Review and Measurements of Benchmark AHB2 Amp

[D700]

https://www.harbeth.co.uk/usergroup...-a-new-amplifier-topology-ahb2-from-benchmark

Thanks, didn’t know Benchmark’s history.

Will AHB2’s new topology improve longevity since it doesn’t get as hot? Or is there inherent advantage in the way it cancels out distortion? I’ve wondered over the years if some brands maintained performance better than others.

 

[RichB]

Thanks, didn’t know Benchmark’s history.

Will AHB2’s new topology improve longevity since it doesn’t get as hot? Or is there inherent advantage in the way it cancels out distortion? I’ve wondered over the years if some brands maintained performance better than others.

In my travels, there have not been any repair posts.

Benchmark offers a 1 year warranty and an "optional" 5 year warranty that requires registration.
The warranty is offered to the original owner and is not transferable.
I don't like those restrictions. We would not accept non-transferable warranty on automobiles.

I spent some time on the phone setting up the Benchmark LA4 and the support was excellent.
It was a bit of a hack to get the LA4 to support discrete input selection via remote but they got it working.
Some improvements requests to the LA4 were submitted, it would not take much to add features to simplify the LA4/HPA4 integration into a combined 2-channel/HT system.

- Rich

 

[zalive]

Well, outside of US/Canada, extended warranty is 2 yrs only. Two years is nothing for the audio product belonging in this price class.
IMO it's not quite acceptable for a company with direct internet sales strategy. Actually it's pretty hard for me to explain why customers outside US/Canada are of less value to the company.
No 30 days trial as well to those international buyers. Again a different policy.
Tells me that company is primarily oriented to the US/Canada customers, and as for all the others, it's a 'buy if you insist' policy.

I wonder about durability/life expectancy of H-Class PS inside. What to expect from it?

Still I don't understand why so restrictive a warranty policy. Does that mean that company fears the significant risk from malfunctioning?
In my eyes, a company which is sure about the quality of their product doesn't mind including extended warranty to all.
In the same manner, warranty restrictions raise some suspicion about the quality...

 

[D700]

To clarify, I was talking about expected performance well past typical warranty period. If it’s got a better chance to sound the same 10-15 years later over another brand, that helps justify the cost.

 

[D700]

In my travels, there have not been any repair posts.

Benchmark offers a 1 year warranty and an "optional" 5 year warranty that requires registration.
The warranty is offered to the original owner and is not transferable.
I don't liked those restrictions. We would not accept non-transferable warranty on automobiles.

I spent some time on the phone setting up the Benchmark LA4 and the support was excellent.
It was a bit of a hack to get the LA4 to support discrete input selection via remote but they got it working.
Some improvements requests to the LA4 were submitted, it would not take much to add features to simplify the LA4/HPA4 integration into a combined 2-channel/HT system.

- Rich

5 years is substantial for a consumer US product. The laws vary widely outside US so am not surprised it’s limited elsewhere.

 

[RichB]

5 years is substantial for a consumer US product. The laws vary widely outside US so am not surprised it’s limited elsewhere.

I don't disagree but ATI is 7 years and transferable.
It is the non-transferable warranty provision that is of concern.

Benchmark builds quality products which is reflected by their scarcity and retained value in the used marketplace.
I actually had an extra AHB2 (manufactured in 2016) that I bought used and sold a month later for about the same price, 25% off list.

- Rich

 

[orangejello]

Happily my AHB2 shipped yesterday. I have a question as to how much or how little I am going to be able to appreciate its performance. As far as bottle necks, I am not concerned about my speakers. They are very good, not state of the art, but very good. Given that one audio engineer was stunned at how much better the miserable but ubiquitous Yamaha NS10 sounded with the AHB2, my speakers should not be a problem.

However, I have unbalanced sources. My vinyl rig is compromised since I snapped the cantilever off of my Lyra Delos and have yet to get it repaired. I am using a NOS Monster Sigma Genesis 2000 now (designed by the ZYX designer back in the day) and I know that it is decent but not as good as the Delos. It feeds a K&K Lundahl stepup transformer into a Audio Innovations tube MM phono preamp. The preamp has a non-stellar noise floor, but is otherwise very good. The other source is a Marantz HD-Dac1 which is pretty good, but I have never seen its measurements.

Both of these feed into a passive preamp which has attenuation and switching built from stellar parts. The RCA output from the passive preamp goes into the RCA->XLR cables (wired as per Benchmark's recommendation). I assume that the low gains setting on the AHB2 will not work due to the converted RCA input which probably won't supply a high enough voltage.

I have read that the best sound is had by using a DAC with balanced outputs straight into the AHB2 low gain setting. Given that I cannot try that, how much do you guys think that I will able to get the measure of the AHB2's performance?

 

[RichB]

Happily my AHB2 shipped yesterday. I have a question as to how much or how little I am going to be able to appreciate its performance. As far as bottle necks, I am not concerned about my speakers. They are very good, not state of the art, but very good. Given that one audio engineer was stunned at how much better the miserable but ubiquitous Yamaha NS10 sounded with the AHB2, my speakers should not be a problem.

However, I have unbalanced sources. My vinyl rig is compromised since I snapped the cantilever off of my Lyra Delos and have yet to get it repaired. I am using a NOS Monster Sigma Genesis 2000 now (designed by the ZYX designer back in the day) and I know that it is decent but not as good as the Delos. It feeds a K&K Lundahl stepup transformer into a Audio Innovations tube MM phono preamp. The preamp has a non-stellar noise floor, but is otherwise very good. The other source is a Marantz HD-Dac1 which is pretty good, but I have never seen its measurements.

Both of these feed into a passive preamp which has attenuation and switching built from stellar parts. The RCA output from the passive preamp goes into the RCA->XLR cables (wired as per Benchmark's recommendation). I assume that the low gains setting on the AHB2 will not work due to the converted RCA input which probably won't supply a high enough voltage.

I have read that the best sound is had by using a DAC with balanced outputs straight into the AHB2 low gain setting. Given that I cannot try that, how much do you guys think that I will able to get the measure of the AHB2's performance?

You will likely have to use high-gain to drive the AHB2 to full volume.
As far as performance, the AHB2 performance is still excellent in high-gain mode. I am using it that way directly driven by the Oppo UPD-205.
Since this outputs 4 volts balanced, it can be driven by the top 2-gain settings.

- Rich

 

[D700]

I don't disagree but ATI is 7 years and transferable.
It is the non-transferable warranty provision that is of concern.

Benchmark builds quality products which is reflected by their scarcity and retained value in the used marketplace.
I actually had an extra AHB2 (manufactured in 2016) that I bought used and sold a month later for about the same price, 25% off list.

- Rich

Great point. I couldn’t find any used.

 

[DonH56]

Found a few patents, need to print and read, but had missed that as of this morning Amir's review is at the top of their reviews page: https://benchmarkmedia.com/blogs/reviews

 

[mshenay]

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:

View attachment 26573​

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:

View attachment 26574​

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 output 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.

EDIT: forgot to run the classic SNR test in the original review:
View attachment 26636

Wow, assuming you play at peak of 120 dBSPL, your noise floor will be at -10 dBSPL! That is absolute silence.

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!

------------
As always, questions, comments, recommendations, etc. are welcome.

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Here we go gent's a proper amp for a set of those Raal headphones lol

 

[Sal1950]

Here we go gent's a proper amp for a set of those Raal headphones lol

What?

 

[Crane]

What?

The Raal headphones which use their ribbon design from speakers apparently connect like a regular speaker, so you need to connect them to a speaker amp because they need that much power.

 

[Sal1950]

The Raal headphones which use their ribbon design from speakers apparently connect like a regular speaker, so you need to connect them to a speaker amp because they need that much power.

Ah, thanks for the clarification.
I'm thinking maybe one of those 70's egg chairs with a pair of Magnpan .7 's mounted earlevel inside them to get to the next level. LOL

 

[Xulonn]

What?

Get with it Sal. These are available for only $3,499!!

 

[Sal1950]

Get with it Sal. These are available for only $3,499!!

KOOL! Maybe I'll order a half dozen for my family members this Christmas. LOL

 

[Skeptical]

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).

I'm using a pair to drive salon2's. No problems what so ever. Great setup!

 

[STUDIO51]

The benchmark AHB2 has really stunning performance. I have used Active Speakers, so I hesitated to move on passive speakers. But AHB2 ended all anxiety. So I was able to purchase the JBL M2 with comfort mind. Here is the AHB2 measurements I measured using APx 555 and Active load box. The AHB2 has very close performance to the measuring instrument, so the load has a great influence on the test performance. The active load box is a load that supports air cooling.
And as you can see from the bottom left of the first photo, it supports 1, 2, 4, 8 ohm load and ± 30, ± 60 load.

The first picture shows the performance when connecting a 2-ohm load in AHB2's bridge mode.
It was able to output 1.6kW constantly without a warning light only when a load without distortion was connected.

This graph is measured by connecting an active load box to APx555. It shows the response to various load situations. The DUT, AHB2, is in stereo mode.

There is little voltage drop until 2 ohms Even when it is 1 ohm, it shows 18 Vrms output. What is very surprising is that it gives a constant output at all loads for capacitance and inductance loads.

Here is an image of the measurement conditions. All measurements were made by inputting 22 dBu sine wave into AHB2. Speakon to XLR cable was used for the connection. All measurements were verified by John Siau .I would also like to thank Benchmark Company, John Siau for making this amazing amplifier, and Allen H. Burdick for the birth of AHB2's birthplace and name.

And if John Siau saw this, I just(An hour ago) ordered one more AHB2 and please let me know when it's ready for shipment.

 

[Sal1950]

.I would also like to thank Benchmark Company, John Siau for making this amazing amplifier, and Allen H. Burdick for the birth of AHB2's birthplace and name.

Welcome to the ASR forum and thanks for adding the data! John does hang out here now and then, also I sure @amirm will be along shortly to give you the official howdy. Looking forward to hearing more about your M2 system, we have at least one other member here using Benchmark ABH2's, DAC3's and JBL M2.
@dallasjustice
https://www.audiosciencereview.com/...m2-audiolense-digital-crossovers-w-subs.2369/

 

[STUDIO51]

Welcome to the ASR forum and thanks for adding the data! John does hang out here now and then, also I sure @amirm will be along shortly to give you the official howdy. Looking forward to hearing more about your M2 system, we have at least one other member here using Benchmark ABH2's, DAC3's and JBL M2.
@dallasjustice
https://www.audiosciencereview.com/...m2-audiolense-digital-crossovers-w-subs.2369/

Oh this is a great coincidence. Before I read your comment, I wondered if amir had already measured the hilo I had, and I eventually found this post.
I found that there were users using HILO and JBL M2, and I was very excited. Thank you for your welcome. I wish I could contribute this site a lot.