Review and Measurements of Benchmark AHB2 Amp

[pogo]

But that doesn't answer my question!?
I personally have had the experience that an amplifier with a moderate damping factor (such as the AHB2) cannot accurately drive my power hungry impedance-critical speakers, which is reflected in a washed-out low-frequency range. With such loudspeakers, a Purifi amp has a clear advantage with its higher damping factor.

 

[Absolute]

Question for people with experience with AHB2 on high sensitivity compression drivers;

Have any of you experienced louder hiss than expected with these amps? I know of one instance where someone sold two of these on because he experienced louder hiss on them than a First Watt amp he had. No matter how the amps were configured they would be more noisy than expected when they should in theory be far more quiet.

Experienced and very knowledgeable dude, so no gain structure errors assumed.

 

[Phorize]

But that doesn't answer my question!?
I personally have had the experience that an amplifier with a moderate damping factor (such as the AHB2) cannot accurately drive my power hungry impedance-critical speakers, which is reflected in a washed-out low-frequency range. With such loudspeakers, a Purifi amp has a clear advantage with its higher damping factor.

Benchmark quote the damping factor of the abh2 as 370 (into 8 ohms). Your speakers would need to offer a fantastically difficult load to generate anything more that fractions of Dbs in frequency response variation. Out of interest what did you calculate the actual damping factor of your amp/speakers to be in order to conclude that you were experiencing a damping factor issue?

 

[Phorize]

But that doesn't answer my question!?
I personally have had the experience that an amplifier with a moderate damping factor (such as the AHB2) cannot accurately drive my power hungry impedance-critical speakers, which is reflected in a washed-out low-frequency range. With such loudspeakers, a Purifi amp has a clear advantage with its higher damping factor.

You might find this useful in predicting whether an amplifier will handle the impedance your system presents. As you can see, with the benchmark we’d be talking about very significant system resistance for you to be able to detect deviations in frequency response.

https://cdn.shopify.com/s/files/1/0321/7609/files/DampingFactorCalculator.xlsx?v=1591278482


What’s the total impedance of your cables and speakers?

 

[RichB]

Question for people with experience with AHB2 on high sensitivity compression drivers;

Have any of you experienced louder hiss than expected with these amps? I know of one instance where someone sold two of these on because he experienced louder hiss on them than a First Watt amp he had. No matter how the amps were configured they would be more noisy than expected when they should in theory be far more quiet.

Experienced and very knowledgeable dude, so no gain structure errors assumed.

Here is a thread by blazar, he reports no hiss with 109 dB efficient horn speakers:

(20) Benchmark AHB2 vs NAD M22 (Hypex) with Very High Sensitivity Speakers | AVS Forum

- Rich

 

[RichB]

^ I just re-read that thread and there a lot of pushback against the AHB2.
However, none of these people level matched amplifiers.

It is expected for the a lower gain amplifier to "lack dynamics" compared to a higher-gain amp, that is, until they are level matched. Then that disappears.

There is a great deal of emotion attached to power amplifiers but the community. I suppose we are all attracted to the power component

- Rich

 

[pogo]

Out of interest what did you calculate the actual damping factor of your amp/speakers to be in order to conclude that you were experiencing a damping factor issue?

The amplifier must ensure that the swinging motion of the membrane is slowed down if there is no tension at the end of a pulse. The uncontrolled oscillation of the loudspeaker induces an electrical voltage in the coil, which is short-circuited via the output amp stage. The generated counterforce shortens the decay time of the membrane. And with a higher damping factor that is audibly better for me in my setup. There is no need to calculate something that can be clearly heard.

See also pictures of my satellites and subwoofer crossover, both of course passive, which are connected in parallel to one channel each.

 

[Phorize]

I suppose the point of calculating damping factor properly is to judge what ball park you are in with an amplifier that has published specs. Obviously the damping factor of the purifi is very high, so it is unlikely to choke on anything. At 370 into 8 ohms the benchmark is less accommodating, but in the real world is highly unlikely to cause issues. You may feel that you can hear the impact of insufficient damping factor on your system and you may be right. What I’m saying is that your odds of finding a side by side abx of these two amps with a system that presents an unusually high resistive load-or at least the sky high load that you infer, is very low. In an effort to be helpful I thought I’d mention that with knowledge of a few parameters you can easily judge on paper how either amp will perform with a certain type of set up-far more reliably BTW than uncontrolled listening tests. So in summary, I think you’ll find that unless you can find such data, or are prepared to acquire both amplifiers and abx them yourself then it will be very much necessary to do the calculations if you would like a meaningful answer to your problem.

 

[Kal Rubinson]

Has anyone ever heard an AHB2 in direct comparison to a Purifi amp? How does the comparison turn out with complex and dynamic music signals (a hearing comparison and not a measured value comparison)?

Sure. I have my AHB2s and the NAD C298s as well as a pair of PSAudio M1200s (ICE Edge). Report in due time.

 

[Phorize]

Sure. I have my AHB2s and the NAD C298s as well as a pair of PSAudio M1200s (ICE Edge). Report in due time.

At the risk as coming across like a pedant, what information does a side by side audition provide that cannot be gleaned from the detailed specifications available for these amplifiers?

 

[DonH56]

At the risk as coming across like a pedant, what information does a side by side audition provide that cannot be gleaned from the detailed specifications available for these amplifiers?

1. Kal does it for a living (sort of) and a lot of people like to read subjective reviews. I find it interesting to read comparisons allowing for listener bias and how the reviewer's system and room differs from my own. I tend to use specs to narrow the field then try to listen and read subjective reviews from folk whose opinions I trust and who have similar systems (Kal fits to a T) and musical tastes (well, less so, not so much into opera).

2. Detailed specs rarely include all the information needed and can be hard to translate to your environment (speakers, listening position, etc.) Output impedance in particular varies widely over frequency, as does speaker impedance, and neither are typically specified as more than a nominal number in a spec sheet. Noise floor is another oft-missing spec, along with a noise spectrum (frequency plot). Two amps even with the same SNR may have a different noise signature that may influence your choice.

Etc.

IME/IMO - Don

 

[rdenney]

At the risk as coming across like a pedant, what information does a side by side audition provide that cannot be gleaned from the detailed specifications available for these amplifiers?

Verification.

Rick “noting, however, that Benchmark stuff usually comes with test data, not just design specifications” Denney

 

[Phorize]

Verification.

Rick “noting, however, that Benchmark stuff usually comes with test data, not just design specifications” Denney

I guess that’s my point, both of these amps have been tested extensively. Anyway, I’ll be labouring the point if I go on, which isn’t fun for anyone

 

[Phorize]

1. Kal does it for a living (sort of) and a lot of people like to read subjective reviews. I find it interesting to read comparisons allowing for listener bias and how the reviewer's system and room differs from my own. I tend to use specs to narrow the field then try to listen and read subjective reviews from folk whose opinions I trust and who have similar systems (Kal fits to a T) and musical tastes (well, less so, not so much into opera).

2. Detailed specs rarely include all the information needed and can be hard to translate to your environment (speakers, listening position, etc.) Output impedance in particular varies widely over frequency, as does speaker impedance, and neither are typically specified as more than a nominal number in a spec sheet. Noise floor is another oft-missing spec, along with a noise spectrum (frequency plot). Two amps even with the same SNR may have a different noise signature that may influence your choice.

Etc.

IME/IMO - Don

I’m certainly not dismissing the value of the sorts of reviews that Kal does, but in respect of the question I was responding to, with these two amplifiers there are extensive test results in the public domain. Perhaps I was sloppy in my posts by conflating specs and test data. Not withstanding the generalities, I still don’t see what discoveries can be made sonically speaking from hearing these amplifiers that cannot be made from published test data

 

[Kal Rubinson]

At the risk as coming across like a pedant, what information does a side by side audition provide that cannot be gleaned from the detailed specifications available for these amplifiers?

Touch and feel.

 

[RichB]

I’m certainly not dismissing the value of the sorts of reviews that Kal does, but in respect of the question I was responding to, with these two amplifiers there are extensive test results in the public domain. Perhaps I was sloppy in my posts by conflating specs and test data. Not withstanding the generalities, I still don’t see what discoveries can be made sonically speaking from hearing these amplifiers that cannot be made from published test data

Amplifiers are not typically measured into load so there can be misbehaviors, changes in linearity and increased distortion.

If you have two amps, it can be fun. Life has intervened to delay my comparison of the AT522NC NCore to the the AHB2 using the MiniDSP SHD.

The SHD has 4 DACs so the channels can be copied with trims to match levels (at least within .5 dB). The amps will go through a simple A/B switch.
It does not matter how this turns out because it wont prove anything to anyone but I like doing this stuff.

- Rich

 

[pogo]

Sure. I have my AHB2s and the NAD C298s as well as a pair of PSAudio M1200s (ICE Edge). Report in due time.

Thank you, that will answer my question

 

[misterdog]

Though it wont tell me if it might improve my sound, in my room, with my source, into my Quad Electrostatic speakers, As against the Neurochrome monoblocks that I'm currently using.
The measurements indicate that it should improve SQ, but the proof would only come from trying it.
Measurements have so far improved SQ dramatically with SMSL M400 and Topping Pre.

 

[joentell]

I think Andrew Jones's twin brother, Owen Jones, had a hand in designing some technology in this. Imagine the conversations those two have?

 

[RichB]

I think Andrew Jones's twin brother, Owen Jones, had a hand in designing some technology in this. Imagine the conversations those two have?

Sure, it might go something like this:

That's one puny amp you have there, over-designed don't you think?
Not at all, but I understand that view listening to your speakers...
Yeah!
Yeah!

... several hours of banter ensue...

Wait, look at the time. Would you like to have tea?
That would be lovely.

- Rich