# Class A/B vs Class D



## JSM-FA5 (Nov 18, 2012)

Before I get flamed this is not a which is better post. I have done some research. From what I have read/seen I have come to this.

Class D is the most efficient class of amps. Also tends to run cooler for longer so most of the time additional fans are not necessary. With that being said why do people choose to run anything other than class D? I have also read multiple times there is no audible difference if both class amps are of good quality.

Is it just for bragging rights and the appearance its self? Or have I missed or misunderstood what I have read?


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## knever3 (Mar 9, 2009)

A few reasons why people would rather run either.

Cost
Size limitations
Current Draw
Power VS Current Draw
SQ
Low ohm options


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## mercury02 (Jul 20, 2014)

Overall I think good amp in class D can keep up with class A/B for subs only.
I think class A/B may have better control overall of sub but it is very small VS
a good class D. if you were running all sealed sub enclosures you could tell
but with ported being the norm they even out quickly for what you would give
up on output in ported VS sealed box is not worth it overall


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## ChrisB (Jul 3, 2008)

Distortion profile. Many lower cost class ab amplifiers won't sound as harsh when driven into clipping and distortion like the class d amplifiers will. 

OTOH, I used to be famous for running a minimum of three times the RMS power that my speakers were able to handle. When I ran those amplifiers near the point of audible clipping, bad things happened... Did you know that passive crossover capacitors would pop like firecrackers when exposed to insane amounts of power?

So my solution to the modern day class ab versus d dilemma is to run a fairly powerful class D amplifier to power my speakers. That way, if I hear harsh distortion, I know to back the volume down.  I just hope I'm not too late in turning down the volume because the damage may already be done....


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## legend94 (Mar 15, 2006)

:dead_horse:


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## squeak9798 (Apr 20, 2005)

legend94 said:


> :dead_horse:


True. But in his defense this is a difficult topic to just "search" due to the quantity of threads, many of which run I to double digit pages as well. Information overload.

However, I think if you hop into the Myth forum here and look for the thread about amplifier class making an audible difference, you'll find enough comments from both sides to thoroughly explain all viewpoints.


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## Rodek (Aug 19, 2006)

For my system, I'm using class d on subwoofer duty and class ab on mids/highs. It was personal preference.


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## JSM-FA5 (Nov 18, 2012)

knever3 said:


> A few reasons why people would rather run either.
> 
> Cost
> Size limitations
> ...


Thanks for the info. Just from what I have seen class D is more efficient at a cheaper cost. So I have wondered why people run Class A/B instead of D since there is no audible difference. Never thought about the ohm load. As I run all speakers at 4 and subs at 2.


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## 1996blackmax (Aug 29, 2007)

I will definately be running class d amps all around whenever its time to switch out. For me, ease of installation is a big plus.


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## 2010hummerguy (Oct 7, 2009)

Pointless debate. So many different AB and D amps. Some great, some not. Impossible to generalize.


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## cajunner (Apr 13, 2007)

I like an amp that sounds good, I have several that come from the pre-class D era, and they sound good.

I am not so ham-fisted as to believe there is no difference at all in sonics between my amps, and feel quite certain that even if I do have "favorites" based on their sonics, I don't really find myself needing to pick, and play the ones that are subjectively, objectively, or even aesthetically best among them. I do however, attempt to use them to their strengths, and if a vehicle requires a set-point of maximum current lower than normal, I'll throw in the class D based on efficiency ratings. 

If I do not approach the car's operational limits, then it doesn't matter.

When the amplifier works, stays on, and plays for as long as I need, there is very little left for me to criticize, they all seem to make the music sound like music should sound, if you're listening to music in a small reflective box that puts you off-center...

really, I have cheap-o amps like Cadence, and Xplod Sony, Dual, etc. and as long as my pre-amp has the ability to force the response into a window of a recognizable nature, I can forget which amp is installed and get on with it.

This may plague some of you golden ears, who just can't wrap your head around the practical nature of my example, and must maintain your air of superiority by having the best, paying for the new, or demanding the special treatment from your audio-monger, and for that I would never condemn, or demean...

because, as the sickness is pervasive and the symptoms treated by rational discussions may then subside over time, it's simply a matter of how afflicted one has become, and how distracting the psychological component of the disease manifests...


haha..


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## kyheng (Jan 31, 2007)

I will use an Audison Voce AV due and compare to Rockford Fosgate's Prime R1200 class D then saying the Rockford amp was rubbish.


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## AAAAAAA (Oct 5, 2007)

One reason to stay AB I suppose is that class D amps destroy radio reception.


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## Bayboy (Dec 29, 2010)

Man.... just buy what you want & can afford. As long as you use it within it's limits and are satisfied, then who is anyone else to say. I still run a Cadence F100-5 I bought for $150 shipped and it sounds powerful enough, can drive most mids to their potential, drives 2 Peerless XXLS without overheating & shutting down, and has cleanly done so for the past couple of years. I do plan to switch it out for two class D JBL, but only for crossover & aesthetic reasons. Other than that... I don't feel the need to chase behind sonic signatures. That's what DSP and specific drivers are for IMO.


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## JSM-FA5 (Nov 18, 2012)

Oh I'll run class D. No doubt. Just cause I can't afford most A/B. I was just wondering for my knowledge why people run Class A/B if they aren't as efficient as class D.


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## Bayboy (Dec 29, 2010)

My only logic to that question is either cost, sonic signature, and possibly features that a comparable class D doesn't have. Everyone will have their own justifications for their choices, but that doesn't make it a hard fast rule for the rest. It is too subjective at that point.


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## WestCo (Aug 19, 2012)

JSM-FA5 said:


> Before I get flamed this is not a which is better post. I have done some research. From what I have read/seen I have come to this.
> 
> Class D is the most efficient class of amps. Also tends to run cooler for longer so most of the time additional fans are not necessary. With that being said why do people choose to run anything other than class D? I have also read multiple times there is no audible difference if both class amps are of good quality.
> 
> Is it just for bragging rights and the appearance its self? Or have I missed or misunderstood what I have read?


For many applications, good amps will sound close enough to eachother to go with the cheaper option (or more energy efficient option). 

It takes considerable time and effort to acquire really unique amps that will stand out from the crowd sonically and noticeably. Often times this requires that the amp is modified.


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## gijoe (Mar 25, 2008)

JSM-FA5 said:


> Oh I'll run class D. No doubt. Just cause I can't afford most A/B. I was just wondering for my knowledge why people run Class A/B if they aren't as efficient as class D.


I think one of the big reasons is that up until the last few years, fullrange class D hadn't really been perfected. Class D used to be great for low frequencies, but could not cleanly play high frequencies. That has changed and class D has gotten very good, but there are a TON of A/B amps around, so it can be pretty cheap to pick up a good A/B amp. 

There are obviously other differences between the two, but there are plenty of people who still don't think that class D is sufficient for fullrange, while many others are perfectly happy with class D and get a much smaller, more efficient amp.


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## captainobvious (Mar 11, 2006)

JSM-FA5 said:


> Before I get flamed this is not a which is better post. I have done some research. From what I have read/seen I have come to this.
> 
> Class D is the most efficient class of amps. *Also tends to run cooler for longer so most of the time additional fans are not necessary.* With that being said why do people choose to run anything other than class D? I have also read multiple times there is no audible difference if both class amps are of good quality.
> 
> Is it just for bragging rights and the appearance its self? Or have I missed or misunderstood what I have read?



Interestingly enough, yes A/B amps are less efficient so more power is wasted as heat. However, most decent class A/B amps have big chunky aluminum heatsinks to dissipate the heat whereas most class D amplifiers are _*so *_compact, that they tend to run very hot themselves. Of course this can't be made as a blanket statement, but there are plenty of A/B amps that will run cooler than some class D amps. You can only cram so much into these small class D chassis.


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## Bayboy (Dec 29, 2010)

The biggest appeal to class D for me is compactness. Having collected a string of matching A/B amps to be able to configure a system how I want in channels & power became a big pain in accompanying space for them. At the time it seemed like a good idea, but in hindsight... not. I don't have golden ears so fitment of gear is a big plus. Surfboards were impressive back in the 90's & early 2K. Now I find it repulsive.


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## 727south (Jul 21, 2009)

My old JL HD900.5 sound like crap compared to my new Gladen XL amp.


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## cajunner (Apr 13, 2007)

I think it's a matter of people who used to get on bandwagons about class D back before the technology improved, not being sufficiently informed on the new crop of higher end stuff to hit the market, that creates the perpetuating idea of class D being inferior and keeping people from incorporating the new architecture in their systems.

the sad, simple truth is that class D will always fit in the space easier, and the cost in electrical system "drag" will be less, so no matter what the science is saying about listener preference, these attributes will dominate.

it has become pretty easy to like a class D amp, even in the bloody full-range and that's a trend that has staying power. 

The surfboard installations of our youth are like the tube amp monsters of our parent's youth, more often seen in attics and thrift shops than actual use in a vehicle, unless there's some quirkiness, in the owner that permits such an extravagance.

I'm sure the second-hand market will support the glut of memory-laden homilies we support, as closet queens and shelf kings, for many moons to come but the death knell on intrusive audio displays, the limiting of functionality for our vehicles, is rapidly sounding in the near distance even as we laud our through-holes for their audio superiority...

the time has come to embrace our new, smaller, more efficient overlords.

God save the queens...


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## Bayboy (Dec 29, 2010)

cajunner said:


> I think it's a matter of people who used to get on bandwagons about class D back before the technology improved, not being sufficiently informed on the new crop of higher end stuff to hit the market, that creates the perpetuating idea of class D being inferior and keeping people from incorporating the new architecture in their systems.
> 
> the sad, simple truth is that class D will always fit in the space easier, and the cost in electrical system "drag" will be less, so no matter what the science is saying about listener preference, these attributes will dominate.
> 
> ...




Pretty much..... try getting rid of some decent A/B amps and see what happens. They have pretty much lost their worth of what they were, even just a few years ago. Nothing to discredit them, but there's a fast diminishing crowd that still demands such. To that, I am already a victim.


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## cajunner (Apr 13, 2007)

Bayboy said:


> Pretty much..... try getting rid of some decent A/B amps and see what happens. They have pretty much lost their worth of what they were, even just a few years ago. Nothing to discredit them, but there's a fast diminishing crowd that still demands such. To that, I am already a victim.


I've been singing this cautionary song for a while now, as it appears the lock on higher end amps being, if not investment vehicles, at least worthy of keeping based on retained value, is no longer a valid proposition.

fools, stuck in the mud of sentimentality, holding on to antiques and talking about the music and equipment of the 90's...

we're all blinking fast, I guess.


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## Bayboy (Dec 29, 2010)

cajunner said:


> I've been singing this cautionary song for a while now, as it appears the lock on higher end amps being, if not investment vehicles, at least worthy of keeping based on retained value, is no longer a valid proposition.
> 
> fools, stuck in the mud of sentimentality, holding on to antiques and talking about the music and equipment of the 90's...
> 
> we're all blinking fast, I guess.



And there's even a worse part to it..... for those that have amps not old enough to consider "old school" even though they're well aged by most standards, are going to take the biggest hit. If you have gear that you are wanting to rid yourself of that falls within that category, better start now.


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## cajunner (Apr 13, 2007)

Bayboy said:


> And there's even a worse part to it..... for those that have amps not old enough to consider "old school" even though they're well aged by most standards, are going to take the biggest hit. If you have gear that you are wanting to rid yourself of that falls within that category, better start now.


right, intrinsic value for stuff that is still big but relatively new, is going down.

I don't know how they put class D amps together for such low prices, unless the heatsink is really the high cost item in the bill of materials.

I figure if there was something cool about an amp 'back in the day' it might hold value for a while but the plain working stock of most lines that used to be solid, can be considered leaky vessels now.


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## ZAKOH (Nov 26, 2010)

The industry is shifting towards Class D amplifiers. Every year more and more companies are going Class D only. Of course, there will be a lot of manufacturers still producing the class A/B amps. They won't go anywhere, but I think in a decade Class A/B gear cater to a small group of enthusiasts and will be treated like turntables or tube amplifiers today.


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## cajunner (Apr 13, 2007)

ZAKOH said:


> The industry is shifting towards Class D amplifiers. Every year more and more companies are going Class D only. Of course, there will be a lot of manufacturers still producing the class A/B amps. They won't go anywhere, but I think in a decade Class A/B gear cater to a small group of enthusiasts and will be treated like turntables or tube amplifiers today.


It would be nice if there was as great a difference between AB and D, as there is between CD and vinyl.

Or tube vs. silicon.

How many people still run their old tube televisions, or computer monitors?

the price on high-resolution computer monitors that were state of the art, tubes, fell through the floor and even in the home office, there is not enough space to fit a big box monitor over a flat panel LCD.

we're no longer in the dawn of class D's blotting out the sum of AB technologies, we're nearing high noon...


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## ChrisB (Jul 3, 2008)

Bayboy said:


> The biggest appeal to class D for me is compactness. Having collected a string of matching A/B amps to be able to configure a system how I want in channels & power became a big pain in accompanying space for them. At the time it seemed like a good idea, but in hindsight... not. I don't have golden ears so fitment of gear is a big plus. Surfboards were impressive back in the 90's & early 2K. Now I find it repulsive.


AMEN! When choosing between one amplifier that occupies a little more space than a sheet of paper that does 150 x 6 or 150 x 4 and 1,000 X 1 @ 1 ohm, it becomes a no-brainer. In class AB power, I don't even want to know how much space 150 x 4 would occupy along with 1,000 X 1.


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## Bayboy (Dec 29, 2010)

ChrisB said:


> AMEN! When choosing between one amplifier that occupies a little more space than a sheet of paper that does 150 x 6 or 150 x 4 and 1,000 X 1 @ 1 ohm, it becomes a no-brainer. In class AB power, I don't even want to know how much space 150 x 4 would occupy along with 1,000 X 1.




Enough to make you rearrange & contort your amp rack into something you originally didn't want. :laugh: I've tried & tried and still couldn't get the amount of power I wanted that two MS-1004 could give in half or less. After I realized that, I gave up, made a purchase, and into the closet the dinosaurs went never to be ran again. Now once the remaining amp is out I am just going to close that chapter & move on.


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## captainobvious (Mar 11, 2006)

cajunner said:


> I think it's a matter of people who used to get on bandwagons about class D back before the technology improved, not being sufficiently informed on the new crop of higher end stuff to hit the market, that creates the perpetuating idea of class D being inferior and keeping people from incorporating the new architecture in their systems.
> 
> the sad, simple truth is that class D will always fit in the space easier, and the cost in electrical system "drag" will be less, so no matter what the science is saying about listener preference, these attributes will dominate.
> 
> ...


Well said!




and to top it off there ARE some very elegant class D designs out there too for those that want a "pretty" amplifier too. Take the Zed Audio lineup for excellent example. Beautiful class D amps and much more efficient than an AB counterpart. I've used quite a few AB and D amps and think the quality class D amps will certainly not be the weak link in a system.I'd be equally happy running JL HD, or Zed Audio class D as I would be running Mosconi or Zapco class AB amps. At that point, it truly is a matter of style, dimensions, featureset, construction quality, warranty, price, etc and not about "sound".


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## RobERacer (Sep 15, 2014)

gijoe said:


> I think one of the big reasons is that up until the last few years, fullrange class D hadn't really been perfected. Class D used to be great for low frequencies, but could not cleanly play high frequencies. That has changed and class D has gotten very good, but there are a TON of A/B amps around, so it can be pretty cheap to pick up a good A/B amp.
> 
> There are obviously other differences between the two, but there are plenty of people who still don't think that class D is sufficient for fullrange, while many others are perfectly happy with class D and get a much smaller, more efficient amp.


Perfected? Well, I would have to disagree with that. Cleaner, smoother, even more listenable at higher frequencies yes but perfected? Far from it. Clearly for the higher end audio installs AB's are goning to be better for a good while yet. Why?
My concern with class D amps is exactly the distortion factor. With good capacitance a very fast power supply switching supply power between the output channels would seem completely inaudible in theory. This happens thousands of times a second so the capacitors don't actually get the time to completely discharge meaning the supply power stays virtually level anyway. This is in fact what we used to know as a switching power supply. I am told this is not precisely true of a "Digital Switching Amplifier" though and that in fact most (AKA all???) digital amps actually convert the analogue signal to digital in order to manipulate it from there. NO-one I have spoken to about it has been completely successful in explaining how they function to me as of yet so they are still a bit of a mystery but what it did come to understand is that they are infact adding yet another DA/AD conversion step in before the signal hits the speakers. Each conversion step adds noticeable distortion to the signal. Think of it like you are photocopying. Do you get a better image if you photocopy the original document or a previously photocopied copy of the document. This is what we call a second generation copy. When you copy a copy that is. The original is better of course and BTW it is no slight difference. Sometimes dependant on the scale of what is being printed words can become completely illegible from the first generation to the second. Digital sampling AKA Analogue to Digital conversion is this same thing in an audio sense. 44,100 times per second a computer takes a snapshot of what the waveform looks like (as scene on an oscilloscope) and records that. When played back it is actually leaving holes where there was nothing actually recorded so there is only sonic incidents 44,100 times in a second. That is a lot though and those holes are very close to inaudible. At least they are very difficult for the average listener to discern and overall leave a sonic that is very smooth even at very high sound pressure levels. What is in fact happening when one reconverts a digital signal is that the converter samples the sample 44,100 times a second. That would be pretty ok if the samples were completely in sync but the problem is they aren't. In fact unless one was able to send the clock pulse from one unit to the other they could virtually never actually line up so what in practice happens is that only a fraction of the sound clips actually have audio and many of them only have part of what was actually sampled in the first place. The other thing to know is that these clips are Hard on's and off's. Some manufacturers employ practices smooth these out a bit called filtering which does make it sound smoother but in reality it is just the same as if you draw with your pencil and then rub the drawing with your finger. The lines started out clear and distinct (detailed) but the more you rub the harder it is to determine where the edges of the lines actually are and the image eventually just becomes one big blur. In audio this often manifests itself in the loss of intelligibility of things like reverb and background instrumentation. Ghost notes on a snare drum for example. Basically all of the really cool audio **** and part of what most of us use to gage the performance of an given audio rig. Frequency response is separate to that as are distortion and noise floor. On my home rig I convert all of the audio once only. Out of my preamp into my amplifiers. Sonically speaking this is one upgrade that I did years ago that all by itself had the greatest impact on the performance of my system save the actual speakers themselves. This also something I regularly do with my clients equipment that never fails to impress. Better intelligibility and much smoother at much higher SPL's. Like I say it is most noticeable in the upper mid range where the program material is perceived as the loudest. Humans hearing is more sensitive there and slowly falls off from there up and down. That said we all hear pretty linearly hence why pink noise (equal energy at every octave) actually sounds so naturally flat to us. This kind of distortion make listening really not enjoyable especially when you turn it up. What is the secret? Stop converting!!! If you have multiple units to manipulate the source before you actually get the signal at speaker power levels to the speakers then keep the signal digital between them all until you are done with the digital equipment. A class A/B amp is and analogue design so the signal is never digital through them. 
In my case I am achieving all of the processing for the speakers in my head unit and it is going right to my amp from there so there is only that conversion in play. This is incurring a limited amount of distortion which is being dealt with in other ways. If I were to include a digital processor to handle eq, time adjustment and x-over I would then be adding yet another conversion and with that much more distortion. Remember the samples not lining up thing? Well, actually that becomes exponentially more with every added generation of resample. If one of the manufacturers were smart they would introduce a box that utilises a USB port on their head units with that building a driver program and maybe a firmware update that allows us to access digital audio in a usable format (toslink or TDIF seem to be the standards) that allows us to get to the processors in digital. Better yet if they all wanted to we could just shoot the signal down USB from one unit to the next. Even the amp inputs as they are typically class D. That would largely negate the class A/B advantage and get us users better virtually lossless and as a bonus noise free audio at the output stage. Actually, it would be almost broadcast grade at the input of the speakers. It just requires the right protocols and a desire on the manufacturers side to have better performance. Does anyone know why the industry ditched digital signal transport in the first place? You already had that before. Toslink and TDIF have been around car audio for a long time. It isn't like the manufacturers don't know the difference either. The truth is we would eventually end up not needing so much D/A conversion and not need to worry about so much noise.


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## gijoe (Mar 25, 2008)

I agree, "perfected" was a not the appropriate choice of words, sorry about that.

I didn't read the rest though, paragraphs would help.


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