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 9 responses by invalid

invalid
1,085 posts
 

I’m sure the circuit can keep up with any musical dynamics, you may have an argument on if it sounds better than straight up class A because of the added circuitry, but there is no way to compare it unless someone comes up with an amp with a switch from this to straight up class A.

invalid
1,085 posts
 

The krell audio standard was the first variable bias amplifier krell made, it was their flagship amplifier at the time 1993 I believe.

invalid
1,085 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.

invalid
1,085 posts
 

The ksa amps with the anticipator circuit also have a couple switches on a circuit board that say relaxed/normal, if switched to relaxed mode it becomes a class A/B amp.

invalid
1,085 posts
 

The bias is always in class A unless you exceed a certain temperature, then the top two bias levels stay in class A/B until the temperature drops. 

invalid
1,085 posts
 

How would you compare it to another amp, unless it has the same exact circuit design one with the anticipator circuit and one without.

invalid
1,085 posts
 

Krell has never been forthcoming with any of their circuit designs and schematics. They also came out with sustained plateau bias long before the FPB series came out.

invalid
1,085 posts
 

It seems like all of A ksa300s weighs 3lbs more than the krell FPB 600,  seems like it should weight more given it's double the power. The only FPB series amp I like are the FPB 750 MCX monoblocks.

invalid
1,085 posts
 

Both the FPB 600 and the ksa300s have the sustained plateau bias circuit, krell just lightened the power supply on the FPB series.

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