Benchmark AHB2 vs NAD M22 (Hypex) with Very High Sensitivity Speakers
Ok lets get my desires and biases out of the way first:
1. I have made it no secret around here that I am high sensitivity speaker fan and I love the sound of my Avantgarde Trio Omega speakers with 109db sensitivity (among the highest out there).
2. I am well aware that pre-amp and amplifier gain structure can result in CRAZY amounts of hiss from the speakers if you don't setup things correctly.
3. I want NO hiss out of the amplifier and NO hiss out of a pre-amp circuitry in order to get baseline room as quiet as possible.
4. I want the NAD M22 Hypex to "win" because I just bought 3 other NAD M27's for surround duties and having a matching set looks pretty cool.
5. Benchmark's crazy good stats (even compared to Hypex modules) swayed me to go ahead and try it. The adjustable gain along with Speakon connectors were a plus. Finally an amplifier that is geared to audiophiles AND pros that also has a 12v trigger. Nice rack mount version that isn't more expensive and doesn't require extra kits of rack ears.
6. I figured both are nice for their highly efficient use of power. Both of these are better in this regard than the Pass Labs Class A amplifier I was using before
7. I won't go over the stats and details of the manufacturer pages here since you can pull that crap up yourself including all the stuff from the Hypex Ncore webpage.
8. All this stuff is hooked up using a crossover of 150hz due to the nature of my speakers and my massive subwoofers (on a Lab gruppen amp) that are doing their own job. Therefore I can't assess the "Bass response" of the amplifiers very well in this setup. Suffice it to say that the Lab Gruppen PLM is an epic beast.
9. This is all running music out of my Marantz 8801 pre-pro which has mediocre output noise performance which is apparently being "fixed" in the 8802. Yes, yes, I know I am crazy using a marantz with this setup... a DAC with gain would be a purist approach. I double duty this system for home theater ... and the marantz lacks a post-crossover digital output for an external dac to workout in this setup.
10. Keep in mind the noise in my room in the quiet of night is around 20db but essentially unmeasurable without VERY expensive stuff.
For starters, I wanted to actually blind A/B these things... unfortunately this was not easily possible due to the significantly different gain's on these amps. The Benchmark has a 22dbu gain and the NAD has a consumer level gain of 26db. With the NAD, I have to use a 20db XLR PAD between the preamp and the amp. The Pre-amp set my speaker levels to zero gain adjustment with the NAD using the speaker calibration. With the benchmark at 22dbu, I did not need an XLR pad and the Marantz set the gain at 7db+ for my main speakers.
Ok so here we go... I am going to stay as objective about my subjectivism as possible.
Noise floor: the Benchmark blows away ANYTHING. At 1m, with no source connected, I could hear no hiss from these speakers. Nothing, including the NAD or the Pass Labs product could do this. To say these speakers are noise magnifiers is the understatement of the year. My Crown XLS amps (with no preamp connected) have hiss so loud that they would unbearable in any usage. The "all amps sound the same" crowd can go F*** themself. As far as noise floor goes, the Benchmark can't be beat. I can hear the hiss with my ear within a foot of the tweeter... but at 14 feet away listening position, you hear nothing.
Just for the hell of it, I turned the benchmark's gain setting to 14dbu (louder)... this was SURE to worsen the hiss and make this totally rigged against the benchmark, right? First with the pre-amp off, I again literally had to be within 1 foot of the tweeter to hear hiss. With the Pre-pro on, I could now hear the subtle hiss of the Marantz 8801 more clearly.
I went back to the NAD just to be sure I wasn't delusional before... nope... the NAD even has a hum from the midrange driver that is audible at the sitting position. The Benchmark had zero midrange hum even with the ear to the speaker.
Ok so clear winner in the noise floor department, the Benchmark AHB2... best amp I have personally ever heard in this regard. The measurements and John Siau's predictions based on his calculations in his emails to be did not lie!
This does not mean the NAD is a bad choice... for the vast majority of folks whose speaker sensitivity likely does not exceed 100db, the NAD's hiss/noise floor is perfectly good. Most would need an ear to the tweeter to hear any hiss at all.
I am simply saying that for very high efficiency speakers, the AHB2's adjustable gain stage coupled with the baseline low noise floor creates a perfect blend that no other solid state amp has accomplished with large spherical horns.
Ok so how do they actually sound? The honest to God truth is that I don't think I can definitively tell the difference in any other characteristics. I listened to the same song for days before this amp came in so I could get a sense of the NAD M22 first.
Both have absolutely neutral sound with no discernible differences in overall characteristics for me. The primary difference being that the noise floor on the Benchmark is better and inaudible whereas the NAD is still audible during silent passages or between tracks. The benchmark is neither "harsh" nor "warm", descriptions used in amplifier aficionado parlance.
For users of high efficiency horns, The Benchmark is a seriously kick butt solid state product! This thing has a 30day return policy from the manufacturer website so I would strongly suggest getting one from there to check it out.
All things considered and their equivalent price... I would says the Benchmark is the best amp I have ever used. For my surround channels, the NAD M27 is a much better price point and perfect for my surrounds that are only 90db sensitivity.