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In Reply to: RE: Class ab amps posted by Tre' on February 02, 2022 at 19:57:43
Finally someone got this right.
The amps don't magically shift between operating modes.
Dan Santoni
Follow Ups:
Pass: " Class B has no bias current, Class AB has a moderate bias current, and Class A has a high bias current. Class AB push-pull amplifiers are hybrids between Class B and Class A. Class AB run Class A at low power levels, and become Class B amplifiers at output currents determined by the bias . " {emphasis added}Pass: " Push-pull amplifiers generally operate in Class A mode up to a point where the output current is twice the value of the bias current. In the Class A region, both halves of the circuit share the signal simultaneously. Beyond that the signal is handled solely by the push (+) half of the amplifier or the pull (-) half. "
What might be fair to say is that A/B amps don't cease being class A when more power is demanded: only the peaks , '+' or '-' of the signal operate in class B mode. There is nothing magical about the shifting.
Dmitri Shostakovich
Edits: 02/03/22 02/03/22
"What might be fair to say is that A/B amps don't cease being class A when more power is demanded: only the peaks, '+' or '-' of the signal operate in class B mode. There is nothing magical about the shifting."
Then the definitions (and distinctions between) of Class A and Class B and Class A/B have lost their meanings.
I think Pass said what he said, the way he said it, just to get a point across to the non technical reader.
I think he was really saying something like this,
The amp is not Class A at low power but it has something in common with a Class A amplifier, the output devices don't reach cutoff (***like in a Class A amplifier***) when at low power. The amp is not Class B but it has something in common with a Class B amplifier when at higher power levels, the output devices do reach cutoff (***like in a Class B amplifier***).
But just because those two thing are "like" Class A and Class B that doesn't make the amplifier a Class A or a Class B amplifier. It is neither, it is a Class A/B amplifier. Class A/B amplifier are there own thing. Nelson was just trying to get non technical people to understand how they do what they do. He was not trying to re-define the meaning of Class A and Class B or Class A/B. All three are already well defined.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
It would appear that you have a new definition of amp classes because Nelson Pass is spot on when it comes to the original definition of Class A, AB and B.
I think I get what you are saying.
In order for class A and B to integrate into A/B, the basis for each is there, but they never truly work as pure now that they are called upon to work together vs how they would work on their own.
It would be like asking an 8 cylinder motor in 4 cylinder variable management mode for better gas mileage, response and RPM's, to give you the identical benefit of a pure 4 cylinder motor. Close but not quite the same.
Motor analogy aside, I wonder if the class B portion of A/B is also somewhat less pure and perhaps audibly different vs a pure class B amp at high volumes.
Jonesy
"I know just enough to get into trouble. But not enough to get out of it."
nt
Dmitri Shostakovich
Devialet amps have what is called "Analog Digital Hybrid ". The voltage gain is Class A, while the current gain is Class D. They have a patent on this.
It's the best sounding set of amps I've heard to date.
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
!
The Mind has No Firewall~ U.S. Army War College.
Check out this link
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
They didn't exactly love it; see link below.
Dmitri Shostakovich
Check out the Stereophile review of the D-Premier. One will get a MUCH different perspective. BTW, JA also measured the unit. Virtually every review of Devialet amps outside of ASR provides the strongest positive recommendations, especially if configured in mono.There are other measurements that reviews could conduct that would provide better insight as to how gear sounds in real world usage. Reviewers don't provide those. I take ASR reviews with large grains of salt.
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
Edits: 02/04/22 02/04/22
If you did, you would see that Amir mentioned John Atkinson's Stereophile review, (see link).As Amir points out, Atkinson's measurements do also reflect the high frequency power limitation. Atkinson is a sort of "glass half full" guy where as Amir is more of a "glass half empty" guy.
Personally I feel that JA too often glosses his reviews to deemphasize components' shortcomings.
Personally I don't think measurements are everything, OTOH I believe there is usually some correlation between measurements and SQ.
Dmitri Shostakovich
Edits: 02/04/22
Read any other review of Devialet, especially the D-Premier. 250, 250 pro, and they universally rate them among the very best available at any price. Some of the sound quality is due to the slick method the DAC is integrated into the power amp section. The fact that the voltage operates in Class A means practically that there is no crossover notches in the audio signal. No one else has come up with this approach. Since pretty much every reviewer greatly praises the Devialet, one naysayer who uses a subset of measurements that don't fully translate to the design objectives does not carry much weight with me, nor dare I say the many other reviewers and owners.
Tweeters aren't meant to take or need a lot of power.
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
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