Can anyone hear when an Amp switches from Class A to A/B

**Shadowfax** · March 29, 2023, 01:36 PM

Oddball question I know but have been thinking about it. For example, my Luxman supposedly does about 6watts at Class A before switching to A/B. So I thought sweet, if I am listening at low levels it must be in Class A and why it sounds so good at that low level. Then at some point the class changes. So the question is, do the original 6 watts sound any different that watt 7 thru 100? If yes, can anyone really hear it or is this more of a measurement thing?

**puroagave** · March 29, 2023, 02:06 PM

Here's a good article by the great JGH himself that speaks to your question: The Great Distortion Delusion | Stereophile.com

I have a few pure class-a amps here (Krells) and a high bias sliding design--by Classé Audio no less (CAM 350). I agree with the article and remain agnostic re specs, class of operation, mfr claims, etc. I base my amplifier buying decisions on sound quality first and foremost.

**MichaelsMinute** · March 29, 2023, 02:23 PM

Originally Posted by Shadowfax

Oddball question I know but have been thinking about it. For example, my Luxman supposedly does about 6watts at Class A before switching to A/B. So I thought sweet, if I am listening at low levels it must be in Class A and why it sounds so good at that low level. Then at some point the class changes. So the question is, do the original 6 watts sound any different that watt 7 thru 100? If yes, can anyone really hear it or is this more of a measurement thing?

Interesting question.

**still-one** · March 30, 2023, 09:11 AM

Over the years I have never been able to hear when any previous amps went from a A to A/B.

Like anything in this hobby I am sure there will be some who hear night and day differences.

**Mr Peabody** · March 30, 2023, 10:38 AM

No. Nelson Pass has a good article on this, my memory is not good enough nor my tech skills to explain it but ever since reading the article I understand you can't hear any difference because it doesn't work like that.

As a side note from what I've been told some higher end amps will begin to sound thinner at high volume when they are running out of power opposed to a hard clip. Another issue could be some amps with Loudness control will make the Loudness automatically back off when the volume rises.

**nicoff** · March 30, 2023, 10:53 AM

Originally Posted by still-one

...
Like anything in this hobby I am sure there will be some who hear night and day differences.

LOL

**Shadowfax** · March 30, 2023, 11:22 AM

So it is probably what I thought, you really can't hear it. So next question which I am assuming is Yes....Can it be measured? And then that leads us down the rabbit hole of Specs that we can't hear and are they sometimes useless.

**atmasphere** · March 30, 2023, 12:14 PM

Originally Posted by Shadowfax

So it is probably what I thought, you really can't hear it. So next question which I am assuming is Yes....Can it be measured? And then that leads us down the rabbit hole of Specs that we can't hear and are they sometimes useless.

You won't be able to hear or measure the difference at the transition point unless there is a very obvious design flaw or malfunction. Think of it as a curve being grafted to a straight line- at first after the transition the curve is so gentle it looks straight. But as power is increased, the difference in linearity becomes more obvious measurably and audibility. Of course, the A region isn't linear either so the curve is really being grafted to a curve. But you get the idea.

**a.wayne** · March 30, 2023, 12:51 PM

Ralph replace the you with an “I cant “ and it all makes sense ..!

Regards

**a.wayne** · March 30, 2023, 12:56 PM

Originally Posted by Shadowfax

Oddball question I know but have been thinking about it. For example, my Luxman supposedly does about 6watts at Class A before switching to A/B. So I thought sweet, if I am listening at low levels it must be in Class A and why it sounds so good at that low level. Then at some point the class changes. So the question is, do the original 6 watts sound any different that watt 7 thru 100? If yes, can anyone really hear it or is this more of a measurement thing?

Depends on your loudspeakers and how perceptive you are , 7 watts class A will carry alot and affect waveform since most domestic listening is in the 1-2 watt RMS range , only dynamic peaks will be in class B, so what becomes audible is recovery and and if any ringing after leaving class A , this along with feedback amount etc ..

So is it audible , thats a big yes in my books ..

Regards

**Shadowfax** · March 30, 2023, 12:58 PM

Originally Posted by a.wayne

Depends on your loudspeakers and how perceptive you are , 7 watts class A will carry alot and affect waveform since most domestic listening is in the 1-2 watt RMS range , only dynamic peaks will be in class B, so what becomes audible is recovery and of and if any ringing after leaving class A , along with feedback amount etc ..

So is it audible , thats a big yes in my books ..

Regards

So my speakers are 92DB, are we saying that listening at about 50 to 70 on the old radio shack meter, I am probably listening to Class A?

**a.wayne** · March 30, 2023, 01:03 PM

RMS wattage yes on peaks no , but mostly yes, typically on high crest recordings 1 watt RMS
Can require as much as 100+ Watts for peaks , at 70 db avg din you are prolly in or below the .5watt rms range , means most of your music waveforms materialize in class A mode before going to class B , very critical for classical soft passages and proper timbre imo ..

Regards

**Mr Peabody** · March 30, 2023, 10:33 PM

Pass LabsLeaving Class A - Pass Labs

**Shadowfax** · March 31, 2023, 07:54 AM

Thanks Mr P, I was looking for something like that before I asked.

**W9TR** · March 31, 2023, 08:20 AM

Originally Posted by Mr Peabody

Pass LabsLeaving Class A - Pass Labs

Thanks for posting - great article.

TL DR There is no physical transition from class A to AB.

**atmasphere** · April 4, 2023, 11:30 AM

Originally Posted by a.wayne

Ralph replace the you with an “I cant “ and it all makes sense ..!

Regards

I can't and you personally can't either. That makes it more accurate. Thanks for the advice.

**SCAudiophile** · April 4, 2023, 04:47 PM

Of all the Class AB amps I've owned and many more I've heard, the transition can not be heard. I am not able to speak to measurement; I don't listen to meters and scopes, I listen to speakers

Can anyone hear when an Amp switches from Class A to A/B

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**Dizzie** · April 4, 2023, 06:52 PM

Originally Posted by SCAudiophile

Of all the Class AB amps I've owned and many more I've heard, the transition can not be heard. I am not able to speak to measurement; I don't listen to meters and scopes, I listen to speakers

Sent from my SM-G998U using Tapatalk

I don't listen to speakers. I listen to music.

**SCAudiophile** · April 4, 2023, 09:44 PM

We are obviously saying the same thing

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**bluegrassphile** · April 13, 2023, 10:41 AM

I can't hear any difference when my Pass Labs int 250 converts at 15 watts. I'm not even sure I've ever gotten into class A/B with my amp. Maybe with the transients? I don't honestly know?

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