• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Review and Measurements of Benchmark DAC3

spaace

Member
Joined
Jun 4, 2018
Messages
46
Likes
8
I haven't been able to scan all the 27 pages, i'm sorry if this has been discussed before.

But does the high output of the DAC provide any real advantage ? Is that a desirable quality in a DAC ?

Thank you in advance for helping out.
 

RayDunzl

Grand Contributor
Central Scrutinizer
Joined
Mar 9, 2016
Messages
13,202
Likes
16,982
Location
Riverview FL
But does the high output of the DAC provide any real advantage ? Is that a desirable quality in a DAC ?

If your associated gear will accept it, use the higher levels.

If not, engage the output pads (XLR only).

The RCA outputs are the usual 2V.

I have a DAC2, the preamp I use after it will accept the 12V/24dBu XLR.

Were I to plug the XLR from the DAC directly into my power amp. I'd need to pad it, as the input sensitivity of the amp is 2.45V
 

spaace

Member
Joined
Jun 4, 2018
Messages
46
Likes
8
If your associated gear will accept it, use the higher levels.

Thanks for helping out Ray. Iam trying to decide if i need to get the Benchmark DAC to go with the abh2 - the combo is expensive and i would prefer to use the SMSL 500 or maybe the RME as my DAC unless of-course the Benchmark's higher output gives it a distinct advantage.

So yes the abh2 will accept the higher output but does the higher output DAC (20 v vs 7v) give any advantage for amplification levels?

Will using a higher output DAC result in a higher output in amplification or a higher SINAD ?
 

Sal1950

Grand Contributor
The Chicago Crusher
Forum Donor
Joined
Mar 1, 2016
Messages
14,073
Likes
16,607
Location
Central Fl
The ABH2 has switchable input sensitivity for optimum performance with any realistic input level.
 

RichB

Major Contributor
Forum Donor
Joined
May 24, 2019
Messages
1,946
Likes
2,611
Location
Massachusetts
The ABH2 has switchable input sensitivity for optimum performance with any realistic input level.

I have no trouble driving the AHB2 directly from the Oppo UDP-205 in the high and mid gain settings. It sounds great too.

- Rich
 

spaace

Member
Joined
Jun 4, 2018
Messages
46
Likes
8
Thats good to know. Thank you all. Wonder why then Benchmark went to the trouble of adding such high output to the DAC. I'm guessing it was costlier than not doing it. Maybe @John_Siau might know. Its a pity the RCA is not so great as per Amirs measurements, it would have made a perfect choice too for folks who need that.
 

RayDunzl

Grand Contributor
Central Scrutinizer
Joined
Mar 9, 2016
Messages
13,202
Likes
16,982
Location
Riverview FL
Will using a higher output DAC result in a higher output in amplification or a higher SINAD ?

I would expect the maximum output to remain the same.

SINAD for this unit as tested - 113db.

Shoutometer says just under 326 miles.

I'd think you could lose a few dB and never notice it unless you were measuring.

I won't win any records for SINAD here, at least not on the more popular end of the scale.

Do I have a noise problem? Maybe measurably, not listenably.

Idle amplifier measurement:
Using a scale that would (Ithink) be equivalent to the XLR output levels at the DAC

1573326649657.png


SINAD (not more than 72dB) is bound by AC Power noise, wherever it is coming from. Cables? Amp output? Not a sterile environment here.
The amplifier spec says it will push 49Vrms (though it is differential, so 138Vpk-pk across the speaker terminals).

Using 49V as the 0dB might press the relative measurement down another 12dB. Unsure how to properly configure things here.


Wonder why then Benchmark went to the trouble of adding such high output to the DAC.

It's designed to be able to be used places other than at home.

Like the RME ADI-2 Pro FS:

Output level switchable +24 dBu, +19 dBu, +13 dBu, +4 dBu @ 0 dBFS

1573326209318.png

http://www.sengpielaudio.com/calculator-db-volt.htm
 
Last edited:

RayDunzl

Grand Contributor
Central Scrutinizer
Joined
Mar 9, 2016
Messages
13,202
Likes
16,982
Location
Riverview FL
Idling today, at the amplifier output, using what may be a more appropriate scaling factor. The interface says the maximum input (0dBfs =26dBu=15.45Vrms) with the minimum gain (input volume knob).

That lowers my idle SINAD to about -85, putting me mid-pack in the amp contest.

1573428623949.png




Making a tone at a reported 4.72Vrms (5W into 4 Ohms) I get this:

The AC noise didn't change, and only a hint of 3rd harmonic poke up out of the noisy flooring.

1573429403043.png


I'm not convinced that's 5W though, if only 83dB is emitted, with both speakers.



Using the million sample FFT:

Is that cheating? I expected the "noise floor" to drop but not the AC noise (maybe it is more variable than constant)
Test tone and 3rd harmonic are still reported at the same level, though.

1573429833386.png



Right or wrong, overlaid with Nord One (Hypex) -rated 96dB SINAD:

1573430687125.png


Ok ,good enough. a little inaudible power noise, cleaner harmonics (but unsure of the exact power level)

I'll go be terrified about whatever worry I come up with next.
 

RayDunzl

Grand Contributor
Central Scrutinizer
Joined
Mar 9, 2016
Messages
13,202
Likes
16,982
Location
Riverview FL
Thats a lot isnt it....is this not desirable ?

That would be the amplifier output as 0dB - 49Vrms, 98V across the speaker terminals, since it is differential and there seems to be some confusion on measuring things, or 138Vpk across the speaker...

The higher "0dB" is the lower (relatively) some unchanging smaller value becomes.

This is all academic, I don't have any pruchase plans.
 

spaace

Member
Joined
Jun 4, 2018
Messages
46
Likes
8
SINAD (not more than 72dB) is bound by AC Power noise, wherever it is coming from. Cables? Amp output?

Does it help to use power conditioners, sine wave ups etc to rectify power noise ? Or ia it a fools errand in a home env ?

ps : what equipment do you use to perform these measurements ?
 

RayDunzl

Grand Contributor
Central Scrutinizer
Joined
Mar 9, 2016
Messages
13,202
Likes
16,982
Location
Riverview FL
Does it help to use power conditioners, sine wave ups etc to rectify power noise ? Or ia it a fools errand in a home env ?

I don't think I'm looking at external power noise - these harmonics could well, I suspect, be present even with a perfect power company sine wave.


ps : what equipment do you use to perform these measurements ?

REW software and a Focusrite Clarett 4Pre.

1573438897065.png


Not the best choice, nor the worst. Serviceable within its range.

But I'm not understanding the voltage levels and calibration issues, especially when measuring balanced vs unbalanced with the Focusrite and REW,, so need to whip out the 'scope to see what's really going on there.
 
Last edited:

Vear

Member
Joined
Dec 28, 2019
Messages
33
Likes
50
I have a DAC2 HGC (w/firmware update). Which set-up is preferable?

1) Using the DAC2 to send the +8.2 dBu/ 2 Vrms "Bypass" level signal into the AUX-input of a pre-amp with a 200mV sensitivity @47k Ω. This arrangement would only put the pre's volume control (no additional gain) in the signal path

- or -

2) Using the DAC2 as a pre-amp (with it's own volume control) into an amp-in section which is rated at 1V @47k Ω.

Both examples using unbalanced RCA. Which would be a better match?
 
Last edited:

John_Siau

Active Member
Technical Expert
Audio Company
Joined
Jul 17, 2018
Messages
184
Likes
1,407
Location
Syracuse, NY USA
I have a DAC2 HGC (w/firmware update). Which set-up is preferable?

1) Using the DAC2 to send the +8.2 dBu/ 2 Vrms "Bypass" level signal into the AUX-input of a pre-amp with a 200mV sensitivity @47k Ω. This arrangement would only put the pre's volume control (no additional gain) in the signal path

- or -

2) Using the DAC2 as a pre-amp (with it's own volume control) into an amp-in section which is rated at 1V @47k Ω.

Both examples using unbalanced RCA. Which would be a better match?
Either connection will work but the direct connection from the DAC2 to the power amplifier will provide the best SNR and lowest THD.
 

Vear

Member
Joined
Dec 28, 2019
Messages
33
Likes
50
Either connection will work but the direct connection from the DAC2 to the power amplifier will provide the best SNR and lowest THD.

Hi John- thanks for the reply, makes sense. I've tried both methods and they do work but I was surprised that at reasonable listening levels the volume knob positions were very close in either setting. In other words, regardless of the path (or volume control) at about 11 o'clock I was getting the same pink noise SPL in both configurations. I get that this could be coincidental and that the scale of the volume controls may be different but it got me thinking about the gain matching differences between the two options.

Actually, the more I think about this the more I think that the 200mV rating of my AUX-input is accounting for the additional 14dB of gain in the pre-amp section which I normally bypass, so that would further reduces the sensitivity. I think that by just keeping the volume control in the signal path (and bypassing the pre-amp gain) my AUX-IN sensitivity is closer to 1V which might explain the similar volume knob levels. Hmm, I will have to investigate this further.

Also, second question - if using the balanced connections from the DAC into a 1V amp, what would be the best jumper setting on the DACs balanced output?
 

John_Siau

Active Member
Technical Expert
Audio Company
Joined
Jul 17, 2018
Messages
184
Likes
1,407
Location
Syracuse, NY USA
The 20 dB pad on the Benchmark DAC1, DAC2, or DAC3, will give you 1.23 Vrms (+4 dBu) on the XLR outputs at 0 dBFS when the DAC volume control is bypassed. You will reach the full 1 Vrms requirement of your amplifier at just 2 dB below the bypass (or calibrated) volume setting, so the gain staging will be almost perfect between the DAC and the amplifier. This assumes that the amplifier sensitivity is also 1 V on the balanced input (check the amplifier specifications to verify this).
 

John_Siau

Active Member
Technical Expert
Audio Company
Joined
Jul 17, 2018
Messages
184
Likes
1,407
Location
Syracuse, NY USA
OK, finally, finally we get to test the statement Benchmark has made about superiority of their headphone amplifiers. For those of you who have not tracked that discussion, it starts with this paper from Benchmark: https://benchmarkmedia.com/blogs/application_notes/12838141-headphone-amplifiers-part-1

In a nutshell, they say that real headphone loads cause far more distortion than dummy (resistive) loads always used for headphone reviews and measurements. To wit, they show these two measurements, the first being with a dummy load:

View attachment 13329

The Benchmark is in navy color at the bottom showing much better performance than the other two competing amps in pink and green. But that is no their point. Their point is that once you replace the dummy load with a real Sony MDR-V6 headphone, their distortion figures do not change but the competitors do:

View attachment 13330

I confirmed that both my Topping headphone amplifier and RME ADI-2 DAC (or was it the Pro?) are sensitive to headphone loads. And indeed their THD+N in above graph shows similar frequency dependence to competitors of Benchmark above.

What was left was verifying that the Benchmark indeed performed as well as they say it does using my instrumentation.

For that, I tried to set my APx555 analyzer very closely to what they have above. I did not have a 60 ohm dummy load but used a 50 ohm which is close enough. Levels were matched nearly the same at 0.5 watt per above graphs. Bandwidth of the analyzer is set to 90 kHz as opposed to 80 kHz but again, close enough.

Here are the results comparing the RME ADI-2 Pro output versus DAC3 using a 50 ohm dummy load:
View attachment 13331

We get pretty nice graphs with the RME ADI-2 Pro now beating the Benchmark DAC3 by good margin (4 to 7 dB).

Now let's replace our dummy load with the real Sony MDR-V6 headphone:

View attachment 13332

Ah, that ain't good! While the RME ADI-2 Pro output changes as I had measured with my other analyzer, so does the Benchmark DAC3!!!

Reading through the paper from Benchmark, it is from DAC1, not DAC3. Benchmark has newer papers on DAC3 with similar claims.

Not shown but I tested with an IEM at much lower level and it too caused a variation in response that was identical between the two amps.

Summary
It is good of Benchmark to raise awareness of measuring with real headphone loads. But the notion that their headphone amplifiers have distortion profiles that are headphone independent, do not seem true. My measurements show similar susceptibility to other high-performance amplifiers.

Sure, if you have a much higher output impedance than what Benchmark has, the effect will be exaggerated. But the core problem remains in all implementations including that of Benchmark DAC3. Bummer!

P.S. I measured the output impedance of Benchmark DAC3 at 0.7 ohms.
View attachment 13333
The RME vs. DAC3 measurements into a headphone load should match very closely (as you have shown). Both have very low output impedances and both have vanishingly low distortion when driving resistive loads.

At the time the Benchmark paper was written, it was common practice to build headphone amplifiers with a 30-Ohm output impedance. The Hifiman EF2A is a carry-over from these older designs.

The plots we published compared the DAC1 headphone amplifier to two headphone amplifiers that had 30-Ohm output impedances. Some of the distortion was produced by the high output impedance and some was created by the fact that neither of these amplifiers could cleanly drive a 60-Ohm resistive load. Here is the 60-Ohm resistive load plot for the same three headphone amplifiers:

1590692305586.png

See: https://benchmarkmedia.com/blogs/application_notes/12838141-headphone-amplifiers-part-1

It is also important to note that we made the measurements in a very quiet room with the headphones on a dummy head. If you leave the headphones open on the bench while running the test, room noise will give you much higher THD+N. You could use a THD only test, or replicate our procedure to get more accurate results.

Nevertheless, the purpose of the paper was to demonstrate the distortion-related advantages of having a low output impedance. A good follow up would be to use a headphone measurement system to determine how much the distortion changes at the acoustic output of the headphone (where it counts).

Here is a plot that compared the DAC1 headphone amplifier to itself after the insertion of a 30-Ohm series resistor:

1590692468020.png

See: https://benchmarkmedia.com/blogs/application_notes/12982989-headphone-amplifiers-part-2

Please note that a 30-Ohm amplifier driving 60-Ohm headphones gives a damping factor of 60/30 = 2. For the purpose of damping, we would like to see a damping factor of at least 10 (see http://www.collinsaudio.com/Prosound_Workshop/Damping_Factor.pdf ).

This means that the lower impedance headphone amplifiers may produce less distortion at the acoustic output. Amplifiers with an output impedance of less than 6 ohms would provide sufficient damping when driving 60-Ohm headphones, but amplifiers with lower output impedances should offer no additional significant improvements in the THD at the acoustic output.

In the output-impedance range below 6-Ohms, audible improvements will be related to achieving a predictable and repeatable frequency response. Like loudspeakers, the impedance of any set of headphones will vary with frequency. The MDR-V6 has a nominal impedance of 60 Ohms, but this changes substantially over the audio band. The output impedance of the amp and the input impedance of the driver form a voltage divider. This voltage divider is frequency dependent because the headphone impedance changes with frequency.

If you do the math, you will find that a damping factor of 100 will keep the voltage-divider frequency response flat to about +0/-0.5 dB. This assumes that there are frequencies where the impedance is 1/3 of the nominal impedance.

It would take a damping factor of 350 to keep this variation below 0.1 dB. This would require an output impedance of 0.17 Ohms when driving 60-Ohm headphones.

Lets assume we need a damping factor of 100. With 60 Ohm headphones this means that we would need an output impedance of 60/100 = 6 Ohms.

Amplifiers with an impedance higher than 6 Ohms may produce audible differences in the frequency response of a given set of 60-Ohm headphones. This implies that listeners may be able to detect the frequency response changes in a level-matched ABX test between two headphone amplifiers if one achieves a damping factor of 100 and the other does not.

On the basis of frequency response alone, the Hifiman EF2A should sound different than the amplifiers with output impedances of less than 1 Ohm, when driving most headphones. This assumes that the amplifiers are perfectly flat into resistive loads. The audible difference will be produced by the unintended voltage divider that is formed by the output impedance of the amplifier and the input impedance of the headphone. The headphone impedance is frequency dependent and this makes the voltage divider frequency dependent.

Look for my upcoming paper on damping factor here:

https://benchmarkmedia.com/blogs/application_notes

It will appear before the end of May 2020.
 

ayane

Active Member
Forum Donor
Joined
Dec 15, 2018
Messages
182
Likes
684
Location
NorCal
Would it be possible for someone with a DAC3 post its spectral output of white noise at 44.1 kHz? I'd like to see the behavior of its digital filter.
 
Top Bottom