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Benchmark AHB2 amplifier measurement by JonMarsh

Dana reed

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#21
Have you heard of anyone using these in mono with a 4 Ohm load like Magnepans? Would be interesting to see how many Watts these can put out to a load like that before clipping and/or thermal issues.
 

restorer-john

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#22
Would be interesting to see how many Watts these can put out to a load like that before clipping and/or thermal issues.
The power output of a pair of those amplifiers in BTL should be sufficient for any (un)reasonable levels in a domestic situation.

See the Stereophile review for test results.

The dissipation capability of the output stage is more than sufficient. There appears to be plenty of supervisory circuitry (thermal sensors on each sink along with likely SOAR/current/DC protection). I wouldn't be concerned about thermal issues with those little beasts, as long as you didn't have them in a situation where airflow was impeded.
 

DonH56

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#23
I have read several reviews from people using them to drive much harder loads than Maggies.

IMD 100 dB below 100W seems pretty impressive but I have not kept up on amps. I too would be curious to see what SOTA is these days, or any days. I expect John to pull some great specs out of some vintage amps now. :)

Cool pix, BTW, wicked busy board... I expected a little more space around the analog signal path but it's hard to tell from the pix, and of course the SMPS moves power noise above the audio band. I suspect the FPGA is part of the power supply tracking system to control and probably used for monitoring and such.
 

restorer-john

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#24
I expected a little more space around the analog signal path but it's hard to tell from the pix
I only have one little concern. Actually 16 of them. The TO-3P spring clips.

I've seen similar ones come off and make a hell of a mess. Lots of heating and cooling cycles, expansion and long term spring fatigue. I note not many manufacturers use them much anymore- they have gone back to an aluminium bar/s screwed to the heatsink to give even pressure on the plastic package.
 

Music1969

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#25
Regarding one of the cons:

"It would be strikingly unfortunate if your preamp is bigger and hotter than your power amp - this is completely plausible with this unit."

What's the issue here? I'm guessing he just means if your preamp has an analogue volume control and the preamp is 'hot' then you'll be using very little volume control / range?

Not an issue with a DAC/Pre combination with digital volume control?
 

DonH56

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#26
I only have one little concern. Actually 16 of them. The TO-3P spring clips.

I've seen similar ones come off and make a hell of a mess. Lots of heating and cooling cycles, expansion and long term spring fatigue. I note not many manufacturers use them much anymore- they have gone back to an aluminium bar/s screwed to the heatsink to give even pressure on the plastic package.
Wow, did not catch that in my first look. I'm with you on that one, though the crossbar approach can have issues too -- hard to apply pressure evenly across all devices. We use something similar on large ASICs but with spring-loaded screws to help even the load. Not perfect, can still get nonplanar force applied, but at least the spring is still captured if it breaks. That said, good spring steel (etc.) can last quite a while and through a lot of thermal cycles.
 

DonH56

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#27
Regarding one of the cons:

"It would be strikingly unfortunate if your preamp is bigger and hotter than your power amp - this is completely plausible with this unit."

What's the issue here? I'm guessing he just means if your preamp has an analogue volume control and the preamp is 'hot' then you'll be using very little volume control / range?

Not an issue with a DAC/Pre combination with digital volume control?
"It's a joke."
 

Dana reed

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#29
The power output of a pair of those amplifiers in BTL should be sufficient for any (un)reasonable levels in a domestic situation.

See the Stereophile review for test results.

The dissipation capability of the output stage is more than sufficient. There appears to be plenty of supervisory circuitry (thermal sensors on each sink along with likely SOAR/current/DC protection). I wouldn't be concerned about thermal issues with those little beasts, as long as you didn't have them in a situation where airflow was impeded.
Thinking of something for a someday wishlist after kids are done with college. For now I’ll use the Schiits and keep the volume to a still (un)reasonable level, just one that doesn’t put them into protection.
 

Olli

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#30
@Olli Very interested to get your feedback on what differences do you hear between the P252 and the AHB.

Well ignore the 3x price differential ;)
I can just say that it sounds absolutely great in my other system. I haven't moved it into my main room to do a direct comparison because I don't have a loudspeaker/amp switch yet and it will involve some gain adjustments inside of the AHBs to match the Hypex specs. But one day I will.

And you're right Alan, the P252 is a real bang for the buck and maybe even regardless of any price difference.
 

Olli

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#31
Have you heard of anyone using these in mono with a 4 Ohm load like Magnepans? Would be interesting to see how many Watts these can put out to a load like that before clipping and/or thermal issues.
My speakers Impedance is 4 ohms nominal, 2 ohms minimal at 80Hz. The AHBs get warm, warmer than my March P252, but they don't get hot. Note that the AHBs only need to power the main speakers above 68 Hz, below that I have 2 subs taking over.
 

Willem

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#32
This is of course a very good amplifier. Even so, I wonder if the engineering excellence translates into an audibly better sound quality, compared to, say, an excellent older design like my Quad 606-2 or its later descendents.
 

March Audio

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#33
I can just say that it sounds absolutely great in my other system. I haven't moved it into my main room to do a direct comparison because I don't have a loudspeaker/amp switch yet and it will involve some gain adjustments inside of the AHBs to match the Hypex specs. But one day I will.

And you're right Alan, the P252 is a real bang for the buck and maybe even regardless of any price difference.
@Olli Thanks. I appreciate it would be a PITA to swap them over but it would great to do a basic subjective comparison/impression. no need for switching between the two. The ahb has got to be one of the current technical references.

It's also of interest because of the fundamentally different design topologies.
 
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DonH56

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#34
My speakers Impedance is 4 ohms nominal, 2 ohms minimal at 80Hz. The AHBs get warm, warmer than my March P252, but they don't get hot. Note that the AHBs only need to power the main speakers above 68 Hz, below that I have 2 subs taking over.
Probably already stated, but the AHB2 is a fundamentally a class-AB amplifier with the SMPS providing class-H operation so the power rails track the signal. That keeps power (and heat) down, but they also add a (relatively) low-power feedforward ("always-on") amp to help compensate crossover distortion. Won't match a class-D design for power efficiency. While I've read of some class-D amplifiers doing something similar, I think the mainstream class-D amplifiers like the P252 do not, thus they will run cooler. Clearly does not impact their performance significantly. :)

Count me as another interested to hear (read) what you think. The AHB2 and March amps are on my short list.

What are your speakers?
 

Willem

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#35
Does anyone know how this feedforward compensating amp system compares to Peter Walker and Mike Albinson's current dumping design?
 

Olli

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#36
My
Count me as another interested to hear (read) what you think. The AHB2 and March amps are on my short list.

What are your speakers?
Will do - just need a quite day to check.

Speakers are Wilson Audio Alexias.

Here‘s a pic of the predicted response in Audiolense of the current set up (subs are 2 Rythmik F18). Haven‘t checked with REW, but will do on that „quite day“ as well.

DFB3F504-56EC-4B0C-991F-C265D0C83F88.png
 

Olli

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#37
@Olli Thanks. I appreciate it would be a PITA to swap them over but it would great to do a basic subjective comparison/impression. no need for switching between the two. The ahb has got to be one of the current technical references.

It's also of interest because of the fundamentally different design topologies.[/
@Olli Thanks. I appreciate it would be a PITA to swap them over but it would great to do a basic subjective comparison/impression. no need for switching between the two. The ahb has got to be one of the current technical references.

It's also of interest because of the fundamentally different design topologies.
Both amps sound great - in their set-ups. But I think it would be misleading to try to describe their sound Sinne these set-ups are totally different.
  • AHBS are in a very open space that has approx 80 m2, ceilings around 5 m. The entire ceiling is treated. Speakers are large floorstanders + 2 18' Subs. Roon is the source, using its digital VC.
  • March P252 is in a 20 m2 room, ceiling 3,5 m, Room is non treated, speakers are (large) bookshelfs + 2 12' subs. Roon again is the source, using its digital VC.
  • Both set-ups are eq'ed with Audiolense, using the same target curve, with a lot of help and great input from @mitchco. Thanks again!
I am using the P252 instead of a much mor expensive Nagra Classic Amp now - again, my judgement is totally subjective, coulnd't do any proper ABX testing. But the Nagra is sold.

I enjoy the small listening room as much as the big one. Both amps sound crystal clear to me.

There are only 2 objective observations I can give for now:
  1. The P252 is dead silent. No hiss at all from tweeters or any other driver. With the AHB, you can hear some (quite) hiss if pressing you ear against the tweeter
  2. As stated before - the P252 never ever gets even remotely warm. So you can put it anywhere, that's nice. The AHBs get warm, not hot. I used a Spectral DMA 260 before with the large floorstanders, which got super hot. Not comparable to that level, but still - the AHBs definitely get hotter than the P252. So they need at least some ventilation.
I am not considering to sell neither the AHBs nor the P252 anytime soon - but the P252 is indeed a fantastic bang for the buck (and a very handsome one on top of it).
 
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pjug

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#38
I only have one little concern. Actually 16 of them. The TO-3P spring clips.

I've seen similar ones come off and make a hell of a mess. Lots of heating and cooling cycles, expansion and long term spring fatigue. I note not many manufacturers use them much anymore- they have gone back to an aluminium bar/s screwed to the heatsink to give even pressure on the plastic package.
Do you have any tips on securing them so that this can't happen?
 

restorer-john

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#39
Do you have any tips on securing them so that this can't happen?
Realistically, I can only see them failing very rarely. That said, even if it happens one in a thousand over ten years, that's a single clip coming off every 2 months (approx) in the wild for a 1000 products (16 per product). (someone can do a better MTBF calculation for me ok?)

Looking at the installation, they must have been pushed on hard (notice the tears on the edges of the insulating silicone impregnated washers), but the aluminium channels are not exactly deep or the spring clip bends tight. Benchmark would be confident they won't come off, but let's face it, they are only there for production line installation time/cost savings. Tapping and individually bolting down each package would add significant time.

I just don't like them. Just one coming off will destroy the entire amplifier from shorting out goodness-knows what. I have found over the decades of repairing gear that anything metal that 'springs' on, can 'spring' off,- regardless of what the designers decades before, said was impossible.

But if you own one. Rest assured, it is a beautiful piece of gear and apart from inspecting the position of the those little clips now and then, or after you move interstate, or accidentally drop the amplifier in your loungeroom, I wouldn't be too worried. :)
 

Kal Rubinson

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#40
Realistically, I can only see them failing very rarely. That said, even if it happens one in a thousand over ten years, that's a single clip coming off every 2 months (approx) in the wild for a 1000 products (16 per product). (someone can do a better MTBF calculation for me ok?)
I hope so. Your analysis doesn't seem with to me but I ain't no expert.
 

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