Polar opposites. Class A is the most inefficient type of operation, drawing about 4 watts for every one watt of input; during this whether they are playing music or not. So they will run cooler at full output than at idle. Class A amps tend to be large, expensive ' and generate immense amounts of heat. Despite this [or because of this if you follow the Audio as Masochist theory] they are regard as the best type of amp by many experienced audiophiles. Class D, on the other hand, can be light, cool running and cheap, they do not draw much current at idle and their design allows them to draw only what is nessary when playing music. Their drawback is that most do not sound that good, so far the ones that sound good are as expensive as other high end amps despite theoretically being easier to build. In a nutshell you could say that the difference has to do with they way they treat current, the D amps can switch very rapidly, the A amps don't switch at all. You can get far more power out of a D amp of a given size than an A amp. All this is vastly oversimplified, I will leave the technical details to others. There is a great deal of lit on both of them.
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This statement is a little general, but applies to many - not all. Disclaimer is that I am a dealer, and ahve sold both class A, AB and D designs over the years, but I no longer sell any class D amplifiers.
To my ears, class A or a strongly A biased class AB amplifier exhibits a more emotional involving sound.
In my reference room I have changed amplifiers from a class D design to an AB with a strong A bias, and WITH ALL OTHER COMPONENTS REMAINING THE SAME, the speakers were much more musical sounding, bass was deeper and more pronounced and the system was generally more enjoyable to listen to.
The class AB amplifer was slightly higher in price, $6000 for the class D monoblocks, versus $8000 at the time for the class AB amplifier, but both are very highly reviewed and well liked brands.
I just sold my Spectron Musician III Mk 2 amp (Class D) and bought a used Pass XA30.5 (Class A).
These two are the best I've had in my system, and I've had a few high-end amps before these (Krell, Karan and Burmester).
If you're leaning towards a Class D amp because of the power and efficiency, I'd readily recommend trying the Spectron.
I have auditioned a few power amps over the last two months looking for the best sound that I can coax out of my Grand Veena speakers.
Here's the list--Bell tubed integrated(1961)..Mac 275 V,
Atma Sphere S30 OTL, Grant Lumley 40 watt EL 34, Art Audio Carissa SET 845, Pass Aleph 3 .
None of the amps outperformed my Red Dragon amps on my speakers.
Comparing the Pass class A amp directly to my D amps--- the Pass had a liitle more control and perhaps bass slam than my current amps, but was a bit more rough around the edges,and didn't have the smoothness on transients and lacked some dimension on cymbals,Perhpas this is a power factor, but my speakers are quite efficient.
In my system,the D amps still are the ones to beat,at least in the price range that I feel comfortable with.
Each amp had it's strengths and weaknesses, I could have lived with any of them if I didn't have the amps I have now.
I just find the sound of my amps seem to have found the right associated gear and sound more balanced, all rounded, than any of the others did.
I should add that I use a tube pre amp(Audio Valve Eclipse)for all my evaluations.
Perhaps my results would be different if I were using a solid state pre.
Not knowing what gear was used at the former D amp dealer ,I am at a loss why he feels D amps are inferior to clas A amps or any other type of amplification.
I pretty much ran the gamut and for the life of me, I couldn't find any amp(cheaper or more expensive)that bettered what I use.
I've had them for about 2 years,(usually the age when I get the urge to look for a "change"for the better)and not for lack of trying, they are staying put.
I know I don't have much D amp experience ,but I've owned a lot of fine amplifiers over the years,and to my ears, the D amps I won have none of the sonic faults that I read so often about.
I can't help but wonder if my amps are really that much better than any other D amps,or if most D amps just aren't as good as mine?
I think as much as anything else, it's about synergy with the rest of one's system, just like any other component in the chain.
The OP asked specifically about design differences in the 2 amps, not which one was 'better'. The latter is impossible to answer, but feel free to state which one you feel is best if you feel like boring the rest of us.
Well if you can read between the lines, you should be able to understand that despite all the different design implimentations(class A, solid state, tube pp, tube set, tube otl) there really weren't night and day differences between any of the amps.
It was obvious to me after doing the comparisons that no one amp was better than what I was enjoying in my current system.
Had one amp of any stripe cleaned the pants off what I use I would have declared it the winner.
But does this mean that class D amps, or specifically my D amps are the best there is ? Of course not, what it does do is illustrate that you can't make generalizations about all D amps having some sort of sonic signiture that is inferior to other types of amp designs.
Boring or not they may be, but these are my experiences ,with my gear in my room.
Synergy really isn't all that hard to accomplish, I think people make way too much of this.
I said I could have lived with any of the amps,so there was synergy with all of them.
Not one amp struck me as being inferior or unlistenable,a high price tag amp wasn't a sure bet for best of show either.
I almost feel Hirschian in admitting that.
Hopefull I haven't bored anyone with this reply, but in all honesty I never said which amp was best, I just said I never found an amp that was better.
Pehaps if I explored the mega dollar amps my findings would be different, but what's the point if I can't afford the price of admission?
I conducted my comparisons with amps that were available to me and that I could afford if one design trumped all others.
Even if that meant coughing up more dough, or spending less than I have invested in my current amps.
So for me, the "design" of the amplifier really wasn't the issue,and it shouldn't be for anyonelse with an open mind and a desire to find out for themselves what all the fuss is about D amps.
Preconceptions about amp designs run wild in this hobby.
Forget about the design, and just focus on what the sound is.
The only way to do that is to compare the amps like I did, not speculate the outcome from your laptop.
IMO, the type of music would strongly lead to one's preference over the other. Class D has all the efficiency and power reserves for strong and demanding type of music. On the other hand, Class A typically has the refinement and finesse to track and amplify the signal more faithfully. Acoustic instruments like flute, oboe, violin, piano, harpsichord...etc., their natural timber and harmonics are somewhat rendered more realistically with Class A amps. With difficult to drive speakers and demanding type of musical preferences, Class D would be the preferable choice.
Heres the deal with class d it absolutely wows you at first,huge wallop of bass,way to much for me,just my opin,extreme power out of class d also,but in long term listening ,i just had a overwhelming feeling of something not right,can i explain it ,of course not.Although system matching is important,but i hate to say this sometimes i think the system matching is just another excuse for a component that just doesnt sound good in the first place.
Inna, I suppose dollar for dollar, D amps win and would likely be close to the ideal in general (97~98% level). Small, light weight, low price ..etc are a big plus for us in a typical home. On the other hand if price, space and heat is not a concern, then the uber expensive high wattage Class A amps would be the ultimate choice that would bring us closer to the last 2~3%.
Ok what class A amps are we talking about, at what prices?
And, what class D amps are we basing our opinions on and at what prices?
I've stated what I use and what they were compared to.
My amps weren't cheap,and they look nice, but that's not why I bought them and have continued to marvel at what they do, especially after comparing them to several other designs at different prices above and below what my amps cost me.
I don't agree that all A amps are great and all D amps are less than great.
The law of averages would have to be that there are some clunkers at all prices in both categories.
Synergy ,who really knows when you have it 100%?
I think all our systems are in a constant state of flux.
The synergy was there when we bought the gear, we just want to fine tune it,not synergize it.
I know what synergy is supposed to mean, and it's another bugaboo term that I try to dismiss.
To me, the ultimate synergy is when the whole becomes one .
When you no longer can tell what component is doing what to the music.
It's a time when you stop looking for the "right" amp to match up with your speakers.
If that's what synergy is, then I guess I am there, but I really don't think I am even close to getting sound that makes you forget you are listening to electronics and electrically reproduced music.
I also dismiss those who say they don't listen to the gear, just the music.
If it wasn't for the gear and the ears"you don't trust" what would this hobby be all about?
Maybe to be a purist music lover, we should all forgo any electronic music reproducing system, forget about going to concerts to give our ears a real sense of what music should sound like, and instead just buy the sheet music, and follow the score and hum along with what we are reading.
I guess I will have to listen to an"uber expensive high wattage Class A" amp to put this one to sleep.
But truth be told, the 1961 20 watt Bell tubed integrated was the marvel of the whole exercise.
Only, however when you know how old a design it is(still uses orig tubes)do you get a feel for how well it performs.
Not hearing it, most would write it off, based on a description of the amp.
Just as most do with D amps, based on what they read.
Not one of the amps stood head and shoulders above the rest, no matter what price or design,synergy or no synergy,they all served the music and did their job.
Yet each amp had a sonic signiture, they didn't all sound the same,but the differences weren't big .
The D amp and the A amps had the best bass control, the PP and SET amps had nice mid range liquid sound,the OTL had a bit of everything and it was the closest to the D amp after the A amp if I had to decide.
It had good bass impact and a nice roundness but not a tubey sound. It was really engaging.
You listened to it, and wanted more.
The old tube pp el34 design had a special magic with drumsticks on cymbals that none of the other amps bettered.But overall clarity was lacking and the bass was too flabby and indistinct.
The A amp ruled the day in bass slam and depth.Drum whacks went thru the floor and bass waves shook the listeneing seat, yet cymbals were harshm strident, the upper rgisters were lacking the three dimensional sound of the tube units.
The SET amp was quite nice, but didn't really do anything to ditinguish itself from any of the other tube amps and they all cost less than it did.
Everything was nice.But not great, just nice, it didn't call attention to itself or any section of the music, maybe it was the most neutral synergistic amp then?
But even if it was the least expensive amp in the comparison(it was the most expensive) I wasn't smitten with it.It didn't move me.
This was one of the reasons the old cheap Bell left such an impression, for most of the same reasons, it also didn't draw attention to itself.
So that brings me to the D amps that I own.
They do as much good and at least as little harm as any of the other amps.
They can draw attention to themselves when bass slam is called for, they have that nice tube like warmth and roundness, they also have that SET see thru mid range,they are well balanced,and can draw you into the music and make you want to listen longer because of their get out of the way character.
Are they perfect?
I know they aren't, that's why I started to look for somethingelse,as I usually change gear every couple of years, the amps were next in line for an upgrade.
But for now ,I am satisfied that they are as good as anything out there class be damned.
Space and heat are not big concerns but price is. Anyway, of what I heard I like LAMMs and Rowlands regardless of their particular designs. And if any system doesn't do PRaT well I am not interested even if it has a midrange to die for. I believe that the rhythm is the foundation of music.
And we are all originally from African continent; you know that,right?
I've ventured into Class D a time or two.I appreciate the advantages associated with this energy friendly design,however,in my opinion,it's just not there yet.At least for me.
The musical presentation is not emotionally immediate or involving and I come to this conclusion not friviously but after several months of listening sessions.Perhaps Class D technology will continue to evolve and at some point I may jump in again.
@ Lacee, specifically with respect to 'synergy'. Agree that as you state 'To me, the ultimate synergy is when the whole becomes one.' which is a nice summation of complete synergy, I suppose. If I infer correctly that that statement is referring to the end listening experience, then it would have to include the room as well.
Certain simple, fundamental starting blocks for synergy: ensuring that output/input impedances match spec-wise. That your amp and speakers are well matched (ie amp not underpowered, or perhaps a low-powered amp designed for crossoverless high efficiency speakers). Maybe buying all the same brand of components. Speaking to the manufacturer of the various components in your system and garnering their opinions and others on equipment matching (hence the bajillions of 'what type of X goes best with Y?' posts).
Beyond the obvious, there are simply times when components work better with some than others. Cabling, etc is also true of this. My synergy comment was meant only as a baseline. Beyond that, IMO Class D vs A comes down to a personal thing, and in the right setup can sound fantastic.
I hope nobody out there writes off Class D as a whole based on others' blanket statements without hearing at least a few different class D amps in their own listening room.
Perhaps my interpretation of synergy is a tad harsh, but I also dislike the term neutral.
What is neutral? Todays neutral amp/cable/? is tomorrows coloured one.
Really up to one's experience and personal opinion.
At best you can only say one cable is more neutral than the other, but which cable- ie is the benchmark of neutrality to which all other cables or components can be compared to?
I hope you can try to understand what I am implying.
I think there is nothing wrong with assembling a system that works together well and plays the tunes, but even a smorgasbord type should do that.Careful matching is the best way to go, but what are we really trying to do when we strive for synergy?
We are trying to cover up one deficiency with another, and to me that's just like using different lenses in photography - distort reality but create a pleasing photo.
Much as in photo shop in digital photog.
Reality is not the issue, but "synergy" is.
Synergy to me in the worst case scenario is when you take a bass shy component , match it to fat sounding cables and run everything thru a tube buffer to smooth out all the rough spots.
In doing so, how much reality and truthfulness to the original have you destroyed?
Is a "musical" sounding system, tuned to make all recordings sound pleasant, whether they are good or bad,the pot of gold we are supposed to be chasing after?
I want my system to be able to differentiate between recordings.
The good recordings will sound great, lesser well recorded will sound as they should sound.That's reality, and if that sucks well you know the rest of the saying.
Why blend everything together in a sonic soup called synergy?
Until we can someday have a set of standards that we can make comparisons to, all we have at our disposal are the old guard terminology.
I believe, from reading the above text, that you asked for an education in class-D vs. class-A design. I do not think that anyone provided that so far. Lacee has vomited a lot of text & bored us w/ his opinions but there is hardly any shred of technical discussion here per what the author of this thread asked for.
I was curious myself about this topic & rather disappointed that not a single member initiated a technical discussion as requested by the author. I did some research & found a very good explanation (NOT IN A NUTSHELL, mind you!) on class-D audio power amps:
class-A amplifiers are more traditional in comparison & are also the most INefficient in their overall power comsumption because the theoretical max. eff. of a class-A power amp is 25% i.e. it burns 4W in order to deliver 1W to the load. Class-A power are, usually, designed with the output power transistors biased at maximum output current bias (hence the heat) whether there is a (music) signal or not. Hence, class-A power amps need to pay a lot of attention to transformer selection & size of the heatsink (to dissipate all that heat from the full-biased output transistors). It is not uncommon for a 100W/ch pure class-A power amp to have its heatsinks measure 54 degrees Celcius. In comparison, the class-D power amp heatsink is as cool as a cucumber. For a class-A power amp, since its current consumption is so high, the transformer size has to be quite large - according to Nelson Pass, 2-3X the calculated value should be chosen from a VA standpoint (if my memory serves me correctly from one of many enlightening white papers). In class-A the designer also has to pay a lot of attention to output distortion by ensuring that the output transistors always remain in the SOA (safe area of operation) otherwise, you'll be SOL ;-) and the amplifier output signal will clip & destroy the loudspeaker either immediately or over (short) time. Needless to say, with the large heatsink & large xformer, class-A amplifiers are very heavy items while the equivalent class-D power amp is much smaller & lighter.
Sonically, class-A & class-D power amps are very different with the class-A sonics being much more appealing TO ME personally but to each his/her own. There is no right or wrong sound - only sound that pleases or does not please YOU, the listener.
You can buy green electricity in various ways, build your own solar roof, or buy Green Power from electric utility (I buy 100% Windtricity from CPS Energy), or get WindBuilder credits from Native Energy. Then you can run Class A amplifier without guilt, or at least less guilt. Sounds better that way. And you can deflect snide comments too.