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Review and Measurements of Benchmark DAC3

Sal1950

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#21
Thanks Amir and Mike!
A long anticipated review with the excellent results expected and hoped for.
(so far) ;)
 
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amirm

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Thread Starter #22
That's his problem; not mine. Mebbe he should stick to Macs.
If you were me and had to download 2-3 of them each week to test something, you would be as grumpy as I about downloading drivers. :)
 
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amirm

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Thread Starter #24
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:

1529891288246.png


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:

1529891388251.png


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:
Benchmark DAC3 vs RME ADI-2 Pro Headphone Dummy Load Measurement.png


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:

Benchmark DAC3 vs RME ADI-2 Pro with Sony MDRV6 Measurement.png


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.
Benchmark DAC3 output impedance measurement.png
 
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RayDunzl

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#26
Why test a 106dB/mw headphone at 500mw?
 

rebbiputzmaker

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#28
As you see, the non-attenuated channel outputs nearly 20 volts RMS, corresponding to whopping +-28 volts or peak to peek! :eek: With that kind of output swing if you are bored, you can hook up the DAC3 to drive your Christmas tree lights! :D
What's the point of having such a non-standard output stage?
 

rebbiputzmaker

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#29
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 amplifier.

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
Foolish for them to try and say their headphone section is immune to real-world load variations, pretty impossible. They might try to do a better job than some, as often times it seems headphone sections are not a primary concern of a DAC manufacturer.
 
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amirm

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Thread Starter #31
What's the point of having such a non-standard output stage?
Ray found out that you can force it into a calibration mode. Other than that, I guess it is a guy thing: if a bit is good, a lot is better. :D
 

jtwrace

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#33

jtwrace

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Sal1950

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#35
Right, and my statement still stands.
That would be quite expensive in any case.
Maybe one day we can get Amir to look at the miniDSP U-DAC8 for the multich guys. At $299 a possible inexpensive solution to the issue.
Kal talked a bit about it this month in Stereophile.
 
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amirm

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Thread Starter #36
Maybe one day we can get Amir to look at the miniDSP U-DAC8 for the multich guys. At $299 a possible inexpensive solution to the issue.
That is very reasonably priced. Let me get through my massive backlog and then pester me to get it and review it.
 
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