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Review and Measurements of Benchmark AHB2 Amp

josh358

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After looing at the manual OKTO Dac8 does not seem to have trims (level adjustments per channel). If that is correct, I don't think you can get good matching between amps and speakers. I need to make level adjustments between my Fronts and Surrounds and they are all Salon2s driven by AHB2s.

If you are using a Trinnov D-Mon, then there is no problem since I assume that it has per-channel trims.

- Rich
The OKTO does have a menu that lets you trim the individual channels.
 

Dacapalooza

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Here are the gain specs bridged:
22dBu (9.8 Vrms sensitivity) is equivalent to 9.2dB gain. 15.2 bridged.
14.2dBu (4 Vrms sensitivity) is equivalent to 17dB gain. 23 bridged.
18dBu (2 Vrms sensitivity) is equivalent to 23dB gain. 29 bridged.
.

Thank you for the bridged gain specs! You sound knowledgeable and like a nice guy.
Sounds too complicated to figure out if 29dB bridged is a better gain match to my system.

For that matter, Everything sounds so complicated here. I think I stumbled upon a very advanced forum thread.
My goal is to know the bare minimum to build the world's most advanced movie audio system - within my room limitation. Until I got to this thread I was 100% confidant I have succeeded. And with so little knowledge. I was so impressed with how little I know.
Now I'm not so sure if I know what I was suppose to. Did I build my system wrong? I still can't think of any way to improve, mind you.

I interviewed every PrePro maker in 2008. They all give me the feeling - like who cares. It's just HT and not music. And they all looked at me weird for caring about HT. Actually I kind of get that feeling here. So many music PC people here :) Maybe times change, but the HT measurements here back up that attitude still.

I (perhaps erroneously?) calculated that step #1 is I need access to the audio geek tech.
HDMI is a closed system and none of the audio geek stuff can even connect. Was going to throw in towel.
Enter Vanity mod. The Vanity allows me to use any DAC/digital device with movies/BD/Streaming. I have an entire DAW now. PrePro duties are divided out to 3 devices. Oppo/Vanity 203 -> Trinnov Demon -> Dac8.
Oppo is my mean, green PCM machine. Nothing it can't PCMisize.
 
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Dacapalooza

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The OKTO does have a menu that lets you trim the individual channels.
Yes. I used them. To test that all was working. I had just received a broken $6K projector. So I was testing everything.
This turned out hard to test. But had fun with the challenge.
The issue is that Trinnov only displays trims in some other measurement that is not dB. I think it is called lufs? And when I googled the lufs to dB calc, it said there was none. Arrg! At least our other American metrics can be calculated. So I guess the world was sick of Americans and their own metric system and made it that we can't just calculate. On behalf of Americans every where: We learned our lesson. We won't create our own metrics any more.
So ran my old Audyssey EQ to get the trim in dB's. Had to pull out my old PrePro for that as well.
 

Dacapalooza

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For me, though, it would be lack of symmetry that would drive me up the wall. Even though intellectually I doubt you'd be able to hear the difference with the gains matched
Agreed.
Asked to be sure. I realized I know so little.

So the 4th channel is waisted. If I did use it I would have had 33% extra usage for free. That did sound attractive. Not using it I lose only 25%.

Still it irks me to have anything hot in my rack any more. That my mere surrounds that can't even face me should produce heat & minimize the life span of everything else. Turns out heat even effect performance. DAC's lose 3db of performance with heat.
I guess I should just buy stereo amp with reasonable performance for surrounds soon.
 

RichB

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JimB

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The absolute sensitivity of individual speakers, and surrounds versus mains, is substantial. You must have the ability to adjust individual speaker levels, AND it should be done BY EAR, so units of settings are not important. You still want your gain structures to be reasonable. But given everything I've read from you, the solution is, clearly, to buy another AHB2 (and again have a wasted channel:D)!
 

RichB

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The absolute sensitivity of individual speakers, and surrounds versus mains, is substantial. You must have the ability to adjust individual speaker levels, AND it should be done BY EAR, so units of settings are not important. You still want your gain structures to be reasonable. But given everything I've read from you, the solution is, clearly, to buy another AHB2 (and again have a wasted channel:D)!

The spendthrift solution is to use 4 AHB2s for 5 channels, bridge or bi-amp to taste :p

- Rich
 

pogo

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Still it irks me to have anything hot in my rack any more. That my mere surrounds that can't even face me should produce heat & minimize the life span of everything else. Turns out heat even effect performance. DAC's lose 3db of performance with heat.
I guess I should just buy stereo amp with reasonable performance for surrounds soon.

Waste heat not only influences what you have described, but also the damping factor, among other things. I also asked the AHB2 manufacturer regarding this, but have not yet received a response. You might want to check out the NAD M28 too. This could be a perfect match for you.
 

Dacapalooza

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I also asked the AHB2 manufacturer regarding this, but have not yet received a response.
In the reviews the AHB2 is said to not produce much heat. So confused why you have questions on Benchmark? Are you asking what is the ideal ambient temperature? And how does performance suffer when not ideal?

You might want to check out the NAD M28 too. This could be a perfect match for you.
Why would I get 7 channels when I only need 1 or 2? And it does not have great measurements. I would be better off space, monetary and measurement wise with pretty much any other brand's Purifi other than NAD. NAD has the worse Purifi measurements somehow...

I was thinking why does the back have to have matching amps more than the right/left side?
So ultimately I think I will get 1 Purifi mono block & ask the manufacture to match it to the AHB2's gain of: "18dBu (2 Vrms sensitivity) is equivalent to 23dB gain."
Also note that my rears, and pretty much every speaker, have different trims anyway. This is so depressing, every day I find out more bad news. Not great that ALL my speaker locations have different trims/gains.

Shame to have an unused channel in "THE QUIETEST, CLEANEST AUDIO AMPLIFIER ON THE PLANET".
 

pogo

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In the reviews the AHB2 is said to not produce much heat. So confused why you have questions on Benchmark? Are you asking what is the ideal ambient temperature? And how does performance suffer when not ideal?

Among other things, the manufacturer has not answered the following questions until this day:

....
If you measure the damping factor on an amplifier, you usually do this with high output levels. At which operating point was the measurement carried out here (input/output level)?
Does the AHB2 have a series scattering with regard to the damping factor (see following re-measurement (<300), which is below the AHB2 spec):

soundstagenetwork
Sent


However, at low levels, most amplifier designs have a damping factor that is 5-10 times lower. Can you provide any DF data regarding different levels?
The internal resistance of an amplifier is also essentially dependent on the circuitry temperature and the load. Do you have any further data on this?
What would the answers look like in bridged mode too?
...
 

RichB

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Among other things, the manufacturer has not answered the following questions until this day:

....
If you measure the damping factor on an amplifier, you usually do this with high output levels. At which operating point was the measurement carried out here (input/output level)?
Does the AHB2 have a series scattering with regard to the damping factor (see following re-measurement (<300), which is below the AHB2 spec):

soundstagenetwork
Sent


However, at low levels, most amplifier designs have a damping factor that is 5-10 times lower. Can you provide any DF data regarding different levels?
The internal resistance of an amplifier is also essentially dependent on the circuitry temperature and the load. Do you have any further data on this?
What would the answers look like in bridged mode too?
...

Can you provide data this statement?

However, at low levels, most amplifier designs have a damping factor that is 5-10 times lower.

Stereophile simulated speaker measurements that show the effects of output impedance which is the number that is used to compute damping factor. These measurements are at 1 watt and yet, there is +- 0.1 dB difference. You seem impervious to data.
Obviously, the AHB2 is not he amp for you.

- Rich
 

RobS

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The heatsinks on the AHB2 are cosmetic. They are actually a safety net for people who want to run tough sine sweep loads which will make the amplifier warmer than when music is playing back. Essentially the heatsinks on the AHB2 are for dudes like John Atkinson and Amir. You shouldn't be concerned about heat, unless your room has sweltering heat.
 

Dacapalooza

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This topic seems advanced so maybe I am misunderstanding, but pogo is not asking if we should be concerned about heat, rather how do the measurements suffer. To back pogo up, he has good reason to ask. The DAC chips have proven to suffer 3dB in performance with not that much heat. I'm sure 3dB below the hearing threshold make no difference in hearing, but he is asking to gather data. Can we squeeze 1dB more out of this thing?
If we are to totally geek out with the amp's measured performance we want to know when it even suffers 1dB. Using the NLS, for example, gains 3dB in performance according to an article I read. Although can't find it now?
 

RobS

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I don't think you need to worry about thermal stability with the AHB2 since its not a traditional Class AB amp where you have to worry about the temperature of the bias, cause it is using a feed forward error correction amplifier (with a little bit of feedback). And there's not much power being wasted as heat either.
 

misterdog

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Think of the planet, all that electricity saved. Climate change will make Covid seem like just a bad hair day.

Superb sound quality to boot.

Fixating over a possible 1dB difference, depending on the PCB temperature affecting the damping factor.
Is. Well, fixating.
The AHB2 is better than probably 95% of amps.
Take it or leave it.
 

Dacapalooza

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What song should I play first? What song did you play first? This will be the biggest advancement I will probably ever hear in my lifetime.
My system wide SINBAD limitation is 70-75dB if I were to guess. My current amp. My DAC is 118. So once I get the amp I'll have a system wide limitation of 113 of the amp/ahb2. I'm glad I got the DAC first in preparation.

I bought a few DVD-Audio's & Pure Audio BD's.
Will Smith, in I Am Legend boasted that Bob Marley is the greatest album ever made. I never heard Hollywood endorse an album before?
So I am thinking of the Legend Pure Audio BD with the 96khz PCM tracks.
I also found quite a few 48/24 DVD with music videos. Mostly 80's. So those will probably go second.

What movie should I play first? Not a lot of uncompressed 48/24 BD's. Most uncompressed are 48/16. Box office wise the top ones are:
Pirates Of The Caribbean & Pearl Harbor.
Although with DD/DTS lossless compression it should not make a difference. So maybe this is wrong way to choose. I started comparing dynamic range of lossless/LPCM vs DD/DTS using the TC electronics' DR meter hardware. Sometimes LPCM is better sometimes it is same.

There are very few 96khz BD's. Asia has these 96khz upsampling BD's. So I bought 96khz upsampled Honest Thief. Native 96khz nothing great. I bought them, but only because it is 96khz.
 
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