Class AB vs. D vs. H Amp - AVS Forum
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post #1 of 33 Old 05-01-2011, 02:29 PM - Thread Starter
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I was wonder which class of amp people prefer to use for high wattage applications, either speaker or subwoofer.

How do amps like monoblocks(class AB) compare with amps like Behringer EP2500/EP4000, Marathon 5050, Face Audio F2000TX, or Wyred4Sound.

Also how important are capacitors in these designs?
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post #2 of 33 Old 05-01-2011, 06:27 PM
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Quote:
Originally Posted by yelnatsch517 View Post

I was wonder which class of amp people prefer to use for high wattage applications, either speaker or subwoofer.

How do amps like monoblocks(class AB) compare with amps like Behringer EP2500/EP4000, Marathon 5050, Face Audio F2000TX, or Wyred4Sound.

Also how important are capacitors in these designs?

Any of the three designs can be a high power amp. So I don't think that's a question worth asking, no offense.

For a light weight amp, you are looking at class D or class H. There are a number of pro amps using class D and class H designs that are quite affordable.

If by capacitors, you mean the reservoir caps used in the power supply, powerful class AB amps will tend to use a pretty large amount of capacitance. Not sure about class H amps. They are more efficient, so perhaps it's less common to use large cap banks, but that's up to the designer (you need sufficient capacitance to reduce power supply ripple - above that, you get some benefit in terms of dynamic power.)

A class D amp can use a "conventional" or switch mode power supply. With a conventional power supply, you need sufficient reservoir capacitance to reduce power supply ripple. Not sure about a switch mode supply, but I would expect less capacitance.

Switch mode supplies seem pretty common in various pro amp designs. They don't have to be class D amps.

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post #3 of 33 Old 05-01-2011, 07:05 PM
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Can you point me in the right direction of pro amps that are class D?
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post #4 of 33 Old 05-01-2011, 07:55 PM
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Originally Posted by Hawkson View Post

Can you point me in the right direction of pro amps that are class D?

Crown and QSC are two major brands.

http://www.crownaudio.com/indexmap.php

http://www.qscaudio.com/products/pro...plifier_Models

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post #5 of 33 Old 05-01-2011, 07:57 PM
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Answering the original question, class D amps have an advantage in the sheer amount of power they can pull out of the wall socket to drive low frequencies at high volumes. So while one doesn't want to generalize too much in this regard, they do tend to be better in this respect.

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post #6 of 33 Old 05-01-2011, 09:52 PM
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While I agree with that to some extent, I sort of think the OP has this idea that there's a best class of amp for high power applications.

And I contend that's only true if you are looking for a lightweight solution.

One way to view this is budget. There's budget power in the pro amp department, and not necessarily class D. IMO, if you want a lot of power cheaply from a well respected company, look at the QSC GX line. QSC GX5 or GX7 seem like winners (but I have never owned one.)

I can't recommend Crown's XLS, even though it looks fantastic on paper, because mine has too much noise. Maybe the XLS 1500 is fine though - it's SNR is better than the 1000. If it is quiet, it's a lightweight amp with plenty of power.

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post #7 of 33 Old 05-02-2011, 12:40 AM - Thread Starter
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Oh, sorry for the confusion guys. I was merely looking for people's personal preference and experience in these various classes of amps for either high power HT speakers, ie. passive JBL screen arrays, JTR speakers, etc. or in subs.

The question about the cap was just another question irrelevant to my first question as I was just wondering how some amps can get away with using much fewer/smaller caps.
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post #8 of 33 Old 05-02-2011, 02:22 AM
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I think this is an intereseting subject... I am receiving my JBL Screen Array speakers today for my new home theater, and have chosen to drive all speakers (LCR + 2 subs) with Behringer EP2500's. They provide more than enough power and I have previously used them and found them very good - and with all the money spent on the home theater, they were the obvious choice as they are very cheap

But I am very curious to what type of improvements I would get by upgrading amps. I know that many in here says, that as long as the amp is kept within its safe zone in regards to power, they all sound the same. This does not make sense IMO.

Others mention that Class D amps does not deliver a tight bass like A/B amps etc etc. I'm confused!

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post #9 of 33 Old 05-02-2011, 06:47 PM
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All amps distort. However, under normal operating conditions, it's normal for amps to have very low distortion.

There's a lot of theories on why amps can sound audibly different. There's blind listening tests showing people have problems telling amps apart though.

No idea why a class D amp would have any issues with bass just because it was class D. I have not read that. I should point out that some subwoofer plate amps use class D (pretty common I think.) It's not as if they can't reproduce low frequencies.

Not being an engineer, I can only speculate. Some speakers have low impedance dips around the bass resonance (you can see the typical bass reflex response curve in some places on line.) Perhaps some class D amps can't deliver the needed current, and the voltage sags resulting in insufficient bass. But that seems like a power supply issue, and not an issue with class D...assuming my theory is anywhere close to correct.

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post #10 of 33 Old 05-02-2011, 08:45 PM
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Quote:
Originally Posted by MichaelJHuman View Post

There's a lot of theories on why amps can sound audibly different. There's blind listening tests showing people have problems telling amps apart though.

There are also blind tests that show amps do color the sound they reproduce.

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post #11 of 33 Old 05-02-2011, 08:47 PM
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Originally Posted by JonasHansen View Post

Others mention that Class D amps does not deliver a tight bass like A/B amps etc etc. I'm confused!

I have done side-by-side tests of three different class D amps and all three of them, had better bass reproduction than class AB amp I was using to compare them with. I suspect a lot of this has to do with their high efficiency which allows their power supplies to recover faster from peaks.

So while it is important to not generalize the performance of few amps to all, my experience with the ones I have tested (Crown, Mark Levinson No 53 and Devialet D-Premier), bass performance is superior.

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post #12 of 33 Old 05-02-2011, 09:28 PM
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Quote:
Originally Posted by amirm View Post

There are also blind tests that show amps do color the sound they reproduce.

Fair enough

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post #13 of 33 Old 05-02-2011, 10:08 PM
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You are a good man Michael .

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post #14 of 33 Old 05-03-2011, 06:27 AM
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If you need really high power ( >1000W range) then you either use class D or H type. Both of them handle low frequencies very well, but have problems with upper frequences. Thus they are mostly usable to power subwoofers.
Class H amps work like AB when signal is low, so there is no difference from pure AB amps if you do not use full power. If you want you system to be really loud, use biamping with class D amp for woofers and AB for the rest. This setup with active (possibly digital) crossover wil give gou best sound and let keep size/weight of eqipment reasonable.
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post #15 of 33 Old 05-03-2011, 08:18 AM
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Quote:
Originally Posted by amirm View Post

There are also blind tests that show amps do color the sound they reproduce.

If an amp colors the sound I would consisder it defective. An amp if designed properly sould basicly be a wire with gain.
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post #16 of 33 Old 05-03-2011, 08:30 AM
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Quote:
Originally Posted by Just cruising View Post

If an amp colors the sound I would consisder it defective. An amp if designed properly sould basicly be a wire with gain.

Wonderful. How did you test your current amp to know it is not defective that way?

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post #17 of 33 Old 05-03-2011, 09:24 AM - Thread Starter
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Quote:
Originally Posted by Just cruising View Post

If an amp colors the sound I would consisder it defective. An amp if designed properly sould basicly be a wire with gain.

If it were only that simple...

I used to believe that, but the more amps I hear, the more I'm beginning to think otherwise.
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post #18 of 33 Old 05-03-2011, 09:41 AM
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We know all amps distort. That's not debateable by sane people.

Amps have various amp linearities. If you read Self's book, he discusses them for typical class AB designs.

By attempting to control various issues in different amp stages, and using feedback, the non linearities can be reduced such that the amp's THD at the lowest point is well below audibility, at least according to what I have read (.3% THD or or so, for a pure tone.)

But there are factors which the above does not address.

Noise may be a factor. Some amps are more noisy than others. My Crown amp has been dissapointing when it comes to noise.

Speaker amp interaction has been blamed. Some sources claim that under certain cases, a speaker may draw high amounts of current causing distortion (as the amp's power supply can't manage and the voltage from the supply will sag.)

Some people say that when some amps overload, they have poor recovery.

As an amp is pushed towards clipping (usually considered to be at 1% THD if not directly measured,) the distortion will increase. Some amps measure their power at a more conservative point on this curve. So they may have more power than you think.

Music/Movies (especially movies) being highly dynamic, may run out of power more often than we think (I have no measurements to prove this.) So when someone says an amp may not be as good as another one, it may be that it's overloading more than the other one...it's power supply can't keep up, regardless of what the power specs say (and note that the power specs are usually based on a static 8 ohm load.)

I don't know that I believe an amp affects soundstage or has a poor midrange or other such statements, unless measurements could be provided to prove this. But I can believe that amps can sound different because they all distort. And may not distort in the same way under the same conditions. And you may not be able to measure this distortion with a simple THD+N test. You may need real world signals with the amp connected to a real speaker to see issues.

"But this one goes up to 11"
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post #19 of 33 Old 05-03-2011, 10:26 AM
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Coming from an old audiophile background this is so true:
"But I can believe that amps can sound different because they all distort. And may not distort in the same way under the same conditions. And you may not be able to measure this distortion with a simple THD+N test. You may need real world signals with the amp connected to a real speaker to see issues."
One of the advantages of tubes vs. transistor is that tubes clip more gracefully. High quality tube amps also provide a deeper soundstage.
One huge advantage of class D is they don't require gobs of current. My HT is in my living room with a remote heater and lights. Don't have the current to drive anything but Class D properly (ice amps Pioneer SC-37).
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post #20 of 33 Old 05-03-2011, 11:23 AM
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Amps are basically voltage gain devices. If properly designed for a given input voltage it will produce the same voltage output across the entire audio spectrum even as the load impendence varies such as speakers do. If it does not then the amp is not linear in its design or is being asked to deliver more current than it can supply. At the same time raw speaker drivers are typically rate across the spectrum based on a voltage level input, 2.83v. When speakers are design the idea is to produce the smoothest or flattest response across the spectrum as the input voltage level is held constant. This is very hard to do for speakers. Not so hard to do for amps. When you add that distortion levels on any good amp is below the audible threshold I really don't understand all the talk about how one amp sounds next to another. ABX testing strong supports that unless operating outside the amps power band or not having a flat response to start with, amps sound about the same. But just for argument if you wanted a certain signature wouldn't it be much simpler and cost effective to use an equalizer?
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post #21 of 33 Old 05-03-2011, 11:42 AM - Thread Starter
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Quote:
Originally Posted by Just cruising View Post

Amps are basically voltage gain devices. If properly designed for a given input voltage it will produce the same voltage output across the entire audio spectrum even as the load impendence varies such as speakers do. If it does not then the amp is not linear in its design or is being asked to deliver more current than it can supply.

That's the problem. You're oversimplifying it. What you're saying is essentially that amp design does not consist of compromises, which is absurd. Everything consists of compromises. Why would there exist different classes of amps and thousands of amp designs if they were all perfect simple voltage gain devices?

What you are confusing is what an amp should do and what they actually do. Amps are designed to be basically voltage gain devices across the entire audio spectrum. Such an amp would be perfect. But we all know perfection doesn't exist in this world. Why? Because of compromises.

In essence you're confusing "properly designed" with perfectly designed.
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post #22 of 33 Old 05-03-2011, 11:47 AM
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yelnatsch, what compromises do you find degrade amplifier performance, and in what way to they act? Thanks.

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post #23 of 33 Old 05-03-2011, 12:02 PM
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Quote:
Originally Posted by yelnatsch517 View Post

That's the problem. You're oversimplifying it. What you're saying is essentially that amp design does not consist of compromises, which is absurd. Everything consists of compromises. Why would there exist different classes of amps and thousands of amp designs if they were all perfect simple voltage gain devices?

What you are confusing is what an amp should do and what they actually do. Amps are designed to be basically voltage gain devices across the entire audio spectrum. Such an amp would be perfect. But we all know perfection doesn't exist in this world. Why? Because of compromises.

In essence you're confusing "properly designed" with perfectly designed.

I would sooner think you don't understand how these circuits work. If you did you would understand that the compromises have more to do with power, weight, size, cost, efficiency , etc than sound quality.
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post #24 of 33 Old 05-03-2011, 12:26 PM - Thread Starter
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Originally Posted by Bob Lee (QSC) View Post

yelnatsch, what compromises do you find degrade amplifier performance, and in what way to they act? Thanks.

Wow, I didn't think someone like you would respond to a thread like this. I'm honored.

I think you're looking for exact specific design compromises between two amplifiers of the same class. I've had plenty of lab experience when I was still in school, but as you know labs are labs and can't possibly replace real world experience so I won't pretend to be remotely qualified to answer a question like that. I'm sure there are a few members on here who are though, including you.

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I would sooner think you don't understand how these circuits work. If you did you would understand that the compromises have more to do with power, weight, size, cost, efficiency , etc… than sound quality.

You don't think those compromises affect the sound at all? The different classes of amps are design compromises themselves, aren't they?
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post #25 of 33 Old 05-03-2011, 12:33 PM
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No, not if they are properly designed. Why would you expect to hear a difference between a H class amp and classic AB class? Or an amp that has a SM power supply verses a non SM power supply. Or an A class verses an AB class as long as the bais is set properly and the distrotion is below threshold?
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post #26 of 33 Old 05-03-2011, 12:44 PM - Thread Starter
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Originally Posted by Just cruising View Post

No, not if they are properly designed. Why would you expect to hear a difference between a H class amp and classic AB class? Or an amp that has a SM power supply verses a non SM power supply. Or an A class verses an AB class as long as the bais is set properly and the distrotion is below threshold?

They shouldn't theoretically assuming measurements are accurate and sufficient. Quick question because I'm curious. How do they measure distortion? Do they play back single frequency test tones or dynamic real world material?
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post #27 of 33 Old 05-03-2011, 01:00 PM
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I could be wrong, but I believe they use pure sine waves. If they say X watts with Y% THD from 20hz to 20khz, I would guess they measure THD at the rater power at 20hz, 1khz and 20khz (at minimum.)

Here's one article -

http://zone.ni.com/devzone/cda/tut/p/id/3007

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post #28 of 33 Old 05-03-2011, 01:09 PM - Thread Starter
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Quote:
Originally Posted by MichaelJHuman View Post

I could be wrong, but I believe they use pure sine waves. If they say X watts with Y% THD from 20hz to 20khz, I would guess they measure THD at the rater power at 20hz, 1khz and 20khz (at minimum.)

Here's one article -

http://zone.ni.com/devzone/cda/tut/p/id/3007

If that's the case... ther's yer problem.

Also thanks for mentioning Rodd Eliott, Michael.

Just cruising, have a read:
http://sound.westhost.com/amp-sound.htm
As always in almost every discussion here it ends up being "but it doesn't show up in measurements." I ask you these questions then:
1. How accurate are those measurements?
2a. Do people even know what to measure for?
2b. Are there variables that exist in the real world unaccounted for in lab measurements?
3. How do these measurements affect actual product design?
4a. At what values are these measurements considered audible?
4b. Who sets these values?
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post #29 of 33 Old 05-03-2011, 01:44 PM
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I haven’t read this article but I have read several books on amplifier design and my back ground is electronics. You ask the question do we know what to measure for? I don’t know, the electronic industry help put man on the moon, makes sure your HDTV works to a very high standard, your cell phone, satellite communications and on and on. Do you really think with amps being some of the first uses for electronics that the engineers don’t know what to test …what is important and so on? If all these amps are so different in sound then why is it in any ABX test on amps that have a flat response, low output impedance and operating within the power band no one can distinguish one amp from another? As long as whatever distortion exists is below the threshold of being audible does it matter?

Of course Rodd does say it all in his introduction to the article “This is largely hypothesis on my part”….” I don't claim to have all the answers, and it is quite conceivable that I don't have any (although I do hope this is not the case). This entire topic is subject to considerable interpretation, and I will try very hard to be completely objective….. Readers' input is encouraged, as I doubt that I will manage to get everything right first time”
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post #30 of 33 Old 05-03-2011, 02:02 PM - Thread Starter
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Quote:
Originally Posted by Just cruising View Post

I haven’t read this article but I have read several books on amplifier design and my back ground is electronics. You ask the question do we know what to measure for? I don’t know, the electronic industry help put man on the moon, makes sure your HDTV works to a very high standard, your cell phone, satellite communications and on and on. Do you really think with amps being some of the first uses for electronics that the engineers don’t know what to test …what is important and so on? If all these amps are so different in sound then why is it in any ABX test on amps that have a flat response, low output impedance and operating within the power band no one can distinguish one amp from another? As long as whatever distortion exists is below the threshold of being audible does it matter?

Of course Rodd does say it all in his introduction to the article “This is largely hypothesis on my part”….” I don't claim to have all the answers, and it is quite conceivable that I don't have any (although I do hope this is not the case). This entire topic is subject to considerable interpretation, and I will try very hard to be completely objective….. Readers' input is encouraged, as I doubt that I will manage to get everything right first time”

My background isn't electronics, but it is electrical and computer engineering. As I posted in my response to Bob, I'm a fairly new graduate(compared to many guys here with 20+ years of experience) so my real world experience is still lacking so I won't pretend to know everything. All I know is that in the numerous projects I did while in school, one thing I learned for sure is that when you've think you checked, double checked, triple checked everything, all the measurements, etc., there's always still one thing that somehow get's excluded and the amplifier, uart, fpga program, autonomous robot, etc. ends up not doing what it's supposed to do.

Like I said, I was an advocate of all amps sound the same, UNTIL I heard ones that didn't. I'm not talking about generate sine waves though. I'm talking about real world material. Even then, I'm not 100% certain the amps were even operating within their limits. I hope they were or else many stated specs are plain lies. I'm not certain of either side of the argument, but merely believe that there exists the possibility that amps could, indeed, sound different. As such, the most logical explanation would be the design of each amp, unless of course you want to believe cables sound different...but that's a whole other ball of wax with many people adamantly believing each side.
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