Benchmark AHB2 Amplifier

[PGA]

All below is using the Benchmark in mono on TAD R1s. It’s been a long while since I had a pure class A amp. Last one was the NRG Control 400 watt monos. Those were fantastic amps in their time in 1990. But they were room heaters, not very practical in Miami. And the last pair of Class D I had were the Bel Canto Ref 1000. But even that was 10 plus years ago. Most recently I had the fabulous sounding Constellation Centaur mono, very classic class AB. For me the treble sounds more natural on the Benchmark, and I hear more details with the vanishing noise floor. Bass slam is fine on both amps, same for dynamics, ease playing loud, plus they both sound great playing at low volume. But each Benchmark is $3000 and each Centaur is 9x that. For me both the Benchmark and Constellation were better than many other AB amps, including Levinson, Pass, MSB, Cello and Spectral. All of those are great at some things but not at everything. But as I said above, mileage may vary!

Regarding load sensitivity, given the regulated power supply on the Benchmark and the very sophisticated protection circuit, I would say they are a rather perfect voltage source into loads down to a couple ohms. When you over drive them they turn off. It’s very hard to overdrive them in mono. But that does not mean you may like them on every speaker as some speakers may sound better with a less perfect but synergistic output stage.

The articles on the Benchmark site are great explaining how these amps work and measure. They have almost no crossover distortion, like a great class A. And they have almost no noise or harmonic or intermodulation distortion. You will surely notice the absence of noise and distortion, but that doesn’t mean that it will surely sound better to you. For some, a little harmonic distortion is a good thing. And for some speakers a higher output impedance at some frequencies may be synergistic.

Kal, thoughts?

 

[Platypus20]

I’m running 2 of the AHB2s and a LA4, bi-amping a pair of Acarian Alon IVs, love them

 

[tmallin]

The Alon IV and the bit later V are among the best sounding dynamic speakers--based on repeated dealer auditions--I never owned. Of roughly the same vintage, the Aerial 10T is another one I found to sound great at dealers but never owned. I was never so taken with later models from Alon/Nola or Aerial.

If you have not already, experiment with tri-wiring the Alons with the Benchmark AHB2 amps in mono bridged mode. You might get yet-better sound.

 

[Platypus20]

I have them set so one amp runs the 2, 12” drivers in the sealed boxes and the second bi-wire to the open baffle mids and highs.
I tried them in mono and like them better this way

 

[Hear Here]

I’m running 2 of the AHB2s and a LA4, bi-amping a pair of Acarian Alon IVs, love them

Odd isn't it - the AHB2 was the biggest disappointment in all the amps I've ever bought!

Perhaps it was because my expectations were too high after a fellow Avantgarde owner was raving about his new find after previously owning many very exotic amps. The AHB2 was then very new and no worthwhile reviews and no local dealers, so I bought unheard from a dealer in Scotland - I live on the South Coast 400+ miles away. After having used SETs for a decade or so since moving to high sensitivity speakers, the Benchmark was drearily dull. It was an amplifier I was never inclined to wind up the volume - more to provide background music!

Kiss of death as far as I'm concerned, so I went on a 12 amp purchasing and dealer-loan spree to find something that provided the excitement that my exciting speakers needed. Class A, AB and D amps from Mark Levinson, GamuT, Micromega, Sugden, Lyngdorf, Accuphase, Bakoon, NAD, Valvet and others were in my system for at least a week. I was expecting a Class A to win out, but in the end I went for the relatively modest Purifi Eigentakt-based Class D NAD M33. No regrets and it offers so much more excitement and musical enjoyment than Benchmark, despite it being an all-on-one that many people still consider a compromise.

PS - I notice that I've previously contributed to this long-running thread, so ignore this is you've read all earlier posts. Certainly the Benchmark is accurate, dead quiet and has other admirable features. It's just a pity it doesn't excite the emotions!

 

[Platypus20]

Yes, very interesting, to me the Benchmarks driving the Alon IVs, is about perfect, the amp is very quiet, delivers everything I both wished for and expected from them. The 2 AHB2, a LA4 and a DAC3 HGC, was my retirement present to myself. I replaced a Conrad-Johnson MF 2300 (240 watt SS amp) and a Conrad—Johnson PF 2L preamp, I’d used them for 25+ years.

 

[shawnf]

I’m running 2 of the AHB2s and a LA4, bi-amping a pair of Acarian Alon IVs, love them

Hi! I am an AHB2 owner and was thinking of purchasing another unit to run in bridged mono. Then I saw your post about biamping.

Can you share and advise how you managed to achieve this? Like how to set up the connections, components used, etc?

FYI I have an MSB Premier DAC and using the built-in preamp into the AHB2. I am planning to test 2 units with a Wharfedale Aura 2 which is currently on loan. I have the SpeakON to Banana plug cable from Benchmark.

Thanks!

 

[tmallin]

In the years since its introduction, some, while acknowledging its matchless specs in terms of low noise and distortion combined with remarkable power output given its small and light form factor, have criticized the Benchmark AHB2's sonics by saying it is lacking in macro dynamic swings. I hear this, but I hear it differently and hear it as a plus for the Benchmark. The Benchmarks lack the overblown-sounding midbass of some other amps which can provide a sense of greater dynamic power. It also lacks the ultimate degree of "splash" on large transients which some interpret as a dynamic limitation. I think this "splash" is actually caused by a blast of slightly distorted sound in the higher frequencies. The Benchmark is ever precise, controlled, and clean, clean, clean, which amounts to "beautiful" sound in my book. Likewise, the Benchmark midbass is fully ample and certainly not lean in any way, just more controlled and defined/less distorted. This "uncovers" the Benchmark's lower bass, revealing more detail, definition, and power in the bottom two octaves.
Click to expand...

One very useful tweak of the Benchmark AHB2 Amp sound, which I think can ameliorate any objections to its sonic presentation is the use of AV Room Service Electronic Vibration Protectors ('EVPs) in place of the amp's stock feet. Why this simple change has a more profound effect on the Benchmark's sonics in my system than on other electronics, I do not know, but there it is. I suggest trying this if you have any reservations about the sound of the Benchmark amp (in my case, a pair of them, run in bridged mono mode).

Remove the two stock rear feet using a #2 Phillips or Pozidriv screwdriver. Replace them with 2-inch square HD (High Density) EVPs. Place them in the rear corners just inboard of the black casing--at the rear corners of and on the silvery bottom plate, in other words. Then center a third 2-inch square HD EVP along the front edge of the silvery bottom plate, just inboard of the front panel. There is no need to remove the two front stock feet of the amp.

That's it. Now see what you think of the sound. Many aspects of the sonic presentation seem yet better in my system, including dynamic headroom and dynamic swings. This is despite the fact that I was already using separate Bright Star Audio Little Rock isolating platforms beneath each amp.

The amps actually seem to be yet more unlimited in their power reserves with this tweak. Using the amps without this tweak with the Watkins Generation 4 speakers (as opposed to the Graham LS8/1s) I was occasionally aware of a bit of high-frequency transient crunch at high SPLs. When I heard this, I would just turn down the volume a notch and this problem would vanish. At first I thought this was just due to dynamic limitations of these rather-small Watkins speakers. But with this tweak, this problem vanished and the speakers play as loud as I want on any material without any apparent "crunch." The apparent frequency response with the Watkins speakers further smooths out when supported by EVPs, the stage expands in all directions, images are yet more focused, the bass further extends and warms a bit.

Unfortunately, this tweak is not as inexpensive as it used to be. When I purchased my EVPs, they were only $40 each. Now they are $119 each. Still, for owners of one or two of these amps, I regard using the EVPs as capable of producing a significant sonic improvement.

 

[Kal Rubinson]

Can you share and advise how you managed to achieve this? Like how to set up the connections, components used, etc?

Speaking for myself (and what is clearly explained in the user's manual), all you need to do, with the power off, is
1. Flip the MODE switch to MONO on each amp.
2. Connect an " SpeakON to Banana plug cable" to the BRIDGED MONO OUT jack on each amp.
3. Connect an XLR input cable to to the 1IN/MONO IN jack on each amp.
Connect each speaker cable to a speaker, power up and play.
FWIW, I don't think this is necessary for those speakers.

 

[tmallin]

Shawnf's question appears to me to be about how to bi-amp speakers with two Benchmark AHB2 amps. The Benchmark manual says:

"The 1&2 OUT NL4 jack can also be used for biamp applications. Use this jack with a four-pole cable to connect both output channels to the high and low drivers in a biamped 2-way speaker. "

Make sure that the SpeakOn connectors you have are the NL4 four-pole variety rather than the NL2. Then the speaker cable you use can be one which is capable of internally providing bi-wired or bi-amped connections. The Canare 4S-11 Benchmark used for its speaker cables is one such cable. While the Benchmark cable page only lists speaker cables with NL4 to NL4 connections, I'm sure Benchmark could provide you with cables terminated with an NL4 SpeakOn at the amp end and two sets of locking bananas at the other end. These cables could then be used for bi-amp or bi-wire connections.

Alternatively, you could use both the SpeakOn and binding post connections of each of two Benchmark amps to bi-amp your speakers.

Kal may well be correct that neither bi-amp nor bridged operation of the Benchmark amps is "necessary" for your speakers. In my experience with these amps, however, bridged operation usually sounds better in that it provides more headroom with at least equally excellent specs and sonics. That greater headroom translates to yet cleaner, more dynamically alive sound at louder SPLs. Of course, if you listen at SPLs which rarely exceed 80 dB or so and don't listen to much orchestral/choral power music, electronic music, or hard rock, you won't need the extra power with any reasonably sensitive speakers.

I have never tried bi-amping with my two Benchmark AHB2's.

 

[Kal Rubinson]

Shawnf's question appears to me to be about how to bi-amp speakers with two Benchmark AHB2 amps.

I responded to his statement: "Hi! I am an AHB2 owner and was thinking of purchasing another unit to run in bridged mono." I didn't read the comments about bi-amping.

Kal may well be correct that neither bi-amp nor bridged operation of the Benchmark amps is "necessary" for your speakers.

Necessary may be subjective in a sense because neither bi-amping or bridging is really required for a functioning system. I do agree that having that the extra headroom gained from bridging can be useful but I have reservations about (passive) bi-amping providing much of it.

 

[shawnf]

Thanks @Kal Rubinson and @tmallin

Will be ordering a couple of cables from Benchmark to test

 

[steve59]

Having never tried the Benchmark I can't comment on them specifically. I've used dozens of different amps, many int's and my experience has been amps with average power ratings, likely even the AHB2 can prevent speakers from sounding their best. I always thought a watt is a watt is a watt, but low sensitivity speakers can cause amps with similar ratings to sound differently.