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Review and Measurements of Benchmark AHB2 Amp

pjug

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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).
Probably you know this, but in case anyone does not: Benchmark only provides specs for bridged operation down to 6 ohms.
 

digitalfrost

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Well I've been waiting for this review, many thanks Amir.

For speaker terminals there are two sets: classic heavy duty banana jacks and SpeakOn. The SpeakOn are locking and provide the best performance. I lost about 3 dB of performance using the banana jacks due to less secure connect there. So the measurements you see are with SpeakOn jacks.

That is insane. May I ask how these cables were terminated on the other side?
 

Umlautica

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It's great to see these results confirm what Stereophile found in their review at https://www.stereophile.com/content/benchmark-media-systems-ahb2-power-amplifier-measurements.

I worry that people will read this and think that this level of performance translates to improved sound quality over the next ~5 measured amps on the SINAD bar chart.

It's already supremely difficult to tell the difference between amplifiers that are in the 0.01% (-80dB) and 0.001% (-100dB) ballpark in tests designed to reveal distortion. Most would argue it's even inaudible for music. Even some of the most excellent loudspeaker drivers have distortion components around 0.01%.

The AHB2 takes it the next order down to 0.0001% (-120dB) which is an impressive feat but drifts from the realities of audio quality. The low noise floor is great for those with 110dB sensitive horns though.

I say this as a happy owner of Hypex NC400 amplifiers who still remembers connecting them. They're great but the sound quality does not live up to the aura around SOTA products such as this. I'd buy them again but having no doubt in the amplifier is really what you're getting at this level.
 

Matias

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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.
My speakers are nominal 4 ohms but most of the frequency range they are in the 2.5 ohms range (Thiel CS3.7). They are current hungry.
 

Soniclife

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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.
This is why I'd like to see testing done to confirm the clip light is completely trustworthy, so you can buy one, drive it harder than you ever would, and if the light stays of your sorted. I would expect Benchmark to get this right, but always good to know.
 

DonH56

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Probably you know this, but in case anyone does not: Benchmark only provides specs for bridged operation down to 6 ohms.

Yes, I know that, but that is nominal spec and nominal impedance. And people do not seem to be having problems in use; there are numerous accounts on various audio fora. A couple asked Benchmark and they said it was OK, or so they told me (I have not asked Benchmark myself; I certainly will before any purchase). They say "Stereo loads as low as 1.4 Ohms can be cleanly driven to full output levels. " which implies 2.8 ohms in bridged operation. That does not mean it is rated to deliver full power, though it probably does, but it is stable. And they say elsewhere "The AHB2 is stable into all loads. " They actually provide some specs for 4 ohms in bridged mode, e.g. "33.16 dBV, 35.38 dBu, 45.52 Vrms into 4 Ohms, bridged mono". Finally, the Salon2's are spec'd as 6 ohms nominal with a minimum of 3.7 ohms at 90 Hz so I think I'll be OK.

Most amplifiers can handle much lower load than spec'd; it comes down to what the limiting factor is. If it goes unstable into low-Z reactive loads then you should not use it. Most amps will not oscillate and self-destruct (at least not most decent ones). They will current- or thermal-limit without providing full output. Most of the time that is no big deal since peaks tend to be short. It is pretty amazing that the AHB2 actually provides 4x the output when bridged; that is the theoretical ideal, but most amps spec about 2x the power in bridged mode, probably due to thermal limits.
 

pos

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Thanks for the review @amirm ! :)
Would be interesting to see this amp compared to a thx789 on a 16ohms load on the same graphs! (1khz spectrum at 5watts, distortion+noise vs power, etc...).
 

filo97s

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The most awaited review is finally here! Thanks amirm, what a beast!
 

filo97s

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John_Siau

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amirm

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Possible to test in Bridge Mode?
Sure. I heard from @John_Siau that it was safe to run it at 4 ohm and indeed it was:

index.php


I updated the review with it.

Notice how exceptionally clean it is at the limit with such low THD+N. You get full transparency and lack of distortion until the amp shuts down at half a kilowatts.
 
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amirm

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That is insane. May I ask how these cables were terminated on the other side?
Which ones, the bad ones or the good ones? The good ones used SpeakOn. The bad ones used banana jacks with screw terminals. Removing the terminal and going with bare wire produced 2 dB better performance. I have solid brass locking banana jacks coming to test to see if it resolves this issue.
 

RayDunzl

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Now, go measure a speaker with it.
 
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Manbeard

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Been waiting for this one. Definitely doesn't disappoint. Thanks Amir and Benchmark for sending you the amps to be tested!
 
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amirm

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Are you able to make some measurements on the efficiency of the AHB2? I am wondering where the Class H power delivery puts this compared to conventional Class AB and compared to Class D.
Sure. It was a manual process so not that many points:
Benchmark AHB2 Amplifier Efficiency Measurements.png


Idle power was about 18 watts. Above wattage numbers are for one channel driven.
 

Matias

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Umlautica

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Impressive idle power consumption. That's better than the NC400+SMPS600 monoblock which I measured at 14 watts idle (28w pair) and the XLS-2502 which is 31w idle.
 
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FrantzM

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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 the second one because of something I was seeing in the measurements that turned out to be my issue, not the amp's. The AHB2 retails for US $2,999 from the company direct.

The AHB2 is a very compact form factor, enabled by use of switching power supply to increase efficiency/density:

There is just a power switch in the front. It might be but I constantly reached for the screw next to it to power it on! Having the power switch be slightly different color or shape may help with this.

There are a set of LEDs that show the status of the amplifier. They are driven by an FPGA (field programmable digital logic) that monitors all aspects of the amplifier and shuts down the unit if stressed. It did so very quickly and efficiently in my testing. Usually this is done with purely analog or maybe a small microprocessor. As such, the coverage of scenarios that could damage the amplifier is much less complete than using the approach Benchmark is using in AHB2.

Here is the back panel:

This is a very minimalistic approach given the small amount of real estate available. Only input is XLR balanced which is just fine in my book. A gain switch allows the input level to be controlled so that you can just use an RCA to XLR adapter and still get full power (2 volt max in high gain). At the other extreme, the low gain setting is designed for professional pre-amps with lots of output, getting its max power at 9.8 volts. Using this scheme, the signal to noise ratio can be improved as you will see in measurements later.

For speaker terminals there are two sets: classic heavy duty banana jacks and SpeakOn. The SpeakOn are locking and provide the best performance. I lost about 3 dB of performance using the banana jacks due to less secure connect there. So the measurements you see are with SpeakOn jacks.

Another minor nit on that note: I had a rather cheap SpeakOn cable and its plug was just large enough to hit the silver screws that the sockets are mounted with. Typical round shaped SpeakOn ones are not an issue. Flush mount screws would solve this problem.

There is a switch for selecting stereo or mono bridged output. The latter quadruples the amount of power available and unlike typical bridging, according to Benchmark comes at no penalty in distortion! I plan to test this later as it has a minimum impedance of 6 ohm so I could not use the 4 ohm setup I used for this testing.

There is a very beefy AC mains cable with really nice locking tabs. Insert it and it stays put unless you push the two red tabs on each side. Nothing is more aggravating than the AC cable coming half-way lose from the IEC socket.

Being a proper company of course the AHB2 comes with full set of regulatory/safety/emissions certifications which is super important with power amplifiers given the high voltages and currents running around in them.

In use the AHB2 stays very cool for a power amplifier when it is idling, outputting little power which was a nice surprise.

As to THX technology, it merges a low-power but very low distortion amplifier with a high power but higher distortion amplifier. The distortion of the latter is not seen because it is producing so much power (so the ratio of distortion is lower). The general scheme is not new, dating back to 1980s but new implementation is. We have seen this in stellar performance of Massdrop THX AAA 789 amplifier which broke new ground in level of distortion and noise. Will the Benchmark AHB2 manage the same? Let's see.

Power Amplifier Audio Measurements
As usual, I start with my 5 watt output test using 4 ohm load using SpeakOn terminals as noted:

View attachment 26575

I hope your jaw is on the floor just like mine was when I saw this picture emerge! :) 113 dB THD+N in a power amplifier? Are you kidding me?

Look at the harmonic distortion. The worst case spike is below -130 dB! This is insanely good. Of course this type of SINAD (signal and noise ratio) crowns the Benchmark AHB2 as the best I have ever tested:
View attachment 26576

The performance was so good I literally had to rebuild my dummy load to get there. Even the quality of the metal used in the connectors matters to get to this level of distortion. I replace all my dummy loads with higher precision ones that have much less VCR (voltage coefficient of resistance). Resistor values can become voltage dependent creating distortions of their own. Up to about 105 dB of THD+N, it doesn't matter but beyond that, the VCR was the dominant distortion, not the Benchmark AHB2 amplifier!

It was requested that I show the breakdown and distortion so here we are:
View attachment 26577

Our best case hearing threshold is -116 dB SPL so no question that this level of distortion is totally inaudible. Separating the noise from THD, we see that it is noise that we are measuring as THD+N, rather than distortion:
View attachment 26578

And this is with exceptional noise performance of Benchmark AHB2 as we see in the graph of THD+N versus power:

View attachment 26579

Even in high gain, the AHB2 easily outperforms the DIY Hypex NC400 I had tested before which used to be the best amp I had tested.

We have 185 watts of power at incredibly low distortion of 0.00016%, besting the company specifications.

Note that the FPGA protection mode kicks in and essentially shots the amplifier down past the limit. You get absolutely distortion-less and noiseless performance until there is no more.

EDIT: here is performance in bridged mode using same 4 ohm load:
View attachment 26592

You get 500 watts of stunningly clean power. Protection circuit shut the unit down after that so it is quite safe to try. With a THD essentially matching the non-bridged mode, there is no reason to be afraid of trying this.

Intermodulation distortion versus power level shows the same story of clean power:

View attachment 26580

If you want to know what you get for extra money over bargain amplifiers, you can see the difference in the above graph. We are not talking about 5 to 10 dB but whopping 40 dB better!

I have had requests for intermodulation distortion using dual 19 and 20 kHz tones. Here is that:
View attachment 26582

THD+N versus input level looks far cleaner than anything I have tested before:

View attachment 26583

Even at the limit of our hearing (20 kHz), we have vanishingly low amount of distortion. The graph is exaggerated so shows a rise there but in absolute levels, despite 90 kHz bandwidth of the test, we have incredibly low THD+N of just .004%.

The sharp spike at 45 Hz in green shows the amplifier going into protection mode. So don't pump that sine wave continuously into it at 133 watts. :)

Frequency response is exceptional too as expected:
View attachment 26581

Since this is not a switching amplifier, there is no filter there allowing the bandwidth to go to 200 kHz and beyond. Lowest band of AM radio is 450 kHz so likely you could use the AHB2 for an AM radio transmitter! :)

Usually when we test switching amplifiers we see all kind of "interesting" things in their outputs above hearing range. The AHB2 is a classic configuration albeit, with a switching power supply so all is well and clean here:

View attachment 26584

My reference graph for the Hypex NC400 used an AES filter (by accident) so I ran the AHB2 both ways, with or without that filter. Using the filter (in green) so the two are equal, we see much cleaner spectrum below 200 kHz and of course, no massive switching spikes. Worst case spike is below -115 dB. In other words, the Benchmark AHB2 is clean even in the areas you are not looking! It is like a restaurant scrubbing their parking lot with soap and pad as well as their dishes. :)

My loose wires on dummy loads is not the best setup for measuring crosstalk but here it is anyway:
View attachment 26585

Where our hearing is most sensitive (2 to 5 kHz), separation is around 100 dB which is way, way more than we need. Despite the small enclosure, the AHB2 manages exceptional numbers here.

Conclusions
It goes without saying that the Benchmark AHB2 breaks new ground with respect to performance of power amplifiers. Using it, you can be assured that any distortion that you hear is from other sources (speaker, source, content, etc.). This is what I look for in high-end audio: absolutely the best performance so no second guessing is involved. You buy once, and you are happy forever!

All of this comes from a company that is a model of transparency with proper and accurate measurements of their products on their site. And importantly, volunteering to have that data shown to be correct by independent sources such as us. Support form the company for me at least has also been exceptional.

Yes, $3,000 is fair bit of money but is pocket change in high-end audio. Sales tax is higher than $3,000 for most of those products! I hear a lot of talk from audiophiles to have the equipment get out of the way of enjoying the music. Well the Benchmark AHB2 at levels that assuredly passes full transparency. So if that is your moto, you better stop buying boutique products with no specs and independent measurements and get an AHB2. Everything you hear then will be what is in your source, not the dirty dishes that your amp my serve your food on.

Needless to say, the Benchmark AHB2 gets my strongest recommendation for power amplifier. The pink panther agrees, having hit the ball out of the park after I took that shot!

------------
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Great Product and as usual most helpful review in other word: EXCELLENT review.

Now Amir you are providing food for the speaker cable manufacturers ?? ... I can see them jumping on this , I quote:
Even the quality of the metal used in the connectors matters to get to this level of distortion.

So now you can see why the Palladium Tellurium Platinum Silver compound with 99.99999 percent OFC laminated under a vacuum, quantum tunneling and cryogenic-ally treated can make a huuuuuuge difference in the sound with blacker blacks and a Milky Way wide soundstage while remainint 100% organic .. Mark my words!! S someone will quote you and their speaker cable will suddenly become 15% more expensive !
:D :D
 

Tks

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I don't understand one statement:

"Look at the harmonic distortion. The worst case spike is below -130 dB! This is insanely good. Of course this type of SINAD (signal and noise ratio) crowns the Benchmark AHB2 as the best I have ever tested: "

How, the THX 789 has a better SINAD though? I understand the spike is the smallest, but not the overall SINAD performance for instance.
 

DonH56

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I don't understand one statement:

"Look at the harmonic distortion. The worst case spike is below -130 dB! This is insanely good. Of course this type of SINAD (signal and noise ratio) crowns the Benchmark AHB2 as the best I have ever tested: "

How, the THX 789 has a better SINAD though? I understand the spike is the smallest, but not the overall SINAD performance for instance.

The THX 789 is a headphone amp, not a power amp.
 
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