Review and Measurements of Benchmark AHB2 Amp

[avanti1960]

It means what you hear will be closer to what the record company released. Whether you like it is another thing.
My personal objective with hifi is basically "high-fidelity" ie as close as I can get to the recording I have bought. I have tried coloured amps but the euphony is non adjustable and doesn't suit all music IME so I don't bother even trying coloured components now (except speakers, none are available with below audible levels of colouration). I find the speaker position in the room makes more difference than any electronics anyway, so one might as well just buy the most accurate amp, since they exist, and get the colour one desires from the speaker and room, since it is unavoidable.

Extremely well said, euphony is non adjustable and doesn't suit all music. This is exactly what I hear but didn't realize it completely until you put it like that. Thank you.

 

[anmpr1]

Every good preamp or source with the same level of transparency, to not down the performance of the AHB2.

This is an important point, and one Benchmark stresses, suggesting limitations with ancillary gear, such as active crossovers, or even substandard interconnects. What is the point of introducing, say, a crossover with 90dB S/N in between your high performance DAC and AHB2? What Benchmark appears to be arguing for is a 'sealed electronic path' using Neutrik quality balanced connectors and SpeakON cables... at least if one is interested in taking advantage of maximum S/N capability.

 

[anmpr1]

thank you! 1) BTW i just heard some lascala speakers and they sounded really nice, you are lucky!

2) i just sold my tube integrated amplifier (rogue audio cronus magnum ii) because I wanted more power... I believe the AHB2 will have all the power I need for my speakers and room.

3) Does this translate into revolutionary state of the art sound quality? Is transparency and openness a strength of the AHB2? I have read some critiques that it can sound dull with respect to dynamics.

1) I would not advise anyone to buy any Klipsch speaker without an extended home loan. At least a couple of weeks of listening. That said, if your tastes run to ancient Chinese acoustic music (bells, drums, other percussion, erhu and guzhen, etc., they are hard to beat! Or if you just want to let your hair down, and kick out the jams with Led Zep...)

2) LaScalas you don't need much power to go loud. At AHB2's power limits (100 to 200 watts per channel 8 to 4 ohm range) I've never seen the amp's clip light flash. If you own less sensitive speakers that suck power like a Dyson Animal, bridged AHB2 are the way to go. With some speakers even that might not be enough, and then you are in to multiple amps/crossovers (and a lot of dollars). But then you have to worry about introducing less capable (S/N-wise) electronics into your chain. I don't see the point of having an active crossover whose S/N is 10 to 15 dB higher than the DAC/amp one is using. Someone could clue me in to how that works and I'd have a better understanding of it.

3) You can read this or that, but the best way to know is to order one, live with it a month, and if it's not what you need, send it back. Benchmark offers a trial listening period.

PS: One reason to do business with them is that they are great folks to work with. You can pick up the phone and talk to someone who will help you, who knows how to help you, and be happy to help.

 

[RichB]

I unplugged the AHB2 while on (not remembering it was) and all per-channel indicators lit up and the blue-power button blinked for over 20 seconds without power attached. It eventually shutdown. When power was restored, it powered on.

Interesting behavior.
I have had the power go out late at night only to wake hours later when the system came back on.

- Rich

 

[Milt]

I would imagine that's some sort of protection spike\shutdown process.

 

[Milt]

Unlikely.

I forgot the winkie.

 

[RichB]

I would imagine that's some sort of protection spike\shutdown process.

While playing music, I unplugged the ABH2 and the output is immediately muted.
There is enough power reserve to mute the system and no issues until the unit fully goes dark.

- Rich

 

[pos]

That is how I typically turn on/off all the elements in my system (DSPs, DACs and amps, namely openDRC-DI, SMSL M8, nc400, THX789 albeit only the off part for that last one unfortunately) using a remote-controlled power outlet.
I expect any well-behaved equipment to handle this kind of situation properly, ie not damage itself or anything downstream

 

[digitalfrost]

I used a master/slave power socket with the AHB2 and experienced the same thing. I emailed Benchmark a video and they said not to worry, it will not damage anything but they would recommend using the 12V trigger anyway. I bought a cheap 12V power supply and connected that to the slave socket and the AHB2 to the permanent one. Works better for me.

Question for other AHB2 owners: Do you get any "thump" sound when muting the amp? I have faintest thump sound. Especially when going from on to mute. It's not loud, but I think given the general quietness of the amp, people with high efficiency speakers could have problems.

 

[RichB]

I used a master/slave power socket with the AHB2 and experienced the same thing. I emailed Benchmark a video and they said not to worry, it will not damage anything but they would recommend using the 12V trigger anyway. I bought a cheap 12V power supply and connected that to the slave socket and the AHB2 to the permanent one. Works better for me.

Question for other AHB2 owners: Do you get any "thump" sound when muting the amp? I have faintest thump sound. Especially when going from on to mute. It's not loud, but I think given the general quietness of the amp, people with high efficiency speakers could have problems.

That makes sense, I prefer using a trigger.
I hear a faint click from the speakers when mute is engaged during power off.

- Rich

 

[STUDIO51]

I used a master/slave power socket with the AHB2 and experienced the same thing. I emailed Benchmark a video and they said not to worry, it will not damage anything but they would recommend using the 12V trigger anyway. I bought a cheap 12V power supply and connected that to the slave socket and the AHB2 to the permanent one. Works better for me.

Question for other AHB2 owners: Do you get any "thump" sound when muting the amp? I have faintest thump sound. Especially when going from on to mute. It's not loud, but I think given the general quietness of the amp, people with high efficiency speakers could have problems.

I have two AHB2s, but the new AHB2's click sound us much louder. So I contact Benchmark with the same symptoms.

Below is the answer from engineering.

"The click is caused by a slight difference in the rate at which the positive and negative rails mute. It is not an indication of a DC offset. Consequently the drivers will not be exposed to a DC offset during operation. There are slight unit-to-unit variations in the magnitude of the tic or pop that occurs when turning the amplifier off. This is normal."

 

[RichB]

I have two AHB2s, but the new AHB2's click sound us much louder. So I contact Benchmark with the same symptoms.

Below is the answer from engineering.

"The click is caused by a slight difference in the rate at which the positive and negative rails mute. It is not an indication of a DC offset. Consequently the drivers will not be exposed to a DC offset during operation. There are slight unit-to-unit variations in the magnitude of the tic or pop that occurs when turning the amplifier off. This is normal."

Thanks for clearing that up. I have 5 of them and they all do it, so I figured this was as designed.

Last night, I had a power outage when using the system that lasted for a few minutes. The RMC-1 and AHB2's all remained off after power resumed. Perfect.

- Rich

 

[JimB]

... I have 5 of them ...

!

 

[ex audiophile]

I've been reading about the benefits of dynamic headroom in amplifiers; however, very few manufacturers offer a specific measurement value for headroom. McIntosh does specify dynamic headroom for their amps, at least the newer SS models that I've been looking at. For instance their new MC462 provides 3 db of headroom. I know this is a complex topic but I would appreciate it if someone could show where in Amir's measurements we can get a feeling for headroom. It seems to be an advantage of high wattage amps, hence the desire among the well to do for huge monoblocks. This AHB2 for instance is not a high wattage amp so is it lacking in headroom? Would the headroom in this amp be significantly better in bridged mode?

 

[avanti1960]

I've been reading about the benefits of dynamic headroom in amplifiers; however, very few manufacturers offer a specific measurement value for headroom. McIntosh does specify dynamic headroom for their amps, at least the newer SS models that I've been looking at. For instance their new MC462 provides 3 db of headroom. I know this is a complex topic but I would appreciate it if someone could show where in Amir's measurements we can get a feeling for headroom. It seems to be an advantage of high wattage amps, hence the desire among the well to do for huge monoblocks. This AHB2 for instance is not a high wattage amp so is it lacking in headroom? Would the headroom in this amp be significantly better in bridged mode?

Headroom is loosely defined as "reserve power" and is somewhat of a gray area when it comes to amplifier specs. Some amplifiers specify "3db of headroom" which should mean that it can deliver transient peaks that call for twice the rated power of the amplifier without "distorting".
However I have yet to see a manufacturer put a distortion spec. to qualify the "3db headroom" specification, not to imply that headroom is a bad thing.
In the case of the AHB2 it seems to be accurately rated, in other words test measurements show that it starts to clip/distort at 108 watts per channel, or 8% above its rated power at 8 ohms. In essence the AHB2 does not have any continuous headroom above its rated power. This is not necessarily something to be concerned about because your need for headroom can begin at a much lower power output depending on how much power you and your system consume while listening. This depends on many things including speaker efficiency, listening position, program material, nominal volume, etc. For example your system could (likely) be quite loud consuming 50 watts and at that point you would have 3db of headroom for peaks in the music, typically bass response transients.
Bridged mono measurements show that the amplifier begins to clip at 410 watts @ 8 ohms, which would yield an additional 5.8 db of headroom vs. the stereo per channel output.
Bridging gives you significant increases in power and headroom. Your system, recordings, listening environment and preferences will determine if you need it.

 

[ex audiophile]

Headroom is loosely defined as "reserve power" and is somewhat of a gray area when it comes to amplifier specs. Some amplifiers specify "3db of headroom" which should mean that it can deliver transient peaks that call for twice the rated power of the amplifier without "distorting".
However I have yet to see a manufacturer put a distortion spec. to qualify the "3db headroom" specification, not to imply that headroom is a bad thing.
In the case of the AHB2 it seems to be accurately rated, in other words test measurements show that it starts to clip/distort at 108 watts per channel, or 8% above its rated power at 8 ohms. In essence the AHB2 does not have any continuous headroom above its rated power. This is not necessarily something to be concerned about because your need for headroom can begin at a much lower power output depending on how much power you and your system consume while listening. This depends on many things including speaker efficiency, listening position, program material, nominal volume, etc. For example your system could (likely) be quite loud consuming 50 watts and at that point you would have 3db of headroom for peaks in the music, typically bass response transients.
Bridged mono measurements show that the amplifier begins to clip at 410 watts @ 8 ohms, which would yield an additional 5.8 db of headroom vs. the stereo per channel output.
Bridging gives you significant increases in power and headroom. Your system, recordings, listening environment and preferences will determine if you need it.

thanks very much; I can't say that i really understand the issue but this helps. It appears that the more clean power you have the better!

 

[Willem]

Within reason yes, and particularly with inefficient speakers in a large room. In that situation it is not a matter of a little bit more but of as much as you can get.

 

[JimB]

thanks very much; I can't say that i really understand the issue but this helps. It appears that the more clean power you have the better!

As long as the higher power amp does not have higher noise or distortion at the levels you actually use. That is, don't compromise performance at the power you actually need and use, for higher power than you need. Otherwise, all things the same except higher power? Sure.

 

[ex audiophile]

Within reason yes, and particularly with inefficient speakers in a large room. In that situation it is not a matter of a little bit more but of as much as you can get.

The system in question is in a 275 sq ft room with reasonable acoustics, speakers are Focal Spectrals with about 87 db efficiency, and i listen from 14 feet away at 80-85db. The current amp is a Mac MC312 and i don't know if the meters are accurate but they often swing between 30-300 depending on the track, rarely close to 300. I think the Mac is fine in this setting but it is moving to another system so i'm looking to replace it with the STR power amp or AHB2. My gut tells me that the AHB2 would have to be in bridge mode to provide enough power reserve so I've ordered the STR amp with 400 per side and able to sustain 800 watt bursts (Audioholics). I have the STR pre so it is also a cosmetic match

 

[Willem]

That is not a very large room, and 87 dB is not terribly inefficient. But if the MAC has to produce 300 watts at times I would stay in that ballpark. However, good power can also be had for rather less (Hypex).