Review and Measurements of Benchmark AHB2 Amp

[GrimSurfer]

The article was published in 1997, maybe it's an "outstanding" figure during it's time, I dunno.

The B60 is now in its third iteration, with some changes in its circuitry. Trying to find the tech review of the newest version, which I'll post if successful. Now where near 0.1 THD+N now.

Though to be clear, my post made no mention of the Bryston being in the same league as the Benchmark. I think I used the term "very nice integrated".

 

[GrimSurfer]

I love my B-60, but it hums when my AC kicks in, I assume because of the temporary voltage drop. My other amps, including a Bryston 3B-SST, are not perturbed by this.

It's not a good idea to put an audio device on the same circuit as an AC, fridge, microwave, etc. Too much potential for line issues, as you're finding. The 3B probably has more than adequate power cap capacity and can take the dip in power. This is the sort of stuff one can expect when you get to that level/price of product.

 

[JohnYang1997]

B60 may not be the one. This one is pretty damn impressive (if you look the last graph).
https://www.soundstagenetwork.com/i...4b3-stereo-mono-amplifier&catid=97&Itemid=154

 

[GrimSurfer]

Well, I think you may need to create a list of superlatives and quantify the THD ranges to end all the confusion.

For example:

Without Peer 0.000005% or less
Superlative 0.00005% or less
Phenomenal 0.0005% or less
Outstanding 0.005% or less
Excellent 0.05% or less
Reasonable 0.1% or less
Below Average 0.3% or less
Poor 0.5% or less
Shocking 1% or less
Dreadful 3% or less
Putrid 5%
etc

This is a good start but we must be careful not to spawn the kind of bullshit that has made the cable industry what it is today. By that I mean chasing specs that eventually become meaningless (along with stratospheric prices for doing so).

For example, 0.0001% THD+N is -120 dB, placing it outside human hearing. Any THD+N lower than that is just "electro porn".

Once a manufacturer designs a circuit quieter than 0.0001% THD+N, we'd benefit from other things such as improved rise time, slew rate, current delivery.

All of this is to say that "superb" begins and ends for THD+N at -120 dB. If you can't hear it, it no longer matters. Just like cables after DBT.

 

[SIY]

THe measurement bandwidth is likely very different in each one.

Maybe, in which case the criticisms of "0.1%" are unrelated to the actual distortion, which looks an order of magnitude (20 dB!) lower in Figure 8. Or Stereophile screwed up some figures, which was not an uncommon thing for them (remember when they were running upside-down impedance plots?). The fact that their simulated speaker gives significantly lower distortion in that plot compared to pure resistance certainly raises some questions...

This does point out the necessity of fully disclosing test conditions for graphs. I've measured one sample of that integrated amp and saw almost no second harmonic, very low third harmonic, almost indiscernible 5th, and the rest were below my (at that time) measurement capabilities. The Figure 8 numbers were closer to mine. Not a record-setting world beater, but a solid and reliable performer.

 

[blueone]

It's not a good idea to put an audio device on the same circuit as an AC, fridge, microwave, etc. Too much potential for line issues, as you're finding. The 3B probably has more than adequate power cap capacity and can take the dip in power. This is the sort of stuff one can expect when you get to that level/price of product.

Perhaps I'm mistaken, but I think the hum being discussed is from the power transformer, not hum through the signal path. Perhaps Daverz can clarify for us.

It seems unlikely someone, even in a small apartment, has wall outlets on the same circuits as kitchen outlets for anything but a window AC unit. On the other hand, when any one of the central AC units come on all of the lights in my entire house dim for a small fraction of a second. It doesn't matter what circuit the lights are on. (I know they're separate circuits, since the AC units are on 240v/60 amp breakers.)

Finally, reading the owner's manual for the latest version of the B60R, it seems to use an unregulated linear power supply. If the mains voltage drops there isn't any circuitry to keep the DC rails from having a corresponding voltage drop.

 

[GrimSurfer]

Perhaps I'm mistaken, but I think the hum being discussed is from the power transformer, not hum through the signal path. Perhaps Daverz can clarify for us.

Mechanical resonance is possible under certain load and supply conditions I suppose. This is probably one of the reasons why Mc uses resin filled transformers.

It seems unlikely someone, even in a small apartment, has wall outlets on the same circuits as kitchen outlets for anything but a window AC unit. On the other hand, when any one of the central AC units come on all of the lights in my entire house dim for a small fraction of a second. It doesn't matter what circuit the lights are on. (I know they're separate circuits, since the AC units are on 240v/60 amp breakers.)

Nothing would surprise me. I say this after having sorted out my home, which was previously owned by an electrical engineer who thought he was an electrician. Phase inversions, floating grounds, inadequate circuits etc.

It's only been in the last few years that the code in some jurisdictions has been amended so that microwaves and refrigerators each have their own dedicated circuits. And then there is the issue of dealing with multiple SMPSs, LED/CFL lighting etc.

The dimming you describe is the AC compressor motor momentarily drawing more current than your home's panel can supply at that particular moment. This isn't unusual because electric motors can draw far more than their rated current at start up. It does, however, suggest a significant power distribution issue that would be wise to investigate if only to rule out issues such as that circuit being improperly configured/wired.

Finally, reading the owner's manual for the latest version of the B60R, it seems to use an unregulated linear power supply. If the mains voltage drops there isn't any circuitry to keep the DC rails from having a corresponding voltage drop.

Interesting!

 

[Kal Rubinson]

Well, I think you may need to create a list of superlatives and quantify the THD ranges to end all the confusion.

For example:

Without Peer 0.000005% or less
Superlative 0.00005% or less
Phenomenal 0.0005% or less
Outstanding 0.005% or less
Excellent 0.05% or less
Reasonable 0.1% or less
Below Average 0.3% or less
Poor 0.5% or less
Shocking 1% or less
Dreadful 3% or less
Putrid 5%
etc

No. Change the last one to:
Musical >5%

 

[GrimSurfer]

No. Change the last one to:
Musical >5%.

LOL. Reading this over breakfast. Almost spit my cornflakes out, Kal!

 

[SIY]

Mechanical resonance is possible under certain load and supply conditions I suppose. This is probably one of the reasons why Mc uses resin filled transformers.

FWIW, I own a 2B which resides in a closet because the mechanical hum from the power transformer is so obnoxious.

 

[RichB]

FWIW, I own a 2B which resides in a closet because the mechanical hum from the power transformer is so obnoxious.

From the best to worst for transformer hum in amps I have owned: Parasound (Almost silent), ATI6000 (Varied from amp to amp), Outlaw 7500, AT3000, Sunfire Signature Grand. Only the Parasound was inaudible from my seated position and remained unaffected by external sources.

Only the Benchmark and AT6000 were silent at all speakers. The rest buzzed from the center and rear channels.

I began with Sunfire amps and now I am back to Class-H without transformers and added distortion. This journey only took 20 years

- Rich

 

[Sal1950]

I'm just having fun. We all know absolute numbers or adjectives are only part of the story.

By that I mean chasing specs that eventually become meaningless (along with stratospheric prices for doing so).

Exactly. I'm kind of surprised we're beating this long dead horse here. All well and good to measure and give due kudos to the products that have achieved such excellent performance. But getting back to the real world, at what point do we have fully transparent amplifiers? IMO that point was passed long ago for properly designed products driving any kind of sane speaker load.
YMMV

 

[RichB]

Exactly. I'm kind of surprised we're beating this long dead horse here. All well and good to measure and give due kudos to the products that have achieved such excellent performance. But getting back to the real world, at what point do we have fully transparent amplifiers? IMO that point was passed long ago for properly designed products driving any kind of sane speaker load.
YMMV

In my experience, new architectures like the AHB2, NCore, and others I have auditioned in my home are reacting differently and are distinguishable.

Perhaps, the answer is not simply found in THD+N < [some magic number] provided by steady-state analysis.
Perhaps, it's power-supply, perhaps phase, perhaps distortion into reactive loads, I don't know but the AHB2 is worth a listen for those interested in making their own determination about the existence of more transparent amps than what was previously considered so.

- Rich

 

[Sal1950]

In my experience, new architectures like the AHB2, NCore, and others I have auditioned in my home are reacting differently and are distinguishable.

Perhaps, the answer is not simply found in THD+N < [some magic number] provided by steady-state analysis.
Perhaps, it's power-supply, perhaps phase, perhaps distortion into reactive loads, I don't know but the AHB2 is worth a listen for those interested in making their own determination about the existence of more transparent amps than what was previously considered so.

- Rich

Have you done that under tightly controlled, closely level matched. DBT's?
At what SPL are they "distinguishable". ?

 

[RichB]

Have you done that under tightly controlled, closely level matched. DBT's?
At what SPL are they "distinguishable". ?

I have level matched SBT's.
Listening at about 80 dB, level matched at 1 watt measuring the voltage driving the speakers and verified using REW and a UMIK-1 microphone.

The AT522NC does not sound like other amplifiers I have owned.

Of course, all amps should be indistinguishable operating at very low levels.

What does Bruno have to say about this?:

https://www.soundandvision.com/content/bruno-putzeys-head-class-d

S&V: Conventional wisdom says a great amplifier has no sonic character of its own and, beyond boosting the signal level, is transparent in the audio chain. But does the nature of high-quality Class D amplification—perhaps through the absence of distortions found in other circuit topologies—produce a particular sonic signature or specific attributes you could describe?

BP: Well, if the amplifier is truly great that’s absolutely right. Sonic signatures are what you get when you approach the same ideal from different angles. There are a few distortion mechanisms conspicuously missing in Class D, mostly those related to the input stage of a Class A(B) solid-state amplifier and nonlinear capacitances. Those are also missing in valve [tube] amplifiers so it’s quite common for people to notice that a Class D amplifier is somehow reminiscent of valve amplification in terms of “sweetness” for want of a better word.

I don't think my observations should be controversial given the differences in design and implementation.

- Rich

 

[SIY]

I have level matched SBT's.
Listening at about 80 dB, level matched at 1 watt measuring the voltage driving the speakers and verified using REW and a UMIK-1 microphone.

Could you describe the setup, the process, the way data was gathered, and controls? This is a remarkable claim.

 

[Deleted member 65]

In my experience, new architectures like the AHB2, NCore, and others I have auditioned in my home are reacting differently and are distinguishable.

Perhaps, the answer is not simply found in THD+N < [some magic number] provided by steady-state analysis.
Perhaps, it's power-supply, perhaps phase, perhaps distortion into reactive loads, I don't know but the AHB2 is worth a listen for those interested in making their own determination about the existence of more transparent amps than what was previously considered so.

- Rich

Assembled a pair of nCore monoblocks with high hopes a few years back. Was utterly disappointed, sounded thin/anemic to me, now sold. Replaced with a Norma Revo IPA-140 integrated amplifier, couldn't be happier.

Been trying to understand why the nCore's disappointed. Only numbers I can find that may/may not explain my experience are the ones below.

Hypex nCore nc400 / Norma Revo IPA-140

Cont. Power @ 8 Ohm (W) ~ 80 -100 / 140

Slew Rate (V/us) ? / 175

Peak Current (Amp) 25 / 150

So, a Class-H amp next maybe.

 

[neutralguy]

Could you describe the setup, the process, the way data was gathered, and controls? This is a remarkable claim.

I know there are many wild subjective claims out there, but I wouldn't call this one remarkable. There is already evidence that op-amp distortions are audible at as low as 0.005%, as discussed here. As posted above, typical listening volumes may be in the tens of milliwatts, for which typical power amplifier noise and distortion might be 0.1%.

From my level matched but sighted AB tests, the AHB2 sounds easily distinguishable from a highly regarded AB space heater amp.

 

[SIY]

From my level matched but sighted AB tests, the AHB2 sounds easily distinguishable from a highly regarded AB space heater amp.

I bolded the key word. This is the most basic control.

 

[neutralguy]

I bolded the key word. This is the most basic control.

Right, which is why this is an anecdote and not evidence. The evidence is linked.