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In Reply to: RE: Class ab and class a posted by itolduso1000timesb4 on March 29, 2022 at 07:31:08
A/B amplifiers operate in A/B, not A.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Follow Ups:
So naim never existed I guess.
Unless it has sliding bias the output devices in a Class A/B are never "biased in the middle of the most linear part of the dynamic operating curve".
Since biasing in the middle of the most linear part of the dynamic operating curve is what gives Class A it's advantages (one being of the lack of generated harmonic distortion) I don't see how any of the power generated in a Class A/B amplifier can be called Class A.
The output devices in a Class A/B amplifier are idling (biased) and operating down in the non-linear "cutoff region". A region purposefully avoided in any good Class A design.
Class A/B is it's own thing. It is not a Class A amplifier that becomes a Class B amplifier when more power is needed. That would be an amplifier that uses sliding bias.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
well said.
Good luck though convincing 99% of the audiophile world though :)
Don't wrestle with pigs. You both get dirty and the pig likes it.
Mark Twain
that talk about the so called "Class A" part of AB operation then turn around and say this,
"Notice how the current fluctuations in a proper Class A amplifier are always centered around the mid-point, that 50% of maximum which is the same as the idle current."
Someone needs to put 2 and 2 together.
"In Class A, the current swings are always centered around that mid-point idle current which is 50% of maximum. This is called "biased around the mid-point of the linear region". That's vital for low distortion. The other classes of operation, Class B and Class AB are definitely not biased anywhere near that mid-point "
That is correct, AB is biased in the non-linear cutoff region.
Or this website that first says
"As we said above, the Class AB Amplifier is a combination of Classes A and B in that for small power outputs the amplifier operates as a class A amplifier but changes to a class B amplifier for larger current outputs."
And then says
"For Class A amplifier operation the switching transistors Q-point is located near to the centre of the output characteristic load line of the transistor and within the linear region."
Sorry but you can't have it both ways. Class A amps never operate in the non-linear cutoff region unless they are being over driven, Class AB amplifiers can't help but operate in the non-linear cutoff region because the output devices are idling (biased) there.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Perhaps it is a sliding bias, I don't know. As I said, Nelson Pass claims the Int-60 puts out 60 watts, with the first being class A, before switching to A/B. You can take it up with him. No one said anything about class B. Other manufacturers do similar, though not as extreme.
Jack
The Pass INT-60 cost about $10k.
I think Tre knows what he's talking about. It would be more wise to pick his brain on the topic.
And I do respect Tre.
Jack
.
Rega RS 10.
Deceptive specs.
Tweeter sensitivity = 88db. no other sensitivity given.
There's a good chance you'll be in A/B territory on any A A/B amp. Not that that's necessarily bad. If you want Class A, you will have to go A all the way.
Jack
Deceptive specs, a British trait I fear.
As I said, 60 watts, the first 30 are class A.
You don't give a price range.
Jack
That was a typo. Someone brought to my attention that the booklet with the product correctly states the efficiency of the speakers is 88 db.
Some (many?) can be biased so that the first few watts are in class A.
Jack
The output devices in a Class A/B amplifier are biased a little bit on. This is to prevent crossover distortion. Because of that there is a time, for the first few watts, that they don't reach cutoff.
That is not Class A operation. Class A operation is much more than just not reaching cutoff.
Again, a Class A/B amplifier operates in what is called Class A/B. Not A then B or A then A/B but A/B. A/B is it's own thing.
The original question should have been, "How many watts can I get from my A/B amplifier before the outputs start to reach cutoff". That would have been a proper question.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
that's paltry and insignificant. You could say that most AB amps do that
or almost one-seventh its rated AB output.
it's a nary heard of Kinergetics KBA 75 and the E bills are climbing a bit more now and will get even worse. Believe it or not my Quad amp with the current dumping is dam close and the current draw is much less.
Again, it depends on how they are biased, as I said in my previous post.
The first few can be quite a few actually. Did you read my other response to the OP?
Jack
and ONLY if you have high efficiency speakers that only need a few watts will it make a difference - you may not even enter AB that way. I know this because I used to have horns. I now live with electrostats and I'm quite happy with them
I am assuming the OP is inquiring about a similar situation.
FWIW, I went from electrostats to horns.
Jack
nice to meet you Jack, I had both for many years but eventually settled down with the love of almost a lifetime, my Uncle's Quad 57's
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