Review and Measurements of Benchmark AHB2 Amp

[rdenney]

I agree that they should be indistinguishable under a tightly controlled double blind test.

Also the 4B3 has 23 and 29 dB gain settings, whereas the AHB2 has 9.2, 17, and 23 dB gain settings. I assume, the sighted test has been made with the 23 dB setting on both amps to have the same SPL.

I wonder how accurate are those gains though: a fraction of dB hotter on the 4B3 and a fraction of dB lower on the AHB2 will make the 4B3 sounds better.

Assuming the gain is set by 0.5%-accurate resistors in both amps and that the gains are by design exactly 23 dB, the error in voltage gain is at most 0.5%. So worst case, there is a 0.5% difference between the two amps voltage gain. As the SPL is driven by power and not voltage, the difference in power/SPL is about 1% or 0.04dB SPL.

Actually, Stereophile´s AHB2 measurements show the 23 dB gain measured at 22.9 dB, so the accuracy of the gain is clearly worst than 0.5% (more like 1%). Assuming 1%, the worst case difference in dB SPL becomes 0.09 dB. Still small, but maybe already perceptible as a sound quality difference.

Edit: added some back-of-the-envelope calculations
Edit 2: added Stereophile measurements of gains

"23 dB" is a completely accurate published representation of something that measures 22.9 dB, if we take the measurement to a decimal place beyond what is published.

But published gain has never been an acceptable means of matching output during a comparison, simply because of that routine rounding that takes place. The only accurate way is to use an AC voltmeter measuring a test tone, say, 1KHz.

Without a voltmeter, one can get pretty close by playing one amp into the right speaker and the other amp into the left speaker, pump a test tone through both, and match levels so that the phantom stereo image is exactly between the two speakers from the listening position. This isn't as precise as a voltmeter, of course, but it should balance the outputs below the threshold of perception at least.

Both amps should be driven in their linear range, too. For these two amps, exceeding that threshold would probably drive humans out of the house, but it bears repeating given that lots of amps that attract favorable comment are far lower in power.

Then, the selection of the amps needs to be unknown to the listener, which isn't that easy to do with amps without some specific switching apparatus that is blindly controlled. But for humans to be able to claim that they hear a difference, that's what it takes. If the listener knows which amp is under test, the evaluation will not and cannot be based solely on what they hear, and they should not trust their perceptions. The same comparison next week might go the other way for reasons exogenous to the amps themselves.

The placebo effect can be real, but it is not repeatable because uncontrollable expectation bias sets in immediately. For me, I expect one amp to sound better, but then I discount that expectation consciously, meaning that now I have two types of expectation bias fighting each other with no way to arbitrate their effect. We cannot transcend those biases. It does not mean we end up with something that is no good, it means that the reason we had for thinking something was better isn't trustworthy or repeatable, and six months from now we might go the other way. (Leading to such earnestly held fantasies as, "I again listened to an AHB and compared it with my Bryston, and, wow!, Benchmark apparently made some changes and this time it blew me away!")

Personally, spending money on the Next Great Amp seems to me an unproductive use of funds. (I'm assuming the current amp has sufficient power to be in its linear range even when driving our speakers during peaks, and that's perhaps a grander assumption than many realize.) I'd think there would be more potential gains with better speakers or, for those who still listen to analog media, better source transducers.

(As much as I admire Benchmark as a company--and I happily own a couple of their products--I run into the same mental issue when considering the AHB as an alternative to my far less expensive Buckeye amp.)

Rick "a reminder" Denney

 

[Angsty]

Don’t discount your own listening experiences with the AHB2. Sometimes an upgrade clicks with our ears and sometimes it does not. All the engineers and physicists in the world can put tons of effort into designing electronics along the best principles and measurements we have, but we can’t control for how the sound gets into your head, and for how you perceive it.

Subjective preference is real, valid, and appreciated, as long as we recognize it clearly as subjective.

I do think subjective preferences matter, especially when you are spending your own money to find what you like. I subjectively prefer my Bryston to my NAD even though I can't reliably tell them apart. So, the Bryston sits in my main system while the NAD awaits use.

The AHB2 is a high-performance amp that doesn't give much room to a competitor on any basis other than maximum power. Then, you can buy two. But that certainly does not keep a person from preferring another make/model of amp because lots of other real-world factors can come into play like fixed gain, input/output options, size, aesthetics, etc. The fixed gain can have a real-world impact on how an amp is perceived way beyond some other measured parameters like THD+N, distortion or output impedance.

I'm a Bryston guy - I'd rather have one 4B Cubed versus two AHB2 monoblocks, but that's just my preference.

 

[Sal1950]

Without a voltmeter, one can get pretty close by playing one amp into the right speaker and the other amp into the left speaker, pump a test tone through both, and match levels so that the phantom stereo image is exactly between the two speakers from the listening position. This isn't as precise as a voltmeter, of course, but it should balance the outputs below the threshold of perception at least.

There are a few tools that any audiophile should have in his drawer. One is a digital multimeter, available on ebay for under $10 delivered.
The other is a way to measure sound level, there are all sort of smartphone apps for this. I'm still using a 30 yo RadioShack meter of which there are also
a crapload available cheap on ebay for under $20

 

[dlaloum]

There are a few tools that any audiophile should have in his drawer. One is a digital multimeter, available on ebay for under $10 delivered.
The other is a way to measure sound level, there are all sort of smartphone apps for this. I'm still using a 30 yo RadioShack meter of which there are also
a crapload available cheap on ebay for under $20

I wonder how many of us still own and use that vintage Tandy/Radio Shack SPL meter!

Mine continues to provide sterling service when needed.

 

[rdenney]

I wonder how many of us still own and use that vintage Tandy/Radio Shack SPL meter!

Mine continues to provide sterling service when needed.

There’s an app for that.

Rick “at least as accurate as the original” Denney

 

[Sal1950]

There’s an app for that.

What's an app ?

 

[Angsty]

The ML333 was "recapped" about 4 years ago along with a major repair at the authorized service facility in LA. Its rated S/N is significantly less than the other two amplifiers. Maybe that is a clue.

I expected the AHB2's to sound better than the 4B3 based on the former's innovative technology, so my expectations did not play out as I had expected.

What innovative technology would have led to that expectation? Both are Class AB amplifiers.

 

[PGAMiami]

Sal, I think there is a market, but I wonder whether Benchmark would sell more amps to audiophiles if Siau made them look prettier.
A more powerful amp that looked prettier and still measured wonderfully well would be well-received, I imagine.
Still, I am NO businessman Maybe not a financial go-er?
Edit: yes, the current iteration has a certain rugged industrial functional charm, but in my opinion is in no way pretty. I have several

Cannot agree more. The technology is spectacular but the industrial design and marketing strategy is sub optimal. I compared a pair of AHB2s to my Constellation Centaur Mono, that without doubt were the most beautiful amps I owned. A week later I sold the Constellations. The Benchmark just sound better, no harshness at all, seemingly unlimited power, extremely detailed sound. And my room no longer heats up. The Benchmark are a true bargain, but they aren’t easy on the eyes!

 

[RichB]

Cannot agree more. The technology is spectacular but the industrial design and marketing strategy is sub optimal. I compared a pair of AHB2s to my Constellation Centaur Mono, that without doubt were the most beautiful amps I owned. A week later I sold the Constellations. The Benchmark just sound better, no harshness at all, seemingly unlimited power, extremely detailed sound. And my room no longer heats up. The Benchmark are a true bargain, but they aren’t easy on the eyes!

I like the look of the AHB2s found them to provide more apparent detail than the ATI6002 amps they replaced.
The AHB2s look like smaller, cuter, Parasounds.
I also appreciate the well implemented protection and clip indictors.

- Rich

 

[Sal1950]

The Benchmark are a true bargain, but they aren’t easy on the eyes!

Oh boy, sorry Mr Siau, but at $3500 for 100 wpc amp I find it difficult to call them a bargain.
Today there are any number of Purifi and Hypex based amps that measure and sound spectacular but sell for half or less that amount.
YMMV

 

[dlaloum]

Oh boy, sorry Mr Siau, but at $3500 for 100 wpc amp I find it difficult to call them a bargain.
Today there are any number of Purifi and Hypex based amps that measure and sound spectacular but sell for half or less that amount.
YMMV

I have a feeling the Trumpian Tariffs will work in Benchmarks favor... for US based consumers like yourself.

For those of us in the rest of the world.... things will most likely tilt in favor of other brands.

Has the Purifi & Hypex pricing been "Tariff adjusted" yet? - not sure what rate will apply to them, or whether it will category or manufacturing nationality based... could be as little as 15%...

Still the value equation is about to have a big fat thumb placed on the scales.

Speaking from an Australian perspective - we havn't seen anything shift either up or down - but then we have been paying a high premium for our gear for many decades (gear often costs double the US price here...).

 

[Sal1950]

I have a feeling the Trumpian Tariffs will work in Benchmarks favor... for US based consumers like yourself.

We'll see, I'm fine with it if it ever happens.
What they charge us, we charge them and vise versa.
That's only fair.

 

[Tom C]

We'll see, I'm fine with it if it ever happens.
What they charge us, we charge them and vise versa.
That's only fair.

Yah that’s right.

 

[Angsty]

I have a feeling the Trumpian Tariffs will work in Benchmarks favor... for US based consumers like yourself.

For those of us in the rest of the world.... things will most likely tilt in favor of other brands.

Has the Purifi & Hypex pricing been "Tariff adjusted" yet? - not sure what rate will apply to them, or whether it will category or manufacturing nationality based... could be as little as 15%...

Still the value equation is about to have a big fat thumb placed on the scales.

Speaking from an Australian perspective - we havn't seen anything shift either up or down - but then we have been paying a high premium for our gear for many decades (gear often costs double the US price here...).

I’m fairly certain that tariffs on imported components like capacitors and transistors will increase the domestic costs of the AHB2, as well. If you like ‘em, better get some before supply chain increases genuinely take hold.

 

[Panelhead]

The price of the AHB2 has already escalated. When I first decided that I needed one they were around 2300.00.
Some may be the change in client. They were a pro audio company. Sold some to audio fanatics. Now that has flipped.
Most recording studios and mastering shops are not usually worried with having SOTA gear.
At least in Nashville. There are a few, expensive gear, even cables. Most use active monitors. No need for an AHB2.

 

[Angsty]

The price of the AHB2 has already escalated. When I first decided that I needed one they were around 2300.00.
Some may be the change in client. They were a pro audio company. Sold some to audio fanatics. Now that has flipped.
Most recording studios and mastering shops are not usually worried with having SOTA gear.
At least in Nashville. There are a few, expensive gear, even cables. Most use active monitors. No need for an AHB2.

I’d certainly expect that Benchmark is following the path Bryston took many years ago - the better margins are on the audiophile side if sufficient volume can be sold.

 

[bigguyca]

The price of the AHB2 has already escalated. When I first decided that I needed one they were around 2300.00.
Some may be the change in client. They were a pro audio company. Sold some to audio fanatics. Now that has flipped.
Most recording studios and mastering shops are not usually worried with having SOTA gear.
At least in Nashville. There are a few, expensive gear, even cables. Most use active monitors. No need for an AHB2.

$2,995 was the initial price from my memory and what I can find online. All of the initial reviews, Stereophile, etc., listed $2,995 as the price. Please supply support for your $2,300 claim.

I've followed the AHB2 since before it was actually for sale.

 

[RichB]

$2,995 was the initial price from my memory and what I can find online. All of the initial reviews, Stereophile, etc., listed $2,995 as the price. Please supply support for your $2,300 claim.

I've followed the AHB2 since before it was actually for sale.

From the 2015 Stereophile review.

 

[bigguyca]

I’d certainly expect that Benchmark is following the path Bryston took many years ago - the better margins are on the audiophile side if sufficient volume can be sold.

Bryston is now a very different company. The original designers and owners are all gone, only the marketing guy, who runs the company, remains the last time I looked. It isn't clear who actually manufactures the Bryston equipment at present. This situation is quite different from Benchmark.

Before I adopted use of the AHB2's I used 4BSST2's which IMNVHO is the best amplifier Bryston has made. Bryston's, at least up through the units I have, were built like a tank with premium parts and of course a 20-year warranty. The schematics for most of the power amplifiers are available.

The Bryston power amplifiers are very interesting in that they have nested feedback, with a feedback loop around the output section with a closed loop gain of 3. Both the emitter and collector of the driver transistors are used to drive the output transistors. The input and voltage gain stages are both regulated with relatively high voltages. The AC power input has a DC blocking circuit. As with the AHB2, Brystons have several settings for the overall gain of the amplifier; two or three settings depending on the specific unit.

 

[Angsty]

@bigguyca - As I indicated earlier in the thread, I’m a Bryston guy. I have a resto-modded 4B-ST. Why did you replace the 4B-SST2 with a pair of AHB2s?