Review and Measurements of Benchmark AHB2 Amp

[yummy]

The ABH2 works with European voltage, 220v, or a non-US version is needed?.

google smps

 

[amirm]

No more off-topic discussion folks. People come here to read about the amp.

 

[amirm]

Time out while I move off-topic posts from the thread.

 

[amirm]

Ok, thread cleaned up as best as I could. See your missing posts in this thread: https://www.audiosciencereview.com/...-debate-thread-about-audio-measurements.2580/

Folks, this amplifier got reviewed when it came out in 2016 and the news of it got lost literally in the noise. Let's not let that happen to it again with this review. People need to know about exceptional audio products and the Benchmark AHB2 is one of those.

 

[Kal Rubinson]

Folks, this amplifier got reviewed when it came out in 2016 and the news of it got lost literally in the noise. Let's not let that happen to it again with this review. People need to know about exceptional audio products and the Benchmark AHB2 is one of those.

2015: https://www.stereophile.com/content/benchmark-media-systems-ahb2-power-amplifier

 

[DonH56]

The ABH2 works with European voltage, 220v, or a non-US version is needed?.

https://benchmarkmedia.com/products/benchmark-ahb2-power-amplifier?variant=585555021

AC INPUT

• Auto-ranging AC Input
• 100 to 120 VAC +/- 10%, 8 Amps, 50 - 60 Hz
• 220 to 240 VAC +/- 10%, 8 Amps, 50 - 60 Hz
• Idle Power Consumption = 20 W
• Standby Power Consumption < 0.5 W

 

[DonH56]

I admire this amplifier, but I have two questions:
1 Will it handle electrostats, and my Quad 2805s in particular?
2 Will the impressive measured performance translate into audible superioity compared to, say, a Quad QSP?

IMO:
1. It will handle ESLs just fine.
2. Too many unknowns; it will have a lower noise floor and lower distortion but whether that is audible to you I could not say. I suspect it would not be audible to me. The AHB2's lower output impedance might make the bass a bit better, and lower noise floor means less hiss in the treble.

Frankly I am not sure I would be able to tell the difference between the AHB2 and my Emotiva XPA-2, but I am anxious to find out. Just not sure I can justify the money outlay right now.

In the past I have been surprised by the times I could and could not tell the difference among power amplifiers. Back then I had many more resources for finding the technical reasons (there always was one or more). The white paper on the Benchmark site about hearing low-level crossover distortion was interesting. That is one of those things you'd think would never be a problem these days, but previously I have noticed crossover distortion and found it much more audible than I expected. I think the trend the past few years (actually, many years) has been toward lower bias levels and that leads to higher levels of crossover distortion. Less power at idle, so less heat, and easier on AVRs with their limited power supply and output capacity as well as limited ability to dissipate heat when crammed into a console, but greater amounts of low-level "grunge" in the sound. I have a bias toward high-power amplifiers and, aside from the obvious headroom advantage with my low-sensitivity speakers, I think the higher idle bias many have and lower output impedance is a player in that.

https://benchmarkmedia.com/blogs/application_notes/power-amplifiers-the-importance-of-the-first-watt

I am starting to really hate the AHB2; it is not something I can really afford, but it is pushing all my buttons.

 

[pozz]

AHB2, not ABH2... From the Benchmark website:

A.H.B.
The letters A, H, and B allude to the unique topology of the amplifier's output stage. The AHB2 combines class-AB, and class-H topologies using a feed-forward error correction system.

But there is much more to the story -

The initials A.H.B. can be found on many of the circuit diagrams of Benchmark's early products dating back as far as 1983. These are the initials of Benchmark's founder, Allen H. Burdick. He personally designed many of Benchmark's early products.

Allen had a life-long passion for audio, and he became one of the leading innovators in the pro-audio industry. The AHB2 is named in his memory.

There are some very interesting short articles on the amp on Benchmark's website: https://benchmarkmedia.com/blogs/application_notes/tagged/ahb2

Including this nice piece on Burdick: https://benchmarkmedia.com/blogs/application_notes/136427911-history-of-the-ahb2-power-amplifier

 

[DonH56]

Feedforward compensation has been around "forever" and I have often used it in a design. I am not sure it has been applied to audio amps before, though I have a vague memory of seeing it back in the 1980's. It is generally more stable, or at least less likely to cause instability, when applied to an amplifier than negative feedback (where loop gain and bandwidth leads to phase shift and oscillation). A judicious bit of feedforward compensation can help keep an amp stable, lower distortion, and increase bandwidth, while still allowing negative feedback and all of its benefits. I'd love to see the patent (may have to look for it) and see the implementation that yields such superb performance especially at low output levels.

 

[JohnPM]

I am maybe stupid but I struggle with the concept of an out of phase odd harmonic. Surely, even if it is out of phase for the first cycle of the fundamental it will be in phase for the second and so on?
Are we saying we can tell which cycle of the fundamental is in phase with the harmonic and which isn’t, or is it bollox?

I think this generally refers to the phase the harmonic has when the fundamental phase is zero. Since the harmonics are multiples of the fundamental they will be back to the same relative phase when the fundamental starts its next cycle, though will have been through 'n' cycles of their own. Different distortion mechanisms produce different harmonic phases. Here are examples of 10% 3rd harmonic with phase 0 (which starts to look square, as one might expect) and with phase 180 degrees, which is quite triangular. What either has to do with "depth" is beyond me, though.

 

[McFly]

Whats with the amp going into protection mode at only 133W@4ohm @45hz? You telling me if i play something from a bass guitarist at nearly full noise it will keep shutting down? I thought it was rated at 190w at 4ohm.

 

[gvl]

Feedforward compensation has been around "forever" and I have often used it in a design. I am not sure it has been applied to audio amps before, though I have a vague memory of seeing it back in the 1980's.

I think Denon used it in their non-NFB amps in the 90s, @restorer-john should have more insight.

 

[restorer-john]

I think Denon used it in their non-NFB amps in the 90s, @restorer-john should have more insight.

Sansui loved their "super feedforward" AU-Dxxx series in the early 1980s.

AUD-11 block diagram:

AUD-11 implementation:

Denon, Yamaha etc used various "direct distortion cancelling" systems too.

I think the most famous would be the Quad 405 from the 1970s.

Attached Quad prepared leaflet (as PDFs below) compiled with two test reports from HFN and Studio Sound, April and March 1976.

 

[LTig]

Sansui loved their "super feedforward" AU-Dxxx series in the early 1980s.

AUD-11 implementation:

View attachment 26729

Q24-Q27 is the correction amp - correct?

 

[LTig]

I think the most famous would be the Quad 405 from the 1970s.

Here is the schematics of the Quad 405 and the service manual.

 

[amirm]

Whats with the amp going into protection mode at only 133W@4ohm @45hz? You telling me if i play something from a bass guitarist at nearly full noise it will keep shutting down? I thought it was rated at 190w at 4ohm.

These sweeps start at 20 kHz and go down so the amp has been enduring full power at higher frequencies for 30 seconds or more prior to it shutting down this way.

 

[Cortes]

It's already supremely difficult to tell the difference between amplifiers that are in the 0.01% (-80dB) and 0.001% (-100dB) ballpark in tests designed to reveal distortion. Most would argue it's even inaudible for music. Even some of the most excellent loudspeaker drivers have distortion components around 0.01%.

Does it mean that valve amps, ~0.1% distorsion (-60dB), are not suitable for classic music, specially orquestral, since they are fully unable to reproduce much of the dynamic range?.

 

[McFly]

Ahh - so these power ratings published by benchmark are also not continuous as per the (insert standard here), as per the similar discussions in the hypex NC400 thread? Im not bothered whether the are or arent, just pays to be transparent.

I own a set of NC400 monoblocks. Love them.

 

[restorer-john]

Ahh - so these power ratings published by benchmark are also not continuous as per the (insert standard here), as per the similar discussions in the hypex NC400 thread? Im not bothered whether the are or arent, just pays to be transparent.

It's likely the protection system is looking at the signal history and as Amir pointed out, his sweeps start at HF and go down. The protection may be interpreting the extended high power, high frequencies as an indicator of possible oscillation.

If the sweeps went the other way (from low to high), my bet is the amp wouldn't shut down at a mere 133W@4ohms@~45Hz.

 

[GrimSurfer]

Does it mean that valve amps, ~0.1% distorsion (-60dB), are not suitable for classic music, specially orquestral, since they are fully unable to reproduce much of the dynamic range?.

Whether or not an amp is suitable is entirely up to the listener. Depending on the piece, it's volume, and the loudspeakers, an amp with 0.1% distortion might have some audible shortcomings. Whether or not these are heard or perceived depends on the hearing acuity of the listener.

Tube amp manufacturers explain this away by saying that their products produce less obtrusive even order distortion, which can be described in all sorts of normative ways. Personally, I find this somewhat disingenuous.

Distortion is distortion. Qualifying it as pleasing is like favouring a carnival mirror to feel better about the trim waistline and expanded chest that one doesn't have.