Review and Measurements of Benchmark AHB2 Amp

[RichB]

A bunch of people are using a pair bridged mono to drive speakers like Salon2's that are ~4 ohms nominal. I believe Kal tested into speakers that dip a bit low and had no problems. That is my end-game plan, but I have corresponded with one person using single AHB2 to drive a pair in a larger room than mine and he does not feel the need for more power. I may start with one or use a set to drive all seven speakers, depends on what stock and bonuses look like this year (pretty ugly, unfortunately).

My friend bi-amped using an AHB2 for each Salon2 but felt that driven by the Oppo UDP-205 he wanted more output. He ended up bridging his AHB2's.
The amps were set to high gain so it could be that he was clipping the input, if he clip lights illuminate in this case.

I drove the Salon2's for a while with a single AHB2 with no problems driven by the XMC-1 (high gain) and now the LA4 (low gain).

Using the LA4, one clip-light illuminates (bi-amped bass section) at +15 playing Lorde Royals. It is quite loud.
I still feel there is a bit of added clarity bi-amped, that and my desire for to preserve my hearing, supports this decision.

In short, you may well be happy with the levels provided by a single AHB2. I'd start there.

- Rich

 

[dkfan9]

Thanks. Your analysis, although extracted from disparate sources, fascinates me because it provides a potential explanation for what I hear as a difference between two excellent (but unequal) amplifiers with a single speaker. I'd be really happy if you based the re-analysis on the F228Be because that is where I heard it most clearly.

Will do!

 

[RichB]

I have both Ncore’s here and Benchmark and I can’t hear any difference with the passive speakers I have here, they are both excellent , quiet compact, efficient.
Keith

They sound similar but different to me driving the Salon2's and M20's.

- Rich

 

[tktran303]

They sound similar but different to me driving the Salon2's and M20's.

- Rich

I take it you have matched the gains when doing listening comparisons?

 

[tktran303]

OK I've skipped 4 pages so I may have missed other discussion on the matter.

One idea: Output impedance (damping factor) differences

Below are the frequency response differences between the A31 and the AHB driving Kal's Monitor Audio Silver 8's. AHB as monoblock in green, AHB in stereo in blue.

Derived by tracing JA's SPL and Impedance Measurements of the Monitor Audio Silver 8's from Kal's review in Stereophile using VirtuixCAD's built in tool. Imported these as a driver into VirtuixCAD, put a .01 ohm resistor inline to approximate the A31's output impedance (from SSN review), a .09 for the AHB, and a .14 for the AHB monoblock (from Stereophile review). Divided A31's FR by the AHB's and AHB Monoblock's in VirtuixCAD, then imported to REW for viewing.

View attachment 26767

The scales have been exaggerated for effect. If you rescale so that each large division is 3 or 5dB...

 

[tktran303]

This is very cool to see-- $3000 dollars is a big investment, but as a guitar store owner I know used to say: "You can buy one $1000 guitar and play it forever, or buy several $300 guitars over the years and then a $1000 guitar. At that point, your $1000 guitar has cost you $2200."

Sure sure, the concept that the poor man pays twice.

But even gear heads have multiple $3000 guitars. It's all part of his disease that audiophiles and muso's have that is Gear Acquisition Syndrome...

Guilty as charged...

 

[dkfan9]

The scales have been exaggerated for effect. If you rescale so that each large division is 3 or 5dB...

Of course. The FR differences shown are less than the differences you could get by altering window sizes on loudspeaker measurements (or by altering the gauge and length of a cable run enough). That doesnt mean they are entirely insignificant. Of course the audible significance discussion is for another thread, a fun discussion in itself. With the total impedance vs FR measurements I'm just looking at what the measureable amplifier differences do to the speaker's output, and the differences are on such a small scale that extreme zoom is the best way to look at them.

 

[Panelhead]

I do not understand the dislike here for Speakon connectors. They are a step up for speaker connections.
Have two amps that have them and on both the difference between them and 5-Way is audible. The 5-Way posts on my two amps are not the quality of the ones used by Benchmark.
Glad Amir can measure what I have heard.
Benchmark uses Canare cables too. That is what you get if you order interconnects or speaker cables from them.
And I am sure this is an excellent product. Benchmark is not cheap, but not Looney Tunes expensive. May need an AHB2 and just do not know it.

 

[RayDunzl]

secret: no transducer can do better than -60db thd+n in audio BW, please don't chase the sun, I know it's sad, but brutal

How about straight THD?

I don't have a noise free measuring tool nor environment...

 

[amirm]

I don't have a noise free measuring tool nor environment...

And I don't have a distortion free measurement mic either. Quite the contrary, the one I have has pretty bad distortion which doesn't affect acoustic measurements but not at all good for distortion tests.

 

[Blumlein 88]

secret: no transducer can do better than -60db thd+n in audio BW, please don't chase the sun, I know it's sad, but brutal

Well, microphones claim it, and seems likely they can. Speakers probably can at least by a little bit if you get the N low enough. I don't think we should discredit a transducer due to external noise. That would be like measuring an amp while you input extra noise and complaining about the results. I get the point, in most environments noise can be an issue.

Speakers would seem to be worse transducers than good microphones so they'll be the bottleneck.

 

[RayDunzl]

the one I have has pretty bad distortion

What is it?

 

[RayDunzl]

And I don't have a distortion free measurement mic either

https://www.ap.com/analyzers-accessories/accessories/measurement-mics/

I'm afraid to look for the prices...

Alternatives

https://earthworksaudio.com/product...ard&tex_product_polar_pattern=omnidirectional

"Handles up to 140dB SPL without distortion" from $499 to $1299, depending on upper frequency limit desired, 23kHz to 50kHz.

 

[amirm]

What is it?

Dayton Audio UMM-6:

 

[amirm]

Alternatives

https://earthworksaudio.com/product...ard&tex_product_polar_pattern=omnidirectional

"Handles up to 140dB SPL without distortion" from $499 to $1299, depending on upper frequency limit desired, 23kHz to 50kHz.

They don't list any THD+N specs. Most measurement mics go up to such high SPLs but that doesn't indicate their distortion levels.

 

[RayDunzl]

UMIK-1 (with a little ferrite on both ends of the cable), plugged into an Anker 7 port powered USB3 hub

 

[BYRTT]

Well, microphones claim it, and seems likely they can. Speakers probably can at least by a little bit if you get the N low enough. I don't think we should discredit a transducer due to external noise. That would be like measuring an amp while you input extra noise and complaining about the results. I get the point, in most environments noise can be an issue.

Speakers would seem to be worse transducers than good microphones so they'll be the bottleneck.

Know below is meant as headroom visual but also it includes relative noice levels, so maybe some relavance
(LINK WIKIPEDIA: https://en.wikipedia.org/wiki/Headroom_(audio_signal_processing)

 

[RichB]

I take it you have matched the gains when doing listening comparisons?

They were voltage matched while driving the M20's with quick switching between amps.

Of course, neither (subjectively) sound like the AT4002:

https://www.audioholics.com/amplifier-reviews/ati-at4002

Also level matched.

- Rich

 

[RichB]

Some DACs add delay to the high frequencies and this seems to make reverberation more audible. The delay is produced if linear-phase filters are not used when reconstructing the analog signal.

The Benchmark DACs use linear-phase filters. Some DACs use filters that change the phase response and this can cause an audible effect.

The Oppo UPD-205 has 7 digital filter settings:

• Brick Wall – Select the Brick Wall filter.
• Corrected Mini Phase Fast – Select the Corrected Minimum Phase Fast filter.
• Apodizing Fast – Select the Apodizing Fast filter.
• Mini Phase Slow – Select the Minimum Phase Slow filter.
• Mini Phase Fast (default) – Select the Minimum Phase Fast filter.
• Linear Phase Slow – Select the Linear Phase Slow filter.
• Linear Phase Fast – Select the Linear Phase Fast filter.

These filters were measured by Archimago blog:

https://archimago.blogspot.com/2018/06/measurements-oppo-udp-205-part-1-output.html

I had tried these in the past, and perhaps they were not working then, but found no identifiable differences.
Since then, Oppo has upgraded the firmware and my setup has been upgraded to use the Benchmark LA4 and AHb2's.
The new signal chain is: Oppo UPD-205 -> LA4 -> AHB2 -> Salon2's,
The Slow, Apodizing, and correct Mini Phase all seem to extend the reverberation and the Linear Phase Fast has the greatest attack.
I settled on the Linear Phase Fast, but understand why others may chose another filter.

Perhaps the biggest effect provided by MQA might simply be the digital filter.
The rest seems to be destructive.

- Rich

 

[Daverz]

Would I really notice a subjective difference going from my Bryston 3B-SST to the Benchmark (other than less heat)? Going from the Hypex NC400 to the Benchmark?

I like the different gain settings, they make a direct connection from a DAC with digital volume much easier.