Review and Measurements of Benchmark AHB2 Amp

[restorer-john]

One thing is guaranteed: if you pick equipment by hearing, you'll be applying the very same mechanism you use when you listen to and enjoy the music. It's apples to apples. Numbers and graphs vs listening to music, that's not apples to apples. No guarantee you'll like it accordingly when you listen to it.

I'm sorry, this flies in the face of every facet in the pursuit of high fidelity reproduction. It makes absolutely no sense whatsoever to me. Every, single parameter in waveform reproduction can be defined in the mathematical domain. An objectively accurate amplifier is just that, accurate.

There is no mystery or black magic in this space, and we have access to equipment which can categorize, characterize and isolate details at levels that no human set of ears and brain can come close to, and you want to trust your fallible made-of-meat ears?

Take the unbiased, scientific approach. Your ears, brain, wife (or partner) and wallet will thank you.

 

[zalive]

Class D proponents of course say no, it doesn't matter.

Those of us who favour completely noiseless High Fidelity equipment might say otherwise. Me, I like my waveforms clean, not fuzzy traces polluted with switching garbage.

That said, not many people listen to square waves or pure sine waves (I do on my bench, but that's me..).

Speaking of which...

Current situation is that, thanks to general use of a lot of electrical devices with SMPS's being pretty common, AC network might be pretty much polluted with various harmonics, including HF noise. While all we need is 50 or 60 Hz AC. Any device is exposed to this, regardless of its class.

What do you think, is it a good idea is to use a certain AC filter for each audio device (or for some particular audio devices) to eliminate at least part of this noise from the AC prior to feeding the device with? And which type of low pass filter should be good for this purpose (or respectively, which for the DAC, which for the amplifier)?

 

[zalive]

I'm sorry, this flies in the face of every facet in the pursuit of high fidelity reproduction. It makes absolutely no sense whatsoever to me. Every, single parameter in waveform reproduction can be defined in the mathematical domain. An objectively accurate amplifier is just that, accurate.

There is no mystery or black magic in this space, and we have access to equipment which can categorize, characterize and isolate details at levels that no human set of ears and brain can come close to, and you want to trust your fallible made-of-meat ears?

Take the unbiased, scientific approach. Your ears, brain, wife (or partner) and wallet will thank you.

I know. But you can't guarantee that a certain individual would prefer absolute fidelity to a device which somehow makes sound things nicer (at least to personal criteria).

Naked truth or a beautiful lie? Isn't this a personal choice? And are we even fully aware what we do like the best?

To make things more complicated...produced recordings aren't exactly a fidelity. It's musical producer's personal view on how a certain music should sound to be liked by most, on a variety of musical systems used by end audience...of which, majority of systems isn't hi-fi at all.

And as for my personal taste, I'll be honest. If recording sounds good, I'd like it to be reproduced with as much fidelity as possible. But if it's a poorly produced recording, I'd prefer it to sound best possible, even if it is not in the direction of fidelity. So what? Fidelity was lost in the production process anyway, and it can't really be restored, so let's go all the way and at least make it sound better, the damage was already done. I want to enjoy the music for what it's worth, and unfortunately for us, some masterpieces of music are just poorly produced, and I don't prefer to eliminate some good music because of the fact. Because to me...it's all because of music, this is how it started and this is how it is stlill. Not because of the sound alone, or sound fidelity alone.

But to make things better: I do think that best objective systems actually generally make music reproduced through them sound nicer. If someone describes a system as 'being punishing to bad recordings' yet it measures good...in my view, some important measurements are likely missing, which would show some serious flaws.

 

[zalive]

Take the unbiased, scientific approach. Your ears, brain, wife (or partner) and wallet will thank you.

One thing must be clear. You can't escape bias no matter what you do. If you trust the measurements and graphs to fully describe the quality of a device (mind, those are not perfect measurements because it's never all being measured, in a real world), you get biased with those numbers and measurements.

 

[restorer-john]

Naked truth or a beautiful lie? Isn't this a personal choice? And are we even fully aware what we do like the best?

To make things more complicated...produced recordings aren't exactly a fidelity. It's musical producer's personal view on how a certain music should sound to be liked by most, on a variety of musical systems used by end audience...of which, majority of systems isn't hi-fi at all.

I understand what you are saying. To me, amplification and source equipment can be almost beyond criticism for accuracy. Speakers/room however, are where it all goes to hell. So two out of three parts of the equation can be as good as I can get them.

The source content is the variable you have zero control over, other than sourcing the 'best' recording of what you want to hear.

 

[MZKM]

To me, amplification and source equipment can be almost beyond criticism for accuracy.

Yeah, but we should realize that buyers get biased easily, even if a Benchmark AHB2 or Hypex NC400 Kit amp measures better, since they don’t look nice or cost 5 figures, a lot of higher end buyers won't even consider them, as they think the much more expensive, nicer looking amp has to sound better.

I’m with you though. I prefer all my components, including the speakers, to be as “uncolored” as possible, and then use DSP to tune to taste. That way, the notion of “system synergy” gets mostly thrown out the window (“Oh, this amp is thin sounding, so it’s best paired with X speaker”).

 

[Kal Rubinson]

I know. But you can't guarantee that a certain individual would prefer absolute fidelity to a device which somehow makes sound things nicer (at least to personal criteria).

Naked truth or a beautiful lie? Isn't this a personal choice?

Sure but, while I can have an productive conversation about audio with those who ascribe to the former, the best I can do for the latter is to wish them good luck and good bye.

 

[GrimSurfer]

This discussion parallels the one on cables.

The cable industry frequently advises that cables be used for a number of hours of "burn in time". Metallurgists and scientists know that, at the voltages and currents used in the audio industry, the notion of changes occurring in the physical or electrical properties of copper wire is utter bunk.

The real issue is psychoacoustic, where the brain requires time to hear what it wants to hear. I think the same thing applies to source material, playback devices, amplifiers, and loudspeakers.

So how is this for an idea: We accept the objective measurement of devices. We audition devices meeting certain performance thresholds (20-20 kHz +/- 0.5 dB, THD+N under -116 dB, etc.). Provided an audition falls within a broadly acceptable range of performance, we then allow our ears to burn-in.

Musicians would call this training one's ear to recognize certain tones, pitches, rhythms. We might call it training ourselves to be objectively better consumers.

 

[March Audio]

Class-D can have different looking 1kHz square waves:
https://www.stereophile.com/content/theta-digital-prometheus-monoblock-power-amplifier-measurements

View attachment 27611
ASR also exposes this high-frequency switching noise.
I don't suppose that most speaker have LPF on the tweeters, does this matter?

- Rich

What the scope sees is not what the speaker reproduces or what you hear. Switching frequency for Hypex amps is around 400kHz. The speaker is a low pass filter with few having response above about 30 to 40 kHz. All that is left is the audio signal.

Tweeter coil heating is a *total* non issue, a few mW. See these two posts here. Also don't forget that inductive reactance doesn't generate heat, its only the resistive component that does, so heat wise its less than indicated below.

https://www.audiosciencereview.com/...of-nord-one-nc500-amp.7704/page-4#post-181509

https://www.audiosciencereview.com/...of-nord-one-nc500-amp.7704/page-4#post-181520

 

[March Audio]

I've yet to investigate these, but I wonder, can the constant presence of the switching frequency:
- lead to heating of the tweeter coil? At what voltage does this become a non issue?
- cause any sort of demagnetization, especially neo (probably not but I'm anal with my engineering).

No and no.

 

[RichB]

This discussion parallels the one on cables.

The cable industry frequently advises that cables be used for a number of hours of "burn in time". Metallurgists and scientists know that, at the voltages and currents used in the audio industry, the notion of changes occurring in the physical or electrical properties of copper wire is utter bunk.

The real issue is psychoacoustic, where the brain requires time to hear what it wants to hear. I think the same thing applies to source material, playback devices, amplifiers, and loudspeakers.

So how is this for an idea: We accept the objective measurement of devices. We audition devices meeting certain performance thresholds (20-20 kHz +/- 0.5 dB, THD+N under -116 dB, etc.). Provided an audition falls within a broadly acceptable range of performance, we then allow our ears to burn-in.

Musicians would call this training one's ear to recognize certain tones, pitches, rhythms. We might call it training ourselves to be objectively better consumers.

I think the cable parallel is over-simplistic and only applicable in that there is a ridiculous amount of bunk and downright thievery.
I agree that there is a reasonable set of specifications that are the minimum requirement for an acceptable product.

There are other aspects of amplifier performance that you will not often find in reviews such as transformer hum and/or speaker buzz. I have been annoyed by both of these issues across many amps from different manufacturers.
These issues are environmental and unpredictable. It is not enough to simply consult AP measurements.
Consumers aware of these potential issues must turn to forums and user reviews for additional information.

My solution is to select balanced components (when possible) that are without large transformers that have SINAD that indicate excellent engineering. It is apparently a surprise that such products actual sound different/better. I am not surprised.

- Rich

 

[GrimSurfer]

I think the cable parallel is over-simplistic and only applicable in that there is a ridiculous amount of bunk and downright thievery.
I agree that there is a reasonable set of specifications that are the minimum requirement for an acceptable product.

There are other aspects of amplifier performance that you will not often find in reviews such as transformer hum and/or speaker buzz. I have been annoyed by both of these issues across many amps from different manufacturers.
These issues are environmental and unpredictable. It is not enough to simply consult AP measurements.
Consumers aware of these potential issues must turn to forums and user reviews for additional information.

My solution is to select balanced components (when possible) that are without large transformers that have SINAD that indicate excellent engineering. It is apparently a surprise that such products actual sound different/better. I am not surprised.

- Rich

Of course the cable theory is simplistic bunk and dishonest. It relies on quirks of human perception... the ability of the ears to adjust to the sound environment and the desire of people to hear what they want to hear.

Transformer hum, chassis vibration, fan noise etc. can all be measured. Speaker buzz is irrelevant for amps -- it's a speaker response issue unless it is part of the waveform.

The point I was making was similar to yours, less the large transformer part (which I don't necessarily agree with).

I don't have a golden ear. Neither do you in all likelihood. The sooner we become attuned to, and select components on the basis of, objectively better sound, the less crap manufacturers will market under the audiophile banner.

 

[SIY]

I admit that I don't read the reviews at Stereophile or Absolute Sound (other than the former's measurement section), but certainly reviews at the late great Audio Critic and my current magazine note things like mechanical noises. Speaker buzz absolutely shows up in standard measurements. I'm not sure where that straw man was stuffed.

 

[blueone]

Speaker buzz is irrelevant for amps -- it's a speaker response issue unless it is part of the waveform.

I think the "buzz" Rich is referring to is the hiss heard from tweeters when the entire audio chain is idle (no program material playing). Some amps produce considerable hiss, though IMO it might be a gain structure issue in the overall signal path.

 

[DDF]

Speaker buzz absolutely shows up in standard measurements.

MLSSAs incoherency distortion test is quite useful for this. A bit like a diffmaker test, it picks up all the non harmonic noise created by a speaker. Only appreciable if a very poor quality or broken unit

 

[daftcombo]

Transformer hum, chassis vibration, fan noise etc. can all be measured. Speaker buzz is irrelevant for amps -- it's a speaker response issue unless it is part of the waveform.

No, on the same speakers some amps can produce hum/hiss,/buzz, others not.

Even some sellers admit it.
https://www.audiophonics.fr/en/full...class-d-stereo-2x50w-8-ohm-black-p-10394.html
https://www.audiophonics.fr/en/full...-xmos-class-d-2x-50w-8-ohm-black-p-11358.html
See the warnings with the yellow background.

 

[SIY]

I think the "buzz" Rich is referring to is the hiss heard from tweeters when the entire audio chain is idle (no program material playing). Some amps produce considerable hiss, though IMO it might be a gain structure issue in the overall signal path.

But if the power amp is causing the hiss or buzz or whatever noise, this is obvious in measurements.

 

[SIY]

MLSSAs incoherency distortion test is quite useful for this. A bit like a diffmaker test, it picks up all the non harmonic noise created by a speaker. Only appreciable if a very poor quality or broken unit

The AP system I use has rub and buzz measurement, likely programmed along those lines. I include them in my speaker reviews.

 

[RichB]

Transformer hum, chassis vibration, fan noise etc. can all be measured. Speaker buzz is irrelevant for amps -- it's a speaker response issue unless it is part of the waveform.

The point I was making was similar to yours, less the large transformer part (which I don't necessarily agree with).

Transformer hum and speaker buzz can be environmental, related to other components, power issues, and grounding.
The Parasound A21, A32, and A51 all had some hiss but very little transform hum but all buzzed in the center and rear channels.
The ATI6000 had more transformer hum that was audible from my seated position but no buzz or hiss from any speakers.
The Outlaw 7500 and Sunfire had transformer hum, hiss at the speakers, and buzz.

All measured by my ears without bias issues
Want to point me to the reviews that indicate that I might experience these issues?

Here is my algorithm:

SINAD (and other objective measurements) * (amplifier design + professional reviews + forum participation) = good purchasing decisions.

Therefore, bad SINAD = no purchase.

- Rich

 

[SIY]

Those issues may or may not be related to the power amp (other than transformer buzz). That's something you'll have to track down. You may have some issues with your sources, no way for me to tell remotely.