Benchmark AHB2 Review (Updated Measurements)

[restorer-john]

I’m getting constant popping from my AHB2 out of nowhere. It was working fine one day connecting via XLR to the source and bananas to my towers. The next day, nothing but popping, even if the source is turned to 0…

Contact Benchmark directly. Send them an audio recording of the issue, with no connection to the amp except the loudspeakers.

In my experience, they are incredibly fast in responding to issues.

 

[Ovo23]

Did Benchmark show their products on axpona? If so, did they reveal any new product ? The latest was almost 5 years ago, while the amplifier ahb2 is more than a decade. I am really looking forward that they can make an amp of 200+w and improve the bridged mode so that it is not only double the power but stable. Besides, I also hope they can create an integrated amplifier. I haven't seen any amplifier in A/B design doing better while spending less than Benchmark and they actually explain every single step they take and how it improved. Even better, I hope I can see it handle even below 2ohm and stable..

 

[fredoamigo]

Did Benchmark show their products on axpona? If so, did they reveal any new product ? The latest was almost 5 years ago, while the amplifier ahb2 is more than a decade. I am really looking forward that they can make an amp of 200+w and improve the bridged mode so that it is not only double the power but stable. Besides, I also hope they can create an integrated amplifier. I haven't seen any amplifier in A/B design doing better while spending less than Benchmark and they actually explain every single step they take and how it improved. Even better, I hope I can see it handle even below 2ohm and stable..

Although very popular with audiophiles, Benchmark is a company with a professional (public) vocation and I don't think that an integrated amp is useful in the pro market.
On the other hand, I find it difficult to improve a product that is already perfect for most users.

 

[etc6849]

Just add an HPA4 if you want integrated amp functionality? They are designed to work very well together.

Besides, I also hope they can create an integrated amplifier.

 

[livinon2wheels]

I use locking ones.

Here are the Specifications for the Amplifier. As expected they are detailed and lengthy:

Manufacturer Specifications:

Continuous Average Output Power​

< 0.0003 % THD+N at full rated power, 20 Hz to 20 kHz

• 100 Watts per channel into 8 Ohms, both channels driven
• 130 Watts per channel into 6 Ohms, both channels driven
• 190 Watts per channel into 4 Ohms, both channels driven
• 240 Watts per channel into 3 Ohms, both channels driven
• 200 Watts into 16 Ohms, bridged mono
• 380 Watts into 8 Ohms, bridged mono
• 480 Watts into 6 Ohms, bridged mono

All speakers have variations in input impedance. Select loads based on nominal impedances not minimum impedances. The AHB2 is stable into all loads. The AHB2 is conservatively rated at an output level where THD+N is < 0.0003 % instead of the more typical 1% THD+N. Power at 1% THD will be higher.

Output Voltage Into Various Load Impedances​

< 0.0003 % THD+N at the following output voltages and load impedances, 20 Hz to 20 kHz

• 29.03 dBV, 31.25 dBu, 28.28 Vrms into 8 Ohms, both channels driven
• 28.92 dBV, 31.14 dBu, 27.93 Vrms into 6 Ohms, both channels driven
• 28.81 dBV, 31.03 dBu, 27.57 Vrms into 4 Ohms, both channels driven
• 28.57 dBV, 30.79 dBu, 26.83 Vrms into 3 Ohms, both channels driven
• 27.14 dBV, 29.36 dBu, 22.76 Vrms into 2 Ohms, both channels driven
• 35.05 dBV, 37.27 dBu, 56.57 Vrms into 16 Ohms, bridged mono
• 34.83 dBV, 37.05 dBu, 55.14 Vrms into 8 Ohms, bridged mono
• 34.59 dBV, 36.81 dBu, 53.67 Vrms into 6 Ohms, bridged mono
• 33.16 dBV, 35.38 dBu, 45.52 Vrms into 4 Ohms, bridged mono

Use dBV to calculate the peak SPL from your speaker/amplifier combination. Use the following formula: Amplifier output voltage in dBV + speaker sensitivity at 2.83V - 9 dB. Example: (29.03 dBV at 8 Ohms) + (90 dB SPL @ 2.83V 1m) - 9 dB = 110 dB SPL at 1 meter

SNR & Dynamic Range​

Rated output relative to output noise, inputs shorted

• 132 dB A-weighted, Stereo Mode
• 135 dB A-weighted, Mono Mode
• 130 dB Unweighted, 20 Hz to 20 kHz, Stereo Mode
• 133 dB Unweighted, 20 Hz to 20 kHz, Mono Mode

Noise Voltage​

Output noise voltage, A-weighted, inputs shorted

• -103 dBV, -101 dBu, 7.1 uVrms, Stereo Mode
• -100 dBV, -98 dBu, 9.8 uVrms, Mono Mode

Use dBV to calculate the SPL of the noise produced by your speaker/amplifier combination. Use the following formula: Amplifier output noise voltage in dBV + speaker sensitivity at 2.83V - 9 dB. Example: Mono mode driving very high efficiency speakers: (-100 dBV) + (104 dB SPL @ 2.83V 1m) - 9 dB = -5 dB SPL at 1 meter. This means that the system noise will be 5 dB below the threshold of hearing when driving speakers with a very high 104 dB efficiency.

Noise Relative to 2.83 Vrms​

Output noise relative to 2.83 Vrms, A-weighted, inputs shorted

• -112 dB, Stereo Mode
• -109 dB, Mono Mode

THD+N​

1 kHz, 80 kHz LPF, at full rated output into any rated load

• < -118 dB (< 0.00013%), Stereo Mode
• < -118 dB (< 0.00013%), Mono Mode

THD​

1 kHz, 20 kHz LPF, at full rated output into any rated load

• < -119 dB (< 0.00011%), Stereo Mode
• < -120 dB (< 0.00010%), Mono Mode

Crosstalk​

• Better than -115 dB at 1 kHz
• Better than -92 dB at 20 kHz

Frequency Response​

• Better than 0.1 Hz to 200 kHz, +0/-3 dB
• -0.01 dB at 20 Hz, -0.17 dB at 20 kHz, 8-Ohm Load
• -0.23 dB at 20 Hz, -0.32 dB at 20 kHz, 4-Ohm Load

Damping Factor​

• 350 at 20 Hz, 8-Ohms
• 254 at 1 kHz, 8-Ohms
• 34 at 20 kHz, 8-Ohms
• 7 at 200 kHz, 8-Ohms

Maximum Audio Output Current​

• 29 A peak, per channel, both channels driven

Input Sensitivity​

• Low-Gain = 22 dBu (9.8 Vrms), Gain = 9.2 dB
• Mid-Gain = 14.2 dBu (4 Vrms), Gain = 17.0 dB
• High-Gain = 8.2 dBu (2 Vrms), Gain = 23 dB
• Use Mid-Gain or High-Gain settings for unbalanced inputs
• Unbalanced inputs require RCA to XLRM adapter cables

Input Impedance​

• 50 k Ohms, normal mode
• 1 M Ohm, common mode

Input CMRR​

• 80 dB at 20 Hz, typical
• 80 dB at 1 kHz, typical
• 65 dB at 20 kHz, typical

Trigger I/O​

• 12 VDC 200 mA current-limited output to trigger turn-on of remote devices
• DC input for slaving to remote devices
• Input responds to 3.3 V logic and higher, VIL = 1.26 V, VIH = 2.7 V
• Absolute maximum input voltage = 30 VDC
• Absolute minimum input voltage = -0.3 VDC
• Input Impedance = 20 k Ohms

Protection Circuits​

• Fully Electronic, No Relays
• Mute Sequencing
• Distortion Detection
• Short Circuit Detection
• Over Current Detection
• Over Temperature Detection
• SOA Detection (Output device safe operating area)

Dimensions​

Non-rack-mount version:​

• 11.04" W x 3.88" H x 9.34 " D - Including feet and binding posts
• 11.04" W x 3.47" H x 8.33 " D - Excluding feet and connectors
• Faceplate height is 2RU

Rack-mount version:​

• 19.00" W x 3.88" H x 10.62 " D - Including binding posts, handles and removable feet
• 19.00" W x 3.47" H x 8.33 " D - Excluding feet and connectors
• 9.09" rack depth, including binding posts, excluding cables
• 11" rack depth, including cables
• Faceplate height is 2RU

Weight​

• 12.5 lbs., 16 lbs. shipping - Non-rack-mount version
• 13.5 lbs., 17 lbs. shipping - Rack-mount version

AC Input​

• Auto-ranging AC Input
• 100 to 120 VAC +/- 10%, 8 Amps, 50 - 60 Hz
• 220 to 240 VAC +/- 10%, 8 Amps, 50 - 60 Hz
• Idle Power Consumption = 20 W
• Standby Power Consumption < 0.5 W

so what is the damping factor at 4 ohms?

 

[pogo]

See here, not bridged: Link

 

[RichB]

so what is the damping factor at 4 ohms?

Here are the Benchmark specs:

Damping Factor​

• 350 at 20 Hz, 8-Ohms
• 254 at 1 kHz, 8-Ohms
• 34 at 20 kHz, 8-Ohms
• 7 at 200 kHz, 8-Ohms

Take these and divide by 2.

- Rich

 

[Julf]

so what is the damping factor at 4 ohms?

"More than enough".

 

[Hear Here]

Buying the AHB2 for me was prompted by rave recommendations from the owner of very costly speakers from the same stable as my own speakers. He had deep pockets and had previously used numerous very costly amps of all types, so (before hearing them and before any worthwhile reviews were released) I bought this amp.

This rash purchase proved both good and bad:

Bad because it sounded so dull and lifeless compared with my previous SETs. It was an amp that never encouraged me to turn up the volume - on the contrary, it sounded little more exciting than "elevator music", even though it may be deadly quiet and accurate elevator music! Kiss of death as far as I'm concerned, whatever the spec says or test instruments say. A pity because it offers a great package on paper, in an attractive case, at a sensible price, with nice features such as adjustable gain - and it subsequently received excellent reviews in places where measurements are as important or even (it sometimes seems) more important than what reaches our ears!

Good because it propelled me into a practical and exhaustive search for a much better sounding amplifier that would genuinely offer as exciting and goosebump-inducing music as the best of my SETs, but without trying to mimic their sound characteristics.

The AHB2 was returned to the dealer after a few months for a greatly appreciated full-value credit note. Over the next many months, I bought (new or used) or borrowed a dozen solid state amps of all persuasions to find one that equalled or exceeded the musical satisfaction of my previous amps. I was not interested in their Class or their measurements - solely in their ability to provide a superb match for my speakers and deliver the most convincing, exciting and natural sounding music I could achieve. However, I was expecting that a Class A may well be the winner and indeed one of these (the excellent Accuphase A-36) was kept for over a year, but in the end, it was a little too "polite" despite its superb construction, features and sound.

Amps from Devialet, Red Wine, Quad, Masterclass Sugden, and Lyngdorf were also quickly eliminated for one reason or another - not necessarily on sound quality grounds.

Mark Levinson, Bakoon, GamuT, Micromega, Valvet and NAD fared better, but the winners on sheer musical enjoyment boiled down to the GamuT D200 Mk III and the recently released NAD M33. Because of the GamuT's bad manners (an alarming thump on powering up or down), it was reluctantly sold to someone with less sensitive speakers. Because the M33 offered superb sound and was so much better value with it's built-in streamer, DAC and (best not engaged) Dirac Live DSP, I went for the NAD M33.

No regrets whatsoever over the 3+ years I've been using this excellent amp, that went on to be awarded Stereophile's Best Amplifier and Best Component of the Year and Editor's Choice. However, it may soon be changed for the new M66 plus a pair of mono amps in all probability - but only if the new combo actually sounds better!

Apologies to owners of the AHB2 (or Sugden, etc) and anyone putting too much faith in measurements but, when all is said and done, it's what things sound like that really matters most. I guess I'll have to take cover having told this tale on this particular forum.

 

[Theta]

Back in 2019, I reviewed the Benchmark AHB2 Stereo Amplifier. I received a second sample from a kind member to update the measurements. Originally the AHB2 cost $3000 but now, $3,500.
View attachment 337815
As you see, it is a compact but very nice looking amplifier. I appreciate the clipping indicator which seemed accurate in testing. Back panel shows both SpeakOn and traditional binding posts:

In my original testing, I used the SpeakOn connectors as that gave better response than the binding posts. They are directly soldered to the PC Board as opposed to extra wiring. The amplifier is so low distortion and sensitive to load modulation that this makes a difference as you see below.

A very nice feature is three different gain settings. Highest saturates around 2 volts, middle 4 volts and lowest around 10 volts. I measured all three in areas that matter.

You can also bridge the amplifier into mono and get massively more power. Again, see below.

Benchmark AHB2 Amplifier Measurements
Let's start with our usual dashboard in low gain:
View attachment 337816
While this is phenomenal performance, we have gone from SINAD of 113 dB to 111 dB. This is due to third harmonic rising (inconsequentially to -120 dB). So ranking goes down a bit:
View attachment 337817
View attachment 337818

Surprisingly, there is not much degradation at higher gain levels:
View attachment 337819
View attachment 337820

This is reflected in the SNR:
View attachment 337822
View attachment 337823
View attachment 337824

I did discover some load dependency:
View attachment 337825
It is well managed though and is outside of audible band.

Intermodulation distortion is expectedly low:
View attachment 337826
View attachment 337827

Crosstalk is a hair worse which could be the different speaker wiring:
View attachment 337828

Let's run our 4 ohm power sweep at all three different gains:
View attachment 337829
You see again the impact of the speaker binding vs SpeakOn. But still excellent performance.
View attachment 337830
The dependency on wiring goes down at 8 ohm due to lower currents involved:
View attachment 337831

Changing frequencies doesn't impact the amplifier power sweep much except at 15 kHz, and even there it is well behaved:
View attachment 337837
Some of the non-linearity may again be due to binding posts.

Amplifier is stable and performant on power up:
View attachment 337832

Benchmark AHB2 Bridge Mode Power Measurements
The amplifier goes into differential mode which in theory quadruples the power. It is however only rated above 6 ohm. I tested it at 8:
View attachment 337833

Benchmark AHB2 Reactive Power Measurements
Using my Loadbox, I tested the amplifier at different complex and resistive loads down to 2 ohm:
View attachment 337834

There is a bit of voltage droop as we go down from 8 ohm but still respectable when you consider how much power is being pumped out (approximately):
View attachment 337835

Here is the same but in bridged mode:
View attachment 337836
As you see, it also doesn't have any issues with reactive/complex loads.

EDIT: forgot to post the pop measurements:
View attachment 340248

Conclusions
Using standard binding posts reduces performance just a bit but certainly nothing to worry about. What we have is still state of the art and one of best ever consumer stereo amplifiers produced.

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

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/

Indeed an exceptional piece of gear, a class G,H amp like SAE, Carver, Emotiva and others, but 3800€ here in Europe, honestly would one hear the diference listening to music, two or 300€ on the used market against 3800€?

 

[Julf]

Apologies to owners of the AHB2 (or Sugden, etc) and anyone putting too much faith in measurements but, when all is said and done, it's what things sound like that really matters most. I guess I'll have to take cover having told this tale on this particular forum.

No need for apologies or take cover as long as you realize that we won't put much weight on your personal, subjective perceptions and preferences - good that you found something that works for you!

 

[Hear Here]

No need for apologies or take cover as long as you realize that we won't put much weight on your personal, subjective perceptions and preferences - good that you found something that works for you!

Yes, I don't expect many here will agree, but it can't denied that the sound we actually hear is more important than what the microphone says we should like to hear. I'm sure everyone agrees with that.

If one carefully reads the "worthwhile" AHB2 reviews (Stereophile, HFN, etc), there are caveats to their general praise of this amp and these relate in part to associated equipment or room features or perhaps subjective opinions of others involved with these reviews. Although such factors will affect the apparent performance of ALL amps, it is significant that honest and comprehensive reviewers of this particular amp have felt the need to draw our attention to these less praiseworthy attributes.

I'd suggest that this is a good amp that should, according to its excellent measurements sound even better, but there are other similarly-priced amps that sound better, yet perhaps measure less well.

As I mentioned rather frivolously elsewhere, this platform is undeniably the best audio forum for the deaf! However many hearing readers must also appreciate these microphone-based reviews as otherwise there wouldn't be so many members contributing and reading. Sadly as a result, they may never experience the aural delights of first-class horn speakers or SET amps.

 

[Julf]

Yes, I don't expect many here will agree, but it can't denied that the sound we actually hear is more important than what the microphone says we should like to hear. I'm sure everyone agrees with that.

I am sure everyone agrees as long as we are talking about the sound that reaches our ears. What happens between the ears is another matter. That is why only double blind listening tests count.

I'd suggest that this is a good amp that should, according to its excellent measurements sound even better, but there are other similarly-priced amps that sound better, yet perhaps measure less well.

I'd suggest that it all depends on the definition of "better". Are we talking about the traditional goal of HiFi ("High Fidelity") - accurate, transparent reproduction of the recorded signal - or whatever happens to be pleasing to your ears?

As I mentioned rather frivolously elsewhere, this platform is undeniably the best audio forum for the deaf! However many hearing readers must also appreciate these microphone-based reviews as otherwise there wouldn't be so many members contributing and reading.

Oh, we must?

Wish your review would have been based on actual measurements with a microphone as opposed to subjective, unverified perceptions.

 

[Timmeon]

Yes, I don't expect many here will agree, but it can't denied that the sound we actually hear is more important than what the microphone says we should like to hear.

Isn't most of what we listen to captured by microphones or even created digitally? Scary stuff for those enlightened by first-class horn speakers or SET amps. Stay safe out there.

 

[blueone]

Yes, I don't expect many here will agree, but it can't denied that the sound we actually hear is more important than what the microphone says we should like to hear. I'm sure everyone agrees with that.

Amplifier measurements are not made with a microphone.

If one carefully reads the "worthwhile" AHB2 reviews (Stereophile, HFN, etc), there are caveats to their general praise of this amp and these relate in part to associated equipment or room features or perhaps subjective opinions of others involved with these reviews. Although such factors will affect the apparent performance of ALL amps, it is significant that honest and comprehensive reviewers of this particular amp have felt the need to draw our attention to these less praiseworthy attributes.

Room features affect the performance rating of an amplifier? That's silly.

I'd suggest that this is a good amp that should, according to its excellent measurements sound even better, but there are other similarly-priced amps that sound better, yet perhaps measure less well.

As I mentioned rather frivolously elsewhere, this platform is undeniably the best audio forum for the deaf! However many hearing readers must also appreciate these microphone-based reviews as otherwise there wouldn't be so many members contributing and reading. Sadly as a result, they may never experience the aural delights of first-class horn speakers or SET amps.

The combination of a SET amplifier and its speakers are an example of random equalization and distortion. As I asked someone yesterday, why are you posting on ASR?

 

[Purité Audio]

If @Hear Here enjoys distortion that is allowed, although I wonder if he could tell the AHB2 and his current NAD which are both fine measuring amplifiers apart without being able to see them.
Keith

 

[WillBrink]

How? This is all inaudible.

Humor and sarcasm?

 

[Hear Here]

Wish your review would have been based on actual measurements with a microphone as opposed to subjective, unverified perceptions.

Unfortunately this is impossible as our ears aren't microphones and our brains are not computers. It's surely unwise to choose anything - hi-fi, car, boat, etc just on specs and/or measurements.

We go for a test drive before buying a car or boat and we visit showrooms to listen to hi-fi. If we are impressed, we arrange a home demo and then buy the item in the knowledge it will offer what we want. Although everyone's idea of perfect sound varies a little, we choose what most pleases us - car, boat, amplifier, speakers - otherwise wouldn't we all end up driving identical cars and listening to identical speakers within a price range we can afford? Surely "character" in an important influence on how we like or dislike cars, speakers, etc and this cannot be measured. Measurements have their place but shouldn't be relied on to make a purchasing decision - we need the test drive or home demo or we are likely to be disappointed!

There's lots of good stuff on this forum if you can see the wood from the measurement trees!

 

[Julf]

Unfortunately this is impossible as our ears aren't microphones and our brains are not computers. It's surely unwise to choose anything - hi-fi, car, boat, etc just on specs and/or measurements.

We go for a test drive before buying a car or boat and we visit showrooms to listen to hi-fi. If we are impressed, we arrange a home demo and then buy the item in the knowledge it will offer what we want. Although everyone's idea of perfect sound varies a little, we choose what most pleases us - car, boat, amplifier, speakers - otherwise wouldn't we all end up driving identical cars and listening to identical speakers within a price range we can afford? Surely "character" in an important influence on how we like or dislike cars, speakers, etc and this cannot be measured. Measurements have their place but shouldn't be relied on to make a purchasing decision - we need the test drive or home demo or we are likely to be disappointed!

Your opinion is noted. You like what you like, and it is probably very different from what I like, but if I want to find out if a piece of gear is well designed and capable of accurate reproduction of a recorded signal, without distortion and coloration, I know my measuring instruments are orders of magnitude more precise than my ears.

 

[Purité Audio]

You could have used measurements instead of trying all those amps.
Keith