Krell anticipator circuits of the 1990s


"Krell FPB-600 Stereo Power Amplifier

This big power amp features the evolution of the plateau biasing circuit introduced in the KSA series of amps. This circuit anticipates the power demands of the output by monitoring the incoming signal as the demand for power increases, the more power the amplifier supplies. After a grace period of fifteen seconds and no additional high current signal demands, the Krell FPB-600 amplifier returns to its appropriate power setting. This feature allows for Class A bias output without all the wasted electricity and heat."

Do you believe the anticipator can up the bias quickly enough?  A guy hits a huge bass drum, the anticipator circuit senses this and ups the bias in time for the hit to be amplified in Class A?

We are talking a micro second.  Once he hit it the start of the moment was over.  This was a con.  Created by Krell because they were under pressure from the emerging green lobby to cut power consumption.  Qualified Krell service engineers have not been able to explain to me how it can work.

Me?  I still have my KRS200s.  Pure Class A.  So there's my answer.

 

128x128clearthinker

@clearthinker I agree with you new is ot a given that it is better. The idea that technology has advanced so much I find interesting what is really new technology in amplifiers? Preamplifier s? Phono stages? There have been both forward and backwards steps in digital. Some components have gotten better. In my personal opinion the levinson 33h s i have, got better with the new caps better than the original ones. I think powercords have got much more balanced in the last thirty years. The hifi receptacle s are much better than the hospital grade which were much better than standard receptacle s. Things have progressed but not everything and the old top of the line new product s are still contenders and the new ones have to be really good to be as good. The only amps that I have heard that I think are better than what I have or possibly are is a pair of de agustino mono blocks I heard in a store demo a couple years back they were there top dog at the time and were really pretty wonderful. Very few times do I listen to a demo and think I could live with that system. This was one of the few times I could say that.

@clearthinker - it sounds like you have already decided that Krell's plateau bias technology is just marketing BS. I read through the patent in detail and, as an EE, I do think it's a clever approach and not just hype. Whether it really improves the sound quality compared to operating the same circuitry with a fixed class A/B bias, I can't say. But I was pretty impressed with the sound quality I got from this amp. When driving various Magneplanar and Revel speakers, I thought the sound quality was on par with the much less efficient Krell MDA-300 monoblocks that my FPB-300 replaced. 

When it failed after 20 years, I decided to trade it in instead of getting it fixed or I would probably still own it.

I like my Pass XA60.8 monoblocks a bit better (as well as my 300B SET amps), but my current speakers are a lot more efficient, my musical tastes have changed, and I generally don't listen at as high a volume as I used to. 

My favorite sounding Krell monoblock amplifiers to present day are the Krell MDA 300. I think the quiescent current per monoblock is 400 watts.🤒 😎

Mike

 it sounds like you have already decided that Krell's plateau bias technology is just marketing BS. I read through the patent in detail and, as an EE, I do think it's a clever approach and not just hype.

Totally agreed. 👍

The same can be said for class G and class H topology.