Class designs? A, B, AB, C, D, etc.

[Drew664]

I'll just say I read the wiki on these designs, and it went right over my head. What I'd like to know is in layman terms, how each amp build effects sound, efficiency, and the build itself.

The spur behind this thought is the big monster that Emotiva is brewing. A 400w x 7 class H amp. Why class H? What's the difference between these builds? Is there a class that tends to perform better for music or HT?

If anyone could shed some light on this, it'd be appreciated. All of my Google searching has resulted in over technical answers.

[naturephoto1]

You may wish to read through the article in Wikipedia:

http://en.wikipedia.org/wiki/Electronic_amplifier

Rich

[Johnny Vinyl]

Originally Posted by naturephoto1

You may wish to read through the article in Wikipedia:

http://en.wikipedia.org/wiki/Electronic_amplifier

Rich

Great minds think alike!

John

[Drew664]

That's actually the exact article I was referring to in my original post. It's just overly technical to understand what separates these amp builds in real world situations.

Still confused.

EDIT:

I'm not 100% confused though. I know that anything past A seems to have bigger and badder amp innards. So you'd want the higher grade amp builds? Is there any amp build that is superior to music or HT?

[naturephoto1]

Originally Posted by Drew664

That's actually the exact article I was referring to in my original post. It's just overly technical to understand what separates these amp builds in real world situations.

Still confused.

Sorry Drew. Amp designs are a bit confusing. Perhaps one of our EEs on the forum or maybe Big Daddy can enlighten us more.

At least for the longest time, Class A followed by Class A/B biased high for class A and/or run in Class A for a fair number of watts have been thought to produce the best audio.

As examples for my own equipment:

My Krell KAV-250a/3 is a 250 RMS watt into 8 ohms class A/B amp; but according to what I have been told by Krell service the amp is supposed to put out approximately 60 watts of Class A power per channel into 8 ohms. The upgrades to the amp have improved the performance of the amp however decidedly.

In the case of my 4 Aragon Palladium 1K monoblock amps they are supposed to be 400 RMS watts into 8 ohms class A/B; they are also supposed to put out 125 watts of Class A power per channel into 8 ohms. The upgrades to these amps have made a tremendous improvement in the performance of these amps.

Rich

[richteer]

Originally Posted by Drew664

I'll just say I read the wiki on these designs, and it went right over my head. What I'd like to know is in layman terms, how each amp build effects sound, efficiency, and the build itself.

The spur behind this thought is the big monster that Emotiva is brewing. A 400w x 7 class H amp. Why class H? What's the difference between these builds? Is there a class that tends to perform better for music or HT?

If anyone could shed some light on this, it'd be appreciated. All of my Google searching has resulted in over technical answers.

The amplifier classes come from how the output stage is biased. Normal push/pull amps have one or more pair of output stages: one to amplify the +ive part of the signal, and one to amplify the -ive part of the signal.

Depending on how well matched the devices are, there will likely be some distortion as the signal crosses the 0V level, turning off one output device and turning on the other.

What I described above is a Class B amp. A Class A amp attempts to get rid of the switching distortion by having the output device turned on all the time. Although this is good for sound quality, it is very inefficient. Hence Class A amps tend to run hotter and use more power than other designs (but also tend to sound the best).

Most amps are a cross between Classes A & B: Class AB, where the amp runs in Class A for some of the time and Class B for the rest.

Class D usually refers to digital--or switching--amps. They're very power efficient (which is why most receivers use them), but arguably have some way to go before they sound as good as the better Class A/B designs.

The Class H to which you refer is probably some marketing bullshit for Class D.

[richteer]

Originally Posted by Drew664

I know that anything past A seems to have bigger and badder amp innards. So you'd want the higher grade amp builds? Is there any amp build that is superior to music or HT?

An amp's class isn't a grade per se. And some Class A amps are huge (just about anything by Krell comes to mind)!

[Drew664]

Excellent. Thank you Rich and Rich.

This has already been very informative. I am glad that I can narrow down my amp searches to a class A design.

I would like to know why a company (I'll use Emotiva for this example since I brought them up earlier) would like to make their flagship amplifier anything but a class A design?

[Audiophile_At_Birth]

Originally Posted by richteer

The amplifier classes come from how the output stage is biased. Normal push/pull amps have one or more pair of output stages: one to amplify the +ive part of the signal, and one to amplify the -ive part of the signal.

Depending on how well matched the devices are, there will likely be some distortion as the signal crosses the 0V level, turning off one output device and turning on the other.

What I described above is a Class B amp. A Class A amp attempts to get rid of the switching distortion by having the output device turned on all the time. Although this is good for sound quality, it is very inefficient. Hence Class A amps tend to run hotter and use more power than other designs (but also tend to sound the best).

Most amps are a cross between Classes A & B: Class AB, where the amp runs in Class A for some of the time and Class B for the rest.

Class D usually refers to digital--or switching--amps. They're very power efficient (which is why most receivers use them), but arguably have some way to go before they sound as good as the better Class A/B designs.

The Class H to which you refer is probably some marketing bullshit for Class D.

Class H is not "some marketing bullshit" for a Class D amp. Look it up in the very same article that the OP is talking about, and educate yourself before making claims like you just did. It makes individuals come off as ignorant.

[JasonR]

That is strange, considering my bottom of the Emotiva line (UPA-2) is a class A/B. If class H is that bad, you would have to wonder why they would be putting it into their top amp. Where is this article you are referring to?

[naturephoto1]

From Wikipedia:

Class G and H
This section may require cleanup to meet Wikipedia's quality standards. Please improve this section if you can. (July 2007)

There is a variety of amplifier designs that couple a class AB output stage with other more efficient techniques to achieve a higher efficiency with low distortion. These designs are common in large audio amplifiers since the heatsinks and power transformers would be prohibitively large (and costly) without the increase in efficiency. The terms "class G" and "class H" are used interchangeably to refer to different designs, varying in definition from one manufacturer or paper to another.

Class G amplifiers (which use "rail switching" to decrease power consumption and increase efficiency) are more efficient than class AB amplifiers. The class G amplifier has several power rails at different voltages, and switches between rails as the signal output approaches each. Thus the amplifier increases efficiency by reducing the wasted power at the output transistors. Class G amplifiers can be used to combine the positives of both the Class AB and the Class D amplifiers in audio applications. It can be used to retain the high efficiency of Class D (while eliminating RF radiation) and the good music quality available with Class AB.

A Class H amplifier takes the idea of Class G one step further creating an infinitely variable supply rail. This is done by modulating the supply rails so that the rails are only a few volts larger than the output signal at any given time. The output stage operates at its maximum efficiency all the time. Switched mode power supplies can be used to create the tracking rails. Significant efficiency gains can be achieved but with the drawback of more complicated supply design and reduced THD performance.

Rich

[Big Daddy]

We had a discussion on Amplifier Classes several months ago.

https://forum.blu-ray.com/showthread.php?t=78772

[Rob J in WNY]

I love threads like these (the tech-head that I tend to be).

Here's an interesting article from the Peavy website which I have referred to in the past, and is not limited to "pro" audio amplifier application.

The Pros and Cons of Amplifier Design

It's a concise, but nice read.

[naturephoto1]

Originally Posted by Big Daddy

We had a discussion on Amplifier Classes several months ago.

https://forum.blu-ray.com/showthread.php?t=78772

It did not touch on Class G and H amps though.

Rich

[Drew664]

Reading through the two articles that do a good job of summing up each class has been good. And for the sake of a contrast argument for class A vs Class H I'll take some choice quotes.

Class A

Pros: Since neither output stage ever turns off, device non-linearity and turn-on/turn-off time can be minimized or ignored, resulting in very low distortion designs.

Cons: As the maximum output is limited to the constant current stage, at idle this stage must put out full power and the variable stage must absorb this full power. Transformer, heat sink, and output stage must be sized for continuous duty at maximum power. Because of cost and the amount of waste heat generated by this approach, Class A only appeals to esoteric hi-fi designers, where lack of efficiency or price is no object.

Class H

Pros: More efficient amplifiers can deliver the same output power with smaller transformers and less heat sink.

Cons: Circuit complexity increases, which adds cost. Switching distortion similar to Class B's crossover distortion occurs at each output level transition.

Conclusion

Highly efficient Class D amplifiers now provide performance similar to conventional Class AB amplifiers if key components are carefully selected and the layout takes into account the subtle, yet significant impact of parasitic components. Greater efficiency, increased power density and better audio performance are driving the increased use of Class D amplifiers with even more improvements on the horizon.

Are we at the tipping point? Do class D/H amplifiers perform at the level of A or AB amplifiers?

And still bringing up the Emotiva line, all of their XPA amplifiers are AB - yet their flagship amp is planned to be class H. I can only think that they are going this route because of how much power they want to give each channel. If the sound performance gap is narrowed to a near inaudible difference, the power efficiency of class H amps might be a deciding factor.

[naturephoto1]

Originally Posted by Drew664

Reading through the two articles that do a good job of summing up each class has been good. And for the sake of a contrast argument for class A vs Class H I'll take some choice quotes.

Class A


Class H


Conclusion


Are we at the tipping point? Do class D/H amplifiers perform at the level of A or AB amplifiers?

And still bringing up the Emotiva line, all of their XPA amplifiers are AB - yet their flagship amp is planned to be class H. I can only think that they are going this route because of how much power they want to give each channel. If the sound performance gap is narrowed to a near inaudible difference, the power efficiency of class H amps might be a deciding factor.

Drew,

I think that the Class H amps combine features of the Class A/B (Output Stage) and Class D (efficiency) abilities.

Rich

[richteer]

Originally Posted by Drew664

This has already been very informative. I am glad that I can narrow down my amp searches to a class A design.

I would like to know why a company (I'll use Emotiva for this example since I brought them up earlier) would like to make their flagship amplifier anything but a class A design?

Because Class A amps tend to be very big and very expensive!

Don't get caught up in the Class A thing; like I said before, it's more of a design classification than a qualitative measure. Doubtless, there are crappy Class A amps out there and excellent Class A/B amps.

[richteer]

Originally Posted by Audiophile_At_Birth

Class H is not "some marketing bullshit" for a Class D amp. Look it up in the very same article that the OP is talking about, and educate yourself before making claims like you just did. It makes individuals come off as ignorant.

I sit corrected (although in my defence, I did say "probably marketing bullshit", i.e., I was hypothesising)!

[rded]

Discussions like this are interesting but make my head swirl I feel I understand amp designs a little more...
I am just a music lover and I don't purchase stuff primarily for their specs and design, rather I pursue the AV gear that performs the best to my eyes and ears and fits the budget especially the WAF.

[zicmubleu]

Originally Posted by Drew664

Reading through the two articles that do a good job of summing up each class has been good. And for the sake of a contrast argument for class A vs Class H I'll take some choice quotes.

Class A


Class H


Conclusion


Are we at the tipping point? Do class D/H amplifiers perform at the level of A or AB amplifiers?

And still bringing up the Emotiva line, all of their XPA amplifiers are AB - yet their flagship amp is planned to be class H. I can only think that they are going this route because of how much power they want to give each channel. If the sound performance gap is narrowed to a near inaudible difference, the power efficiency of class H amps might be a deciding factor.

From a purely electronics design standpoint advances in switching power supplies most likely have allowed the Class G and now Class H designs to rival a Class A amp on a much lower cost basis. Think of the advances in electronics in the last 20 years, Class A is from the earliest days of circuitry design. Emotiva is simply riding the wave of electronic design enhancement possible by microprocessor controls in the power supply. Only time will tell if they effectively implemented it, but unless you have Naturephoto or Richteer's ear and ability to hear minute differences in sound I would bet that the Emotiva will sound great and is a good bang for the buck.