Review and Measurements of Benchmark AHB2 Amp

[Sonnie]

I did not see any mention of this when I searched, but search could have missed it I suppose.

Is there any particular reason you did the measurements using the 9.6v setting on the amp?

 

[RichB]

I did not see any mention of this when I searched, but search could have missed it I suppose.

Is there any particular reason you did the measurements using the 9.6v setting on the amp?

I recall reading somewhere that you loose about 3 dB of SINAD going to AHB2 high gain mode. I have not noticed any difference between AHB2 high/low gain in sound quality or audible noise.

For my main system, I use the AHB2s for the FR/FL in low gain mode driven by the LA4.
LA4 input 1 is the Oppo UDP-205 XLR dac out (Fixed volume) with the LA4 providing volume control (the AHB2s in low gain).
LA4 input 2 is the Emotiva RMC-1 (variable volume) with the LA4 with fixed gain.

Do you still have your AHB2s?

- Rich

 

[Billy Budapest]

In the other thread, Benchmark answered my question

Which thread? There are a lot of AHB2 threads!

 

[misterdog]

I recall reading somewhere that you loose about 3 dB of SINAD going to AHB2 high gain mode.

https://www.audiosciencereview.com/...-to-hypex-nc400-audio-measurements-png.26579/

Page 1.

 

[amper42]

https://www.audiosciencereview.com/...-to-hypex-nc400-audio-measurements-png.26579/

Page 1.

And you loose another 3dB if you use banana plugs. Pretty soon you're within range of the Purifi.

 

[RichB]

And you loose another 3dB if you use banana plugs. Pretty soon you're within range of the Purifi.

Oh dear, I use these locking banana plugs:

Home

Angled Locking Stacking Banana Plug with Dual Set Screws Poly Shell and Insulated Thumbscrew 2 PairThese locking, expanding banana plug connectors are manufactured with color-coded polycarbonate shells for quick polarity identification and protection from possible short-circuiting contact. The...

www.parts-express.com

I bought some Neutrik NL2 SpeakON connectors but they were a pain to put together. Maybe someday...

- Rich

 

[Sonnie]

Oh dear, I use these locking banana plugs:

Home

Angled Locking Stacking Banana Plug with Dual Set Screws Poly Shell and Insulated Thumbscrew 2 PairThese locking, expanding banana plug connectors are manufactured with color-coded polycarbonate shells for quick polarity identification and protection from possible short-circuiting contact. The...

www.parts-express.com

I bought some Neutrik NL2 SpeakON connectors but they were a pain to put together. Maybe someday...

- Rich

I have the Speakon cables from Benchmark.

John Siau did make a fair argument in response to my question today that the unit will perform better with sources using higher voltage levels, such as in pro audio.

However, Amir also measured the unit at other gain settings and the difference was insignificant (all of the measurements are below the audible threshold).

 

[elvisizer]

Is it make more sense to use -10 db in this case?

if the ahb2's aren't already in low gain mode it would make more sense to switch to low gain on there than to attenuate -10 at the dac2 output. if you're already at low gain on the ahb2's and it's still too loud and you want to go higher on the dac2's volume control, then do the -10.

 

[Sonnie]

I recall reading somewhere that you loose about 3 dB of SINAD going to AHB2 high gain mode. I have not noticed any difference between AHB2 high/low gain in sound quality or audible noise.

For my main system, I use the AHB2s for the FR/FL in low gain mode driven by the LA4.
LA4 input 1 is the Oppo UDP-205 XLR dac out (Fixed volume) with the LA4 providing volume control (the AHB2s in low gain).
LA4 input 2 is the Emotiva RMC-1 (variable volume) with the LA4 with fixed gain.

Do you still have your AHB2s?

- Rich

Yes... still have them. Not using the right now... using the Sanders Magtech. I'll probably be selling the AHB2's shortly. Great amps, just not quite what I'm looking for to power the 15A's... as you already know.

 

[Spocko]

And you loose another 3dB if you use banana plugs. Pretty soon you're within range of the Purifi.

My AHB2 will be receiving SINAD challenged but DSP optimized signals from my Trinnov ST2 so arguably, I've paid extra to be just behind the Denon X3600H - this is what we Audio Adventurers call shabby chic: match best in class performance with a curio product and pray that the whole is greater than the sum of its parts!

For my next trick shabby chic project, Perlisten speakers matched to the Radio Shack Realistic Optimus STAV-3670 Receiver with Dolby Surround - resurrecting the magic with perfect directivity speakers See in this image it says "Professional Series" which means a higher level of performance during a time before ASR, this was a stamp of approval you could trust!

 

[Sonnie]

My AHB2 will be receiving SINAD challenged but DSP optimized signals from my Trinnov ST2 so arguably, I've paid extra to be just behind the Denon X3600H - this is what we Audio Adventurers call shabby chic: match best in class performance with a curio product and pray that the whole is greater than the sum of its parts!

Still all inaudible differences right? Although our minds might still see it as different, our ears won't hear it. Hopefully our mind won't start hearing it in addition to knowing it.

 

[Spocko]

Still all inaudible differences right? Although our minds might still see it as different, our ears won't hear it. Hopefully our mind won't start hearing it in addition to knowing it.

Agreed! I'm surprised nobody here has attempted double blind testing of SINAD differences between the highest performing stack (all Benchmark from DAC to Preamp to Amp), a well regarded modern AVR (Denon 3700H) and an expensive but audiophile approved stack (Pass Labs solid state or McIntosh tubes). Would be interesting to see what the "listener preference" ends up being. Just like there is definitely a listener preference for the "Harman curve", is there a listener preference that's completely divorced of SINAD measurements?

This is a completely reasonable comparison I believe as it truly separates the emphasis paid to SINAD alone versus other considerations heretofore unknown that may take priority. We don't know what we don't know, so this comparison is definitely something that needs to be examined. I understand the necessity for high SINAD when processing content as you always lose something after every layer of processing, but for playback, I'm curious to see what listener preferences really are when determining the importance of SINAD.

 

[RichB]

Still all inaudible differences right? Although our minds might still see it as different, our ears won't hear it. Hopefully our mind won't start hearing it in addition to knowing it.

The best I can do for observe subjective audible differences is to use the MiniDSP 4 DSPs to level match its two outputs to within 0.1 dB (measured with a voltmeter). Both amps are connected to a A/B switch output connected to Revel M126Bes.

Thus far, I have done only sighted quick switching but may do SBT at some point. With this rig, my impression is that the AHB2 does add some clarity, observable in percussion. The attack is better resolved by the AHB2 when compared to a Sunfire Cinema amp and also compared to an ATI AT522NC (Hypex NCore). These observations remained consistent at 1 watt and 10 watts.

This seems unlikely do power or SINAD. If I had to guess, it would be the differences are attributable to feedback handling that is less effective at higher frequencies in many amplifiers.

- Rich

 

[Sonnie]

The best I can do for observe subjective audible differences is to use the MiniDSP 4 DSPs to level match its two outputs to within 0.1 dB (measured with a voltmeter). Both amps are connected to a A/B switch output connected to Revel M126Bes.

Thus far, I have done only sighted quick switching but may do SBT at some point. With this rig, my impression is that the AHB2 does add some clarity, observable in percussion. The attack is better resolved by the AHB2 when compared to a Sunfire Cinema amp and also compared to an ATI AT522NC (Hypex NCore). These observations remained consistent at 1 watt and 10 watts.

This seems unlikely do power or SINAD. If I had to guess, it would be the differences are attributable to feedback handling that is less effective at higher frequencies in many amplifiers.

- Rich

You are talking about something different here... he was referring to what he had "feeding" the AHB2's... not the amps vs other amps.

 

[RichB]

You are talking about something different here... he was referring to what he had "feeding" the AHB2's... not the amps vs other amps.

Whether source components or amplifiers, I suspect that many on ASR believe that audible differences observed in the home are invalid and SINAD is all that is needed.

For amps, we are not measuring a representative set of reactive loads. Reactive loads that can impact linearity and the effectiveness of distortion control mechanisms, especially at higher frequencies. For me, SINAD like other measurements are like a resume. A bad showing excludes consideration.

For source components, the input impedance may have a similar effect.

As far as comparing a SOTA SINAD stack to something less, that is more difficult without introducing components into the signal path. The last experiment I tried was comparing these paths:

1) Oppo UDP205 (Fixed Volume) XLR -> Benchmark LA4 (Volume Control) -> AHB2s -> Salon2s
2) Oppo UDP205 (Fixed Volume) XLR -> Emotiva RMC-1 (Volume Control) -> LA4 (Fixed Volume) -> Salon2s

Since both the LA4 and RMC-1 have 0.5 dB volume precise (0.1 dB) matching cannot be guaranteed.
The comparison was very close and I don't think I would pass a blind. This comparison involves the RMC-1 analog path only, so not the entire product and not indicative of HT performance.

IMO, this is a good SINAD provides some insight of the performance of an HT processor, but very little information of the effectiveness in real use. The center channel is not measured and there are no comparative measurements with processing engaged.

There is no reason to faithfully believe that all DSP/REQ/PEQ processing paths are equally well implemented.

SINAD is a good measurement that has proven motivational to some manufacturers. There are examples where newer produces appear with improved SINAD performance. Where SINAD sells, well get more of it. Where BS sells, we certainly get more of that.

I bought the AHB2s only after until a friend brought one over and we compared it to the ATI6002.

- Rich

 

[Sonnie]

Agree... but to the point he and I were making is that we likely won't hear any difference between a SINAD of 98dB vs 99dB. Someone might hear a difference between the two preamps, but I highly doubt it would be because of the SINAD variance being 1-2dB... it will likely be from something else.

 

[tmtomh]

Whether source components or amplifiers, I suspect that many on ASR believe that audible differences observed in the home are invalid and SINAD is all that is needed.

For amps, we are not measuring a representative set of reactive loads. Reactive loads that can impact linearity and the effectiveness of distortion control mechanisms, especially at higher frequencies. For me, SINAD like other measurements are like a resume. A bad showing excludes consideration.

For source components, the input impedance may have a similar effect.

As far as comparing a SOTA SINAD stack to something less, that is more difficult without introducing components into the signal path. The last experiment I tried was comparing these paths:

1) Oppo UDP205 (Fixed Volume) XLR -> Benchmark LA4 (Volume Control) -> AHB2s -> Salon2s
2) Oppo UDP205 (Fixed Volume) XLR -> Emotiva RMC-1 (Volume Control) -> LA4 (Fixed Volume) -> Salon2s

Since both the LA4 and RMC-1 have 0.5 dB volume precise (0.1 dB) matching cannot be guaranteed.
The comparison was very close and I don't think I would pass a blind. This comparison involves the RMC-1 analog path only, so not the entire product and not indicative of HT performance.

IMO, this is a good SINAD provides some insight of the performance of an HT processor, but very little information of the effectiveness in real use. The center channel is not measured and there are no comparative measurements with processing engaged.

There is no reason to faithfully believe that all DSP/REQ/PEQ processing paths are equally well implemented.

SINAD is a good measurement that has proven motivational to some manufacturers. There are examples where newer produces appear with improved SINAD performance. Where SINAD sells, well get more of it. Where BS sells, we certainly get more of that.

I bought the AHB2s only after until a friend brought one over and we compared it to the ATI6002.

- Rich

My understanding is that when it comes to the higher-quality amp designs - the Hypex and Purifi modules, and most Class AB amps designed for use in conventional midfield/far-field speaker/component setups - it's been shown that load-dependent frequency response variations are not a real concern. To be clear, I get that some of the cheaper Class D chip amps have shown that load dependence. But when it comes to the Hypex, Purifi, Benchmark, and other amps in that general class, my understanding is that the evidence already exists to show that this concern is unwarranted. Am I mistaken?

 

[pma]

My understanding is that when it comes to the higher-quality amp designs - the Hypex and Purifi modules, and most Class AB amps designed for use in conventional midfield/far-field speaker/component setups - it's been shown that load-dependent frequency response variations are not a real concern. To be clear, I get that some of the cheaper Class D chip amps have shown that load dependence. But when it comes to the Hypex, Purifi, Benchmark, and other amps in that general class, my understanding is that the evidence already exists to show that this concern is unwarranted. Am I mistaken?

That's correct, their FR is almost independent of load impedance until you go down to extremely low impedances below 2ohm. Then it depends, but even then UcD, NCore and Purifi would be excellent. Re class AB, depends, below 2ohm.

 

[tmtomh]

That's correct, their FR is almost independent of load impedance until you go down to extremely low impedances below 2ohm. Then it depends, but even then UcD, NCore and Purifi would be excellent. Re class AB, depends, below 2ohm.

Thanks for the reply and confirmation.

In that case, I would argue that whatever the problems - or I would say limitations - of the SINAD measurement by itself, folks should stop using "load dependence" as a reason that SINAD is a bad measurement, because for loads of 2 ohms or more, amps with high SINAD are also load-invariant, and conversely the load-dependent amps are in the lower SINAD range. So it's not like @amirm is testing amps with 100dB SINAD (or even 90dB SINAD, as far as I recall) that have load-variance problems.

The only situation where SINAD could get you in trouble with load variance would be a situation like the one @pma was posting about the other day: you are looking for a very inexpensive (like less than $150), speaker amp and you are trying to make a good decision between various amps in that low range. In that case it seems there will be some that will be fairly load-invariant and others that won't.

 

[anmpr1]

I'm surprised nobody here has attempted double blind testing of SINAD differences between the highest performing stack (all Benchmark from DAC to Preamp to Amp), a well regarded modern AVR (Denon 3700H) and an expensive but audiophile approved stack (Pass Labs solid state or McIntosh tubes). Would be interesting to see what the "listener preference" ends up being.

The sort of ABX test you are describing will not tell you anything about 'listener preference'. It will only tell you whether someone is able to reliably distinguish between two audio feeds. And as has been demonstrated time and time again, at the usual levels of distortion and S/N, it's all random guessing.

That said, I immediately 'sensed' that the AHB2 was a marked sonic improvement over a 1960s tube design I built myself. In fact, I think the AHB2 is pound for pound and dollar for dollar a remarkable achievement, and represents good value, for what it is. And the folks at Benchmark are good guys.

However... could I distinguish between the two in an ABX? I don't know. Possibly. Depending. I know that with no signal, turned all the way up, the residual noise of the tube amp is evident with my ears, next to the speaker horn. The AHB2 is silent. So if I'm listening to balls to the walls silence, if it's John Cage's 4'33" turned up to 11, then I'm at 100%.

Taken together, I thoroughly enjoy my poorly measuring tube amp, the one with horrible SINAD, as much as my AHB2. For different reasons, of course.