New Krell Amps.

[dallasjustice]

I wonder how they will compare with the evo amps? I just can't imagine this new line is going to sound anywhere close to the evo amps. The trafo on the new monos is only single 750 VA.

 

[Tom B.]

I miss the FPB Mono series, such as the 350 MCs all the way up to the FPB750MCx's. Build quality was waaaaay over the top.

Sigh.........

Tom

 

[Morbius]

They are using a 'new' type of adaptive or sliding bias, which is claimed to maintain Class A operation by adjusting the output transistor bias in real time. Whether this is considered "true Class A" is likely to be debated!

Bill,

The definition of Class A is quite clear; a Class A amp has the active element ( tubes or transistors ) in the conducting state through out the full wave cycle.

That is the case with the Krell amps; going back to their first attempts at adaptive bias, namely the "sustained plateau bias" scheme.

Since the transistors are always conducting; never going in to either saturation nor cutoff; then the amp is clearly Class A, and has all the advantages of a Class A amp ( ex. no crossover distortion )

Dr. Gregory Greenman

 

[audio.bill]

Bill,

The definition of Class A is quite clear; a Class A amp has the active element ( tubes or transistors ) in the conducting state through out the full wave cycle.

That is the case with the Krell amps; going back to their first attempts at adaptive bias, namely the "sustained plateau bias" scheme.

Since the transistors are always conducting; never going in to either saturation nor cutoff; then the amp is clearly Class A, and has all the advantages of a Class A amp ( ex. no crossover distortion )

Dr. Gregory Greenman

Dr. Greenman - I appreciate your clarification of specifically what defines Class A operation. I'm an Electrical Engineer and fully understand what defines the various operational classes in amplifier design. There have been numerous engineering attempts over the years at using adaptive/sliding bias with varying degrees of success. I merely meant to point out that in audiophile circles whether such designs perform up to the level of a constant high bias Class A design is likely to be a subject of much debate. Naturally this will be based upon their relative subjective performance, but isn't that part of what makes high end audio so interesting and emotionally engaging?

 

[Roger Dressler]

Since the transistors are always conducting; never going in to either saturation nor cutoff; then the amp is clearly Class A, and has all the advantages of a Class A amp ( ex. no crossover distortion )

A transistor in saturation can still conduct. That's how we make clipping.

 

[Gregadd]

Fans worked fine on the n.y.a.l. Moscode 600.
Did you see the Hunt For Red October?

 

[mep]

What was the last amp/preamp designed by Dan before he lost control of his company and someone else started designing Krell gear?

 

[microstrip]

Dr. Greenman - I appreciate your clarification of specifically what defines Class A operation. I'm an Electrical Engineer and fully understand what defines the various operational classes in amplifier design. There have been numerous engineering attempts over the years at using adaptive/sliding bias with varying degrees of success. I merely meant to point out that in audiophile circles whether such designs perform up to the level of a constant high bias Class A design is likely to be a subject of much debate. Naturally this will be based upon their relative subjective performance, but isn't that part of what makes high end audio so interesting and emotionally engaging?

The main question is if the artifacts introduced by modulating the bias current are not degrading the sound quality. One of the often forgotten advantages of class A is minimizing thermal distortions, perhaps modern semiconductors and circuit topologies are much less sensitive to fast thermal variations. Another one is power supply induced variations - a class A amplifier will have much less variations due to signal amplitude than a sliding bias one. However brilliant designers can probably compensate for these effects - some people considered pure class A as a brute force solution. But its proponents and supporters consider other operating regimes as a compromise solution for those who accept less than perfection... As you wisely say, all this makes high end audio so interesting and emotionally engaging.

 

[mep]

I would still like to know how many pure Class A watts the KSA-250 puts out.

 

[Peter Breuninger]

I'm holding on to my KMA 400s for a reason. Designed by Dan, blessed by Dan two years ago on a visit. He is one of the best audio electronics designers ever born. The Evos are great but not designed by Dan the man.