Krell anticipator circuits of the 1990s

@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.

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?

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.

Thanks for your posts.  I think so far 3.5 to 0.5 in support of my position.

@jew16384   You offer suggestions as to elements of the design that might be engineered with the objective of moving instantaneously from Class B to Class A bias.  (Put like that it sounds an impossibility).

You say ' Of the speed of the gain decision must be quick.'  Indeed it must.  What I asked is can it be quick enough to amplify a signal just heard in pure Class A.  i.e. to change bias instantaneously.  That is an impossibility.  The only way of doing it would be to buffer the signal and amplify it later. when the Class A bias had been achieved.  But that would entail all sorts of dither and clock distortions, turning an analogue signal effectively into digital when I wanted to listen to LPs.

@jew16384

Yes it is unneeded complexity.

Note: I can't get a 'retransmission' of what comes out of the groove on my LP.

I don't think cost was a main motivator; look at the price of Krells until D'Agostino sold and the price of D'Agostinos now.  More like 'price no object'.  Neither was lowering the weight and size an issue.  Just look at today's big amps, even if they are all AB hybrids.

No, the green lobby was the big motivator as I suggest in my post.  That is why there are few pure Class A amps today and to my knowledge no really big ones.

I want the dynamics I paid for in my media (mainly LPs).  That's why I keep the KRS200s (in fact uprated to 400w/side for a UK Krell dealer, from whom I bought them way back.

@invalid     Sorry.   I meant to type KRS200s.

@yyzsantabarbara 

Thanks for letting me know.  But I will stay with my KSA200s.  Don't want computerised bias shuffling.  Keep it simple, as someone here rightly said.

@yyzsantabarbara   Yes I did watch the video.  This adds nothing to the story.  The Krell personnel say the Class A watts output is varied according to monitoring of the watts of the signal output.  It does not say how it is done - 'we've found a way...', 'a very high degree...'., 'this is completely new...'.  All this is marketing puff.  It does not say how long the amp takes to adjust the bias in response to the measured output.

Since Krell must know the length of the delay, we are left to assume it must be relatively long.  If it were so short that there is an argument that its effect is inaudible, Krell would surely have told us the details.  This is all very unsatisfactory and in the result I continue to use my KRS200s.

Indeed.  If they don't tell us the details then we can be pretty sure it's a pig in a poke.

It may even be the iBias circuit is a spoof.  If there is anything good to tell then they will tell it.  They are protected by patents, after all.

If it sounds impossible then it probably is impossible.

It's interesting that the subject of my initial post:1990s anticipator circuits, continues into new Krell products being launched right now, nearly 30 years later.  Brought my subject right up to date.  Maybe they're still selling the same old tat.

Not at all like Krell's first product, the KSA50 which was and remains wonderful.  I still use the one I bought nearly 40 years ago, in my second system.  Not even a service required, although use has been sparse these 30 year.

I still don't believe it.

@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.

@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.

@retiredfarmer     Thanks for your understanding and kind words.  I agree with all you say.

I do take Stereophile (not AS as I have been a John Atkinson fan for the whole of his journalistic career) and am keen to keep up with all the new products.  But like with my cars I don't change equipment very often and very rarely sell anything.  Now approaching my mid-70s I am increasingly finding new products, especially cars, are not to my liking and that I get more pleasure and satisfaction with the older stuff I already have.

Neither am I much of a tweaker.  I use stock mains cable and have had my heavy Kimber speaker cables 20+ years and all Kimber silver interconnects for longer than that.  I am sure someone will tell me they oxidised years ago but the music still sounds great to me.

Perhaps one should not generalise about blue collar people, but one thing most of them do not do is love their work; maybe it's not that kind of work.  I loved my work and got as much out of it is from my down time.  Spending most of the time working it is crucial that it is found enjoyable.

Yes I love Da Vinci and Monet but also Dali, although I can't do the really modern stuff.

@yyzsantabarbara    I am not up with the new Krell to which you refer.  However, surely if it stays in Class A all the time then it is a (pure) Class A amp.  If this is the case it has no need of iBias monitoring or adjustment as it is in Class A all the time.

So what am I missing?

@johnlnyc 

Martin Collums doesn't add anything to the debate.  He eulogises the anticipator circuit.  But he doesn't say how long it takes for the bias to be changed.  That still hides behind the emperor's new clothes.

At this point it is necessary for me to repeat the question in my OP: how long does it take for the amp to react to the increased current generated by the signal (the big bass drum hit) before the bias is restored to Class A.

No-one has told me.  But it will be longer than it takes for the initial pulse of that drum hit to pass.

@invalid    What makes you sure the circuit is fast enough?  What evidence do you have?  I know of no evidence that has been published?

Of course it can be compared in the same way any alternative components are compared.  Listen to one, then the other.

@invalid    You used the term 'sounds better'.   We are comparing different amplifiers all the time and expressing opinions as to which sounds better (to the listener).  None of these has the same circuit design, yet we express opinions, sometimes vehemently.

By the way, what makes you sure the circuit is fast enough??

@johnlnyc    Thank you for this input.

As in my OP, the anticipator circuit is claimed to monitor the output from the pre-amp and adjust the bias quickly enough so that the change has taken effect before that output is amplified.  A tall order I think.

At the introduction of the FPB series environmental issues were discussed.  My KRS200s draw more than 1kW per side.

Just because an idea is patented doesn't mean it is effective.

As a manufacturer previously claiming the benefits of pure Class A, if they wished to sell FPB prorduct it was encumbent on Krell to claim they had overcome the disadvantages of Class AB designs.

Yes the circuit could be proven on the bench but it has not been.  The time that the circuit takes to adjust the bias has never been revealed or found.  To that extent it is a secret circuit.

The paper you publish does not speak of the time it takes to change the bias.

I never said it was claimed the circuit could tell the future.  It does claim it can change the bias quickly enough in response to changes in the signal.  We don't know if that claim is true or not.

Very much as I thought.  No point in carrying power supply capacity that will never be used.