The famous AB test between amplifiers

[END WAY]

Hi everyone
I have read a lot on the web that if we match the outputs of the amplifiers in an AB test we would not be able to find any auditory differences. Let's say we choose a Carver 360 vs Topping LA90 amplifier, would the results be the same? Does anyone have a different opinion?

My opinion is that differences can be found in an AB test, but not with the traditional method of fast switching. In fact, I would say that if we were to do the tests in this way, even if we listen to one in stereo and the other in mono, we still wouldn't hear any differences.

 

[Jimbob54]

Ive translated but please post in English in future as this is an English language based site. Thanks

 

[DonH56]

In English, using Google Translate:

Hello everyone
I have read a lot on the web that if we compare the outputs of the amplifiers in an AB test we would not find any auditory difference. Let's say we chose a Carver 360 amp vs. a Topping LA90, would the results be the same? Does anyone have a different opinion?

In my opinion, differences can be found in an AB test, but not with the traditional quick-change method. In fact, I would say that if we did the tests this way, even if we listened to one in stereo and the other in mono, we wouldn't hear any difference.
---
This subject has been discussed many times here and elsewhere. The answer is "it depends", on things like the noise floor, power requirements (volume and dynamic range of the source), and speakers (load) used.

If by "traditional quick-change method" you mean DBT or ABX testing, then most certainly that would show differences, but is generally a harder test to set up since you need the hardware (and potentially control software) to do a rigorous test. Auditory memory is very short, ~6 seconds per various studies (which I do not have memorized), so long-term listening tends to mask differences. The result I have found many times with long-term testing is that an obvious difference I thought I heard was there all along when I went back to the other amplifier.

 

[PAA]

Hi everyone
I have read a lot on the web that if we match the outputs of the amplifiers in an AB test we would not be able to find any auditory differences. Let's say we choose a Carver 360 vs Topping LA90 amplifier, would the results be the same? Does anyone have a different opinion?

My opinion is that differences can be found in an AB test, but not with the traditional method of fast switching. In fact, I would say that if we were to do the tests in this way, even if we listen to one in stereo and the other in mono, we still wouldn't hear any differences.

In order to hear (or see on the instruments) the difference, it is necessary to use the SWDT test modified by Bob Carver. To do this, it is necessary to carefully equalize the amplitudes of the output voltages and measure (look at the oscilloscope with isolated inputs or listen on the phones) the voltage between the outputs.

 

[JSmith]

Carver 360

Did you mean the Carver 350?

Carver Raven 350 Review (Tube Amp)

This is a review and detailed measurements of the Carver Raven 350 tube monoblock amplifier. It is on kind loan from a member and (I think) costs US $4,750. The 350 is not a bad looking amp. It has the same "orange peel" paint job of the previous Carver 275 amplifier I reviewed. At 42 pounds...

www.audiosciencereview.com

JSmith

 

[Blumlein 88]

In order to hear (or see on the instruments) the difference, it is necessary to use the SWDT test modified by Bob Carver. To do this, it is necessary to carefully equalize the amplitudes of the output voltages and measure (look at the oscilloscope with isolated inputs or listen on the phones) the voltage between the outputs.

Or record or measure with a good ADC using an attenuator circuit. Then you can drop the results into Deltawave and listen, ABX-test or whatever you wish to do with the differences.

 

[JiiPee]

This may be a heretical opinion, but why bother?

I can understand intellectual curiosity, and I appreciate the urge for engineering excellence, but if the sonical differences between two amplifiers are so small, that intricate testing methods are required to reveal them, is it not in practice more or less waste of time and effort, if in the end the goal is just to have equipment that is good enough for enjoyable music listening?

 

[Pareto Pragmatic]

To really test differences between D versus A/B topologies you not only need to match levels, but you also need two amplifiers with very similar noise and distortion measurements.

The carver and the topping are not even close. I did look for a couple of options, but could not find a good matched pair in the short time I looked.

 

[Purité Audio]

One would hope that booth noise and distortion would be inaudible.
Keith

 

[sergeauckland]

To really test differences between D versus A/B topologies you not only need to match levels, but you also need two amplifiers with very similar noise and distortion measurements.

The carver and the topping are not even close. I did look for a couple of options, but could not find a good matched pair in the short time I looked.

In a way, that's the point. Two amplifiers can be grossly different in measurements, but both are still audibly transparent and therefore indistinguishable in a blind test.

Our hearing is hugely inferior to measurements.

S.

 

[Pareto Pragmatic]

In a way, that's the point. Two amplifiers can be grossly different in measurements, but both are still audibly transparent and therefore indistinguishable in a blind test.

Our hearing is hugely inferior to measurements.

I actually have no interest doing in such tests, just pointing out what it would take to set one up.

Any amplifier that is audibly transparent will sound the same, that's my expectation and I can't see how it would be otherwise. Any amp that measures the same will sound the same regardless of topology. That said, I think sometimes people talk past each other when using the phrase "measure the same".

Consider two non-transparent amps. Two amps could both have the same s/n and 0.01% THD but one throws a lot of odd harmonics, the other even. Or one has a lot of harmonics at a low level, the other has fewer but they spike higher. They measure the same (sinad) but they don't measure the same (distortion in detail versus overall).

I think that is how people actually experience two amps that "measure identically" but "sound very different". It comes from limited measurement detail.

 

[voodooless]

but both are still audibly transparent and therefore indistinguishable in a blind test

Well, these two are not equally transparent, just check the frequency response of the Carver:

This might be audible. Also with an efficient speaker, the 50/60 Hz hum may be audible if you turn up the volume... You would not even need a signal to tell them apart. And the 44 SINAD certainly comes into the realm of audible as well.

 

[DVDdoug]

Of course, SOME amplifiers ARE defective or inferior...

My opinion is that differences can be found in an AB test, but not with the traditional method of fast switching. In fact, I would say that if we were to do the tests in this way, even if we listen to one in stereo and the other in mono, we still wouldn't hear any differences.

"Fast switching" refers to quickly (or instantly) switching between A and B. You could listen to A for five minutes (or as long as you like) and then instantly switch to B and then listen to B as long as you like. If it takes several minutes to disconnect one amplifier and connect the other, our auditory memory isn't as good. If you wait until the next day it gets even more difficult to reliably hear a difference.

In an ABX test, the listener is (theoretically) allowed to listen as long as they wish, and switch as often as they wish (between A, B, and X) before making a conclusion. And the ABX test has to be run several times to get a statistically valid result. (If you run the test just once, you have 50/50 chance of "guessing" X correctly.)

If there is a difference or defect with modern solid state amplifiers, it's usually noise. Frequency response and distortion are almost always better than human hearing unless it's over-driven into clipping (distortion). A good tube amp will be the same but it's harder and more expensive to make a good tube amp. (McIntosh has made good tube amps since the tube days.)

even if we listen to one in stereo and the other in mono, we still wouldn't hear any differences.

In some cases that's true - I have a program called Wave Repair for "cleaning-up" digitized vinyl records. On of the click removal methods is to copy the good channel into the bad channel when the click is only in one channel, or when it's offset in time between left and right. When you lose stereo for a few milliseconds, you don't notice it!

 

[sergeauckland]

I actually have no interest doing in such tests, just pointing out what it would take to set one up.

Any amplifier that is audibly transparent will sound the same, that's my expectation and I can't see how it would be otherwise. Any amp that measures the same will sound the same regardless of topology. That said, I think sometimes people talk past each other when using the phrase "measure the same".

Consider two non-transparent amps. Two amps could both have the same s/n and 0.01% THD but one throws a lot of odd harmonics, the other even. Or one has a lot of harmonics at a low level, the other has fewer but they spike higher. They measure the same (sinad) but they don't measure the same (distortion in detail versus overall).

I think that is how people actually experience two amps that "measure identically" but "sound very different". It comes from limited measurement detail.

If both amps have 0.01% THD, then it doesn't matter what the harmonics are, as they are all inaudible. Typically, with the normal spread of harmonics, it's hard to hear anything below 1%, which is why 0.1% was the 'holy grail' for amplifiers back in the 1950s. Our ears haven't evolved in the last 70 years to be any better at hearing distortion.

Incidentally, in the days of magnetic tape recordings, tape recorders had 3% distortion on peaks, and some magnificant recordings were done then, with no noticeably audible distortion.

There is no mechanism by which an amplifier can create a load of higher harmonics without also creating lower harmonics.

S

 

[DonH56]

One thing perhaps worth noting is that it is virtually impossible to match the performance of a "worse" amplifier to a "better" one with passive components; it is usually the other way around. You can add noise but not take it way, you can change the frequency response but not extend it, you can increase the output impedance but not reduce it, you can (probably) match phase but cannot decrease delay, etc. By modifying internal circuits you can get closer but it is usually easier to degrade than improve. Carver matched his SS amp to a tube amp; what if the challenge had been the other way around? I could make a SS amp sound like a SET, but making the SET match a SS amp would probably be impossible without fundamental circuit changes.

 

[kemmler3D]

I actually have no interest doing in such tests, just pointing out what it would take to set one up.

Any amplifier that is audibly transparent will sound the same, that's my expectation and I can't see how it would be otherwise. Any amp that measures the same will sound the same regardless of topology. That said, I think sometimes people talk past each other when using the phrase "measure the same".

Consider two non-transparent amps. Two amps could both have the same s/n and 0.01% THD but one throws a lot of odd harmonics, the other even. Or one has a lot of harmonics at a low level, the other has fewer but they spike higher. They measure the same (sinad) but they don't measure the same (distortion in detail versus overall).

I think that is how people actually experience two amps that "measure identically" but "sound very different". It comes from limited measurement detail.

Agree but I think it's worth mentioning this is pretty rare, you really have to go looking for amps where the distortion products are ever audible during normal listening. It's much, much less common than the subjectivist crowd would have you believe.

 

[Pareto Pragmatic]

Agree but I think it's worth mentioning this is pretty rare, you really have to go looking for amps where the distortion products are ever audible during normal listening. It's much, much less common than the subjectivist crowd would have you believe.

I actually had no idea that 0.01 would be inaudible, I just picked a number. "Limits of audibility" is not something I think about much, or have read about other than in passing. So thanks for that bit of knowledge!

If we go SINAD, there are a bunch in the 80s. Fosi V3 stereo version is 88. Match that up to an A/B with a sinad of 88 and many would say that measures the same. Just to try to rescue my main point.

 

[antcollinet]

This may be a heretical opinion, but why bother?

I can understand intellectual curiosity, and I appreciate the urge for engineering excellence, but if the sonical differences between two amplifiers are so small, that intricate testing methods are required to reveal them, is it not in practice more or less waste of time and effort, if in the end the goal is just to have equipment that is good enough for enjoyable music listening?

So much this.


The problem is we get so many people claiming they can hear night and day differences in excessively unlikely situations - pointing them at properly controlled testing is the only way to stop them misleading other newcomers.

 

[antcollinet]

If we go SINAD, there are a bunch in the 80s

Sinad 80 is the same as 0.01%. Sinad bigger than that is even lower. Basically 80 or above is going to be transparent for everyone in real world listening with speakers.

 

[Pareto Pragmatic]

Basically 80 or above is going to be transparent for everyone in real world listening with speakers.

I have seen 96 as the cut off point for "inaudible" mentioned several times. That's what I have been using at the cut point when thinking about things. This would be in the context of A/B testing.

Using an a/b switch and blinded, I was able to pick out differences between 88 and 106, volume matched, and pick the 106 sinad amp as having less noise (to my ear). But the 88 had load dependency feeding into 8 ohm speakers raising the high end (which is likely what I heard as more noise).

I appreciate the time you are taking here, thanks!