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
invalid
1,180 posts
 

There is opto-couplers in my ksa 300s amp. It will give you 300 watts of class A power for only a little while as the heat sinks aren't big enough to sustain it. If it gets to a certain temperature it will be class A/b on the top two bias levels until the temperature comes back down.

retiredfarmer's avatar
retiredfarmer
342 posts
 

I heard  a set of bryston  7b monoblocks  compared  to the krell fbp600. I am not s bryston  fan but I found them to sound much better in that system  that day. A friend used to have a set of krell kma monoblocks  I really liked them. I never liked the 600. 

bsmith
68 posts
 

ksa 80 from 1991 never been serviced.

Brings it everyday.

So much power it scares me.

jaytor's avatar
jaytor
762 posts
 

Here is a link to Krell's patent describing their plateau biasing method. It adjusts the bias based on the amp's load current requirements, not the input signal. It seems pretty clever to me. 

Krell patent

clearthinker's avatar
clearthinker OP
1,582 posts
 

@jaytor   I think you've probably been taken in by the hype, because if it could change the bias instantaniously it would indeed be 'pretty clever'.

@retiredfarmer   As in many cases, a manufacturer's first products are the purest, possibly because they are conceived without thought of saleability and profit.

As I recall it, the progression from the start in I think 1983 was: KSA50  KSA100, KMA100 - two bridged KSA100s essentially, KSA80 - replaced KSA50, [possibly a couple more], KRS100, KRS200.  As I recall that ended the pure Class A series by the late 1980s.  I still have KSA50 as well as my KRS200s, and a very good sounding amp it remains after 40 years.  All progress is not good progress.

More to discover