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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

Showing 2 responses by johnlnyc

johnlnyc's avatar
johnlnyc
59 posts
 

Maybe Martin Collums in his Stereophile review, gets it.

“Krell's regulation feature is still more impressive when you take into account Krell's "Sustained Plateau Biasing," a patented Krell technique that provides an effective equivalent to class-A biasing—without a long-term power dissipation penalty—by anticipating the size of any and every musical event (footnote 1). It uses high-speed current-feedback circuitry to do this, then holds these required levels in a static condition for tens of seconds after the event is over. This minimizes any possible dynamic interaction of bias level with sound quality. The FPB 600's seven stages of bias represents the highest evolution yet of this technique…”

 

 

johnlnyc's avatar
johnlnyc
59 posts
 

Where’d this “anticipator circuit” come from? 
I also don’t think any “green revolution” is impacting class A amplifier design and production. Anymore than it is driving development or sales of  class A/B,D etc….

As I see it, Krell has been attempting to improve their amplifiers by innovation which includes removing/addressing issues with class A amplification while maintaining the benefits. Heat, and efficiency being the problems with fully class A.

I doubt Krell is just tossing about ad claims to sell product. They are not a mass market company looking to move amps and ramp up production.

I do not, I am no engineer, think the OP bass drum analogy accurately describes what Krell is doing here. It is a sort of straw man. The process is patented. It can be proven on the bench and to the ears. It either delivers its goal or it does not.

It is not as some seem to think, a secret circuit that can tell the future. In the end does it deliver on its promise?

https://www.hificlube.net/media/11276/krell_ibias.pdf 

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