Review and Measurements of Benchmark AHB2 Amp

[DonH56]

We ran a surround system at two trade shows where we had 5 AHB2 amplifiers driving 5 Salon 2 speakers. Each amplifier was running in bridged mono. We have many customers who are using the AHB2 to drive the Salon2. They can be driven in stereo or bridged mono mode.

That sounds like an excellent idea. I have six and a Voice2 center. I need a volume discount. A BIG volume discount.

 

[daftcombo]

FWIW, my speakers have often been criticized for having 'aggressive highs', but I find that in almost all cases of that sort of thing, it's the recording. Good speakers are hell on bad recordings.

Can you give a small list of good and bad recordings according to you?

 

[etc6849]

Anything from AIX Records has had outstanding dynamic range (best available):
https://www.aixrecords.com/

2L, everything I've heard from them has had top notch dynamic range as well:
http://www.2l.no/

Chesky Records, most stuff has decent dynamic range:
http://www.chesky.com/

Decent database on the dynamic range of recordings:
http://dr.loudness-war.info/

Can you give a small list of good and bad recordings according to you?

 

[Kal Rubinson]

Anything from AIX Records has had outstanding dynamic range (best available):
https://www.aixrecords.com/
2L, everything I've heard from them has had top notch dynamic range as well:
http://www.2l.no/
Chesky Records, most stuff has decent dynamic range:
http://www.chesky.com/
Decent database on the dynamic range of recordings:
http://dr.loudness-war.info/

Is dynamic range your only/main criterion?

 

[March Audio]

Indeed. Their spec at 100 watts is 0.008% which translates into a SINAD of just 89 dB. The Benchmark AHB2 clocks at 117 dB at the same power level:

Can you add to the gamut of tests a measurement of output noise? Say uV rms 20Hz to 20KHz

 

[RichB]

Can you add to the gamut of tests a measurement of output noise? Say uV rms 20Hz to 20KHz

Noise above 20 kHz should also be measured.

- Rich

 

[amirm]

Can you add to the gamut of tests a measurement of output noise? Say uV rms 20Hz to 20KHz

I don't have the amps anymore so no. But otherwise, yes, I can measure them although you could work backward to compute them from SNR measurements.

 

[amirm]

Noise above 20 kHz should also be measured.

- Rich

YOu can see the noise in FFT spectrum:

I can look up the FFT size and based on that, you can back out FFT gain and arrive at actual noise floor from graphs like above.

 

[March Audio]

Noise above 20 kHz should also be measured.

- Rich

I'm interested in what you can actually hear. How this relates to potentially audible hiss levels which can be an issue with high sensitivity speakers

 

[March Audio]

I don't have the amps anymore so no. But otherwise, yes, I can measure them although you could work backward to compute them from SNR measurements.

This was more from a future perspective. I think it's safe to say the AHB is all but silent

 

[anmpr1]

What was the old amp? Do you EQ?

No EQ. I was using 3 different amplifiers. A 6V6GT based stereo tube amp (probably 12 watts/ch); two home made EL-34 monophonic amplifiers I built (about 30-40 watts per channel; a Yamaha AX something or other (100 continuous watts per channel with significant dynamic power--163 watts into 8 ohms and 266 watts in 4 ohm measured by David Rich in Audio Critic #25). My speakers are 105dB SPL with one watt input (it says here), so power was never a limiting factor with any of the amps, at reasonable listening level.

I was originally going to get something aesthetic; you know, 'old school' hi-fi looks, Luxman integrated amplifier. The Lux was about the price of the HGC/AHB combo. But it's hard to argue against what Benchmark is selling, for the price they are selling it for. If I was able to wave a magic wand I'd like my Benchmark HGC to have a mono switch and balance, along with sub-sonic filter for analog. I'd like the amp to have Binghamtom Blue watt meters with peak/hold. With everything encased within an Accuphase rosewood sleeve. But you can't have everything. Can you? On the other hand, Syracuse is probably not that far from Binghamtom, so maybe B-mark could drive down and borrow a few of those meters. LOL

 

[anmpr1]

Can you give a small list of good and bad recordings according to you?

Not a big list, but I can give an example, so you get the idea. Two off the top of my head come to mind: The Trumpet Kings Meet Joe Turner, at least on my copy, is shrill as hell, with no depth. An example of a good recording, IMO, would be the Sheffield Labs Mackowicz thing. However, as far as musical quality of performance goes, The Trumpet Kings blow away Adam Makowicz.

PS: I recently came upon a recording I thought I'd lost in a divorce (you know how that goes). Stan Getz/Albert Daily. The liner notes say it was recorded with 2 mics directly in to a Levinson LNP-2 preamp, into a Levinson modified Studer A80. When I first heard it I thought the balance was off. I'll re-listen with my new system and see.

PSS: bad recordings include almost anything that was heavily multi-miked, in the classical department. DGG and CBS were notorious for that. Also, any solo piano (Chopin, etc) where the mics are stuck inside the piano cavity. Those will never sound very realistic, unless the perspective is one of the player, and not an audience sitting 20 feet away.

PSSS: I don't want to mention pop-style recordings, but some of them are just plain goofy. Instruments wandering around all over the place.

Finally, I don't want to disparage the German label too much. If the recordings were not always great, the performances were always a cut above. Just listened to a 2 volume set of Bach solo cello suites on DGG. It's hard to screw that up, and it sounded great. I don't know how it was recorded, but the sound was pretty natural.

 

[anmpr1]

Can you give a small list of good and bad recordings according to you?

Part II: In my previous reply I mentioned the Getz/Dailey duo recording. I hadn't listened to it since I have my new gear, but it's as I remember. Tenor sax localized well, with at least average to better sound. Yamaha piano dull and lifeless, not localized, seemed to be positioned well behind the saxophone, making the overall balance between the two instruments poor. What this shows is that you just can't take super duper audiophile gear (minimalist B&K microphone setup, Mark Levinson electronics, Studer tape machine) and create something interesting, by itself. Someone who knows what they are doing has to man the console.

On a lark I played another analog recording from a few years later: Pharoah Sanders' rendition of 'Polka Dots and Moonbeams'. Pharoah's sax sounded intimate... you could hear the reed vibrating. William Henderson's piano was really alive... an almost crystalline effect on the piano's high keys. Mixed so that one instrument did not drown the other out, like on the Getz recording. I don't know what gear was used during the Sanders session. So I can't comment on that.

The point: even excellent equipment like Benchmark will not make a poor to average recording sound better in your living room. In fact, it might make it sound worse, subjectively, than it would otherwise be, if you were using lesser gear.

 

[tensor9]

I'm curious, if measurements are so good in bridged mode into 4 Ohms, why does Benchmark not advertise it on their website?

 

[restorer-john]

I'm curious, if measurements are so good in bridged mode into 4 Ohms, why does Benchmark not advertise it on their website?

They do actually. You just need to do the calculation yourself for power. The PSU clearly either drops to the low rail or loses regulation. But that's not surprising. Clearly for marketing purposes, they just didn't want a 518W bridged mono into 4 ohms number as it doesn't look as impressive as the others above it.

 

[tensor9]

They do actually. You just need to do the calculation yourself for power. The PSU clearly either drops to the low rail or loses regulation. But that's not surprising. Clearly for marketing purposes, they just didn't want a 518W bridged mono into 4 ohms number as it doesn't look as impressive as the others above it.

View attachment 29806

Makes sense.

 

[tensor9]

Is the AHB2's slew rate really only 16V/microsecond? That's a bit sluggish no? Or is it just not important?

 

[restorer-john]

Is the AHB2's slew rate really only 16V/microsecond? That's a bit sluggish no?

Not really.

For operation without slew-induced distortion, the following formula can be used:

where f= frequency and V= the peak voltage

It's a nominal 100W amplifier @ 8ohms. That's 40V peak.

Plugged into the formula at 20KHz (max rate of change of a 20KHz sine is 0.125V/uS), we need only around 5V/uS.

Or it is happy out to above 60,000Hz at full power.

If we look at the maximum rated voltage swing of 56.57Vrms (for the bridged mono into 16ohm) , that is 80V peak.

Plugged into the formula, at 20Khz we need around 10V/uS.

Or it is happy out to above 30,000KHz.

Obviously, at low powers and low voltage swings, 16V/uS will push the slew induced distortion free response out to several hundred KHz.

 

[DonH56]

John beat me to it (working late last night).

Also note very high slew rates are not necessarily a good thing except for marketing. Wider bandwidth means greater noise, more power expended to support the extra bandwidth, and potentially lower stability among other things. It is one of those things that you want enough of but not too much. Unfortunately the audio marketing world thrives on excess (not just audio...) and manages to make customers believe it.

 

[scott wurcer]

It's more complicated than that, an ordinary class A/B amplifier biased heavily in class B would be unlikely to have stellar THD performance without a healthy margin over the theoretical limit on slew rate. The internal slew rate in this case is larger than the output slew rate at the zero crossing. I suspect (not really, I know) the error correction schemes in the Benchmark are necessary to compensate for this. If one simply does not have quiescent power as a design parameter there are other paths to sub-ppm distortion amplifiers. No criticism implied or intended, just that if you allow for 50W quiescent power in a 100W amp it is easier to achieve linearity before any feedback or error correction.