Benchmark Media Systems AHB2 power amplifier Associated Equipment

Sidebar 2: Associated Equipment

Manhattan System
Digital Sources: Sony XA-5400ES SACD/CD player, Oppo Digital BDP-105 universal BD player, Baetis XR2 PC-based music server, Benchmark DAC2 HGC and exaSound e28 D/A processors. QNAP TS569L NAS.
Preamplifier: Audio Research MP1 (multichannel).
Power Amplifiers: McIntosh MC303, NAD M22, Parasound Halo A 31.
Loudspeakers: Bowers & Wilkins 800 Diamond.
Cables: Digital: AudioQuest Vodka (HDMI) & Carbon (USB), Black Cat Veloce, van den Hul Flat 180 (HDMI). Analog: AudioQuest Earth/DBS balanced. Speaker: AudioQuest Oak/DBS biwire. AC: AudioQuest NRG-10, JPS Aluminata.
Accessories: Environmental Potentials EP-2450 power conditioner, CyberPower 850PFCLCD AC filter (supplied with Baetis server).

Connecticut System
Digital Sources: Oppo Digital BDP-103 universal BD player; Mac mini server running Boot Camped Windows 7, JRiver Media Center; miniDSP U-DAC8 DAC with UpTone Audio USB Regen USB repeater.
Preamplification: Marantz AV8801 preamplifier-processor.
Power Amplifier: Bryston 9BSST2.
Loudspeakers: Monitor Audio Silver 8.
Cables: Interconnect: AudioQuest Vodka (HDMI), Kubala-Sosna Anticipation (RCA) & Fascination (XLR). Speaker: Kubala-Sosna Anticipation & Fascination. AC: Kubala-Sosna Emotion.
Accessories: Brickwall Series-Mode 8R15AUD surge suppressor.—Kalman Rubinson

Benchmark Media Systems, Inc.
203 E. Hampton Place, Suite 2
Syracuse, NY 13206-1633
(800) 262-4675

eriks's picture

Nice review, but I'm still trying to get my head around a single person liking both Monitor Audio Silver series speakers as well as B&W 800 series speakers. Maybe B&W has changed much in the last 5 years. Also might be nice to add the MA Silvers to the "Associated Equipment" list. Now that I think about it, I have only heard B&W's high end played by Krell equipment when my buddy Dan was still in charge. I may need to reset my expectations of the brand now.

John Atkinson's picture
eriks wrote:
Also might be nice to add the MA Silvers to the "Associated Equipment" list.

It's always been there: look under the "Connecticut System" subhead.

John Atkinson
Editor, Stereophile

eriks's picture

Didn't realize the two were separated! Makes more sense though.

Kal Rubinson's picture

This helps to minimize any corrupting interactions between them.

HammerSandwich's picture

This is one heck of an amplifier!

"However, I was surprised to find that the S/N decreased slightly when the amplifier was very hot."

JA, I believe you have (re-)discovered Johnson noise.

John Atkinson's picture
HammerSandwich wrote:
JA, I believe you have (re-)discovered Johnson noise.


Seriously, the rise in the noisefloor, though small, was a little greater than I was expecting.

John Atkinson
Editor, Stereophile

billyb's picture

Great article! Thank you for reviewing this amplifier and testing it so thoroughly. I wish more equipment could spec out so well. As this highlights the issue of measurements vs subjective listening, would you consider dispatching this amplifier for a second opinion? Would one of the other writers at Stereophile care to listen? Perhaps Mr. Dudley or Reichert could give their impressions since they have different equipment preferences? It would be fascinating to juxtapose viewpoints on this amplifier.

dce22's picture

This amp is designed to show good THD+N on the AP test you can't correlate this measurements to the other amps tests in stereophile because the amp has no gain it puts AP generator/analyser in the low distortion field if you loopback AP2 you will see that from 10-500mvRMS has 0.015-0.0004 THD+N if you add 23db gain to that line the amp that has no distorion has to have THDvsPower graph line from 0.003-0.0003 downward slope strait line from 100mW to 30Watts then flatten's out toward 100 Watt on 80kHz bandwidth, if put the analyser in 20kHz bandwidth the line will be lower but still the same shape like this

as is measured on a class a amp with lower distortion then AHB2 and when you crank the volume control on the pre-amp to compensate for the low gain you will amplify the noise of the DAC or Phono-pre up to levels of the other amps so low noise in the AHB2 is just red herring if you lower the designed gain of any amp the noise gets lower as well.

PS. To John Atkinson you cant measure AES48 compliant device's noise by shorting it to the GND you will pickup noise from the enclosure, you need to short out the signal wires or put a resistor between them.

Ishmael's picture

You might have a good point in there somewhere, but the use of punctuation would sure help us decipher it. Did you hammer out your comment on a vintage cell phone or something?

dce22's picture

My apologies im always not very good at this grammar... today :)

AHB2 is a excellent amp you just can't look at the THD+N graph and directly compare to the other amps with "normal" gain structure.

elvisizer's picture

the ahb2 is not "designed to show good THD+N on the AP test". It's designed to work with professional line levels, which allow lower noise and distortion because the amp has lower gain.
If your equipment doesn't support professional levels, you can switch the ahb into higher gain mode.
there's nothing shady going on here, you just don't understand the design.

eriks's picture

Hi Stereophile,

This isn't necessarily directed at Benchmark, but I would really like to see that Stereophile will be publishing THD+N at 1 watt instead of at full power. Of course, it IS included in the charts, but I think reporting this as it's own number would go a long way to improving the quality of amplifiers instead of the power of amplifiers. Even if we set a target for 2017, I think it would be a good improvement for the 21st century.



johnf's picture

Will M22 be reviewed soon?

dumbo's picture

As a current owner of a few DIY Hypex NC400 amplifiers I see some of the measurements of this Benchmark amp looking very similar to what has been seen in the Hypex amp/smps modules in terms of low distortion figures. Given that both units use an SMPS power supply I wonder how different the two units would sound from one another. Or more appropriately, how little sound signature each of the two amps impose on the original source material.

There are many folks who claim that Class D amps sound very flat and lifeless (I don’t agree) but is this claim due to the use of an SMPS or more to do with how a Class D amp works compared to their Class A/B brothers?

I dont think Stereophile would ever measure a Hypex NC400 amp given its DIY status but it would be very interesting to see a comparison of this benchmark unit which appears to be well liked by the reviewer up against the Hypex offering. Both units would fit within the criteria of being light weight, quite powerful and fairly inexpensive. Maybe the reviewer could consider one of the Hypex units in his search for a replacement amp which meets his needs.

If measuring a DIY Amp against an OEM would burn too many bridges for Stereophile then I think another alternative would be to put the Merrill Audio Veritas on the test bench instead as it should be just as impressive in terms of measured performance.

pablolie's picture

I had both poweramps in and compared them for over a month. In the end I picked the NAD M22. It just seemed more *fun*, seemed to add some sparkle. Mind you, it was of course extremely close, and sometimes I thought I was just imagining it all. But during extended listening I kept thinking I was having more fun listening to the M22, there seemed to be additional extension and a nano-ounce of extra clarity. BTW the NAD M22 has built-in Hypex Ncores, not a DIY, and supposedly NAD adds some tweaks to the design.

Associated equipment was
Source: Benchmark DAC2HGC (I feed it via Squeezebox Touch, library for more critical listening is FLAC)
Speakers: Totem Element Fire and also KEF LS50.

PS: It's also worth noting that the $12k Theta Digital Prometheus -which received much praise from Stereophile ("measured performance of Theta Digital's Prometheus is superb")- is also based on a Hypex Ncore design.

johnny p.'s picture

If Kal says he can 'hear new details in his old amp', he at least owes us an update. Say in a few months - to see if the details were retained.

TJ's picture

Kal, it's reasonable that the AHB2 could be a better match with one set of speakers than another. However it seems puzzling that once you heard a mismatch with the Monitors, you could then identify a sound problem with this amp on the B+Ws, but only on one recording. How would one know which playback is more faithful to the original recording, the AHB2 or collectively the other amps chosen for comparison? Is it possible that the nice "bell-like" quality of her voice on the other amps could reflect some coloration that's cancelled in the AHB2 circuitry?

RaimondAudio's picture

Measurements were made with what gain?

hifiluver's picture

astonishingly good measurements. good luck benchmark. real cutting edge stuff. you deserve all the success.

JRT's picture

On the measurements page, the caption under figure one mentions red colored curves twice, while there is only one red curve, and does not mention the green colored curve at all. I suspect that the green colored curve is the one with the 2_Ohm load.

Typos happen. Thank you for the measurements.

BTW, I am surprised that I have not noticed that before, because I have probably looked at this webpage more than a dozen times since it was first posted more than 5 years ago.