Benchmark AHB2 Review (Updated Measurements)

[pogo]

NAD seems to be able to squeeze more power out of their amps than the basic Purifi 1ET400 design I wonder how they did this

Performance depends on physical implementation and system-level circuitry/configuration (thermal system, power supply section, ...).
Not without reason, the C298 dynamic power is 750W into 2ohm and 450W into 1ohm (current limited)
Same measurements at hifinews for the AHB2: dynamic power is 346W into 2ohm and 230W into 1ohm
Default setting not used by NAD:
Output power into impedances <3.2 Ω may be limited by the Over Current Protection system.

 

[Gringoaudio1]

This is hugely interesting. You’d have thought that the NAD C298 would behave similarly to the AHB2 right up to the point where the current limit cuts in. On the basis that for a significant part of your listening you were probably well below the current limit it seems strange that there is a loss of bass and that an experienced reviewer, such as yourself, would have detected a clip condition either hard or soft anyway

NAD seems to be able to squeeze more power out of their amps than the basic Purifi 1ET400 design I wonder how they did this and whether this may have compromised performance under very unusual conditions?

Perhaps the concept of EPDR should be revisited for class D amps. Clearly the dissipation characteristic of the amp + its associated SMPS will be significantly different under reactive load conditions than a class AB amp.
As to why the 2 great amps sound different - more lab work for @amirm?

Why? AHB2 is not a class D or even Purifi amplifier.

 

[enricoclaudio]

L7 already tested it with APx555 before so nothing new would come anyway.

Measurement of Benchmark AHB2 Power AMP - L7Audiolab

台式设备

www.l7audiolab.com

@amirm first Benchmark AHB2 review was performed back on 2019, 3 years before L7

Review and Measurements of Benchmark AHB2 Amp

This is a review and detailed measurements of the Benchmark AHB2 Amplifier using THX technology to reduce distortion. I was going to request one for testing due to membership demand but to my pleasant surprise, the company volunteered to contact me and send not one, but two units! I requested...

www.audiosciencereview.com

 

[David_M]

Finally...an amp that is able to play 20Hz signals at full power without shutting down. Its unfortunate I have to say this but I'm still not sure why the NCore amps and maybe Purifi ones have this issue.

 

[EdW]

Performance depends on physical implementation and system-level circuitry/configuration (thermal system, power supply section, ...).
Not without reason, the C298 dynamic power is 750W into 2ohm and 450W into 1ohm (current limited)
Same measurements at hifinews for the AHB2: dynamic power is 346W into 2ohm and 230W into 1ohm
Default setting not used by NAD:
Output power into impedances <3.2 Ω may be limited by the Over Current Protection system.

Thank you for providing the performance data for the 2 amplifiers. Very useful information. A naive reading of these performances might suggest that the C298 could outperform the AHB2 into the low impedance load that the Estelon Aura loudspeaker presents at low frequencies. It might be interesting to know whether a higher current 1ET7040 based Purifi amplifier would suffer the same LF performance difficulties.

I notice from your post #314 that you suggest that the C298 may be driving the speaker from an impedance which is too low. That is an interesting thought - a small series resistance or a longer speaker lead could demonstrate this. If this proves to be the case it might suggest that the speaker has been voiced at the design stage with an amplifier with a relatively high output Z compared to C298.
All idle speculation on my part.
Perhaps also a warning to purchasers of new speakers that some caution in selection is needed (I would have been extremely wary seeing an impedance curve like that) and advice to loudspeaker designers to ensure that extremely low impedances may limit the range of amplifiers with which they will work.

 

[EdW]

Why? AHB2 is not a class D or even Purifi amplifier.

Sorry I didn’t make it clear. The EPDR comment was an aside. When comparing class AB and class D amplifiers EPDR is probably only relevant for class AB and a different metric is needed for class D to represent the stress presented to the amplifier by difficult loads.

 

[DSJR]

This. I got my last pair of Salk speakers built with speakon inputs to be used with my AHB2 amp.

My previous pair was connected using BJC sonically welded locking banana plugs. I thought at the time was there no better cable one could use. The sonic welding made the cable very secure with no chance of losing strands over time (strand bits on my self made ones would slowly break over time) and the locking bananas were easy and fast to screw in and tighten.

Now with the new speaker, the speakon connector is literly plug and play easy. No screwing, no finding positive/negative end, no tighten. Another benefit is no banana or spades stick out the back of the speaker (My previous speaker has unnecessarily hefty and stylish bananas plug plate sticking out the back). New speaker is flat on back without the need for an indentation. I cannot imagine if being faster or easier than a speakon connector.

Makes you wonder what exactly is wrong with the whole world for using anything but speakon connectors. If you have an AHB2, it is worth looking into utilizing them. They are very affordable to order or build.

Old habits die hard, or rarely get challenged...

I sold a client a Quad 707 power amp which had speakons instead of the previous and subsequent 4mm 'banana' posts. I spent an age fitting said plugs which didn't favour chunky cables I recall. A long time ago now (sorry) and things may well have changed. A forum owner bought a Neurochrome amp and imported it. First thing he did was drill the case for chunky 4mm sockets, apparently wiring said sockets out of phase with each other - and not even noticing so the story goes... Such is life in the audiophile fraternity away from sites like this one... @Mart68 may confirm.

Had I the money, I'd have no qualms whatsoever in owning one or two of these power amps, nor the dac and headpbone amp. They seem able to handle low impedance speaker loads quite happily in bridged form (unlike my old Crown which would go into self protection limiting almost certainly in bridged mode) and seven grand isn't a high amount for high end products - How much are Amir's Levinsons, even the smaller 'stereo' one? I'm sure they're excellent amps, but as good as a benchmark?

 

[DavidEdwinAston]

The only way I might possibly be enticed away from my stacked AHB2s would be by a single compact, lightweight multichannel amp of comparable (or better) performance. Purely for aesthetics.

Given the esteem you are held in here Kal, I'm disappointed that anything could possibly entice you away from this product!
"You will not be able to hear any difference"!

 

[pogo]

It might be interesting to know whether a higher current 1ET7040 based Purifi amplifier would suffer the same LF performance difficulties.

The results with a 7040 or 9040 will be identical. There is also no problem with the Purifis!
A separate thread should really be opened for this topic/issue.

 

[peng]

The only way I might possibly be enticed away from my stacked AHB2s would be by a single compact, lightweight multichannel amp of comparable (or better) performance. Purely for aesthetics.

Are you using them in bridged mode?

 

[peng]

Perhaps the concept of EPDR should be revisited for class D amps. Clearly the dissipation characteristic of the amp + its associated SMPS will be significantly different under reactive load conditions than a class AB amp.
As to why the 2 great amps sound different - more lab work for @amirm?

I am sure the dissipation characteristics will be different but as you alluded to, if in fact, Kal used them in well below current limit (voltage limit too I would say) conditions, then I doubt such different behavior under reactive load conditions would result in the difference in that bass response behavior. Not to doubt anyone hearing that unusual behavior, but it is mysterious enough for people to resort to guessing/speculating, and too bad no one has the time and resource to really investigate this matter on a test bench with the necessary instruments.

 

[EdW]

I am sure the dissipation characteristics will be different but as you alluded to, if in fact, Kal used them in well below current limit (voltage limit too I would say) conditions, then I doubt such different behavior under reactive load conditions would result in the difference in that bass response behavior. Not to doubt anyone hearing that unusual behavior, but it is mysterious enough for people to resort to guessing/speculating, and too bad no one has the time and resource to really investigate this matter on a test bench with the necessary instruments.

Worstcase loading for class D is certainly a worthy topic of discussion and anyone with a user friendly version SPICE (contradiction in terms?) or perhaps Matlab and some time on their hands could scope the problem.
One logical explanation as to why 2 great amps, the C298 and the AHB2, sound different in the bass region on the Estelon Aura speaker has been put forward by @pogo in #314 where he suggests damping factor is the cause. In which case both amps are blameless and the speaker would appear to be particularly fussy about its drive conditions

 

[peng]

Worstcase loading for class D is certainly a worthy topic of discussion and anyone with a user friendly version SPICE (contradiction in terms?) or perhaps Matlab and some time on their hands could scope the problem.
One logical explanation as to why 2 great amps, the C298 and the AHB2, sound different in the bass region on the Estelon Aura speaker has been put forward by @pogo in #314 where he suggests damping factor is the cause. In which case both amps are blameless and the speaker would appear to be particularly fussy about its drive conditions

Thanks for clarifying, I think loading for both classes are worthy topic of discussion anyway. As to Mr. Pogo, I ignore him if he simply repeats the same thing about EPDR and DF because I see no evidence he actually understands the details, or theory/principles involved and I think he just learnt some buzz words, make it a bigger deal and never let go. I could be wrong, but for now I'll read his other posts, until he gives me reasons not to.

 

[12Many]

Hi Amirm,

This being a Power Amp, how am i going to connect this to my Pre Amp?,
i see no RCA nor balanced inputs.

They sell a connector that coverts your RCA to a balanced connector.

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[RichB]

I am sure the dissipation characteristics will be different but as you alluded to, if in fact, Kal used them in well below current limit (voltage limit too I would say) conditions, then I doubt such different behavior under reactive load conditions would result in the difference in that bass response behavior. Not to doubt anyone hearing that unusual behavior, but it is mysterious enough for people to resort to guessing/speculating, and too bad no one has the time and resource to really investigate this matter on a test bench with the necessary instruments.

I don't think that protection mechanisms require the amplifier to be stressed, they limit preemptively.
Additional testing would be wonderful.

- Rich

 

[Kal Rubinson]

Given the esteem you are held in here Kal, I'm disappointed that anything could possibly entice you away from this product!

Well, we are half way through some major renovations and aesthetics are important. Having the three (or four) AHB2s stacked to the side still means 3 (or 4) each of power cords, XLR cables and speaker cords and arranging them carefully. Since I swap review devices in/out, I need access to all connections and cannot hide or build in the cables. If I had a single small multichannel amp, there would be only 1 AC cable and the others would be more easy to arrange. That's all.

"You will not be able to hear any difference"!

And that's a good thing.

 

[Kal Rubinson]

Are you using them in bridged mode?

Yes.

 

[Ajax]

I suspect that the new Purifi 1ET9040 will beat the AHB2 rather comfortably in nearly all aspects of performance, but remember this new amp is likely to be considered 2024 SOTA.
Though whether you would hear any differences between them below clip - either voltage or current seems unlikely. Both have dynamics beyond the range of human hearing.

Puts into perspective what a magnificent feat of engineering the AHB2 represents.

It still competes well with today's SOTA amps ..... 10 years after it was first manufactured.

 

[EdW]

Puts into perspective what a magnificent feat of engineering the AHB2 represents.

It still competes well with today's SOTA amps ..... 10 years after it was first manufactured.

Exactly my point. The AHB2 is a great amplifier but from a few years back. But SOTA class D amps will inexorably displace the very best class A or AB amps for power audio amplification. The performance strides made by Bruno Putzeys in his latest design give us lower cost, lower dissipation, lower THD, much lower IMD. These last few years have seen the greatest jump in amplifier performance since the invention of negative feedback. Come to think of though Bruno’s designs rely greatly on novel and ingenious ways to implement feedback. Formidable engineering indeed.

 

[AdrianusG]

Yes Benchmark sells their own cable adapters here: https://benchmarkmedia.com/products/benchmark-rca-to-xlrm-adapter-cable

Only 3 pages in and we are already going off topic. Can we try a little harder to stay the course for the first 10 pages?

Well, looks like i don't have to worry about adapters for this amp at all, because in Holland it's seemingly forged from unobtanium!,
official sales price here 4370 Euro's.
aka, completely out of my budget.