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Benchmark ahb2 power amplifier

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23 minutes ago, barrows said:

As i recall this is a low gain amp (I need to go back and look at the Stereophile measures), low gain is a sure way to reduce noise.  I suspect the rest of the engineering is good as well

IIRC, the three gain settings measured at 23dB, 17dB and 9.2db.

 

23 minutes ago, barrows said:

Of course nothing comes for free, with this low gain one will have to have higher gain in the source to reach the same levels in a given system context, higher gain in the source means higher noise there, so no free lunch.

Agreed.  In my case, I have a preamp with lots of output but with a bothersome noise floor that is unaffected by its volume setting and sources that are very quiet.  Turning down the gain in the AHB2 is easily compensated by the preamp but the result is greatly reduced noise at the end of the chain.


Kal Rubinson

Music in the Round

Senior Contributing Editor, Stereophile

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@Kal Rubinson, right, so the amp suits your system well.  Also, when bridged, and at the highest gain setting, the AHB achieves a more typical gain.


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@Miska, yeah agreed.  We have this problem because there are no real standards for home audio.  Couple that with the high variability of average levels on recordings (loudness wars...), and gain matching and needs get complicated.  In many home systems people are throwing away performance by having awkward gain structures, requiring lots of attenuation.

i DIY my DACs, and so can adjust output capability to suit the system at hand, but even then I find I have to have a fair bit of 'extra" gain to accommodate many audiophile recordings with low average levels and high dynamic range (Reference Recordings, Channel Classics, etc)-then I have t apply quite a bit more attenuation for contemporary pop, like Lorde or something.


ROON: DSD 256-Signature Rendu optical--Buffalo PRO or DSC-2--Ncore 400 Stereo-Focus Audio FS888-JL E-112 sub-Nordost Tyr USB, Cardas Clear AC, Iconoclast XLR, Nordost Frey speaker, cables, Synergistic Blue & Hi Fi Tuning Supreme Cu Fuses, Dark Matter system clarifiers.    Design/Build Consultant with Sonore

 

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I think running their DAC straight to their power amp is what Benchmark would like you to do.

 

 


"The overwhelming majority [of audiophiles] have very little knowledge, if any, about the most basic principles and operating characteristics of audio equipment. They often base their purchasing decisions on hearsay, and the preaching of media sages. Unfortunately, because of commercial considerations, much information is rooted in increasing revenue, not in assisting the audiophile. It seems as if the only requirements for becoming an "authority" in the world of audio is a keyboard."

-- Bruce Rozenblit of Transcendent Sound

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1 hour ago, Miska said:

I hope more amps would come with adjustable gain - not just volume trim pot, but really a gain adjustment. Because this would allow running DAC straight to power amp and without having need for lot of attenuation. Because it is quite counterproductive to bash out 2V from DAC, then attenuate it to 100 mV in preamp and then amplify it again to 2V in power amp (or something like that)...

 

Hi Miska

I agree with you, however it's not so easy as different gain settings normally require changes to the compensation network values.

Regards  

Alex


How a Digital Audio file sounds, or a Digital Video file looks, is governed to a large extent by the Power Supply area. All that Identical Checksums gives is the possibility of REGENERATING the file to close to that of the original file.

 

PROFILE UPDATED 18-06-2019

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1 hour ago, Ralf11 said:

I think running their DAC straight to their power amp is what Benchmark would like you to do.

Indeed, I did run three DAC3s into three AHB2s very successfully except for the inability to use the volume knobs.


Kal Rubinson

Music in the Round

Senior Contributing Editor, Stereophile

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7 hours ago, barrows said:

@Miska, yeah agreed.  We have this problem because there are no real standards for home audio.  Couple that with the high variability of average levels on recordings (loudness wars...), and gain matching and needs get complicated.  In many home systems people are throwing away performance by having awkward gain structures, requiring lots of attenuation.

i DIY my DACs, and so can adjust output capability to suit the system at hand, but even then I find I have to have a fair bit of 'extra" gain to accommodate many audiophile recordings with low average levels and high dynamic range (Reference Recordings, Channel Classics, etc)-then I have t apply quite a bit more attenuation for contemporary pop, like Lorde or something.

 

Sure there are some differences and adjustment needs. But with suitable gain structure you can get very close to 0 dB attenuation with those highest quality recordings and get the best performance too. And still be safe with the louder lesser quality ones to rely on just small amount of digital adjustment for example from the player application.

 

Now I bet many audiophiles rarely if ever go to less than -20 dB attenuation. Same with my pre + power amps, quiet listening can be -50 dB volume and the loudest -20 dB. With loudspeakers that have way under 90 dB sensitivity.

 

Of the DACs best situation is with Holo Spring, since it puts notably lower output level with DSD inputs.

 

With headphone amps situation is much better, many HP-amps have switchable gain, so I can get better gain matching with headphones which is anyway what I mostly use for listening.

 


Signalyst - Developer of HQPlayer

Pulse & Fidelity - Software Defined Amplifiers

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4 hours ago, Daverz said:

Just wanted to mention that Benchmark's new line-level preamp starts shipping tomorrow.  It's basically the HPA-4 without the headphone amp.

 

https://benchmarkmedia.com/products/benchmark-la4-line-amplifier

 

I would just get the HPA-4 instead, the price difference for leaving out the headphone power stage is relatively small...

 


Signalyst - Developer of HQPlayer

Pulse & Fidelity - Software Defined Amplifiers

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5 hours ago, Kal Rubinson said:

Indeed, I did run three DAC3s into three AHB2s very successfully except for the inability to use the volume knobs.

 

But with that combination you probably get very good performance thanks to good gain matching and then it should be within bounds of safely relying on software digital volume...

 


Signalyst - Developer of HQPlayer

Pulse & Fidelity - Software Defined Amplifiers

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6 minutes ago, Miska said:

Now I bet many audiophiles rarely if ever go to less than -20 dB attenuation.

  You aren't wrong !

That's also why my own DIY Class A Preamp has a very modest gain of only 3.2 times

Very few people have the volume control /attenuator at even as high as half way much of the time.


How a Digital Audio file sounds, or a Digital Video file looks, is governed to a large extent by the Power Supply area. All that Identical Checksums gives is the possibility of REGENERATING the file to close to that of the original file.

 

PROFILE UPDATED 18-06-2019

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23 minutes ago, sandyk said:

That's also why my own DIY Class A Preamp has a very modest gain of only 3.2 times

Very few people have the volume control /attenuator at even as high as half way much of the time.

 

Preamp with gain of 1 is more than enough. I'm not sure if my preamp has any gain. And then at least 10 dB off the typical power amp gain and then it starts to become useful... In many cases, having just 2x gain throughout the entire pipe would be enough.

 


Signalyst - Developer of HQPlayer

Pulse & Fidelity - Software Defined Amplifiers

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28 minutes ago, Miska said:

In many cases, having just 2x gain throughout the entire pipe would be enough.

 

 Agreed, but FM  Stereo for example, has a lower output level than CD, with many Phono preamps even lower.

 HDTV with Multi Channel Dolby Audio can even need up to a 500% (!) increase in level too.(as seen with Video editing S/W)


How a Digital Audio file sounds, or a Digital Video file looks, is governed to a large extent by the Power Supply area. All that Identical Checksums gives is the possibility of REGENERATING the file to close to that of the original file.

 

PROFILE UPDATED 18-06-2019

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Some Accuphase amps have gain settings. However, their prices are steep. Always wanted to have a go with one since I love Japanese manufactured products. 

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12 hours ago, barrows said:

As i recall this is a low gain amp (I need to go back and look at the Stereophile measures), low gain is a sure way to reduce noise.  

It is not too clear, but it seems that JA's noise testing in Stereophile was done using the highest gain setting, and he also said the noise difference at different settings was only 3dB.

https://www.stereophile.com/content/benchmark-media-systems-ahb2-power-amplifier-measurements

"The AHB2's channel separation was superb at >110dB in both directions below 2kHz, and still 90dB at 20kHz. The wideband S/N ratio, measured in the high-gain, stereo condition with the input shorted to ground and ref. 1W into 8 ohms, was very high, at 89.3dB. Reducing the measurement bandwidth to 22Hz–22kHz increased the ratio to 106dB, while switching an A-weighting filter into circuit increased it further, to 108.5dB. Referenced to the AHB2's clipping power of 100W, this is equivalent to a dynamic range of 128.5dB, which is close to the specified 132dB. The S/N ratio did increase by around 3dB in the lowest-gain condition, implying that the specified ratio was measured in that mode. However, I was surprised to find that the S/N decreased slightly when the amplifier was very hot."
 

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5 hours ago, Miska said:

But with that combination you probably get very good performance thanks to good gain matching and then it should be within bounds of safely relying on software digital volume...

I am not sure what you are suggesting but I when I said........

11 hours ago, Kal Rubinson said:

Indeed, I did run three DAC3s into three AHB2s very successfully except for the inability to use the volume knobs.

I was referring to a temporary situation but it reveals my personal preference for a physical knob control.  AFAIK, the only multichannel DACs that have a physical volume knob are the Merging (NADAC and Hapi) and the upcoming OKTO.  Do you know of any others?


Kal Rubinson

Music in the Round

Senior Contributing Editor, Stereophile

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1 hour ago, psjug said:

It is not too clear, but it seems that JA's noise testing in Stereophile was done using the highest gain setting, and he also said the noise difference at different settings was only 3dB.

The value of the lower gain settings is not that it reduces the noise contribution of the amp but it, effectively, attenuates the noise contribution from its sources.


Kal Rubinson

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13 minutes ago, Kal Rubinson said:

The value of the lower gain settings is not that it reduces the noise contribution of the amp but it, effectively, attenuates the noise contribution from its sources.

Got it.  The low gain means the source SNR is not compromised; i.e. source S is as high as reasonably possible.

But still some of us were wondering if the Benchmark numbers might be inflated because of the low gain in the amp.  So that is why I put up a copy of JA's description of his tests.

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7 hours ago, Miska said:

 

Sure there are some differences and adjustment needs. But with suitable gain structure you can get very close to 0 dB attenuation with those highest quality recordings and get the best performance too. And still be safe with the louder lesser quality ones to rely on just small amount of digital adjustment for example from the player application.

 

Now I bet many audiophiles rarely if ever go to less than -20 dB attenuation. Same with my pre + power amps, quiet listening can be -50 dB volume and the loudest -20 dB. With loudspeakers that have way under 90 dB sensitivity.

 

Of the DACs best situation is with Holo Spring, since it puts notably lower output level with DSD inputs.

 

With headphone amps situation is much better, many HP-amps have switchable gain, so I can get better gain matching with headphones which is anyway what I mostly use for listening.

 

Yes, totally agreed.  In my case I set the gain of the DAC such that indeed I only use a few dB of attenuation with the lowest average level recordings.  But I apply a -5 dB reduction in software before my oversampling step (to DSD 256) to avoid clipping in the oversampling.  I do play music quite loud here as well (rural home, hurray!).  I end up with my DACs set for about 4 V output at 0 dB (balanced), and this works well for my my amp and speakers (my Amp reaches 200/400 watt output at 2 volt input).  I still end up applying quite a bit of attenuation for contemporary pop like Lorde.

Of course there are a lot of DACs with much higher output levels, 6-8 V is fairly common for balanced outputs.  And most folks not applying a reduction somewhere (like I do for oversampling) probably have too much gain and are using more attenuation than would be ideal.  A reasonable solution for computer audio folks would be too apply some reduction in software.  At 64 bits no one should be too concerned about applying, say, a 6 dB reduction in ROON or HQPlayer to reduce overall gain and allow their final volume control (even analog) to be operating more ideally. 


ROON: DSD 256-Signature Rendu optical--Buffalo PRO or DSC-2--Ncore 400 Stereo-Focus Audio FS888-JL E-112 sub-Nordost Tyr USB, Cardas Clear AC, Iconoclast XLR, Nordost Frey speaker, cables, Synergistic Blue & Hi Fi Tuning Supreme Cu Fuses, Dark Matter system clarifiers.    Design/Build Consultant with Sonore

 

                                                                                                  SONORE computer audio

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1 hour ago, psjug said:

Got it.  The low gain means the source SNR is not compromised; i.e. source S is as high as reasonably possible.

But still some of us were wondering if the Benchmark numbers might be inflated because of the low gain in the amp.  So that is why I put up a copy of JA's description of his tests.

 

Even if it is "inflated", you still get the benefit in the end because you don't have the excess gain...

 


Signalyst - Developer of HQPlayer

Pulse & Fidelity - Software Defined Amplifiers

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2 hours ago, Kal Rubinson said:

The value of the lower gain settings is not that it reduces the noise contribution of the amp but it, effectively, attenuates the noise contribution from its sources.

Kal, a more clear way of stating the above might be to say: the lower gain setting in my system reduces the amplification of the source noise (as it does not really attenuate it) such that it is no longer audible.  Or something to that effect.

 

Suffice it to say, proper gain matching in a system to where the user does not have to apply high levels of attenuation (using the volume control) can result in improved system performance, and it is likely that a lot of audiophiles are leaving some performance on the table in this regard.  If one's volume control never goes above -20 dB, then one could benefit from changing the gain structure/relationships between their components.

 

As to noise of the AHB amplifier itself, I am sure it is a very low noise design, but I would be careful directly comparing JA's measurements with those of other amplifiers with different gains, as this would be an unfair comparison.  I re-read the measurement section of the review and still could not find exactly what gain settings were used for which measurements.  But, I am not criticizing the AHB, from a measurements standpoint it is pretty clear that it performs very well indeed.  I would like to see a higher power amp from them though, as the increase in output impedance when bridged would bother me a little.


ROON: DSD 256-Signature Rendu optical--Buffalo PRO or DSC-2--Ncore 400 Stereo-Focus Audio FS888-JL E-112 sub-Nordost Tyr USB, Cardas Clear AC, Iconoclast XLR, Nordost Frey speaker, cables, Synergistic Blue & Hi Fi Tuning Supreme Cu Fuses, Dark Matter system clarifiers.    Design/Build Consultant with Sonore

 

                                                                                                  SONORE computer audio

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I've been using this amp for a couple years now, in its lowest gain setting and in stereo mode (not as monoblocks).  It's dead quiet.  I've never heard a quieter amp.  I also use an ARC LS28 which is probably the only color I've allowed in my system, or at least that I've been able to reasonably control.  As far as tube pre's go it's fairly quiet itself compared to what else I've used in the past.


Digital chain: Synology DS1815+ -> Linear Solution OCXO switch-> Custom 2016 Server (sCLK-EX modified motherboard, Mutec REF 10)-> AL NUC NA->  Holo Spring L3 -> Audio Research LS28-> Benchmark AHB2 -> Paradigm Persona 9H, JL Fathom sub

Power: Paul Hynes SR7, Uptone LPS-1.2, sPS-500, Topaz 91001-31 Isolation Transformer

Analog chain: VPI Prime with Ortofon Quintet Black cart -> Simaudio Neo 310LP-> Audio Research LS28-> Benchmark AHB2 -> Paradigm Persona 9H

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John - what gain setting are you using on the LS28?


"The overwhelming majority [of audiophiles] have very little knowledge, if any, about the most basic principles and operating characteristics of audio equipment. They often base their purchasing decisions on hearsay, and the preaching of media sages. Unfortunately, because of commercial considerations, much information is rooted in increasing revenue, not in assisting the audiophile. It seems as if the only requirements for becoming an "authority" in the world of audio is a keyboard."

-- Bruce Rozenblit of Transcendent Sound

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