from a high-impedance source to a low-impedance load, essentially eliminating the cable's effect on signal transmission. And, if you're using a CAST CD player, the signal can be taken straight off the DACs without going through a current–voltage conversion stage.

That, says Krell's CEO and chief designer, Dan D'Agostino, is crucial. When D'Agostino was working on Krell's CMT, "I noticed that every time we did an I-to-V conversion, the converter added noise and grain and messed with detail, so I just said, 'Wouldn't it be wonderful if we didn't convert this at all and ran it as a pure current signal from input to output?' Once we thought of it—well, it would be wrong to say it was simple, but getting out of the voltage-gain mindset was the 'ah-ha!' moment, and the rest was just engineering. And engineering is what we do."
Transfering from high impedance to low impedance?
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Old 31st May 2007, 03:26 PM   #2
Hartono is offline Hartono  Indonesia
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Hi David,

Yes current output , the current output like to see very low impedance.

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Old 31st May 2007, 03:41 PM   #3
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This is also interesting

"Class-A is a needy technology in terms of space, heat management, and efficiency, which nobody knows better than Krell. The problem with not using class-A is notch distortion, which is where our driver stage comes in. The driver stage, designed like a mini-output stage, takes over and shoulders the load, just bulling the output stage through the area where notch distortion would occur if it weren't being controlled by the driver. The pre-driver stage is designed to deliver massive throughput—Dan D'Agostino calls it 'Hoover Dam'—and the input stage is a triple-cascoded current mirror, which is low distortion, which means we aren't introducing errors at that point that get amplified down the line."
The notch distortion (x-over distortion?) is canceled by the driver stage? What is this, somekind of EC?
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