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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
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clearthinker OP
1,582 posts
 

@invalid    I am aware of these facts.

Not so long.   I believe the first variable bias Krell was the KSA300S, launched in 1994.  The first of the FPB series started in 1997.

invalid
1,187 posts
 

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

clearthinker's avatar
clearthinker OP
1,582 posts
 

Thanks, right.  It was 35,000 1993 dollars.  KRS200s were around $30,000 in the late 80s, so very much on a par.

Looking around the used ads I find KRS200s are regularly priced around double the 1990s FPBs.  I wonder if this is related to sound quality?

invalid
1,187 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.

clearthinker's avatar
clearthinker OP
1,582 posts
 

I'm not sure one should evaluate amplifiers by weight although when I bought my first CD player I didn't do any auditioning but just chose the heaviest in my (low) price range on the basis it probably had the best build quality.  Little did I (or anyone else then) know that the SQ in CD players (and all digital sources) depends almost only on the clock, jitter and DA converters.  Reading error even in a flimsy plastic 50c computer drive is only a couple of bits per million.

I doubt the anticipator circuits account for much weight, but compromised Class A working should allow some weight reduction as the power supply section accounts for most of the weight.

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