Benchmark AHB2 amplifier - what to expect?

Thanks, Randy. I forgot about their 30 day trial policy. Now, it will take some skills to convince my wife it is absolutely necessary.

Mapman, thanks.  I know it was a while ago, but how would you assess trebles?  Was it an "airy" presentation?  My Rowland is a little bit on the darkish side according to one editorial review.  AHB2 might be good step-up for me from entry level class D, not to mention that is also very efficient with idle power of only 20W total and 0.5W at standby.  I also like the fact that it utilizes quiet SMPS  since it is efficient, plus line/load regulated and not sensitive to DC on mains (no transformer buzzing etc).

Mapman, that is what I suspected - newer class D amps use either Hypex or Pascal modules.

Randy, I suggested, that it is the very last moment we can buy something like that, since we're retiring in May.  I also stressed out benefit of additional amplifier to make second system (Paradigm Studio/60 v2, Benchmark DAC1, Rowland 102).  SHE SAID YES!!! and I placed the order a moment ago.  With 30 day free trial (when ordered directly from Benchmark) I don't risk anything.

Willemj, It is combination of class AB and class H, where supply voltage is modulated according to amplitude of the input signal in order to reduce wasted power.  I wouldn't mind good class D, but Benchmark AHB2 got Stereophile 2017 recommended component class A and has great reviews everywhere else (I'm already tired from reading reviews).

Thank you all.  I will post small review.

Aberyclark, I sure will, but it will only be my impression, coming from entry level class D.  There are more experienced people to write reviews.  Also, remember that I'm not looking for "warm" sound.

I don't like too warm, because that, to me implies a shelved down presence region and recessed high end.

Not only that.  According to technical director of Benchmark Media John Siau, overly warm sound can make instruments with complex overtones, like piano, to sound like out of tune.

Thank you Mapman.  One of my resolutions is to spend much more time with music (and perhaps little dance) and much less with TV.

John Siau said that warm sound is great for voice or guitar but bad for instruments that have more complex harmonic structures than simple overtones.

His exact quote:

Personally, I do not like what warm sounding equipment does to the sound of a piano. Warmth is wonderful on vocals, guitars and certain instruments, but it beats against the streched overtones of a piano. The overtones in a piano occur at slightly higher than harmonic ratios, and these create beat notes with the exact integer ratios produced by electronic equipment (and speakers). Too much harmonic distortion will make a piano sound out of tune.

When amp sounds bright or warm it means that it is adding own harmonics to the music.  Slightly warm amp might be nice to shield against bright sounding records, but many people made a quest of finding the warmest sounding gear, warmth being treated as a virtue - the more the better.  I prefer an amp that doesn't have character of its own.

Toetapaudio, thank you for the info. I will keep it in mind. SST Ampzilla Monoblocks are too expensive for me, but perhaps Son of Ampzilla II is worth listening to, if Benchmark doesn’t work for me. I suspect that it has a lot to do with amp-speaker synergy. Many reviewers praised imaging of AHB2 including depth of the soundstage while one guy stated that it was the worst imaging he ever heard - completely flat with no depth whatsoever. He even said that his 10 year old son called it awful sounding. How this could be? I can understand that AHB2, being very revealing, can mercilessly uncover shortcomings of the system or recording, but I don’t know how imaging can be so bad, while it is supposedly great with another amplifier.

On the other hand nothing surprises me after reading reviews of electric toothbrush on Amazon. One guy wrote that toothbrush is no good and gave it one star, the reason being that it stopped working after it was bitten by his dog. Perhaps there is not a lot of idiots, but they must be strategically placed, because I encounter one every single day.

Viber6, I got AHB2 on Friday and so far I like what I hear.  It started with recessed midrange, then sharp midrange, then softer midrange with extended highs.  Bass got deeper.  It sounds like if I would add sub to my older class D.  What shall I expect in the future?  How did it change in 60 days?  My guess is that it will become a little bit more open and refined.  Even now, it is far better than previous class D amp.  Veil on the treble is gone, both extensions improved, better imaging, incredible bass control and slam, nice and natural attack and decay.
Bryston is great amp (I read reviews),  but it costs more and doesn't have as high WAF (wife acceptance factor), since AHB2 makes pair with DAC3 HGC.  I bought new since it is hard to find used one, while new registered original owner gets 5 year warranty (and 30 day trial).

Viber6, It is strange that Benchmark specified 18A max current with 18A current protection threshold and both channels driven, while now they specify 29A at 1ohm, both channels driven.  Perhaps they improved something or is it just specsmanship?

Douglas, Thank you for a fine review.  I had similar problems with position of connectors.  My speaker cable wires are thick and don't bend 90deg.  It forces them to go down on both sides of XLR input plug.  Since wire on the outside of the plug encroaches on both 12V  1/8" connectors I had to force the 1/8" plug in (almost impossible).

I find performance of the bass phenomenal.  There are low notes that were completely missing before (why?), not to mention better dynamics.  That is really strange since my speakers are benign load (6ohm, 3.6ohm min) while Rowland 102 has 5Hz -3dB limit and DF=4000 at low frequencies.  AHB2 has 0.1Hz -3dB limit and DF=350 at 20Hz.  I also find improved overall clarity from bass to high treble.  Unfortunately some recordings still sound veiled while some others now sound thin (veiled before).  It sounds wonderful on fine records but also ruthlessly reveals shortcomings of the poor recordings.  Imaging is improved, both width and depth. 

I played drum solo on Chesky Records test CD and was absolutely stunned.  It sounded like live set of drums playing in my living room.  Bass control is better than before and the transients are fantastic. Pink Floyd's "Hey You" shook my windows and made me jump at the moment when drums and bass came in.  Also sibilants are strong, but very clean, while upper trebles are delicate without brightness.  Violins "sing" and trumpets have wonderful "bite".  Shirley Horn "You won't forget me" title song with Miles Davis solo sounds great.  Same for "It had to be you" with Brandford Marsalis solo.

I put my ear, as close as I could, to the tweeter and it was completely silent.  Heat sinks get very warm when playing at high level for extended time, but stay lukewarm at comfortable listening levels.  So far AHB2 has only 25 hours of play time, but I expect further improvements to be subtle.  To your suggestion about incorporating pink LED I have to say NO (I was awake).

I encountered strange problem at the beginning.  My remote stopped working.  I tried it with different sets of batteries.  I unplugged AHB2 and DAC3 to no avail.  After about 20 min it started working again by itself.  I thought, that since power timer on AHB2 was set to 40min it could've turn off DAC3 since it works both ways, but now I cannot repeat it - it turns on fine in the morning.  I hope it was just a fluke.  I'm going to disable this timer anyway (don't need it).

Randy, you mean my clumsy attempt to write review? Yes it was in comparison to Rowland 102, but it is likely not very useful, since Rowland 102 is based on old, first generation of Icepower modules. I can only say that AHB2 sounds wonderful to me and it is getting better in all respects every day, but again it means nothing taking into consideration my limited experience. Rowland was a good amp (I keep it for the second system), but AHB2 is outstanding.

I found interesting discussion on Audioasylum :
http://https//www.audioasylum.com/messages/amp/205426/review-benchmark-ahb2-with-avantgarde-speakers-what-a-disappointment

OP calls AHB2 a big disappointment in comparison to his SET amp, while in follow up discussion another person has completely different view. At one point John Siau, a lead engineer at Benchmark, explains why opinions can be so different.

I solved the problem with my remote. Receiving diode in DAC3 had one pin poorly soldered. This pin connects to ground plane that sinks a lot of heat. It looked like soldered by somebody who doesn’t have any experience (or is blind). I fixed it to avoid shipping it back and forth, but I would expect better from Benchmark. The problem is that almost everything else is SMT - a well controlled process, but hand soldering depends on the skill of a person. RCA was famous for cold solder joints in their TVs (I had one with two cold joints), because it was most likely assembled by cheap unskilled labor.

I appears that link above doesn't work, not to mention very long discussion.  Let me show quotes from original post and two responses.

OP:

I don't pretend to be a professional reviewer (in fact this is the first time I've been moved to review any equipment), so can't explain exactly the differences, but it was akin to listening to a live acoustic performance versus listening to music through loudspeakers. The difference was not slight - it was dramatic. There is no "tingle factor" and no goose-bumps when listening with the Benchmark. If anyone says that the Benchmark is more accurate - frankly I don't care - I listen to music with my ears, not an oscilloscope! It was dull and lifeless by comparison. If you listen to live music there's inevitably background noise (you're sharing the auditorium with other people) and the acoustics are possibly not as good as a recording studio, but despite all the drawbacks, live music is so much more exciting to listen to. Similarly with the valve amps, an evening listening to music is thoroughly enjoyable. With the Benchmark it was little better than loud background music. Furthermore, the inclination was to turn down the volume of the Benchmark and turn up the SETs - inaccuracies, slight background noise and all! Music should be a thrilling experience and the Benchmark sadly doesn't offer thrills.

Response1 (John Siau):

Peter,

This is John Siau, VP of Benchmark.

Thanks for taking the time to document your experience with the Benchmark AHB2.

The AHB2 is well suited to use with high-efficiency speakers. The low noise allows noise-free operation with very high efficiency speakers.

Of equal importance, the AHB2 virtually eliminates the zero-crossing distortion that is normally produced conventional Class AB push-pull output stages. This is especially important for high efficiency speakers because the amplifier will spend so much time in low power region where crossover distortion can become most audible. The AHB2 behaves like a Class-A amplifier in that it is free from this very objectionable form of distortion.

But the AHB2 isn't for everyone. If you prefer an amplifier that enhances your listening experience then the AHB2 is not for you.

Your SET amplifier is specifically intended to add the euphonic qualities produced by the single-ended tube topology. This specific character is produced by the unique non-linearities that are characteristic of single-ended tube topology. The SET topology provides significant coloring of the music in a way that many people enjoy. If this is what you prefer, then you will be very unhappy with most other power amplifiers.

The AHB2 and SET amplifiers are on the very opposite end of the spectrum. You are completely correct when you say that the difference is dramatic.

The AHB2 is a much different listening experience. In contrast to an SET amplifier, the AHB2 is designed to be virtually distortion-free. The output of the AHB2 will sound exactly like the input. The AHB2 will not enhance or improve what goes in.

Please understand that this is a mater of taste. Many people enjoy the coloration produced by SET amplifiers.

Amplifiers can fall into three categories:

1) Amplifiers that add nothing to the audio
2) Amplifiers that add musically-disturbing distortion
3) Amplifiers that add musically pleasing coloration

The AHB2 falls into category 1, your SET amplifier falls into category 3.

Technically "coloration" is distortion but I think the word "distortion" gives a completely misleading description of something that may actually enhance the sound.

Again, it comes down to a matter of preference.

Response 2:

My experience with the Benchmark AHB2 driving sensitive speakers is somewhat different. In my current setup with Benchmark DAC2 HGC/AHB2, I am driving a pair of Klipschorns with a 105 dB sensitivity so in that sense they would be comparable to the Avantgarde speakers.

In my 25 years of of experience with mostly tube amplifiers of all sorts, I have never come across a more emotionally involving amplifier than the AHB2. It is exactly because it doesn't "interpret" the music by adding coloration or any artificial sense of ambience or reverberation that it is so fascinating to listen to. The AHB2's ability to reproduce the timbre and texture of acoustic instruments is beyond anything I have experienced before - just listen to brass or woodwind! - and the precision with which it reveals the actual acoustic properties of the recording venue, whether it be a small café or a concert hall, is second to none. At least to my ears. I think what captured my attention from the very first instant was how honest and genuine the sound is. If it is in the recording, it is there, otherwise not.

This amplifier keeps me on the edge of my seat in excitement and anticipation even with recordings that I have known for years and not thought very highly of, so in my view it is the very antithesis of boring. I don't remember having ever been so moved by reproduced music as with this Benchmark combo. FYI, I almost exclusively listen to classical music and much of it in hi-rez, but I have to say that well-recorded CDs are also much more enjoyable and listenable now than before.

Karsten