Superfi or madness

[Macca]

A lot of Krells use their 'Sustained Plateau Bias' circuit:

Krell's "Sustained Plateau Biasing," a patented Krell technique that provides an effective equivalent to class-A biasing—without a long-term power dissipation penalty—by anticipating the size of any and every musical event. It uses high-speed current-feedback circuitry to do this, then holds these required levels in a static condition for tens of seconds after the event is over. This minimizes any possible dynamic interaction of bias level with sound quality.

The KSA50S which has this feature only gets moderately warm unless you thrash it at high levels.

The older models don't have this feature, for example the KSA100 mk2 with its twin fans puts out 650 watts of heat through its top vents, pretty much the same as a domestic convection heater. But it is 100 watts in class A. In the winter you don't need any other source of heat in the room.

[Pharos]

The theoretical figure is 50%, the figure in practice is likely to be a little lower.

My 45% was given as a maximum theoretical efficiency.

[Lawrence001]

A lot of manufacturers try and get round the class A efficiency issue with varying solutions. I'd be interested to compare them to see which get subjectively closest to the class A sound.

I suspect the answer would be there's no such thing as a free lunch but would like to be pleasantly surprised.

[Macca]

A lot of manufacturers try and get round the class A efficiency issue with varying solutions. I'd be interested to compare them to see which get subjectively closest to the class A sound.

I suspect the answer would be there's no such thing as a free lunch but would like to be pleasantly surprised.

Is there actually a class A sound? I'm not sure there is. I suppose years ago when crossover distortion was still a thing then class A was a solution to that, but now it seems a bit superfluous.

I got three different class A power amps here but I choose to use one in favour over the others. So if class A does matter to the sound whatever it might be doing seems to be eclipsed by some other factor.

Also one of the amps (an XTZ) can be switched between class A and class AB and doesn't - at least to me - sound any different, although it does get quite a bit warmer.

[Pharos]

The real dislike was with class B, and Xover distortion was very evident in their early days both by ear and measurement.

I think now that most A>AB, (and probably the Krell approach) have solved it all, and that even class D is extremely good.

[Barry]

Having looked into it a little more, it seems the efficiency of a Class A amplifier depends on the nature of the load, which under "usual configurations" (inductive or transformer coupling to the load) the efficiency can be as high as 50%. But with capacitative coupling the efficiency falls to 25%.

https://en.wikipedia.org/wiki/Power_amplifier_classes
https://www.electronics-notes.com/ar...-f-g-i-s-t.php
https://www.electronics-tutorials.ws...ier/amp_5.html

My speakers are Quad 57s, electrostatic speakers in which the nominally capacitive load is connected to the amplifier output via a transformer. The load in practice varies from being largely inductive (due to the transformer) at low frequencies, to being largely capacitative at higher frequencies. What this means to the overall efficiency of the amplifier I hesitate to say. But they do get hot - too hot to be used during the summer months!

[Barry]

The real dislike was with class B, and Xover distortion was very evident in their early days both by ear and measurement.

I think now that most A>AB, (and probably the Krell approach) have solved it all, and that even class D is extremely good.

Class D amplifiers are improving all the time, and will probably be the norm for audio amplifiers in the future.

[Pigmy Pony]

Oh not visiting me then


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I know, I would love a week's holiday down your way, but accommodation prices are taking the piss. Anita found somewhere in Wales where a caravan would cost us a grand for the week. In a bloody caravan! In Wales! God knows what it would cost to stay somewhere proper.

But I may still get to darken your door because:

I told her I'd empty the tools out of the van, and that could be our accommodation. Not so much a poor man's camper van, more a rich man's tent. I've not had the van long enough to make it into a shit pit, and I've seen somewhere tents/awnings that attach to side of van to give extra space, and which can be detached from the van when going out for the day.

There would even be room for the Fireblade to go in the back, so I can get out for the day ragging round the country lanes while Mrs. P stays behind to make me dinner. Starting to sound like the best holiday ever!

About that last paragraph: that's me dreaming, she'd never allow that

[legb4rsk]

I don't know - what does the giraffe think?

He's not going to stick his neck out.

[Barry]

He's not going to stick his neck out.

Boom Boom!