Review and Measurements of Benchmark AHB2 Amp

[GoldenOne]

I'm in EU and I got my amp from SCV Distribution, I could disable the auto-off timer. I have the running pretty much 24/7 controlled via the 12V trigger. Before that, I had it on a power/slave power socket which also worked.

When you press and hold your power button what happens? And does it explain how to turn it off in the manual that came with yours?
Hopefully @John_Siau can clarify if this is simply a manual printing difference, or an actual hardware/firmware change, but I cannot seem to disable the auto shutoff no matter what I try.

Holding down the power button on mine the mute lights come on, the left temp light flashes on and off slowly (but will immediately turn off if I let go of the power button), and then a few seconds later the unit powers off (regardless of if I am still holding down or had let go of the button).
The auto-shutoff feature remains on no matter what I do.

https://streamable.com/zmohah

 

[anmpr1]

Mine does that... but it's not really a pop. I'd call it a snap. If it was a crackle I'd be more worried. It's been a year (almost) since I took possession; extremely happy. I don't know if I could tell it apart from anything else in a level matched ABX... however it sure sounds subjectively 'cleaner' than the amps it replaced. In any event, it will be my last amplifier. Unless I get the urge to build something. Then I'll get my wife to talk me out of that. Better to build something practical--like shelves for the garage.

 

[etc6849]

Thanks for these great technical explanations. I'm still greatly enjoying my AHB2 amps you sold me in 2017

I am curious how many ms of bass delay you'd expect to see between an AHB2 and an amp such as the aforementioned Accuphase (given the AHB2's best in class bandwidth)?

My room is actively tri-amped and well treated. Output is fed from my RME soundcard digitally into Xilica XD4080 speaker processors, and I'm using RME's totalmix for volume control. I'm using FIR filters for the three way speakers and a low order bessel filter for the woofers crossing to 5 subs. Even crossed to multiple subs to eliminate room issues and using a lot of bass traps I could never get a perfectly flat group delay curve. I suspect my small room is the only remaining limiting factor. It is interesting how Dirac improves group delay though.

10 AHB2 amps tri-amping 5 speakers and crossed to 5 JBL Fathom subs:

Same room and system, Dirac versus no EQ:

In a different room, I briefly drove my front woofers with an Emotiva XPR-2 amplifier prior to going all out and ordering another 8 AHB2's to fully tri-amp my surround system. I remember noticing a drastic difference in driver control when eliminating the front speaker crossovers and going full-active even with my old Emotiva amps, and an even bigger improvement in clarity when I switch to using all AHB2 amps in my system. I attributed the difference I was hearing between the AHB2 and the XPR amps to be mainly from the lower distortion, although my setup is drastically different from Coach Kaarlo's.

I wonder if or how well Dirac or similar correction software could correct the phase issues you point out that are due to an amplifier's short comings? I don't think Dirac is going to improve an amplifier's distortion, but it would seem that correcting time delay differences and small SPL errors like +/- 1dB are definitely possible and would make for an interesting double blind test.

Regardless, from experience, even with Dirac on my old amps, I'm definitely not giving up my AHB2's! I still haven't heard a system that sounds better, and that's comparing several 6 figure systems I've heard in much bigger rooms to mine.

With the Accuphase, the combination of late delivery and less damping will emphasize the bass on some recordings. You seem to have found one recording where this added emphasis was desirable in your room with your speakers, but it is quite likely that the bass in a different recording would sound uncontrolled.

0.56 dB may not sound like a lot, but keep in mind that it has been shown that A/B and A/B/X tests should be level matched to +/- 0.1 dB.

But there are more issues:

At the crossover frequencies, the speaker impedance can change very rapidly. If the amplifier output impedance is too high this variation in the load impedance can impact that phase alignment between the two drivers at the crossover point. This change in phase alignment can have a big impact on the amplitude response at the crossover frequency.

 

[digitalfrost]

No - was told it was normal. It's not bad enough to do any damage. Just a bit annoying.

https://www.audiosciencereview.com/...ements-of-benchmark-ahb2-amp.7628/post-298242

The thump/click/whatever is indeed normal.

 

[RichB]

It is normal. I have 5 AHB2's and all tick on power off.
It is soft and will not cause damage.

- Rich

 

[BYRTT]

...I am curious how many ms of bass delay you'd expect to see between an AHB2 and an amp such as the aforementioned Accuphase (given the AHB2's best in class bandwidth)?...

1st order high pass 0,1Hz verse 5Hz is roughly as below curves roughly because i didn't use a real spice program but used free Rephase with huge taps of 1048576 output a frd-file and therefor as we get closer to DC point we see a little kink in 2-3Hz area and also lowest point of X-scale is 2Hz for free REW so it can't present the 0,1Hz amplitude roll off.

 

[Mikechw]

No - was told it was normal. It's not bad enough to do any damage. Just a bit annoying.

Yes, my pair of AHB2 also have a click noise when its muting..

 

[RPG]

Mine, too.

 

[anmpr1]

It is normal. I have 5 AHB2's and all tick on power off.

Just out of curiosity, when you turn them off do you use the 'trigger' switch function? I'm wondering whether they all turn off together, or is the turn off consecutive, one after the other?

 

[JP]

Together.

 

[RichB]

Just out of curiosity, when you turn them off do you use the 'trigger' switch function? I'm wondering whether they all turn off together, or is the turn off consecutive, one after the other?

They are all triggered however, there is a tick, when powered off with the power switch as well. I also tested with no input connected, no change.

- Rich

 

[STUDIO51]

Just out of curiosity, when you turn them off do you use the 'trigger' switch function? I'm wondering whether they all turn off together, or is the turn off consecutive, one after the other?

When used with Benchmark dac, it is turned on and off in the order of DAC-> AHB2.
The setting I am using is DAC3-> AHB2-> AHB2. Both AHB2 are turned on and off simultaneously.

 

[Nybto]

Just ran into a problem with my AHB2. I managed to blow both fuses, but I thought the amp was switched off at the time! I was moving my rack into its new location. I had the RH speaker cable connected to the amp but not to the speaker and it was probably shorted. I think I may have jiggled the power plug on the back of the amp while doing something else and maybe it was only partially engaged. Anyway, I heard a bit of gentle ticking and then realised everything had gone off. So it had triggered the RCB on the house circuit and blown both fuses on the amp!

Luckily Benchmark provide a pair of replacements so its all up and running fine now. But I am worried because I don't understand why it happened. If the amp was actually powered on without me realising then I would have expected it to go into protection mode for the speaker short circuit.

I did notice, when I had replaced the fuses and connected the power, the lights came up on the front even though I had not yet touched the power button - could be a factor, given the power plug may have been making and breaking when the incident happened.

If anyone can explain it I would appreciate it.

 

[helom]

I took delivery of an AHB2 yesterday. I've been curious about this amp for a long time but certainly wasn't sold on the idea that its better measurements would translate better sound, as my outgoing amps measure very well for a traditional class AB design. Well, so far I'm quite impressed. It sounds cleaner than my outgoing monoblocks and I feel I'm noticing more low-level detail. All this despite that I'm currently pairing it with the preamp section of an integrated, and unbalanced connections. Low-SPL dynamics also seem superior. So far I'm very pleased but the real test will come when I use it to drive my Maggie .7s this evening.

 

[helom]

Last night I spent a couple hours powering my Maggie .7s with my single AHB2. I played a wide variety of tracks, at SPLs averaging in the mid to high 80s, with dynamic peaks around 95b, which is plenty loud for most listeners and louder than I typically listen. I sit ~9 feet/ 3 meters from the speakers.

The amplifier's clipping LED flashed only once, during the crescendo of a very dynamic orchestral recording. At no point did I detect any audible signs of distress (panel slap, etc), not surprising given the measured performance of these amps.

Further, of all the amps I've used with the Maggies, the lone AHB2 sounds most authoritative, even more so than my class AB monoblocks, which are capable of 310 watts into 4 ohms, stable into 2 ohms. A single AHB2 sounds more powerful in practice than those two 23lb bricks, which happen to have the largest toroids I've ever encountered. The Benchmark also sounds smoother, with greater detail and dimension, yet none of the fatiguing, analytical character I tend to hear in class D products. Bear in mind this is using the AHB2 with an unbalanced source and its highest gain setting. I'm not even using Benchmark's adapter cables, just some cheap RCA to XLR adapters I bought off Amazon, plugged into my Analysis Plus Oval One interconnects.

For reference, my DAC is the Pro-Ject Pre BoxS2 Digital. My Yamaha A-S1100 is serving preamp duties. CD transport is a Yamaha BD-A1060. Room is 15.5' x 26 x 8' and open to a hallway and stairwell (quite a lot of volume to pressurize).

I'm really enjoying this amp.

 

[AudioEnthusiast]

I’ve had mine for 3 months now, and I’ll say this: it makes it hard to end my listening sessions. I just want to keep going!

 

[helom]

I was getting a slight buzz from my tweeters when using RCA to XLR adapters to connect my 1100's preamp section to the AHB2 (sounded more like SMPS noise than typical ground-loop buzz). so figured I'd buy Benchmark's special adapter cables. Well, no change in noise. When my 1100 is connected to my old monoblocks via RCA there is no buzz, only a low level hiss. Any ideas? Eventually I'll move onto a balanced preamp but wanted to live with my current setup for at least a few months.

 

[anmpr1]

I was getting a slight buzz from my tweeters when using RCA to XLR adapters to connect my 1100's preamp section to the AHB2...

Unless it is defective, a normally functioning AHB2 is the quietest amplifier you can currently purchase (at least it's the quietest that I know about). Upstream faults are going to be magnified accordingly. Can you try a PC digit feed (bitperfect) into a stand alone DAC of decent quality? Bypassing the Yamaha preamp section and using PC software to control volume? That is a place to start.

I've read stories of folks with highly sensitive loudspeakers who claim that other amps produce HF hiss, but with the AHB2 everything is clean. My loudspeakers are on the sensitive side (105dB/watt/meter) and with the DAC3 HGC/AHB2 turned up all the way I hear no hiss or other noise artifact.

 

[helom]

Unless it is defective, a normally functioning AHB2 is the quietest amplifier you can currently purchase (at least it's the quietest that I know about). Upstream faults are going to be magnified accordingly. Can you try a PC digit feed (bitperfect) into a stand alone DAC of decent quality? Bypassing the Yamaha preamp section and using PC software to control volume? That is a place to start.

I've read stories of folks with highly sensitive loudspeakers who claim that other amps produce HF hiss, but with the AHB2 everything is clean. My loudspeakers are on the sensitive side (105dB/watt/meter) and with the DAC3 HGC/AHB2 turned up all the way I hear no hiss or other noise artifact.

I can try my DAC/preamp combo directly into the AHB2. Still won't be balanced but I've gotten my system completely quiet using it with my other amps. If that doesn't change anything I might contact Benchmark.

 

[Mikechw]

Well my speaker's tweeter hisses when I put my PC near it.. Sometimes there are other interferences.