Class A amplifiers - which are considered the best

@Doggiehowser

The construction of the Karans are obviously different to a "traditional" Class-A design, as explained below(source: http://www.6moons.com/audioreviews/asi4/3.html):

"All Karan power amplifiers are characterized by a continuous sliding bias control. This is unlike the sliding bias used by Krell. Krell raised and lowered bias in predetermined steps like Mayan pyramids. In Karan designs an electronic circuit measures the incoming signal’s amplitude. If there's need for additional output power, the current on the power rails which supply the class A output transistors is raised instantaneously. When the input amplitude goes down again, the bias follows suit. This way the output transistors always obtain the right amount of current and the operational temperature of this hugely powerful class A amplifier remains luke warm even when driven very hard."

I can't tell how this might influence the character of the sound, but it seems like a very clever design with the benefits of less power consumption, (much)less heat and the possibility of a more compact(well...:) enclosure.

Didn't Nelson Pass create the sliding bias thingamabob?
:)

So does this sliding bias affect what George was talking about earlier when he said there was no way amplifiers could do 100s of watts of power in Class A mode?

I remember being approached by someone in the early 90s that held a patent to a sliding class A bias system (for transistors). As innovative as he is, I don't think Nelson created that. As I recall, it showed up on the Krell amps first.

We didn't go for it because our amps are tube. But I have thought about a tube-implemented class A system over the years. It might cool our amps off a bit!

George, I'm mightily impressed by your abilities (to take on such a challenging project) Beautiful work.

Your real name should be Georgehifi+!!

03-06-12: Doggiehowser: Didn't Nelson Pass create the sliding bias thingamabob? :03-06-12: Doggiehowser

In actual fact my ex boss (Steven Deratz) invented the first sliding bias system back in 1978 and had a world wide provisional patent on it for a couple of years. But his system worked a bit like negative feedback, it monitored the signal and tried to adjust the bias up and down in real time which was a loosing battle because it was never in real time, just like global negative feedback.

I don't think Nelson ever had an auto bias system just an optical bias system which was on the S300/S500 MkII's, when he did Class A he went more for the real thing.

Later Krells plateau bias where it kick it up and stays for a while and gradually comes down is the next best. But think about it the initial (first) transient is not in class A because it lags behind like my ex boss's system (so it's class B "harsh") then if successive transients "lower" than the original follow all's good they are in class A, if higher they are in class B again, and if there is a quite passage the bias drops down again and it starts all over again.
This is why, I strongly believe that proper hard biased Class A cannot be by any auto adjustable type system.

Cheers George