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

Showing 2 responses by mceljo

mceljo
1,351 posts
 

@dlcockrum - My friends amplifier is a Krell KSA-100S.  It has sustained plateau biasing with four lights on the front to indicate the various levels.  Not quite the same implementation, but similar concept.

mceljo
1,351 posts
 

A friend of mine has one of these Krell amplifiers, I think.  It has about 5 different ranges that are identified by lights on the front.  The example you give is very specific and it's almost always possible to find a specific example to expose a design flaw because every design has compromises.  The way I would look at it is that there could be something lost when the amplifier is first triggered to the next level and then anything within that level would be unaffected until it dropped down a level or was triggered to go to the next.  I would think that by watching the lights it would be possible to estimate the number of times that something was potentially lost during the initial instantaneous need to go up to the next level.  I think it's obvious that the sound would be expected to be something less compared to another Krell running wide open all the time, but there's reasons that make that design not ideal (though not released to the SQ most likely).

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