Review and Measurements of Benchmark AHB2 Amp

[yyzsb]

I was trying to decide last night whether to buy a NAD C298 or March Audio Purifi amp. I want to use it driven by a Matrix Audio Mini-i-3 Pro DAC direct to amp. Normally I hate doing DAC direct to amp but this is a system for background music in a noisy area.

My 2 channel system is an all Benchmark setup, DAC3B | HPA4 | AHB2 x 2. I removed the DAC3B and HPA4 and then added the Matrix DAC. It sounded good, clean, and quiet. However, after about 60 minutes I was starting to get ear fatigue. I then put the Benchmark gear back into the system and ditched the Matrix. Listening to the same tunes again was now fatigue free. So I now know the Matrix either needs some warmth in an amp or I need to ditch it and buy another Benchmark DAC.

The Matrix measures great but I want also want to read some subjective comparisons. I am looking forward to Kal's review of the gear mentioned above. It may give me an idea of how to pair those amps with source gear.

 

[SIY]

So I now know the Matrix either needs some warmth in an amp or I need to ditch it and buy another Benchmark DAC.

Or...? I think you left something out...

 

[yyzsb]

Or...? I think you left something out...

I am slow, what did I leave out?

 

[Kal Rubinson]

So I now know the Matrix either needs some warmth in an amp or I need to ditch it and buy another Benchmark DAC.

Why would you prefer to use a DAC that needs a crutch when there are others that do not?

 

[misterdog]

I am slow, what did I leave out?

Loudspeakers ?

The Matrix measures great

Had you read this ?

https://www.audiosciencereview.com/...-short-story-about-matrix-mini-i-pro-3.17701/

 

[yyzsb]

I saw that and then a few posts that the issue was resolved. That may have been in another ASR thread where Matrix participated. I had been using the Matrix with the Topping A90 headphone amp and the Meze Empy headphone. It sounded great. Had no pops or other sound anomalies. I now realize the reason that it sounded great was because the Meze Empy is a warmish headphone.

Taking the Matrix to my dead neutral 2 channel system I could hear the deficiency in this DAC. Of course there are 3 ways to solve this. Keep using it only with the A90 and Meze, sell it, or get a warm amp.

The speakers at the end of my 2 channel system are a completely refurbished (by me) Thiel CS3.7 with OEM Thiel parts (done Oct 2020). I also have Convolution based DSP running on ROON for this system. The DSP was done by a profession sound engineer who is considered an expert in this field. I also have Audience FrontRow speaker cables with SpeakON terminations that were measured (or commented) on this site to be better than banana to the AHB2. So I have some pretty amazing 2 channel as a baseline.

It is not easy to say that getting another DAC would have been better. The Matrix has some of the best connectivity options for streaming.

Anyways, I am looking forward to Kal's reviews on the Purifi amps that I may get if I ditch the Matrix.

 

[rdenney]

Is it a deficiency or a matter of taste?

John Atkinson, in one of his Rocky Mountain presentations on YouTube, described the Benchmark as astonishingly undistorted, to the point that it challenged the limits of his test equipment, but “lifeless”. But he was clear—in the same paragraph, he said the “best” amp he had ever heard had 2nd-harmonic distortion of over 3%, and he thought that contributed to a great-sounding amp.

Okay. But that would only work with some music, and some sets of mastering decisions. It would certainly represent the musical art being reproduced differently that the artist intended. And I would not be able to appreciate the sound made by, for example, a tuba player in a concert hall, because it would change the characteristic timbre of the instrument, which already depends on a specific array of overtones.

I don’t really want the amp adding audible second harmonics to sounds. Atkinson is a bass player, and is perhaps accustomed to evaluating amplified instrument sound—the added distortion might give him something he wants from a bass amp anyway. I’m a tuba player, and want the instrument to sound like a tuba in a room, not a euphonium (which is pitched an octave higher). I have heard expensive audio equipment that makes a tuba sound like a euphonium.

I would, of course, expect him to realize that the Benchmark has relatively low voltage gain and needs the preamp to drive a higher level for the same output sound before any comparison could be made.

Rick “who needs to do those measurements again” Denney

 

[yyzsb]

Is it a deficiency or a matter of taste?

John Atkinson, in one of his Rocky Mountain presentations on YouTube, described the Benchmark as astonishingly undistorted, to the point that it challenged the limits of his test equipment, but “lifeless”. But he was clear—in the same paragraph, he said the “best” amp he had ever heard had 2nd-harmonic distortion of over 3%, and he thought that contributed to a great-sounding amp.

Okay. But that would only work with some music, and some sets of mastering decisions. It would certainly represent the musical art being reproduced differently that the artist intended. And I would not be able to appreciate the sound made by, for example, a tuba player in a concert hall, because it would change the characteristic timbre of the instrument, which already depends on a specific array of overtones.

I don’t really want the amp adding audible second harmonics to sounds. Atkinson is a bass player, and is perhaps accustomed to evaluating amplified instrument sound—the added distortion might give him something he wants from a bass amp anyway. I’m a tuba player, and want the instrument to sound like a tuba in a room, not a euphonium (which is pitched an octave higher). I have heard expensive audio equipment that makes a tuba sound like a euphonium.

I would, of course, expect him to realize that the Benchmark has relatively low voltage gain and needs the preamp to drive a higher level for the same output sound before any comparison could be made.

Rick “who needs to do those measurements again” Denney

I made it real simple for myself. I wanted an amp that was preferably 11 inches or less wide and sounded great with my KEF LS50. I just went and bought another AHB2 and will use it with the Matrix until I unload that. Overkill for this background music application but it is only money that I do not have.

I likely love the lifeless sound as JA describes. Sign me up for 3 of those please.

 

[Coach_Kaarlo]

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?

This has been discussed.

https://www.audiosciencereview.com/...ements-of-benchmark-ahb2-amp.7628/post-549830


Actually, most REAL speakers have impedance values FAR lower than their stated nominal value (and higher also).

For example the Revel Performa 3 F208's drop to 3.4 ohms @ guess where.....? Right at 90Hz. And they measure 4.5 ohms @ 25Hz.


Luckily John Siau shared a spreadsheet where one can calculate the damping factor of the ENTIRE system (including speaker cable length and impedance).

This ACTUAL system based calculation makes a difference to damping factor (DF).

1. Peak DF of 185 (mono) drops to 78 (when using 3 foot Canare 4S11 cables, with 4 ohm nom. speakers).
2. Peak DF of 370 (stereo) drops to 85 (when using 10 foot Canare 4S11 cables, with 4 ohm nom. speakers).
3. Worst case impedance related frequency response variation 0.14dB (Benchmark stated ideal is 0.1dB for inaudibility).

This is a crude and simplistic example, but I think it highlights the problem with some of the comments on this thread. The speakers, and cables, are an integral part of the performance of the amplifier, and do make a difference to the sound the amplifier reproduces - in the real world. This is quite different from saying there is some problem with the AHB2 as it sits on the test bench being measured in isolation. No doubt the amplifier measures impeccably well in isolation, with simulated loads, and at 8 ohms. Tick!!

What I am suggesting is that with certain speakers the AHB2 has clearly audible, repeatable, and measurable flaws or deficits in it's performance - some of which can be reduced by doubling up with 2 amps in bridged mono. I have tested, measured, and tried to solve this performance issue many many different ways; changing room correction to improve freq. response and remove nulls, different PEQ filters, different speaker cables (lower impedances), different speakers, different amps, measuring in freefield to remove room effects - this thread is littered with my attempts to understand this clearly measurable problem and try to solve it.....as yet I have been unsuccessful in doing so with the AHB2.

Most experienced contributors on here just suggest buying a more dynamically capable amplifier - something I may yet do. Alternatively a couple of good subs crossed high might help the AHB2's cope better.


BUT, as far as I know Benchmark Media (nor @amirm, or anyone else that I am aware of) have not yet measured the AHB2 in mono and published the damping curve. Nor has anyone listed the bridged mono slew rates, or voltage rise time, or max instantaneous current (29A into 1 ohm in stereo I think). In actual fact Benchmark list impedances below 6 ohms nominal as possible reasons for amplifiers warnings and protection limits - although I am pretty sure the AHB2 can drive loads down to 2.6 ohms in mono.

So before we make assertions like ""Your speakers would need to offer a fantastically difficult load to generate anything more that fractions of Dbs in frequency response variation."" Perhaps we can get all of the facts required for an informed discussion - and no doubt my contribution is missing a few also!

 

[DonH56]

Using an amplifier in bridged mono actually doubles the output impedance and thus halves the damping factor.

Aside from noise floor that may cause audible hiss in some applications, I think (complex) output impedance is perhaps the most important parameter to measure and understand.

 

[Coach_Kaarlo]

Using an amplifier in bridged mono actually doubles the output impedance and thus halves the damping factor.

Aside from noise floor that may cause audible hiss in some applications, I think (complex) output impedance is perhaps the most important parameter to measure and understand.

https://www.audiosciencereview.com/...ements-of-benchmark-ahb2-amp.7628/post-550042

 

[RobS]

Since we are talking about damping factor.

Why would you want to halve the damping factor if you run the AHB2 in mono? Wouldn't the AHB2 in stereo have a better control of the speaker's drivers motion? And you would arguably have a tighter low end with a higher damping factor too.

It seems this is the argument against running AHB2 in mono.

Or are there benefits to mono operation? I ask because I have a stereo AHB2 and considering another to run mono for 4ohm 200W (power handling) speakers, but I'm already getting 190W in stereo at a high damping factor.

 

[DonH56]

Since we are talking about damping factor.

Why would you want to halve the damping factor if you run the AHB2 in mono? Wouldn't the AHB2 in stereo have a better control of the speaker's drivers motion? And you would arguably have a tighter low end with a higher damping factor too.

It seems this is the argument against running AHB2 in mono.

Or are there benefits to mono operation? I ask because I have a stereo AHB2 and considering another to run mono for 4ohm 200W (power handling) speakers, but I'm already getting 190W in stereo at a high damping factor.

The main reason people bridge their amplifiers is because you get four times the power (theoretically; in practice in tends to be someplace between 2x and 4x). You are putting two amplifiers in series (sort of) so double the output impedance and thus half the damping factor.

There is a lot of debate about just how low output impedance needs to be (or high high damping factor) and it very much depends upon the impedance profile of your speakers.

 

[ciotime]

I need some advice. I'm quite interested in the Benchmark AHB2 and with Amir's glowing reviews the more I'm convinced. I'm still a newbie and would really appreciate all your inputs if these are the correct amps for my Dali Oberon 7. These are rated at 130 Watts per channel into 6 Ohms, both channels driven which my Dali's are. Is that enough power? I keep reading people always recommend to get more power than needed for headroom etc thus my dilemma. I'm gonna be using these as my external amp for the Denon X3700H. Mainly for movies as well as some music listening. Room is 13'X19'X8' and I sit about 11' from the speakers. I've listed below the Dali Oberon specs...thanks.

Frequency Range (+/-3 dB) [Hz] 36 - 26,000
Sensitivity (2,83 V/1 m) [dB] 88.5
Nominal Impedance [ohms] 6
Maximum SPL [dB] 110
Recommended Amplifier Power [W] 30 - 180
Crossover Frequency [Hz] 2,300

 

[RichB]

I need some advice. I'm quite interested in the Benchmark AHB2 and with Amir's glowing reviews the more I'm convinced. I'm still a newbie and would really appreciate all your inputs if these are the correct amps for my Dali Oberon 7. These are rated at 130 Watts per channel into 6 Ohms, both channels driven which my Dali's are. Is that enough power? I keep reading people always recommend to get more power than needed for headroom etc thus my dilemma. I'm gonna be using these as my external amp for the Denon X3700H. Mainly for movies as well as some music listening. Room is 13'X19'X8' and I sit about 11' from the speakers. I've listed below the Dali Oberon specs...thanks.

Frequency Range (+/-3 dB) [Hz] 36 - 26,000
Sensitivity (2,83 V/1 m) [dB] 88.5
Nominal Impedance [ohms] 6
Maximum SPL [dB] 110
Recommended Amplifier Power [W] 30 - 180
Crossover Frequency [Hz] 2,300

It depends on your room and listening habit.
My room is 15x30x12 feet. The Salon2 specs are similar:

Frequency Response 3 dB from 23 Hz to 45 kHz
Nominal Impedance 6 ohms (nominal) 3.7 ohms (minimum @ 90 Hz

Your speakers are slightly more efficient and also may handle less power.
I have no issues driving the Salon2s to levels I find sufficient at my listening position.

So about 104 dB with both Salon2s is obtained with 128 watts which the AHB2 will deliver into 4 Ohms (the Salon2s hover around 4 Ohms).
This is computed using a 0 DBFS (maximum volume) at clipping.
Basically, I can turn up any digital source to -13 without clipping the AHB2.

- Rich

 

[ciotime]

It depends on your room and listening habit.
My room is 15x30x12 feet. The Salon2 specs are similar:

Frequency Response 3 dB from 23 Hz to 45 kHz
Nominal Impedance 6 ohms (nominal) 3.7 ohms (minimum @ 90 Hz

Your speakers are slightly more efficient and also may handle less power.
I have no issues driving the Salon2s to levels I find sufficient at my listening position.

View attachment 114411

So about 104 dB with both Salon2s is obtained with 128 watts which the AHB2 will deliver into 4 Ohms (the Salon2s hover around 4 Ohms).
This is computed using a 0 DBFS (maximum volume) at clipping.
Basically, I can turn up any digital source to -13 without clipping the AHB2.

- Rich

Thanks for the advice. Room is 13'X19'X8' and I sit about 11' from the speakers. I was told to get 2 of them to get more power...bridge mode thereby using 1 for each speaker but if 1 AHB2 is good enough to drive the 2 speakers the better...saves me from spending double.

 

[RichB]

Thanks for the advice. Room is 13'X19'X8' and I sit about 11' from the speakers. I was told to get 2 of them to get more power...bridge mode thereby using 1 for each speaker but if 1 AHB2 is good enough to drive the 2 speakers the better...saves me from spending double.

The option for another amp is always there if you need it.

- Rich

 

[RobS]

The main reason people bridge their amplifiers is because you get four times the power (theoretically; in practice in tends to be someplace between 2x and 4x). You are putting two amplifiers in series (sort of) so double the output impedance and thus half the damping factor.

There is a lot of debate about just how low output impedance needs to be (or high high damping factor) and it very much depends upon the impedance profile of your speakers.

Ok so to give you an example here:

Would this result in a mismatch with having monoblock AHB2?

I don't see Benchmark rating 4ohm monoblock either. Is that because it can hit protection or clip early?

 

[RichB]

Ok so to give you an example here:

Would this result in a mismatch with having monoblock AHB2?

I don't see Benchmark rating 4ohm monoblock either. Is that because it can hit protection or clip early?

It should fine because there are number of users (and I have a friend) using the AHB2 bridged to drive the Salon2 and it dips below 4 Ohms.

- Rich

 

[RobS]

Ok thanks for your help. Is there an increase in dynamics by having two AHB2 amplifiers bridged in mono? Or any other technical benefit that increases sound quality? Or is it just a matter of getting enough headroom for the dbSPL you need where you sit and your room?