[cfranchi]

I’m looking at 2 headphone amp, one is class A, the other is class AB. What advantages would bring the class A amp ?

 

[bagwell359]

AB shuts off/on very quickly to save heat and energy. Depending on the accuracy of your system and ears, you might be able to detect some aspect of this. Loss of detail, a slight mechanical notch.

Outside of a a pair of 200 wpc AB Classe amp I used for about six months in 1994, I've used amps that were all Class A or sliding bias Class A since 1984, so that's my answer.

 

[Sovkiller]

You will never hear the differences...I had both, and even an amp with both options, and nobody I know off, was able to hear any difference...if power is not a restriction, I will run it class A, but it will not keep me awake if I have to live with AB my whole life....

 

[bagwell359]

You will never hear the differences...I had both, and even an amp with both options, and nobody I know off, was able to hear any difference...if power is not an option, I will run it class A, but it will not keep me awake if I have to leave wiht AB my whole life....

Well, I won't argue with your experience/opinion. But for me a Bedini 25/25, Pass x-150, Pass Stasis 3, Pass Aleph 5, Krell KSA-50, Krell KSA-100 (all Class A) sounds notably different from an Ampzilla, SAE 31B, Classe CA-400, Classe CA-100, Hafler DH-200, Bryston 3B (Class AB). All amps I've owned, running moderate to exotic loads, with excellent front ends for the era.

 

[Sovkiller]

Well, I won't argue with your experience/opinion. But for me a Bedini 25/25, Pass x-150, Pass Stasis 3, Pass Aleph 5, Krell KSA-50, Krell KSA-100 (all Class A) sounds notably different from an Ampzilla, SAE 31B, Classe CA-400, Classe CA-100, Hafler DH-200, Bryston 3B (Class AB). All amps I've owned, running moderate to exotic loads, with excellent front ends for the era.

Well different amps may sound different, just because of topology, sound signature etc...I compared the same exact amp running class A and AB, just because the amp has the option, and there was no difference...

 

[SilverEars]

From what I understand it's the way the signal wave is output on Class A that it cannot have cross-over distortion. It's the way transistor switching was made so that there is no blips at 0 voltage reference that there's switching delay causing cross-over distortions.

Informative article with Benchmark first explaining what cross-over distortion is, and claiming to have solved the cross-over distortion with feedforward solution.

https://benchmarkmedia.com/blogs/application_notes/131424519-amplifier-crossover-distortion

 

[bagwell359]

Well different amps may sound different, just because of topology, sound signature etc...I compared the same exact amp running class A and AB, just because the amp has the option, and there was no difference...

I was involved in dozens of blind A/B tests in the 80's and 90's and since the equipment was very revealing in general the differences were not difficult to identify - but one has to avoid the SE vs balanced issues, running amps incapable of running the speaker load, etc.

What amp are you talking about? What is the rated power in A and AB? In A does it run ONLY A, or does it slide into AB? A full Class A amp runs very hot, is very large, and costs a lot to design and build. If anyone was going to fork out that money, why would they run in AB - outside of the lower temps, less AC used and more WPC - there isn't another reason I can name outside of curiosity.

 

[bagwell359]

From what I understand it's the way the signal wave is output on Class A that it cannot have cross-over distortion. It's the way transistor switching was made so that there is no blips at 0 voltage reference that there's switching delay causing cross-over distortions.

Informative article with Benchmark first explaining what cross-over distortion is, and claiming to have solved the cross-over distortion with feedforward solution.

https://benchmarkmedia.com/blogs/application_notes/131424519-amplifier-crossover-distortion

That's the general reason given. In real life in my experience is: the definition in the mids and highs on pure class A cannot be matched by AB no matter how huge and mighty it might be. Class A bass outside of the bass cannons Krell and Pass (not the Aleph series) have often struck me as lacking impact (even adjusted for volume down to .01 db)

For instance my Rag 1 in #1 position is supposed to be all class A - and the limit is 4 WPC. Position #3 is AB and goes to 100 wpc/4 ohms. #2 is the mystery, I think its 4 wpc class A, then goes AB up to about 16 wpc. There is some sort of "strapping" or rebiasing going on to get to #3. It doesn't sound that good, only on speakers at break the lease levels does it sound OK. #1 clearly gives the best detail, but the bass lacks drive (like a pre-amp w/o an active gain stage). #2 is the most useful overall, but, lacks some detail vs #1. On a crappy 70's era CD one would be hard pressed to find a difference. But a bit perfect MQA of something well recording? Child's play.

 

[Sovkiller]

I was involved in dozens of blind A/B tests in the 80's and 90's and since the equipment was very revealing in general the differences were not difficult to identify - but one has to avoid the SE vs balanced issues, running amps incapable of running the speaker load, etc.

What amp are you talking about? What is the rated power in A and AB? In A does it run ONLY A, or does it slide into AB? A full Class A amp runs very hot, is very large, and costs a lot to design and build. If anyone was going to fork out that money, why would they run in AB - outside of the lower temps, less AC used and more WPC - there isn't another reason I can name outside of curiosity.

I used to run it on Class A, but not because I hear any difference, I didn't need more power and it was there, so why not using it, but it did get a lot hotter in class A...it was the Marantz PM7200....

 

[bagwell359]

I used to run it on Class A, but not because I hear any difference, I didn't need more power and it was there, so why not using it, but it did get a lot hotter in class A...it was the Marantz PM7200....

Interesting piece - an integrated with those amp options and a pre for that price? Sells itself. I was busy during the roll out of this integrated, and when in audio land focused on other matters.

I read quite a few reviews - pro's and a lot more hobbyists. The line was pretty close on the "Class A vs AB easy to hear - or not" question. One thought struck me, that the pro A is better than AB folks were selling something, but another thought also hit - people buying into Class A at this price many of the users may not have had good enough equipment/recordings to show it off. Not that they couldn't hear it if it was there, just the tools being worked with didn't measure up.

I think you are talking about one piece, and that your conclusion based on that may be dead on. I was talking about other pieces and I might be dead on too. So it seems absent testing the exact same stuff, we're at an impasse.

I know this, if the Marantz PM7200 amp could be run by an external pre-amp in balanced mode, I'd buy one to see for myself.

 

[Sovkiller]

Interesting piece - an integrated with those amp options and a pre for that price? Sells itself. I was busy during the roll out of this integrated, and when in audio land focused on other matters.

I read quite a few reviews - pro's and a lot more hobbyists. The line was pretty close on the "Class A vs AB easy to hear - or not" question. One thought struck me, that the pro A is better than AB folks were selling something, but another thought also hit - people buying into Class A at this price many of the users may not have had good enough equipment/recordings to show it off. Not that they couldn't hear it if it was there, just the tools being worked with didn't measure up.

I think you are talking about one piece, and that your conclusion based on that may be dead on. I was talking about other pieces and I might be dead on too. So it seems absent testing the exact same stuff, we're at an impasse.

I know this, if the Marantz PM7200 amp could be run by an external pre-amp in balanced mode, I'd buy one to see for myself.

I do not have a multithousand dollar setup, butpretty decent, two Oppos, one Sony ES, a bunch of SACD's, blue rays, CDs as well, the fronts are the Axioms M80 with a Velodyne sub, my real state is limited, but I have heard differences in other parts, like for example two different versions of the same recording, different sources, but I agree the most critical part of the system is not the electronics but the mechanical parts, the transducers, the better the speakers the easier is to pinpoint differences...the Axioms are far from being the best for that, but they are pretty decent....the amp was very solid, my brother still have it, it began to give me problems with remote, and I bought another Marantz, same problem, now I have a Teac Ai-1000, no tone network, just a plain basic integrated amp, and sounds very good...and it is AB....

 

[KC2020]

Class A amps avoid the inherent distortion from an output component, tube or transistor, changing states. It's really that simple. A low power amp, i.e. a headphone amp, enjoys the luxury of class A without creating a lot of heat or consuming a lot of power.

Given the choice, if a designer is seeking sonic excellence, there's no reason to not choose class A for a stand alone HP amp unless trying to keep cost down or deal with the heat / power aspect.

Often a class AB headphone stage offers an advantage when it's built into an integrated amp or receiver. AB amps often don't age well and evolve to being A or B but not a good A or B. Though that takes a very long time if to happen if it happens at all.

FWIW, I am an audio engineer with 30+ years of experience.

 

[Sovkiller]

Class A amps avoid the inherent distortion from an output component, tube or transistor, changing states. It's really that simple. A low power amp, i.e. a headphone amp, enjoys the luxury of class A without creating a lot of heat or consuming a lot of power.

Given the choice, if a designer is seeking sonic excellence, there's no reason to not choose class A for a stand alone HP amp unless trying to keep cost down or deal with the heat / power aspect.

Often a class AB headphone stage offers an advantage when it's built into an integrated amp or receiver. AB amps often don't age well and evolve to being A or B but not a good A or B. Though that takes a very long time if to happen if it happens at all.

FWIW, I am an audio engineer with 30+ years of experience.

What listening distortion? People use tube amps with a 3-5, 10% distortion and claim them to sound better, second harmonics, third harmonics, total BS....Solid state amps distortion are 100 time less sometimes, is there anybody able to hear that, really?
In headphone amps it is OK, if you are going to just relate on power consumption, as you said, the power is not much of difference, and the way they work is better, not that you can hear it, but maybe measurable better, (at frequencies outside the listening spectrum probably) but if you are an electronic engineer, you also know that the differences in audio measuring are no relevant, all electronic engineers agree on that, you can have a flat sounding amp that sound less desirable than other, less flat....otherwise we will never jump out of the class A amps, and now we are in class D, or worse....my friends that are enginnerrs agree on that, at least.
All my desktop headphone amps are class A, but I recently I purchased the Oppo HA-2SE because of the class A headphone amp, the look, and the reputation, I own several Oppo players, even while the headphones for me from them were a failure, sounded like crap, my phone the LG V20 is based in the DAC previous to the one used on the Oppo, so my comparison was merely the amp and not the DAC...even with a better DAC, the result was that there was no difference...I later I used the W3 from Rudistor, who uses an amp AB topology, and different DAC's, and in both cases I preffered the W3, as an amp, or as an amp/DAC. BTW the Oppo lasted 6 hours on battery, the W3, almost 48 hours, Oppo was sold...I'm charging my W3 right now, for my daily session after all weekend listening to it...
Please all these are my personal experience, and my personal opinion, take it as ignorant as they could be....

 

[KC2020]

What listening distortion?

I said that class A avoids the inherent distortion of class AB. I didn't say anything about hearing harmonic distortion. What's being avoided by using class A is actually intermodulation distortion. But you don't really hear that either.

What you do hear is that instruments sharing certain frequency ranges don't sound right. A lack of clarity, a loss of the natural character of the individual instruments.

That exquisite 100 year old Bosendorfer piano doesn't sound right when the cellist simultaneously plays the same note. The upright bass looses presence when the drummer hits the kick drum as the bass player plays a note that's near the drum's note.

 

[Sovkiller]

I said that class A avoids the inherent distortion of class AB. I didn't say anything about hearing harmonic distortion. What's being avoided by using class A is actually intermodulation distortion. But you don't really hear that either.

What you do hear is that instruments sharing certain frequency ranges don't sound right. A lack of clarity, a loss of the natural character of the individual instruments.

That exquisite 100 year old Bosendorfer piano doesn't sound right when the cellist simultaneously plays the same note. The upright bass looses presence when the drummer hits the kick drum as the bass player plays a note that's near the drum's note.

Well, I do not think that any recording gear, in any studio, or theater, that are nowhere around the audiophile quality, will be able to record these differences either, most of them, are far worse than the audiophile amps and gear we have home, most of them, ridiculous amps and mike pre-amps, standard cables, and even the mikes are nothing out of the ordinary...My main concern was always, while selecting my gear and headphones, is on how accurate a recording is? Can anybody say for sure?