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Review and Measurements of Benchmark DAC3

eyes-on-you

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Not exactly. This configuration gives the lowest output noise, but the signal level is reduced more than the noise, so the SNR is actually reduced. In the -10 dB setting, you will not be able to drive the AHB2 to full output. If you do not need the full output, you could run at the -10 dB setting. The output noise will be inaudible either way.

Let me ask you while I catch you here.

Using the volume pot higher than 12 o’clok position with the -10db settings better than using a volume pot around 9 o’clock with the 0db pad setting?
 

JohnM-73

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I'm close to buying a Dac3 HGC, but before I did I wanted to ask if the linearity issues discussed earlier in this thread, when using the unbalanced outputs only, were ever addressed? I'd be using it with unbalanced outputs for a good 6+ months into my Quad 606, before I'm able to afford a used AHB2, so decent unbalanced out performance is still important to me before I get to that point. Thanks.
 

terfenol-D

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I'm close to buying a Dac3 HGC, but before I did I wanted to ask if the linearity issues discussed earlier in this thread, when using the unbalanced outputs only, were ever addressed? I'd be using it with unbalanced outputs for a good 6+ months into my Quad 606, before I'm able to afford a used AHB2, so decent unbalanced out performance is still important to me before I get to that point. Thanks.

I’m fairly certain the unbalanced outputs linearity issues will not interfere with your enjoyment of the DAC3. I do not believe the issues mentioned enter into audible territory.
 

Sal1950

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eyes-on-you

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Manual said that DAC2 only support 24/96 via Toslink.

I have use D2 Toslink input since 1 year. When a try to play 24/192 track, blue light blinks and music can not played.

I have try a lot Toslink cables but it’s not change since when i connect a Supra ZAC Toslink cable.

On the D2 input with Supra; music plays 10 seconds, after that some interruption occur and music continue for ten more seconds. It’s repeats during whole track.

Today i want to try D1 optical input (never used before) and surprise!

DAC2 plays 24/192 tracks via toslink, all interruption has gone.

If DAC does not support, how it is possible?

If it is support why it could not play on D2 input.

Any idea?
 

¥€$

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My unit's volume pot has a tendency to "migrate" upwards over time because of power cycling. I had the volume set at 12 o' clock about a year ago, but a while ago I noticed that it had risen for almost half a notch. Does this mean that the internal volume setting had also risen? It is regrettable that the volume pot automatically dims the volume before the DAC is powered off, this puts strain on the motor. If it didn't, there would be no such problem that I described. Is it a safety measure?
 

audiopile

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My use of the DAC-3hgc has changed a lot over the years- really appreciate the user's manual - this DAC has been a real Swiss Army Knife audio product for me. I am particularly impressed with the manual because my "new" smart? phone comes with a 152 page manual and I'm still wading thru it to get to the three or four functions i want to actually use. The Benchmark manual is a fine example of printed communications art.
 

Sal1950

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I am particularly impressed with the manual because my "new" smart? phone comes with a 152 page manual and I'm still wading thru it to get to the three or four functions i want to actually use.
I've got no use for one of those things. My flip-fone does everything I need and for the rest I can wait till I get home to my real computer. My yearly costs with TracFone is under a $100 a year and it will make any phone call I'll ever need and take pictures and short video to boot.. I won't let those media thief's get any deeper in my pockets than they already have.
 

HiFidFan

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I've got no use for one of those things. My flip-fone does everything I need and for the rest I can wait till I get home to my real computer. My yearly costs with TracFone is under a $100 a year and it will make any phone call I'll ever need and take pictures and short video to boot.. I won't let those media thief's get any deeper in my pockets than they already have.

Interesting name though "TracFone"
 

Sal1950

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JClarkw

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View attachment 14057
The above is a linearity measurement on a Benchmark DAC3. This plot includes the unbalanced outputs (green trace - left, red trace - right) and the balanced outputs (yellow trace = left, magenta trace = right)... This can make it look like the XLR outputs have better linearity, but this is not the case. Inside the DAC3, both sets of outputs are derived from the same analog output of a differential amplifier that follows the ES9028PRO D/A converter. This means that the apparent differences in linearity shown in Amirm's linearity measurements of the DAC3 are a physical impossibility. This does not mean that his measurements were wrong, it just means that noise was interfering with his measurements. The solution is to use a narrower bandpass filter...
Dear John and Amir -- I'm no expert on making/interpreting these measurements; but I've read over this thread pretty carefully, and there's something here that I still don't understand:

Near the end of Amir's post (https://www.audiosciencereview.com/...asurements-of-benchmark-dac3.3545/#post-85547), he shows a "linearity" comparison of the Benchmark DAC3 (original test unit) unbalanced and a Topping D50. Even after his measurements on the second unit directly from Benchmark, he finds this measurement of the DAC3 inferior to the balanced (see https://www.audiosciencereview.com/...nts-of-benchmark-dac3.3545/page-18#post-91447), hence to the D50, so my question below may still be relevant.

The argument has been made, apparently persuasively, that Amir's DAC3 "linearity" measurement suffers from noise/distortion in the DAC+measurement setup. This in spite of his measurements on the DAC3 and D50 showing that the THD+N ratio and the SINAD are quite comparable between them. So why do the linearity plots of the DAC3 unbalanced and the D50 look so different? Seem to me that both DACs should suffer equally from this same measurement issue. Not so?
 
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JClarkw

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I don't think we ever got resolution on the linearity issue. My tests include sharp filters on either side of the test tone so doesn't get corrupted by noise or distortion.
Thanks, Amir -- I was never clear how much filtering you did in your linearity plots. As I understood it, John Saiu argued that you didn't filter enough of the noise/distortion to see the "true" linearity at low levels. You countered that extreme filtering obviated the real-world value of the test. Have I got any of that right?

We'll hope John responds... -- JClarkW
 
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amirm

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You countered that extreme filtering obviated the real-world value of the test. Have I got any of that right?
??? No. I didn't say that. The test has value in showing absence of noise/error in low level detail.
 

JClarkw

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??? No. I didn't say that. The test has value in showing absence of noise/error in low level detail.
Amir -- Sorry I misunderstood. Do you agree that you and John Siau disagreed about the methodology, and perhaps about the purpose, of a linearity measurement? If so, can you articulate this disagreement?

Also can you confirm that your methodology for linearity testing of the DAC3 and the D50 was the same?

I can't be the only one that's confused. This thread has become very long and complex. The issue is important to me because I have to live with unbalanced outputs from whatever DAC I purchase. Best Regards -- JClarkW
 

JClarkw

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??? No. I didn't say that. The test has value in showing absence of noise/error in low level detail.
Amir -- From you post, https://www.audiosciencereview.com/...ents-of-benchmark-dac3.3545/page-8#post-85873, here's the statement that confused me:

"Linearity is the ultimate test of a DAC: that it has a straight line transfer function between input digital samples and output analog. That output analog must be definition include all contributions including noise and distortion.

"Checking just the level after removing all noise and distortion is an academic exercise devoid of real world value."
[emphasis mine]
 

John_Siau

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Like all Benchmark converters, the balanced outputs on the DAC3 deliver professional +24 dBu output levels while the RCA outputs deliver 2 Vrms (8.2 dBu). This means that the level difference between the XLR outputs and the RCA outputs is approximately 16 dB. In contrast, most consumer-grade XLR outputs deliver 4 Vrms (+14.2 dBu) at full output. This means that the output level difference between XLR and RCA outputs is just 6 dB on most devices while it is 16 dB on the DAC3. The higher, professional output levels allow for an improved signal to noise ratio. This means that there will be a larger difference between the performance of the XLR and RCA outputs on the DAC3 than there will be on products with consumer-grade XLR outputs.

Amir's RCA vs. XLR linearity measurement discrepancy on the DAC3 is caused by the 16 dB difference in level at the input to the test equipment. Further discrepancies can be caused by ground loops between the test equipment and the DAC when measuring the RCA outputs. No matter the cause, the difference is caused by a difference in SNR and not by a difference in linearity.

It is easier to achieve a high SNR in the connection between the unit under test and the test equipment when the interface is balanced. It is also easier when the signal level is increased.

It is not at all surprising that Amir was able to achieve a more accurate linearity measurement using the XLR outputs. A simple SNR test would show similar differences.

A linearity test ceases to be a linearity test when the signal approaches the combined noise floor of the DAC and the test set. Once the noise floor is reached, the test is no longer measuring linearity. This is why "linearity" tests always show a higher than expected output at very low levels. The shape of that low end of the measurement can be influenced by the auto ranging of the test equipment. Also, the low end of the curve may not be repeatable, because it is beyond the measurement limits of the test gear. In other words, the voltage measurement function within the test set has its own limitations and these can change the shape of the linearity curve at very low levels. I have two APx555b analyzers, an AP2722 and an AP2522. All 4 of these machines will show different results on the same DAC once the signal drops below the measurement noise floor. Our results also differed from those on Amir's APx555, even when we performed measurements on the same DAC3.

No conclusions should be drawn from the apparent difference in Amir's "linearity" measurements of the RCA vs. XLR outputs on the DAC3. The apparent differences lie below the measurement limits of the test setup.

Sigma-Delta converters have near-perfect linearity. The linearity curve will be a straight line until the noise floor of the measurement is reached. In contrast, multibit ladder network D/A converters will show substantial linearity errors with the worst errors happening where the MSB is changing state (near 0 VDC).

Just to be clear, there is nothing wrong with Amir's measurement techniques. It is just wrong to draw conclusions about measurements that are beyond the limits of the test setup. These test limits are significantly different when there is a 16 dB difference is signal level. The matter is even worse when the lower signal is unbalanced.

The +24 dBu at 0 dBFS balanced XLR linearity measurement is much more accurate than the +8 dBu at 0 dBFS unbalanced RCA linearity measurement. The difference underscores the advantage of using balanced interfaces. It also demonstrates the advantage of using +24 dBu (at 0 dBFS) professional levels instead of +14 dBu (at 0 dBFS) consumer levels.

If you are driving consumer-grade XLR inputs, the DAC3 has passive 10 dB pads that will drop the output level from +24 dBu to +14 dBu. These pads are not necessary when driving other Benchmark devices. For example, the Benchmark AHB2 power amplifier is designed to accept professional +24 dBu signal levels. The AHB2 has a gain of 9.2 dB. This allows the amplifier to reach its full output with a +22 dBu input signal while reserving 2 dB for headroom.
 

JClarkw

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...A linearity test ceases to be a linearity test when the signal approaches the combined noise floor of the DAC and the test set. Once the noise floor is reached, the test is no longer measuring linearity. This is why "linearity" tests always show a higher than expected output at very low levels. [Emphasis Mine] The shape of that low end of the measurement can be influenced by the auto ranging of the test equipment. Also, the low end of the curve may not be repeatable, because it is beyond the measurement limits of the test gear. In other words, the voltage measurement function within the test set has its own limitations and these can change the shape of the linearity curve at very low levels. I have two APx555b analyzers, an AP2722 and an AP2522. All 4 of these machines will show different results on the same DAC once the signal drops below the measurement noise floor. Our results also differed from those on Amir's APx555, even when we performed measurements on the same DAC3...

Just to be clear, there is nothing wrong with Amir's measurement techniques. It is just wrong to draw conclusions about measurements that are beyond the limits of the test setup. These test limits are significantly different when there is a 16 dB difference is signal level. The matter is even worse when the lower signal is unbalanced...
John -- Thanks for coming back to this thread! Though I have science and engineering experience myself, I'm certainly not an expert on high-end audio measurements. That said, your argument about noise influencing "linearity" at the low end makes sense to me. I have three remaining puzzles:

1) Amir's linearity measurements on the second (good) DAC3 unit show the unbalanced trace decreasing at the low end, not increasing as you state above.

2) Amir's presumably identical linearity test on the Topping D50, which has only RCA outputs, looks much better than the second DAC3 unbalanced. Yet his measurements of THD+N and SINAD are quite comparable between the D50 and the first (defective) DAC3. If these values improved significantly in the second unit (not measured by Amir), that would seem to make the paradox even worse, not so?

3) I don't think Amir has completely specified the filtering used in his linearity measurements. He said just above, "My tests include sharp filters on either side of the test tone so doesn't get corrupted by noise or distortion." Earlier he mentioned a figure of 50dB as the depth of the 200 Hz-wide bandpass filter. He has not, to my knowledge, stated if he's using a specific one of the built-in filters in the test unit, as you did in your post at https://www.audiosciencereview.com/...nts-of-benchmark-dac3.3545/page-15#post-90480.

Best Regards to All -- JClarkW
 
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nomograf

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John,

As a daily user of a DAC3 in a professional mastering studio it's great to see you here and communicating technical issues with such clarity!

I used to work at PMC Speakers for many years and would occasionally drop by your booth at AES, and always enjoyed our chats and learned something every time.

There's an active system with ABH2 in my future, looking forward to it.

Cheers,
Ruairi
 
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