2. amps-preamps
  3. 178665-147550

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
jaytor's avatar
jaytor
765 posts
 

@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. 

dlcockrum's avatar
dlcockrum
2,190 posts
 

Perfectly stated @jaytor. +1

ditusa's avatar
ditusa
1,887 posts
 

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

imhififan's avatar
imhififan
2,205 posts
 

 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.

 

clearthinker's avatar
clearthinker OP
1,582 posts
 

@jaytor ​​@imhififan      Well, if you read my first post you will have seen I do not believe the claims made.  I decided that in the 90s when the FPB amps were introduced.  I examined the proposition and discussed it with a Krell service engineer.  I do not believe the current of the signal can be determined and the bias changed before that signal is amplified.  I am not an EE but I have read the patent and it says nothing of the quantum of this time delay.  If this is not known then the system's suitability for audio use cannot be approved.

Amplifiers have very many functionalities apart from audio and Classes B thru H have their valid uses where their differing topologies suit the required functionality.  But for audio amplification none can deliver the sound quality of Class A.

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