Review and Measurements of Benchmark AHB2 Amp

[misterdog]

DB loss is not the real problem, but the undesired higher swing out amplitude, i.e. the input signal is not properly followed, which leads to a washed-out bass range with complex music signals.

No such issues with my Quad ESL's.

In fact quite the opposite.

 

[pogo]

The Stereophile measurements into their simulated speaker load indicates that the A21 (DF 1100) and AHB2 (DF 350) clearly that DF is not the most important factor in tracking the the input signal (frequency response).

If you measure the damping factor on an amplifier, you usually do this with high output levels. However, at low levels, most amplifier designs have a damping factor that is 5-10 times lower. Was that also taken into account in the analysis? For example, does the AHB2 manufacturer provide any DF data regarding different output levels?

 

[pogo]

No such issues with my Quad ESL's.

In fact quite the opposite.

As I mentioned earlier this depends on the complex load to drive, you will perceive a big difference to none at all or in between.

 

[RichB]

If you measure the damping factor on an amplifier, you usually do this with high output levels. However, at low levels, most amplifier designs have a damping factor that is 5-10 times lower. Was that also taken into account in the analysis? For example, does the AHB2 manufacturer provide any DF data regarding different output levels?

Honestly, I tire of presenting measurements and quoting the excellent work of others,
These Stereophile measurements into simulated speakers are described below each at 2.83 volts so the power levels are 1 watt, 2 watts, and 4 watts into 8, 4, and 2 Ohms respectively.

According to your logic, the damping factors would show an issue with the AHB2 but no, it's not there.

Do you have an analysis to share?

- Rich

 

[pogo]

All of these measurements are known. But my question was not answered:

Does the AHB2 manufacturer provide any DF data regarding different output levels (or someone has measured it once)?

From my point of view, such data reflect the amplifier behavior in the very dynamic real world, which can be heard very clearly in certain setups. Maybe someone else has this data.
In addition, another axis is basically missing in your presented measurements, i.e. the time axis, in order to show the swing out behavior.
But that would also mean using other test stimulis.

It is a bit odd to paste a chart from Dr. Floyde Tool's article titled: "DAMPING DAMPING FACTOR AND DAMN NONSENSE" and claim it proves the importance of damping factor

This article does a good job of showing how a DF can act in the real world, as I pointed out earlier. What is so clearly measurable will of course also be perceived. The conclusion of the author within this article is up to you.

 

[RichB]

All of these measurements are known. But my question was not answered:

Does the AHB2 manufacturer provide any DF data regarding different output levels (or someone has measured it once)?

From my point of view, such data reflect the amplifier behavior in the very dynamic real world, which can be heard very clearly in certain setups. Maybe someone else has this data.
In addition, another axis is basically missing in your presented measurements, i.e. the time axis, in order to show the swing out behavior.
But that would also mean using other test stimulis.

This article does a good job of showing how a DF can act in the real world, as I pointed out earlier. What is so clearly measurable will of course also be perceived. The conclusion of the author within this article is up to you.

DF is another measure of output impedance (OE). Perhaps, EE's can weigh in here but OE clearly varies with frequency not power, at least not significantly. It is simply not discussed. In fact the papers are quite old because the conclusions were QED.

The "proof" image you posted shows the difference between DF of 0.5 and 200 and provides no scale.
Dr. Flyod Toole:
Damping, Damping Factor, and Damn Nonsense (diyaudioprojects.com) (1975)
The image with scale shows the almost no difference (<1 dB by eye) that compared DF of 200, 4, and 1.

No one is denying that DF matters, it is just that it matter up to a point and then it doesn't.
It is load dependent so you will see the point of vanishingly returns stated at 10, 20, 50 and maybe 100 to achive +/- 0.1 dB.
Benchmark chose +/- 0.1 dB as the maximum value that has been shown to be virtually undetectable in ABX tests.

Here is another often quoted article: The Damping Factor Debate What do the numbers really mean and do very high amplifier damping factors have any noticeable effect on performance? By GEORGE L. AUGSPURGER, James B. Lansing Sound Inc. (1967). Hmm, JBL there is something vaguely familiar about that name
The Damping Factor Debate (diyaudioprojects.com) (1967)
Butler Audio (Text version)

CONCLUSIONS
It should be obvious at this point that the quoted damping factor of an amplifier is important only if the figure lies somewhere below 20 or so. Changing the damping factor from 2 to 20 does change the performance of the loudspeaker system (for better or for worse, depending upon the speaker). But trying to prove that a damping factor of 200 or even more is somehow better than one of 20 is pretty unconvincing because the effective difference in the practical case cited is only that between 1.25 and 1.32.

But someone is bound to insist that exhaustive tests have been made with such and such amplifier and that a very high damping factor is better than one down around 10 or 15. "The bass is just a little cleaner, just a little more natural and open" is the way the argument usually runs.

In a given situation, this may very well be true. Rs is a byproduct of negative feedback. The more such feedback that is thrown into a power amplifier circuit, the lower the generator impedance and the higher the damping factor. The point is simply that if a lot of feedback has to be used to lick the distortion in a particular circuit, fine - use it. But don't believe that the reason it sounds good because of some astronomically high damping factor.

When I get a letter from someone who is worried about buying a certain amplifier because it has a specified damping factor of "only" 15 to 16, I can't help but remember an old, old joke. It goes like this:

A scientist is giving a public lecture. During the course of his speech, he predicts that in 100 billion years human life will become extinct. A man in the audience, obviously upset, asks the lecturer to repeat the statement.
"I said", quotes the professor, "that in one hundred billion years, human life will no longer exist."
"Oh, thank goodness", replies the man, much relieved, "I thought you said one-hundred million!".

Here are some more examples of the practical effects for Damping Factor:
DEFINING "DAMPING FACTOR" by John L. Murphy
Butler Audio

Now if you are concerned about DF and ringing:

• Start analyzing your room acoustics with REW
• Buy better speakers
• Rip out your crossovers, replace them with active crossover and 2 or three amplifiers

I enjoyed reading the papers by Toole and Augspurger now appreciate that the effects of DF have been understood for over 60 years. Some things are timeless.

- Rich

 

[Dacapalooza]

Question:
I ordered 2 AHB2's for front 3 channels. I have a single remaining channel in my 5.1 system. Rather than waist it, I was wondering if bad idea to mix amps for the surround. Mix it with a single Purifi mono block maybe? I have Trinnov D-Mon to calibrate the channels.

I was going to use my current front Krell mono blocks for the surround.
Upon further thought, not worth the heat. If I retire them, the Trinnov will be the only heat producing device.
And for mere £625.00 for single mono, I will have a significant upgrade to surrounds and ALL my channels will be up to date with current tech. Amps are connected to Okto Dac8

 

[RichB]

Question:
I ordered 2 AHB2's for front 3 channels. I have a single remaining channel in my 5.1 system. Rather than waist it, I was wondering if bad idea to mix amps for the surround. Mix it with a single Purifi mono block maybe? I have Trinnov D-Mon to calibrate the channels.

I was going to use my current front Krell mono blocks for the surround.
Upon further thought, not worth the heat. If I retire them, the Trinnov will be the only heat producing device.
And for mere £625.00 for single mono, I will have a significant upgrade to surrounds and ALL my channels will be up to date with current tech. Amps are connected to Okto Dac8

What are your speakers and listening habits, music versus HT?

- Rich

 

[Dacapalooza]

What are your speakers and listening habits, music versus HT?- Rich

Front: 3 * Revel F206 - 9 Y/O. Will replace in 1 year with F226BE's
Surround: 2 * M205. Will replace in 1 year with 2 of my current fronts, the F206. Thinking of replacing 2 -3 years after that with new be bookshelf: M126Be.
Sub: SVS Ultra 16

I am 100% Movies.

 

[RobS]

Does anyone have pro audio recommendations for a balanced preamp to go in front of the AHB2, outside of Benchmark's LA4 Line amplifier? All I need is one input and output XLRs. I was looking at the measurements on the SPL Volume2 here but not sure if that would be a good match.

 

[RichB]

Front: 3 * Revel F206 - 9 Y/O. Will replace in 1 year with F226BE's
Surround: 2 * M205. Will replace in 1 year with 2 of my current fronts, the F206. Thinking of replacing 2 -3 years after that with new be bookshelf: M126Be.
Sub: SVS Ultra 16

I am 100% Movies.

You have time to decide. I'd see if the the AHB2 stereo drives the F206's to your desired levels. The clip indicators are accurate so they will provide and indication if running out of power.

My brother in law has F206 driven by and A21 that was a big improvement over the Outlaw M2200 amps.
At some point, I will bring over an AHB2 and my MiniDSP SHD to level match and A/B compare the two amps.

- Rich

 

[RichB]

Does anyone have pro audio recommendations for a balanced preamp to go in front of the AHB2, outside of Benchmark's LA4 Line amplifier? All I need is one input and output XLRs. I was looking at the measurements on the SPL Volume2 here but not sure if that would be a good match.

I use a MiniDSP SHD in my office primarily for its PEQ and Dirac option.
Unfortunately, the Roon endpoint is not working and the Roon Bridge has issues.
The MiniDSP SHD was measured here: Minidsp SHD Review Updated (DSP, DAC & Streamer) | Audio Science Review (ASR) Forum
Full disclosure, the latest SHD ships with a new processor and power supply so it is not exactly the same as the unit measured.

- Rich

 

[RichB]

Front: 3 * Revel F206 - 9 Y/O. Will replace in 1 year with F226BE's
Surround: 2 * M205. Will replace in 1 year with 2 of my current fronts, the F206. Thinking of replacing 2 -3 years after that with new be bookshelf: M126Be.
Sub: SVS Ultra 16

I am 100% Movies.

I'd be tempted to move the F206's to the rears. The sense of immersion improved when I upgrade my rears to match the Salon2s.
I had approval to upgrade the speakers but not the number of speakers

- Rich

 

[JimB]

You have time to decide. I'd see if the the AHB2 stereo drives the F206's to your desired levels. The clip indicators are accurate so they will provide and indication if running out of power.

My brother in law has F206 driven by and A21 that was a big improvement over the Outlaw M2200 amps.
At some point, I will bring over an AHB2 and my MiniDSP SHD to level match and A/B compare the two amps.

- Rich

I think he is asking about using his 'spare' AHB2 channel (since he is using only 3 of the 4) for one of the surround speakers and ADD a single channel of something else for the remaining surround channel - something like a mono Purifi amp. I'd say, sure! Both have balanced inputs. Consider the gain structure. Which Purifi amp are you considering? Try to have comparable gain (or 3 dB less since the output of the Purifi is 2x the AHB2) with the Purifi input buffer as you have with the settings (there are three choices) you run on the AHB2. It doesn't have to be exact. I'm sure you can channel level match with your pre/pro/AVR, right?

 

[Dacapalooza]

You have time to decide. I'd see if the the AHB2 stereo drives the F206's to your desired levels. The clip indicators are accurate so they will provide and indication if running out of power.

Oh, right. I almost forgot that 100 watts might not be enough. But I think 100 watts is way more then I use based on my ammeter readings.

Also, I am in this weird state of replacing my speakers in a year. Even if not enough, maybe it will be.
I replace speakers & amp every 10 years. Happy 10 my Krell mono blocks, you treated me well if not the audio signal.
The F226BE is 90db sensitivity, while the F206 is 88. So will need less power.
I would love to get the Salon's, or bigger Be. But I need all 3 speakers to fit under my screen.

..Consider the gain structure...Try to have comparable gain...the Purifi is 2x the AHB2.

That is my real question. Can I have mismatched gains and let my Trinnov D-Mon level match the surrounds.

Would never do this for fronts.
Surrounds don't face my ears, so I would think the fidelity loss is not likely to be heard. The fidelity loss of making the amp's needless gain and the Trinnov to lower. That is my question. Can a professional and/or ASR member audio person hear if the surrounds gains are messed with so aggressively.
I could simply get a stereo Purifi for my 2 surrounds. But was wondering if the AHB2 tech is too good to waist. And messing with mismatched gains is worth it. Since it is surrounds no one can possibly hear the gains are being messed with?
The only way to gain match is to match all the other channels. The surround will even share with center channel in same AHB2. I am connecting with Pro devices so will use AHB2 highest gain.

the Purifi is 2x the AHB2.

2x is with the AHB's highest setting?

Which Purifi amp are you considering?

The smallest. Love small form factor. I have to research that. I think the March looks the smallest.

 

[josh358]

The smallest. Love small form factor. I have to research that. I think the March looks the smallest.

One thought -- if you buy a single monoblock, it might be hard to sell later on. A bridged stereo amp might make more sense, but then why not just use it in two channels and waste the extra channel on the ABH2's?

What about bridging the center AHB2? Typically, 60 percent of the sound is in center channel, so you'd be getting a very slight boost in maximum signal level -- sort of. At any rate, it would feel more symmetrical than using only half of the AHB. Then put a 2 channel Purifi on the back and you won't have to worry about a lopsided configuration.

 

[Dacapalooza]

One thought -- if you buy a single monoblock, it might be hard to sell later on.

Selling is not a factor. I will never sell. Too lazy to deal. Ha, my wife makes fun that I should open musuem.

What about bridging the center AHB2? ... you'd be getting a very slight boost in maximum signal level -- sort of

bridging = loss of fidelity. So will try not to bridge. Also, it is not sort of. According to a couple of pages ago, the gain is around 6 dB bridged so will have lopsided front gains.

60 percent of the sound is in center channel

I have been using 6 meters for a couple of years now. I have seen almost every 3D/4K blu ray there is since I got my meters. Plus still get new release BD's from Netflix. Movies span the last 20 years. So feel I have a good representation of how Hollywood uses the speakers.
I would say 95+% of the time all speakers, across all genres, have all speakers engaged. Like birds chirping during a conversation and flying around all speakers. Hollywood goes all out to create immersive scenes in pretty much every scene ever. I turn off fronts a lot just to appreciate the great lengths that the recording engineers go to.

Albeit, the center gets higher volume. If we were to divide out the dB, than yes center gets the bulk. But would say more like 70-80%. Center meters are usually double of all other speakers.

I very rarely watch streaming. As it just sounds bad to even me. I can't hear differences in amps nor DACs. (Although I could be trained to, so that is good enough for me to purchase these hi-fi) In the Netflix/Amazon original movies are the only movies where I see just the center many times. Weird. As they are only recording engineers to do that.

 

[JimB]

... That is my real question. Can I have mismatched gains and let my Trinnov D-Mon level match the surrounds.

I sure hope so. For the surrounds, nuances of damping factor are less likely to be heard, and I suspect you'll have long speaker cables anyway, so super high DF is lost. As for mismatched fidelity, transparent is transparent (one expects), especially for surrounds. The Purifi is a nominal 200W/chan amp versus 100W/chan for the AHB2. But it is the gain you need match, approximately.

You could think of a stereo Purifi (relatively cheap) for the surrounds (still needs gain matching, but that is expected with difference speakers, anyway), or your single channel path. Depending on your experience, you could always add another single channel of the same later if really desired, but that is significantly move expensive than a stereo Purifi. I really think you'll be fine with any of these approaches. Just my opinion...

 

[RichB]

Question:
I ordered 2 AHB2's for front 3 channels. I have a single remaining channel in my 5.1 system. Rather than waist it, I was wondering if bad idea to mix amps for the surround. Mix it with a single Purifi mono block maybe? I have Trinnov D-Mon to calibrate the channels.

I was going to use my current front Krell mono blocks for the surround.
Upon further thought, not worth the heat. If I retire them, the Trinnov will be the only heat producing device.
And for mere £625.00 for single mono, I will have a significant upgrade to surrounds and ALL my channels will be up to date with current tech. Amps are connected to Okto Dac8

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

 

[josh358]

Selling is not a factor. I will never sell. Too lazy to deal. Ha, my wife makes fun that I should open musuem.


bridging = loss of fidelity. So will try not to bridge. Also, it is not sort of. According to a couple of pages ago, the gain is around 6 dB bridged so will have lopsided front gains.

I very rarely watch streaming. As it just sounds bad to even me. I can't hear differences in amps nor DACs. (Although I could be trained to, so that is good enough for me to purchase these hi-fi) In the Netflix/Amazon original movies are the only movies where I see just the center many times. Weird. As they are only recording engineers to do that.

I don't think even the most golden ear could hear the difference when an amp is bridged! If anything, the amp sounds better since it's less likely to get into its nonlinear region. Gain is another issue, but it's easy to make a pad if you don't want to sacrifice a bit on the altar of audio compulsiveness.

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, I'd always be wondering if they matched. Up front, you might have issues if the amps have different group delay -- but I imagine the room correction would take that out even if they did, and I'm not sure if makes a difference in the first place, since moving your head will alter the relative phase of the left and right channels more than the amps would.