# Class A/B vs Class D amplifiers.



## Devourment (Jan 23, 2010)

How much more power does a A/B amplifier use vs a Class D? 

I'm wanting to go full range Class D (HDP 5 to be exact) in my Scion to keep it as efficient as possible. I don't want no headlight dimming or anything like that. So my curiosity has peaked. 

I've been totally avoided A/B's due to them putting more strain on the electrical but I don't want to avoid them if the difference isn't that big.


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## mires (Mar 5, 2011)

What size alternator do you have in your Scion?

I grew up in Fort Worth by the way and plan to be back their real soon. Best city on earth!


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## Devourment (Jan 23, 2010)

mires said:


> How much total power will you be running?
> 
> I grew up in Fort Worth by the way and plan to be back their real soon. Best city on earth!


Umm. I'd say no more then 1300 watts. Give or take a couple hundred. If that answers your question. My 'planned' setup as of now is Hertz HSK 163's, HDP 5, Audison Bit.10D, and eventually a single Hertz HX250 (Hi-Energy 10") sub. Nothing totally over the top. 

And yes sir, I agree with you. I sincerely love Fort Worth. To hellllllllllllllllllllllll with Dallas though.


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## jpswanberg (Jan 14, 2009)

class d uses less than class b (class a/b) which uses less than class a. Stephen Mants at zedaudio.com has some good reading on amp classes and efficiencies. Roughly, class d tends to be twice as efficient as class ab.


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## chad (Jun 30, 2005)

Well not really twice as but certainly more than.... When designed properly.


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## Devourment (Jan 23, 2010)

Awesome. Thanks for the info guys.


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## Serieus (May 27, 2011)

i believe i remember reading somewhere that "efficient" class a/b amps are around 60% efficient at full output, and efficient class d's are around 80-84% at full output. i do believe that the difference is much larger when the amps aren't running at full capacity, which is all the time unless you like to listen to test tones


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## mires (Mar 5, 2011)

jpswanberg said:


> Stephen Mants at zedaudio.com has some good reading on amp classes and efficiencies.


I found the link you were talking about and figured I should post it here for the OP. Good Stuff!

Amplifier Efficiency


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## Devourment (Jan 23, 2010)

mires said:


> I found the link you were talking about and figured I should post it here for the OP. Good Stuff!
> 
> Amplifier Efficiency


Awesome! Thanks for the link.


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## Jsracing (Apr 1, 2011)

Class A/Bs average 50% efficiency, so if your amp makes 400W, it will consume 800W. Some Class A/Bs claim 60%, but I'm doubtful on that number.

Class Ds average 80% with lower ones around 75% (such as Kenwood Excelon) and higher ones close to 90% (Eclipse ICE, JL XD/HD). So if you consume the same 800W, the amp will be capable of 640W on average. Or if you make the same 400W, you'll only consume 500W, so a difference of 300W or more.

YES, a BIG difference. I was a huge A/B fan for a loooong time (been in audio for a while now) and still love my old Zapcos (and other old school amps), but I've switched to Class D and doubt I'll ever go back.


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## mires (Mar 5, 2011)

Devourment said:


> Awesome! Thanks for the link.


No problem. Just don't let it talk you into going class D


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## bassfreak85 (Jul 26, 2009)

Knowing what I know, I'll stick to highend a/b or g/h amps long before I'd go with d..
The class d sounds fine but if you are going to spend a lot of money and install it properly go with a good highend amp..
If you run a sub do d but for your highs get a/b or g/h..
arc makes excellent amps that are more efficient and are reknoun for great sounding Amps..
WoofersEtc.com - KS 125.2 Mini - ARC Audio 2 Channel 250 Watt Amplifier
WoofersEtc.com - KS 500.1 Mini - ARC Audio 1 Channel 500 Watt Amplifier


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## ZAKOH (Nov 26, 2010)

You don't need to worry about lights dimming unless you run monster power to sub stage using a dedicated subwoofer amplifier providing >1000 watts RMS and blast music at full volume.

I don't remember the details, but if you dig through the archives of Pasmag amplifier reviews, you could get some approximate typical measurements. If I remember correctly, a modern Class D amplifier should have 80-85% efficiency with 4ohm impedance. A Class A/B should have around 60-65% efficiency with 4ohm impedance. The difference is not huge. I would prefer the Class D because they generate less heat and require smaller heat-sink, resulting in neater package. If you bought a Class A/B 5-channel amplifier with comparable power, it should probably measure around 20 inches in length.


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## subwoofery (Nov 9, 2008)

Jsracing said:


> Class A/Bs average 50% efficiency, so if your amp makes 400W, it will consume 800W. Some Class A/Bs claim 60%, but I'm doubtful on that number.
> 
> Class Ds average 80% with lower ones around 75% (such as Kenwood Excelon) and higher ones close to 90% (Eclipse ICE, JL XD/HD). So if you consume the same 800W, the amp will be capable of 640W on average. Or if you make the same 400W, you'll only consume 500W, so a difference of 300W or more.
> 
> YES, a BIG difference. I was a huge A/B fan for a loooong time (been in audio for a while now) and still love my old Zapcos (and other old school amps), but I've switched to Class D and doubt I'll ever go back.


FYI, a good class A/B can be really efficient. The Mosconi AS 100.4 for eg. is 75% efficient. <-- clearly more than 50%

Kelvin


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## Devourment (Jan 23, 2010)

ZAKOH said:


> You don't need to worry about lights dimming unless you run monster power to sub stage using a dedicated subwoofer amplifier providing >1000 watts RMS and blast music at full volume.
> 
> I don't remember the details, but if you dig through the archives of Pasmag amplifier reviews, you could get some approximate typical measurements. If I remember correctly, a modern Class D amplifier should have 80-85% efficiency with 4ohm impedance. A Class A/B should have around 60-65% efficiency with 4ohm impedance. The difference is not huge. I would prefer the Class D because they generate less heat and require smaller heat-sink, resulting in neater package. If you bought a Class A/B 5-channel amplifier with comparable power, it should probably measure around 20 inches in length.


That's another selling point to them as well. They generally have a really small foot print which is great because I'm wanting to mount these under my seat. 

My old car had my mono amp and my 4 channel amp screwed to the back seats inside the trunk. It was an 08 Mazda 6. I liked the setup I had it in but I want a much cleaner, efficient, setup in my new car. 

Also, I've used Arc Audio's KS line. I had a KS 300.4 that I used for my Morel Hybrid Ovation's. Great amps. I like trying different stuff though, so I'm going with Hertz this go around. 

Got to love car audio.


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## chad (Jun 30, 2005)

Serieus said:


> i believe i remember reading somewhere that "efficient" class a/b amps are around 60% efficient at full output, and efficient class d's are around 80-84% at full output. i do believe that the difference is much larger when the amps aren't running at full capacity, which is all the time unless you like to listen to test tones


Actually class A/B amps are most efficient when running full bore because when they are tapping the rails in voltage output they are acting more like class D


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## kmarei (Nov 13, 2009)

Jsracing said:


> Class A/Bs average 50% efficiency, so if your amp makes 400W, it will consume 800W. Some Class A/Bs claim 60%, but I'm doubtful on that number.
> 
> Class Ds average 80% with lower ones around 75% (such as Kenwood Excelon) and higher ones close to 90% (Eclipse ICE, JL XD/HD). So if you consume the same 800W, the amp will be capable of 640W on average. Or if you make the same 400W, you'll only consume 500W, so a difference of 300W or more.
> 
> YES, a BIG difference. I was a huge A/B fan for a loooong time (been in audio for a while now) and still love my old Zapcos (and other old school amps), but I've switched to Class D and doubt I'll ever go back.


by that same arguement
the Prius is much more efficient than most car's we're driving
but we don't all drive it
if you're after the best efficiency then sure class D rocks
but if you don't care about power usage (within limits of course)
Class A/B still has its benefits
i've had both, and i did notice a difference
but
if we're talking midbass or subs, then Class D destroys A/B
and since that's where most of your power is, there is no reason not to use both
an A/B pushing your tweeters and mids (4x50 or so)
and a nice beefy Class D for subs/midbass
i'm using a XD600/1 on a 2 ohm sub
pushing out 600w rms
and after a long drive, the amp is a little warm
if that was one of my older Soundstreams, i'd have 1st to 2nd degree burns


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## Serieus (May 27, 2011)

chad said:


> Actually class A/B amps are most efficient when running full bore because when they are tapping the rails in voltage output they are acting more like class D


good information, thank you! that's what i meant by what i typed but i didn't know the reasoning and such.


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## Pimpnyou204 (Jul 13, 2011)

Ive ran a/b and g/h and to be honest i really think it comes to the type of person you are. A/B IMO can clip real harsh and fast. However my G/h was more tolerable but once you reached a point it was like wow. if you ran a class D within power requirements I would bet you would be ok. Class D gernerally gives you more power allowing for more headroom and that doesnt mean ok i can turn my speakers up to 200 a channel. It means stick it 120 each.. then when a spike hits your not running your amp so hard already so it beomces much more tolerable for the amp to deliver the power. 

SQ comps have been won with class D G/H and a/b. Cant be too much difference if your keeping it under clipping and if there is.. apparently no one can realize it so why bother.


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## MarkZ (Dec 5, 2005)

Pimpnyou204 said:


> Ive ran a/b and g/h and to be honest i really think it comes to the type of person you are. A/B IMO can clip real harsh and fast. However my G/h was more tolerable but once you reached a point it was like wow.


This is a great example of how we need to be careful when we attribute the differences we hear to only one factor. Isn't it possible that the A/B amp might have sounded harsher because it was different from top to bottom (different manufacturer? different overall design?) from the class G/H amp? Could the difference have been because the amps had different power outputs? Maybe the gain settings were different? There are lots of factors to consider aside from output class.

The reason I'm asking these questions is because class G and class H amps *are* class A/B amps.  The differences between them are not in the output stages, but rather in the power supplies (with the exception of the commutating diode, which is no longer an issue in modern designs). Granted, this could still lead to some sonic differences, but you're looking under a microscope here if you're trying to assign sonic differences to the output class by itself.


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## minbari (Mar 3, 2011)

MarkZ said:


> This is a great example of how we need to be careful when we attribute the differences we hear to only one factor. Isn't it possible that the A/B amp might have sounded harsher because it was different from top to bottom (different manufacturer? different overall design?) from the class G/H amp? Could the difference have been because the amps had different power outputs? Maybe the gain settings were different? There are lots of factors to consider aside from output class.
> 
> The reason I'm asking these questions is because class G and class H amps *are* class A/B amps.  The differences between them are not in the output stages, but rather in the power supplies (with the exception of the commutating diode, which is no longer an issue in modern designs). Granted, this could still lead to some sonic differences, but you're looking under a microscope here if you're trying to assign sonic differences to the output class by itself.


took the words out of my mouth. class G/H is class A/B with a variable power supply.


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## MarkZ (Dec 5, 2005)

Rereading my post, I didn't mean to make it sound like it's impossible for the power supply to impart sonic differences in the amplifier, ESPECIALLY during clipping. But, IME, the differences between types of class A/B output stages can be even bigger than the differences between power supply topology.

People try to categorize amplifiers and then assign differences they hear to that categorization, and the categorization may have NOTHING to do with what they're hearing. I remember when Crutchfield used to categorize amps based on whether they had bipolar or MOSFET outputs. Like who gives a ****? And then they had people seeking out amps with Darlington outputs because the write-up that their marketing department came up with was "higher gain"...


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## minbari (Mar 3, 2011)

MarkZ said:


> Rereading my post, I didn't mean to make it sound like it's impossible for the power supply to impart sonic differences in the amplifier, ESPECIALLY during clipping. But, IME, the differences between types of class A/B output stages can be even bigger than the differences between power supply topology.
> 
> People try to categorize amplifiers and then assign differences they hear to that categorization, and the categorization may have NOTHING to do with what they're hearing. I remember when Crutchfield used to categorize amps based on whether they had bipolar or MOSFET outputs. Like who gives a ****? And then they had people seeking out amps with *Darlington outputs because the write-up that their marketing department came up with was "higher gain"...*


technically darlingtons do have higher current gain. what is does in an automotive amplifier that is almost 100% voltage follower........you got me


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## Jsracing (Apr 1, 2011)

kmarei said:


> by that same arguement
> the Prius is much more efficient than most car's we're driving
> but we don't all drive it
> if you're after the best efficiency then sure class D rocks
> ...


I made no statement that we should all run class D amps. The OP inquired about AB vs D efficiency which I responded to. Subwoofery added additional info of a standout performing AB thats higher efficiency (thats really an outlyer).
I have both also, and have had many very good ABs. IMO and IME, the sonic differences lie more with amp mfrs and their specific designs and implementations, rather than classes. I think a well executed class D gives up little, if any, to an equally well executed AB. The argument of classes and sonic character of amps, be it due to class type or mfr, is an endless debate that isn't what the OP requested.

To the OP:
As another poster mentioned, ABs only reach those stated efficiency numbers at full tilt. There far less efficient, I.e. 20% at 1/3 volume (just an example), under normal operation. Class Ds are also less efficient at partial volume, but still typically maintain greater than 60%. You can research the endless debate of sonic signatures to make your own decision for how much you will let that topic weigh on your final decision. But in terms of efficiency, it is significant.


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## james2266 (Sep 24, 2009)

Jsracing said:


> I made no statement that we should all run class D amps. The OP inquired about AB vs D efficiency which I responded to. Subwoofery added additional info of a standout performing AB thats higher efficiency (thats really an outlyer).
> I have both also, and have had many very good ABs. IMO and IME, the sonic differences lie more with amp mfrs and their specific designs and implementations, rather than classes. I think a well executed class D gives up little, if any, to an equally well executed AB. The argument of classes and sonic character of amps, be it due to class type or mfr, is an endless debate that isn't what the OP requested.
> 
> To the OP:
> As another poster mentioned, ABs only reach those stated efficiency numbers at full tilt. There far less efficient, I.e. 20% at 1/3 volume (just an example), under normal operation. Class Ds are also less efficient at partial volume, but still typically maintain greater than 60%. You can research the endless debate of sonic signatures to make your own decision for how much you will let that topic weigh on your final decision. But in terms of efficiency, it is significant.



I found the statement I outlined in Red to be very interesting. I have not really had enough experience with too many different manufacturers of amplifiers. I have read numerous times how some amps have a 'warm' sound whatever that really means. I once asked what 'warm' means in an amp and was told once that it is a slight rise in frequency response around 80 Hz. I don't believe this as truth tho as I have heard so many times that this amp is warm, that amp is warm but they are only performing tweeter duty and/or midrange duty. The amps I have been told are warm are usually of the exotic European kind - Audison, DLS, Mosconi, etc. The others are said to be colorless and they are usually of the USA made variety TRU, Zapco, etc. Is there any truth to this or another way of discovering strong amp candidates for certain frequency duties?


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## MarkZ (Dec 5, 2005)

Sometimes when people refer to an amp as "warm", the amp tends to have higher distortion than other amps (it's often said that it's the even order distortion that's responsible). I suspect it probably also has to do with a falling high frequency response and the behavior at clipping. It would be interesting if someone could post a study that relates subjective impressions like this to manipulations of certain parameters.


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## james2266 (Sep 24, 2009)

MarkZ said:


> Sometimes when people refer to an amp as "warm", the amp tends to have higher distortion than other amps (it's often said that it's the even order distortion that's responsible). I suspect it probably also has to do with a falling high frequency response and the behavior at clipping. It would be interesting if someone could post a study that relates subjective impressions like this to manipulations of certain parameters.


I, for one, would be extremely interested in reading such a study. Thanks for your description of 'warm'. I think it makes alot more sense now. Another question related to this- Is it possible to actually get a completely realistic sounding playback through uncolored speakers using one of these 'warm amps'? I am starting to once again feel as though I do not have the right amp for the sound I am trying to obtain. Sigh... Does this ever end?


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## MarkZ (Dec 5, 2005)

You're far more likely to find an uncolored amp than an uncolored speaker.


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## BuickGN (May 29, 2009)

MarkZ said:


> Sometimes when people refer to an amp as "warm", the amp tends to have higher distortion than other amps (it's often said that it's the even order distortion that's responsible). I suspect it probably also has to do with a falling high frequency response and the behavior at clipping. It would be interesting if someone could post a study that relates subjective impressions like this to manipulations of certain parameters.


Kind of like trying to relate Klippel results to what you hear, I would love a test like this and I would be willing to donate a McIntosh and JL HD....hint.....hint... to anyone reading. 

I obviously haven't done much research on the subject but is it proven or at least very likely that a "warm" amp has more distortion, whatever type of distortion that may be? Now I'm going to spend the next week searching on this topic.


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## james2266 (Sep 24, 2009)

BuickGN said:


> Kind of like trying to relate Klippel results to what you hear, I would love a test like this and I would be willing to donate a McIntosh and JL HD....hint.....hint... to anyone reading.
> 
> I obviously haven't done much research on the subject but is it proven or at least very likely that a "warm" amp has more distortion, whatever type of distortion that may be? Now I'm going to spend the next week searching on this topic.


Let us know what you find. I will do the same here and will report too although I am not exactly sure what keywords to search.


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## kmarei (Nov 13, 2009)

Jsracing said:


> I made no statement that we should all run class D amps. The OP inquired about AB vs D efficiency which I responded to. Subwoofery added additional info of a standout performing AB thats higher efficiency (thats really an outlyer).
> I have both also, and have had many very good ABs. IMO and IME, the sonic differences lie more with amp mfrs and their sWpecific designs and implementations, rather than classes. I think a well executed class D gives up little, if any, to an equally well executed AB. The argument of classes and sonic character of amps, be it due to class type or mfr, is an endless debate that isn't what the OP requested.


I hope you did not take what I said as an attack on you
I was just commenting on your quote about efficiency


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## subwoofery (Nov 9, 2008)

I tried to relate distortion to what we hear but I couldn't back up my findings due to my lack of links related to that... 
http://www.diymobileaudio.com/forum/1425818-post366.html 

I'm pretty sure I'm close but I can't prove it lol

Kelvin


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## MarkZ (Dec 5, 2005)

I think you can do things in a much more controlled manner. Manipulate FR, distortion, etc in software with a pair of headphones, and see if you can evoke some of the subjective experiences you guys are talking about.


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