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Class A vs AB vs D amplifiers

boomtheroom

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Hi all
Iv always been under the impression that class A AB amplifiers sounded better than class D , however less powerful at same cost etc..
Now days with modules like the purifi , some say the class D exceeds the latter classes... in what respect are we talking, and how does this relate to
sound , detail , low background noise , channel separation, and imaging...
Ive heard the terminology Grainy withe older class d amps.. is this now changed?
thankss!
 

kemmler3D

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Ive heard the terminology Grainy withe older class d amps.. is this now changed?
Long story short, yes. So-so class-D designs have load dependence and don't always have flat frequency response. So that could easily lead someone to call it "grainy" if the treble was going all over the place in an old, cheap design.

in what respect are we talking,
Modern high-end Class D amps have as good or better noise, distortion, and power than most of the Class A or A/B amps out there, and especially when you compare by price.

and how does this relate to sound , detail , low background noise , channel separation, and imaging...
Simply put, today's good Class D amps are just plain good, in all of those aspects.

To put it another way - many of the Class Ds you can get today (a fun example is the Fosi V3 monoblock) have ideal frequency response in the audible band, inaudible noise, and inaudible distortion. Once you check those boxes, there is no other way for the amp to mess up your sound.

So, yes they've done it, they've made Class D as good as anything else.
 

dlaloum

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Short answer - Yes.

Some of the more economical class-D "chip amps" can be load sensitive, and get a bit messy at the high end on differing loads - but the better designs don't have this issue.

The quality manufacturers/designs classA/AB/D all sound the same in double blind tests.

So at an engineering level, there is no reason to use Class A anymore (just wasting power as heat) - and AB vs D, are usually much of a muchness in terms of idle/standby power consumption, and pretty closely match in real life use too.

There are state of the art designs in each category, that achieve measurable results far beyond any audibility threshold... those are typically far cheaper now than they were 30 years ago, but still not exactly chump change.

A $100 ClassD chipamp - may well have issues (as described above!) - where a similarly priced AB, will suffer from lack of power, but won't misbehave otherwise.

The other thing to look out for, is traditional AB designs have substantial headroom above and beyond their rated loads... Typical Class D designs don't. - Hence a 50W AB may be able to put out 75W or even 100W for brief periods of time, where a class D design might be rated at 75W... and peak at either 75W or marginally more (like 80W).

Often these limitations are due to the use of regulated SMPS power supplies for ClassD and unregulated transformer based power supplies in AB. An AB with a SMPS might also end up with its rated and max power being quite close to each other - also the amount of capacitor reserve in the design will determine the short term peaks possible...

Look at Benchmark for SOTA class AB, and Hypex/Purifi/ICE for Class D modules (and many manufacturers who then use the modules in their amps)
 

voodooless

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See my quote here:


Don’t be one!

And for that matter, read the whole thread…
 
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boomtheroom

boomtheroom

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AHH so when they say the Nad m23 is load independent , more so than any other a/b amps its eliminating the old plague that once infected the class DS amps?
mentioned in this review (
)
 

voodooless

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Some of the more economical class-D "chip amps" can be load sensitive, and get a bit messy at the high end on differing loads - but the better designs don't have this issue
“Economical” anything has issues, this is not specific to Class D. They may have different issues for sure. but that’s just the compromises you’ll have to make, and you can choose.

Often these limitations are due to the use of regulated SMPS power supplies for ClassD and unregulated transformer based power supplies in
This has nothing to do with the amplifier type. Any amp class can use any supply type.
 

voodooless

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TonyJZX

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i think if you are an older gent like most of us here you will have always been on A/B

i think class A is not a 'thing'... its one of those Sugden english things that most people will not gravitate too

i'm a recent user of class D amps but I really dont prefer them but I realise my preference is not rational... i just prefer the sound of large 19 x 19 40lb class A/B amps

but those cheap class D amps you can really just buy and swap out and experiment

i think this place is witnessing the cusp of PFFB units taking over and I think this will be the next 'thing' that we experiment with

i'm awaiting fosi and o-noorus company's new stereo pffb offerings which have not yet eventuated

aiyima's a70 and the fosi monoblocks are on some peoples' radar here and they are cheap enough to try and flick if you dont like them

i suspect i will still prefer class a/b
 
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boomtheroom

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just never understood the difference, other than a/ b uses alot of power and were bigger, but generally had less distortion..
something that ie.. the purifi modules have now helped with.
 

voodooless

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just never understood the difference, other than a/ b uses alot of power and were bigger
Class A burns a lot of power for sure, but the difference between AB and D in a domestic environment is probably way smaller than you think. @restorer-john has a nice polarizing thread about this in his usual blunt fashion ;) :


but generally had less distortion..
That hasn’t been true for a very long while now :) You can get all sort of distortions with all kinds of amp classes.

That is really the issue here. It’s just best to look at every individual item and judge it based on its objective performance. Generalizations aren’t very helpful.
 

Jim Taylor

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It’s just best to look at every individual item and judge it based on its objective performance. Generalizations aren’t very helpful.

This is the key! Iteration is everything. That's why measurements have become so important.

Many of the paradigms and assumptions that laid the foundations for our electronics world were laid in the 1950s and were based on tube gear. Many of those assumptions and paradigms (like the beliefs relating to classes of output bias that you've mentioned) have stubbornly survived into the present day. But the electronic world is different now.

We've moved beyond Univac. :D :D

Jim
 

dlaloum

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Where can you find such tests?

good article here makes reference to several...
 

pogo

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Where can you find a current test that also takes into account the latest Class-D implementations (purifi, ...)?
You can clearly hear differences on certain speakers when you compare them with an AHB2, for example.
 

dlaloum

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Where can you find a current test that also takes into account the latest Class-D implementations (purifi, ...)?
You can clearly hear differences on certain speakers when you compare them with an AHB2, for example.
With amps - they only sound different when pushed to the limits of their performance envelope...

So those that tend to get "unhappy" with difficult loads (low impedances, high phase angles) will start to sound different quite quickly on such speakers.

But if you run all the amps being compared into high efficiency (say 92db/wm) 8ohm speakers with no deep dips or high phase angles - all the amps will sound alike. (and a 25W amp will probably suffice for 99% of situations! :) )

Within their rated performance envelope, any decently engineered amp will sound like every other decently engineered amp.

But yes, absolutely, on certain speakers (I own such a pair!) - different amps will sound different.... but that's because some of them are starting to distort substantially as they reach their limits. Also keep in mind that current limiting and phase angle related issues are not obvious like clipping... they can manifest relatively mildly as a reduction in imaging quality, soundstage, clarity of vocals, etc....

This is why I am very keen on having amps tested and rated at 2ohm (and preferably 1 ohm as well) - this would show up the limitations of many amps.... and be very helpful for those of us with speakers that really do test those limits.
 

Willem

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I for one would like to see amplifiers tested with electrostatic speakers. I am still using a refurbished 2x140 watt Quad 606-2 with my Quad 2805 electrostats. It is a very good amplifier and probably designed with the particular challenges of an electrostatic load in mind. Even so, I would love to see how the combination Quad 2805 and a modern Purifi or Hypex amp would measure. The Quad current dumping design was brilliant, but it is a pretty old design by now.
 

dlaloum

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I for one would like to see amplifiers tested with electrostatic speakers. I am still using a refurbished 2x140 watt Quad 606-2 with my Quad 2805 electrostats. It is a very good amplifier and probably designed with the particular challenges of an electrostatic load in mind. Even so, I would love to see how the combination Quad 2805 and a modern Purifi or Hypex amp would measure. The Quad current dumping design was brilliant, but it is a pretty old design by now.
If you look at the Benchmark AHB2 amp, you will see that it is a much modernised current dumper, and fully SOTA.

The Quad amps are great as they are "unconditionally stable into any load" - that means they can even handle a load of 1ohm (or less) effectively pretty much a short circuit!

Into such loads (and many stats are in that category) - you may/will be current limited, which will limit how much power you can put into that load - but the stats don't need a heap of power....

Quad 606/707/909 are still great amps today. My Crown XLS2500 has a heck of a lot more power... but it is redundant power - back to back comparisons with the Quad's has them sounding pretty much the same... (my speakers present a similar load to stats... and I used to run 989's and 63's)
 

Somafunk

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I have the option of Class A and Class AB on my Hiby R6 iii dap and can switch instantly between them, you’d think that if there was a difference I would be able to hear using sensitive and accurate iem’s but there is absolutely sod all difference, apart from Class A drains the battery twice as fast and heats up the player for obvious reasons, it could be handy on cold winter days though.
 
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boomtheroom

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Nad M23 has had some of the best reviews after reading a few...
 
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