THX Acrhomatic Audio Amplifier / Benchmark AHB2

[RichB]

This is a good interview by Scott Wilkinson with Laurie Fincham, senior VP of audio research & development for THX, Ltd.,
The Benchmark AHB2 is the first incarnation of this technology. It forward feedback switching power supply amp that is light weight with very high signal to noise.

The Benchmark AHB2 specs are here:

SPECIFICATIONS

Output Power

1 kHz, < 0.0003 % THD+N
◦100 W/channel into 8 Ohms, both channels driven
◦130 W/channel into 6 Ohms, both channels driven
◦190 W/channel into 4 Ohms, both channels driven
◦240 W/channel into 3 Ohms, both channels driven
◦200 W Bridged Mono into 16 Ohms
◦380 W Bridged Mono into 8 Ohms
◦480 W Bridged Mono into 6 Ohms

SNR
◦132 dB A-weighted, Stereo Mode
◦135 dB A-weighted, Bridged Mono
◦130 dB Unweighted, 20 Hz to 20 kHz, Stereo Mode
◦133 dB Unweighted, 20 Hz to 20 kHz, Bridged Mono

THD+N

1 kHz, 80 kHz LPF, at full rated output into any rated load
◦< -118 dB (< 0.00013%) - Stereo Mode
◦< -118 dB (< 0.00013%) - Mono Mode

THD

1 kHz, 20 kHz LPF, at full rated output into any rated load
◦< -119 dB (< 0.00011%) - Stereo Mode
◦< -120 dB (< 0.00010%) - Mono Mode

Crosstalk
◦Better than -115 dB at 1 kHz
◦Better than -92 dB at 20 kHz

Frequency Response
◦Better than 0.1 Hz to 200 kHz, +0/-3 dB
◦-0.01 dB at 20 Hz, -0.17 dB at 20 kHz, 8-Ohm Load
◦-0.23 dB at 20 Hz, -0.32 dB at 20 kHz, 4-Ohm Load

Damping Factor
◦350 at 20 Hz, 8-Ohms
◦254 at 1 kHz, 8-Ohms
◦34 at 20 kHz, 8-Ohms
◦7 at 200 kHz, 8-Ohms

Maximum Audio Output Current
◦18 A per channel, both channels driven
◦18 A protection shut-down threshold

Input Sensitivity
◦Low-Gain = 22 dBu (9.8 Vrms), Gain = 9.2 dB
◦Mid-Gain = 14.2 dBu (4 Vrms), Gain = 17.0 dB
◦High-Gain = 8.2 dBu (2 Vrms), Gain = 23 dB
◦Use Mid-Gain or High-Gain settings for unbalanced inputs
◦Unbalanced inputs require RCA to XLRM adapter cables

Input Impedance
◦50 k Ohms, normal mode
◦1 M Ohm, common mode

Input CMRR
◦ 80 dB at 20 Hz, typical
◦ 80 dB at 1 kHz, typical
◦65 dB at 20 kHz, typical

Trigger I/O
◦ 12 VDC 200 mA current-limited output to trigger turn-on of remote devices
◦DC input for slaving to remote devices
◦Input responds to 3.3 V logic and higher, VIL = 1.26 V, VIH = 2.7 V
◦Absolute maximum input voltage = 30 VDC
◦Absolute minimum input voltage = -0.3 VDC
◦Input Impedance = 20 k Ohms

Dimensions

Non-rack-mount version:
◦ 11.04" W x 3.88" H x 9.34 " D - Including feet and binding posts
◦ 11.04" W x 3.47" H x 8.33 " D - Excluding feet and connectors
◦Faceplate height is 2RU

Rack-mount version:
◦19.00" W x 3.88" H x 10.62 " D - Including binding posts, handles and removable feet
◦19.00" W x 3.47" H x 8.33 " D - Excluding feet and connectors
◦9.09" rack depth, including binding posts, excluding cables
◦11" rack depth, including cables
◦Faceplate height is 2RU

Weight
◦12.5 lbs., 16 lbs. shipping - Non-rack-mount version
◦13.5 lbs., 17 lbs. shipping - Rack-mount version

I don't like the 1K power ratings but the Speakon connectors, XLR only inputs, and gain controls are interesting.
It seems a bit underpowered for $3K.

How about a review of this little beasty?

- Rich

 

[Irvrobinson]

If I were Benchmark I wouldn't submit it for a review. It'll be panned by the emotiva-and-crown-are-cheaper-per-watt crowd. Full-range speakers are the only high-end products acceptable here.

Anyway, I'm still annoyed with Benchmark over that ported-speakers-all-have-one-note-bass fiasco they started awhile back.

 

[AcuDefTechGuy]

If I were Benchmark I wouldn't submit it for a review. It'll be panned by the emotiva-and-crown-are-cheaper-per-watt crowd.

Forget Emotiva and Crown. What about this ATI AT1202 120 WPC x 2Ch amp for $600?

http://www.classicaudioparts.com/index.php/amplifiers/ati-at1202-two-channel-x-120-watt-amplifier-b-stock-120-v.html

Lexicon or Mark Levinson could turn this ATI amp into a $2.5K amp and call it a bargain compared to a $3K 100WPC amp.

 

[ski2xblack]

Cool engineering statement, but to me those specs seem like some sort of unicorn hunt, as they're all so far below audible thresholds I doubt any practical benefit. I mean, really, when it comes to being audibly transparent, an amp either is or it isn't. These amazing specs won't make it more transparent than transparent, will it? That's ridiculous. And it's not really that great in the power department.

I would take the ATI over the benchmark myself. Glad I got mine when I did, the 602 is a hundred bucks more than I paid.

 

[slipperybidness]

SMPS....I'll pass!

 

[gene]

Man the Santa belly laughs are a bit hard to stomach... Laurie looks like he want's to be somewhere else in much of the video.

The fear of crossover distortion in Class AB amps has been nullified over 20-30 years ago. It's really not an issue anymore with employment of quality transistors and good amp design. Notice how those statements weren't even qualified in the video.

Rail switching amps have also come a long way as you can see in my review of the Emotiva XPR-1. Measuring the switching point from low to high rail was almost undetectable and it happens at high power (>300 watts) so its unaudible. The XPR-1 runs cool to the touch regardless of how hard you drive it. So switching rails is nothing new here. It's been done and done well.

You can get pretty good results with SMPS supplies but they don't have much dynamic range at all as you can see in my test results for the IQ Audio amp I tested.

Some Questionable Claims:

• The SNR figures seem a bit too good to be true. 132dB SNR a-wt? At what power level, 100 watts? That would be 112dB at 1 watt which I've never seen any amp measure that quite.
• The distortion barely changes with output level. Really? I'd like to see an FFT of this amp at 1 watt and rated power.

I'd like to get one of these amps on my test bench to be sure, but I'm a bit skeptical about the claims. $3k for a 100wpc amp is a bit spendy but if it does everything that Laurie claims then it could be a pretty cool product.

 

[slipperybidness]

You can get pretty good results with SMPS supplies but they don't have much dynamic range at all as you can see in my test results for the IQ Audio amp I tested.

Agreed, but to me the cons of SMPS far outweigh the pros. Unregulated symmetrical DC power supply is by far the best approach to build an amp P/S.

SMPS are much more complex and thus more likely to fail, SMPS generate RF noise so that must be dealt with, and as you mentioned the lack of headroom.

But, I will concede that SMPS are much better now than they were in the past.

 

[slipperybidness]

Agreed, but to me the cons of SMPS far outweigh the pros. Unregulated symmetrical DC power supply is by far the best approach to build an amp P/S.

SMPS are much more complex and thus more likely to fail, SMPS generate RF noise so that must be dealt with, and as you mentioned the lack of headroom.

But, I will concede that SMPS are much better now than they were in the past.

I guess I should also make the less-cynical point of view.

The "best" method of amplification is pure class A. Yet, class A has it's own set of challenges, mostly heat (a real concern for a Texas summer!), weight, cost, and the silly inefficiency of class A.

But, I think the future of amplification will be class D and SMPS! Like it or not, that's where we are headed. The modern challenges are to overcome the downsides of these approaches and topologies.

I would suspect that when class AB hit the market, it was a similar situation. But, how many of us run true class A anymore? I'll bet 90% are class AB, 5% class A, and 5% class D, or somewhere in that general range.

Most of my stuff is class AB. I have a tube class A. I only run class D in my car's subs. As far as class D goes, I would probably be OK with buying either QSC or Crown due to the bullet-proof reliability and the excellent customer service.

 

[RichB]

I'd like to get one of these amps on my test bench to be sure, but I'm a bit skeptical about the claims. $3k for a 100wpc amp is a bit spendy but if it does everything that Laurie claims then it could be a pretty cool product.

If they don't want the amp on your bench, that speaks volumes.
Call me a conspiracy theorist but class-d measurements are hard to come-by.

- Rich