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Review and Measurements of Benchmark AHB2 Amp

bigguyca

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That's a cool thought but moving the amps closer does not work in my living room.
I am not a EE so I don't know if the benefits of reducing resistance at some point become overshadowed but adding capacitance or inductance?

- Rich

If the balanced signal cables are made longer then the added capacitance will form a low pass filter with the high input impedance. If the speaker cables are made longer the increase in inductance will form a low pass filter with the small impedance. In either case the similar effects are likely very small unless one is having the sort of week were one concentrates on minutia. Lockdowns can increase the frequency of such weeks.

Semi-related thoughts on speaker cables:

In the area of speaker cables there are potential issues with smaller gauge cables and longer lengths. If one were to build, for example, a switch box to switch between various amplifiers and a loudspeaker system to evaluate if a difference between the amplifiers could be heard, then it would be good minimize the resistance of the cabling. This can be done by maximizing the gauge of the cable, and minimizing the cable length. For example, using small gauge cables that were 40 feet long with say 16 gauge wires would be less than optimum.

At .004 ohms per foot, 80 feet of 16 gauge wire would have resistance of .32 ohms. The resistance would cause frequency response variations based on variations in the impedance of the loudspeaker. The inductance of the relatively long speaker cables would also form part of a filter that would somewhat reduce the high frequencies.

With any loudspeakers with passive crossovers, it is important to minimize the resistance of the speaker cable, but this is particular important for higher quality loudspeakers with higher order, precision crossovers and tight driver tolerances. If Salon2's were used for the amplifier test, then the maximum allowed length of 16 gauge speaker cable would be 9ft. With high quality speakers with passive crossovers saving a few dollars by using small gauge speaker cable can be a false economy.
 

Archaea

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If you are referring to our switch box testing. We had 40 foot of 12 and 14 gauge copper cable. Each of the four boxes was wired with identical cables from the same spool.

20 foot to switch box. 20 foot to speakers.

I will measure resistance on the device and supply pictures. If you think resistance is too high please let me know. The Roger Russel Wire table says 14 gauge copper at 40’ is inaudible.
 
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tpaxadpom

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Over the last 20 years, I have owned the following Bryston amps, 3B-ST, 4B-ST, 4B-SST, PowerPac 300, 7B-SST. I have also owned the AHB2. The AHB2 is smoother on top, you hear more details because the amp is insanely quiet, and no fatigue compared to the Bryston amps I have owned. Bryston does have more power in stereo configuration.

I also recently did a comparison of the Bryston BHA-1 vs the Benchmark HPA4 headphone/preamps on the same system. Again the Benchmark was smoother, more details, and no fatigue. I sold the BHA-1

The only Benchmark piece that I thought was fatiguing was the DAC1, unlike the DAC2 or DAC3.
The only Benchmark product I have auditioned years ago when it came out was DAC1. It was at some dealer house and with no returns offered. I brought Adcom GCD-700 5 disc cd changer which I used as a source for DAC1. Well let's just say DAC1 stayed with the dealer. I couldn't stand the sound for more than a minute. Headache is the right word to describe the sound. It sounded like someone applied 6dB highness filter to it. The upper end was quite transparent, but midrange and bass were synthetic. Since then I never even looked at Benchmark products but likely heard their dads in various installs without paying attention. Glad to hear I am not the only one who formed similar opinion, though I also heard next generation of DACs have addressed that problem. I wouldn't mind trying ahb2 in my system against modified Parasound JC1. I wish I knew someone locally who own it (or preferable a pair).
 

yyzsb

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The only Benchmark product I have auditioned years ago when it came out was DAC1. It was at some dealer house and with no returns offered. I brought Adcom GCD-700 5 disc cd changer which I used as a source for DAC1. Well let's just say DAC1 stayed with the dealer. I couldn't stand the sound for more than a minute. Headache is the right word to describe the sound. It sounded like someone applied 6dB highness filter to it. The upper end was quite transparent, but midrange and bass were synthetic. Since then I never even looked at Benchmark products but likely heard their dads in various installs without paying attention. Glad to hear I am not the only one who formed similar opinion, though I also heard next generation of DACs have addressed that problem. I wouldn't mind trying ahb2 in my system against modified Parasound JC1. I wish I knew someone locally who own it (or preferable a pair).

I have a single AHB2 running in stereo driving a very power hungry Thiel CS3.7. The speakers are in a small room and I have DSP via Convolution file. The DSP was done by a professional. Yesterday, I wanted to see if running the AHB2 in mono on a single speaker would make a difference. It was a big change in fact. The bass improved the sound got louder (I think that is just the 6 dB increase for mono). I also got a bit of fatigue since the bass was a little too much (even with 1 speaker) with the Convolution filter I was using. I have a second Convolution filter that was flatter in the bass area and I switched to that. The sound was perfect after that.

So my subjective observation is that I will be getting a second AHB2 to run in mono. Even at low to moderate volume the extra power made a big difference. The amp is actually not rated by Benchmark for mono operation with my speakers (2 -3 Ohm). However, those measurements have some caveats and I should be getting around 700 watts @ 2 Ohm with the monos.

Benchmark does have a 30 home trial on the AHB2.
 

awdelft

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Hi all,
I could not find: is the negative output of AHB2 grounded or floating? If floating can we assume the feedforward correction is implemented by inverted signal on the negative output (as proposed in the 1980's) , thus simplifying the combination of main and correction amp signal?
 

onununo

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I ordered a second AHB2 from a dealer. Benchmark web site says they are in stock.
Hit yyzsb, I am a little curious. Did you succeed in making this amp drive 2 ohms in bridged configuration? It is equivalent to making it drive 1 ohm in stereo mode!... And if so, did you really manage to get 700W into 2 ohms?
 

digitalfrost

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https://www.stereo.net.au/reviews/benchmark-ahb2-power-amplifier-review

I often use a PS Audio PS10 power mains regenerator because it makes a massive difference to my reference system's sound in some instances. When I first fired up the AHB2 without it, the soundstage was surprisingly two dimensional. I live in central London, where there's a lot of noisy mains, and I found the Benchmark to show this in no uncertain terms. Hooking it up to the PS10 brought the soundstage back to something approaching what I'm used to from my reference VAC PHi 200 valve monoblocks.
 

RichB

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SIY

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This just shows how delusional sighted and uncontrolled hifi reviews and reviews are. stereo.net.au is full of such nonsense.
I'd love to see an explanation of how mains noise can affect soundstage. Especially in a continual, rather than intermittent way.
 

scott wurcer

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I'd love to see an explanation of how mains noise can affect soundstage. Especially in a continual, rather than intermittent way.

It must have been the Kraftwerk.
 

Coach_Kaarlo

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I love that the reviewer shares insights into small details of the sound reproduced while never sharing a single measurement of either of the listening spaces used.

The language used is as useful as it is unambiguous. Not a meaningful measurement in sight - just wistful dreamy nonsense references to some imagined and oh so clearly audible differences. I guess if one is vague enough then no one knows exactly what you mean - emperor's new clothes effect.

And equally incredible that he chose to drive a pair of power hungry B&W802's with a single AHB2 amp - and concluded all is well.....of all that might be audible perhaps that was the elephant in the room......



Honestly the shite that is printed in these rags isn't worthy of use for wiping up the aforementioned substance.
 

RichB

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Here is where I stopped reading the Steronet review:

There was plenty of power and space, and a generally broad-shouldered and gutsy sound. Yet compared to my reference tube design, I did find the palette of colours to be more limited; the AHB2 made everything seem just a little warm, and the texture of the instruments wasn't quite as well resolved.

This man needs am amp with "broad shoulders" and a "palette of colors".
He is clearly a wind instrument ;)

- Rich
 

pogo

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Has anyone ever heard an AHB2 in direct comparison to a Purifi amp? How does the comparison turn out with complex and dynamic music signals (a hearing comparison and not a measured value comparison)?
 

Phorize

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Has anyone ever heard an AHB2 in direct comparison to a Purifi amp? How does the comparison turn out with complex and dynamic music signals (a hearing comparison and not a measured value comparison)?

This would be an absolutely pointless exercise. Take the Amir’s rigorous test results from this site, add a basic understanding of the thresholds of human hearing and what you have is all the evidence you need that they would be utterly indistinguishable in an ABX.
 
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