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What are the reasons to choose Class A/AB/H over D in this day and age?

levimax

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OP answer: I for one am not at all comfortabile with all that ultrasonic garbage entering my speakers so AB it is here.
This issue has been discussed a lot on these boards and the objective answer is it is low enough in level and will be filtered out "naturally" so that it is not a worry. I am kind of old school and always thought the "ideal" amp is a wire with gain. Class D is certainly not that (bandwidth limited and extra HF content) but practically speaking a good class D is a step forward in performance and efficiency.
 

NiagaraPete

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I believe that most class AB amps don't have more than two year warranty. NAD amps have a two year warranty regardless of whether they're class AB or class D.
When I bought my amps they came with a five year warranty. Just saying.
 

ZolaIII

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I strongly advise you all to look at the classes as they are defined and stop mixing class D to G-H.
 

SIY

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OP answer: I for one am not at all comfortabile with all that ultrasonic garbage entering my speakers so AB it is here.
I have four different Class D amps on hand. The absolute worst one in this respect puts out under a volt at AM radio frequencies, which causes as close to zero current in the loudspeaker as I can measure.
 

SIY

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the_hamster 2

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It will be a tough decision for me when/if I have to replace my Adcom GA555. So used to the size/weight/look of the type of amplifier I've known for my entire awareness of Hi-Fi
I recently swapped out my 555 MkII for an Audiophonics Hypex for driving two vintage a/d/s tower speakers, and other than gaining a lot of real estate in my hi-fi cabinet, hard to distinguish any real diff. in playback quality. The Adcom now used with B&W CM-4 with good success.
 

Ken1951

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I recently swapped out my 555 MkII for an Audiophonics Hypex for driving two vintage a/d/s tower speakers, and other than gaining a lot of real estate in my hi-fi cabinet, hard to distinguish any real diff. in playback quality. The Adcom now used with B&W CM-4 with good success.
What will likely be the determining factor for me will be what my small local dealer carries at the time. Not ordering anything unless absolutely necessary.
 

Jim Matthews

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They make millions of iphones, they fail so there's a commercial market for fixing them. Class d amps are made by the thousands, tens of thousands if lucky, and the manufacturers don't offer repairs.
This economy of scale is key to secondary markets. Up until very recently, most of the better products I could afford started as dorm room projects at MIT.

The current crop of fine products at reasonable prices is a result of over capacity in the Chinese and Taiwanese fab plants. We're really fortunate that this stuff is available, let alone affordable.
 

gnickers

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Looking at recent reviews (Topping PA5) and the well established Class D amps from Hypex and Purifi I fail to see how - looking from at a straight rational and scientifc viewpoint - an amp should be anything besides Class D nowadays.
The Benchmark AHB2 is an exception of course but I expect to see more amps like the PA5 that deliver exceptional performance in Class D in a small and efficient form factor, and even improving over time.

This thread is not supposed to be a subjective fundamentalist discussion.

I'd just like to know technical reasons why there is still a place for A/B/AB/H in the future.
I don't think there is any technical reason to own a class A or class A/B amp anymore. I currently own 3 class D amps because i prefer the small size, simple functionality, cooler operating temperature, and the energy savings. As to longevity they have a lot fewer parts and less complexity than your typical stereo amp. That plus the low heat should result in long life. With this all said, i still drool over classic silverface receivers, Nak tape decks, R2R's and vintage TT's - but i'm past owning big old analog stuff anymore.
 

antennaguru

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Class D Modules are meant to be disposable and replaceable, not repairable. I have Class A and AB amps that are decades old, and repairable if they need it. I also have some Class D modules I packaged for some systems, in my effort to embrace new tech. That some use more or less power is inconsequential to me and my electric bills - the difference in the bills just wouldn't be noticeable.
 

Willem

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Your old amplifers can be repaired easily because they were built with discrete off the shelf components, just like my old Quad 606-2 amplifier. That no longer applies to most modern class AB amplifiers, so they cannot be repaired easily anymore either. I also disagree that in the past washing machines and the like were more reliable. I would say on the contrary.
As for electricity consumption, this is not only about your electricity bill, although here in Europe electricity costs rather more than in the US. The world is trying hard to reduce energy consumption, and this means that low energy consumption is an increasingly important design criterion for appliances of all kinds. Here in the EU there are now mandatory standards for all kinds of appliances, and they have often halved electricity consumption, of not more in some cases. Add up all that, and the result is meaningful. Some appliances do indeed not consume much, but others do, and they are not always the ones you think of first.
 
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MakeMineVinyl

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Your old amplifers can be repaired easily becasue they were built with discrete off the shelf components, just like my old Quad 606-2 amplifier. That no longer applies to most modern class AB amplifiers, so they cannot be repaired easily anymore either.

That is absolutely false. Most non-bespoke parts are just as easily obtainable for new amplifiers as older ones for anybody who can navigate to places like Digikey.com. What isn't routinely available is the firmware used in many products if something like a microcontroller needs to be replaced.
 

sergeauckland

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That is absolutely false. Most non-bespoke parts are just as easily obtainable for new amplifiers as older ones for anybody who can navigate to places like Digikey.com. What isn't routinely available is the firmware used in many products if something like a microcontroller needs to be replaced.
The parts may be available, but Surface Mount components require much more specialist rework stations rather than just a soldering iron and a solder-sucker. The VLSI chips often used also don't lend themselves to signal-tracing for fault-finding, as it's near-impossible to know whether a chip itself is faulty, or one of the support chips it needs to work. Then there's the issue of adequate service documentation, so no, new amplifiers, of whatever class aren't user-repairable and may not even be manufacturer-repairable other than by board replacement, costing as much or more than just buying a new one. Once the warranty has expired, it's pretty much a throw-away item, and even in-warranty, if the user has to ship the item back to wherever, shipping costs may just not make it worth bothering with.
The business model now is to make it cheap and throw it away. Fortunately, that's also been accompanied by a large increase in reliability, but it doesn't help if one's unlucky.

S.
 

AdamG247

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Traditional class A and A/B amplifiers tend to be more interesting as objects in their own right, and thus lend themselves to audio as a hobby. This is doubly true of vacuum tube amplifiers. Class A and A/B amplifiers are relatively (or literally) massive and you can clearly see the technology in action. The sheer presence of these amplifiers is the point; pride of ownership is part and parcel for these amplifiers. They are the logical complement to beautifully finished and imposing loudspeakers.

Class D amplifiers are more like appliances, and its difficult for me to view them as an object of fascination. They are more for the person who wants efficiency in a box which does its job to near technical perfection and otherwise gets out of the way. They are for people who are more interested in the end product - the music or movie sound - and less interested in the bits which are making it possible.

Myself, I'm firmly in the class A / A/B camp, and almost exclusively vacuum tube. I can sit and be fascinated by the glowing tubes while enjoying the music they are enabling. A class D amplifier holds about as much fascination for me as my toaster or lawn sprinkler controller.
Best explanation for why some prefer x versus y. Excellent articulation of the possible driving customer desires and motivations. :cool:
 

MakeMineVinyl

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The parts may be available, but Surface Mount components require much more specialist rework stations rather than just a soldering iron and a solder-sucker. The VLSI chips often used also don't lend themselves to signal-tracing for fault-finding, as it's near-impossible to know whether a chip itself is faulty, or one of the support chips it needs to work. Then there's the issue of adequate service documentation, so no, new amplifiers, of whatever class aren't user-repairable and may not even be manufacturer-repairable other than by board replacement, costing as much or more than just buying a new one. Once the warranty has expired, it's pretty much a throw-away item, and even in-warranty, if the user has to ship the item back to wherever, shipping costs may just not make it worth bothering with.
The business model now is to make it cheap and throw it away. Fortunately, that's also been accompanied by a large increase in reliability, but it doesn't help if one's unlucky.

S.
I don't question that the troubleshooting skills and required kit are vastly different with modern gear, that's why a logic analyzer is part of my workshop arsenal. I can do soldering of SMD down to about 0402 size components and I've replaced 64 pin ICs with nothing more than a magnifier, soldering iron with a small tip, 0.010" solder and soldering wick. For anything more than the occasional work, a SMD working station would be required, but those are relatively inexpensive. True, schematics are generally not available, but the major reason is lawyers and lawsuits. A schematic is tacit permission to muck around inside something, and a sufficiently evolved idiot will find a way to prove their status as an idiot.

I would add too that at least at our company, we do not make throw away components and never have! They're made to the same standard as components made all the way back to the 60s. Obviously there are other consumer electronics manufacturers who aren't quite so conscientious. :(
 

Lambda

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The parts may be available, but Surface Mount components require much more specialist rework stations rather than just a soldering iron and a solder-sucker.
I can replace an EPS8266 processor with nothing but A Candle, toothpicks and bit of flux if i have to.
All this is thanks to modern super heat resistant PCB material and solder mask. just smear it on fry it an surface tension assembles it for you.
you can get a hot air soldering station from amazon with same day delivery for 40€
How is this specialist?
There are probably also people complaining that want point to point wire wrap vacuum tube construction back...

The problem with Repeatability is not modern Construction.
It is serialized Parts, Lack of documentation and Firmware.

Not so long ago a TV, or HiFi came with schematics documentation and service manuals where available.
Now They sand of part numbers, cast part in black Epoxy and Encrypt the firmware.

 
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antennaguru

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I am weary of generalizations about energy consumption/savings and prefer actual measurements and calculations in dollars per month!

Accordingly, I took ACTUAL measurements of the Kilowatt-Hours consumed by a simple audio system using 4 different power amplifiers. I then applied assumptions of how many hours per month the system would be used, and applied the average electricity rate I pay at our two homes (energy cost plus delivery cost).

The monthly audio system energy consumption cost summary is as follows:
  • Class D IcePower 125ASX2 module with Class A input buffer stage = $0.6825
  • Class AB LM3886 Chip Amp using a large linear PS = $0.7875
  • Class AB Naim NAP-250 Clone (discrete transistors) using a large linear PS = $0.70875
  • Class A 25wpc using discrete components with fixed bias and using a large linear PS = $4.85625
These calculations show little to no monthly operating cost difference between Class D and Class AB energy costs per month, with a small increase for Class A energy cost per month around the price of a cup of coffee at Starbucks. IMO these monthly operating cost differences do NOT move the meter, and should be removed from the advantage discussion for Class D amplifiers.

For anyone that wants to dig deeper into the calculations and assumptions, feel free:


Amplifier Energy Cost Comparison.png
 
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