Review and Measurements of Benchmark DAC1 USB DAC

[Crane]

The DAC1, DAC2 and DAC3 all have internal pads on the XLR outputs that should be used to set the output levels to the range that is required by the downstream device. This will allow direct interfacing to virtually any pro or consumer product.

The maximum output from all three devices is approximately the same. It is about 27.5 dBu. The calibrated level is +24 dBu at 0 dBFS prior to the pads. Consumer-grade XLR inputs will require the use of the 10 dB pads. Some power amplifiers will require the use of the 20 dB pads. The Benchmark AHB2 power amplifier is designed to accept full studio-level balanced signals (in low gain mode) and the pads should be set to 0 dB.

Turning down the volume control is not a substitute for selecting the proper pad setting!

Excessive use of the volume control skews the measurements by adding excessive noise. This in turn impacts the linearity measurements, which at their low end are really SNR measurements. The tests should be run at or near maximum volume (or the calibrated switch on the back of the DAC1 should be enabled).

At the calibrated volume setting (and any pad position) the DAC1 will deliver a SNR of 114 dB unweighted and 116 dB A-weighted. (19.4 bits unweighted)

In contrast:

At the calibrated volume setting, the DAC2 will deliver a SNR of 123 dB unweighted and 126 dB A-weighted. (20.9 bits unweighted)

At the calibrated volume setting, the DAC3 will deliver a SNR of 126 dB unweighted and 128 dB A-weighted. (21.4 bits unweighted)

The DAC2 and DAC3 are 9 to 12 dB quieter than the DAC1. This increases the effective bit depth by up to 3 bits.

The DAC1 was introduced in 2002, but was definitely ahead of its time. In 17 years we have gained about 3 bits in effective performance. THD has also been reduced. But, the biggest sonic improvement may be the elimination of the clipping intersample peaks that exceed 0 dB FS. The DAC2 and DAC3 have 3 dB of headroom above 0 dB FS. See:

https://benchmarkmedia.com/blogs/application_notes/tagged/inter-sample-overs

for a series of papers on this topic.

There are still thousands of DAC1 converters in daily use in recording studios around the world. Many others have upgraded to the DAC2 or DAC3.

Loving the inputs john, you guys are doing great work for our community and should add on to it by sending dac3 and hpa4 to amir for testing

 

[John_Siau]

Afaik you could jump through some hoops and avoid ASRC or something to that extent in earlier ESS chips, but mainstream products typically didn't do it as it was tricky and probably not blessed by ESS. ES9038PRO has proper support for external sync mode which effectively kills ASRC, several DACs expose this mode to the user, e.g. Matrix XSabre PRO.

The key is to scale the digital audio down by 3 dB before it goes into the ESS. If you don't do this the upsampler in the ESS overloads when it attempts to reconstruct intersample peaks that exceed 0 dB FS. These overloads produce percussive bursts of high-frequency noise and the "characteristic ESS sound". This defect is completely avoidable. The cost is 3 dB of the SNR. A good exchange from my perspective.

 

[John_Siau]

I took a shot at this but somehow I didn't capture the actual FFT signal. Here is the data anyway:

View attachment 13842

I may have been recording this without turning on the generator. Not sure. Either way I was surprised to see all of those spikes.

This doesn't look right to me. Not sure what this is.

 

[John_Siau]

I have an application note that I wrote in August of 2015 where I made side-by-side measurements of the DAC1 and DAC2:

https://benchmarkmedia.com/blogs/ap...chmark-dac2-vs-dac1-side-by-side-measurements

I simultaneously measured a DAC1 and a DAC2 with exactly the same measurement parameters. In all cases 0 dBr is +24 dBu at 0 dB FS.

The results for each test are overlaid on top of each other. There are 12 separate plots. In every plot, the DAC1 is shown in red and the DAC2 is shown in green. These differences represent 10 years of progress between the introduction of the DAC1 (2002) and the DAC2 (2012). Here is one sample plot:

 

[Silou]

I have a few questions regarding the DAC1 since I think it is an interesting device afterall.
1. How powerful is the headphone amp inside the DAC1?
2. Is it possible to use the two headphone outputs for the same headphone to achieve a balanced connection and increase the output power? (like the ADI-2 Pro from RME)
3. Is the linearity thing a problem too with the other digital inputs?

 

[amirm]

I don't have the unit to test again but I would guess that which digital input you use, doesn't make a difference in linearity.

 

[Silou]

Do you think the measurements would improve if you use the settings John_Siau mentioned in post #59?
Are the measurements he posted comparable to your current AP analyzer measurements?

 

[amirm]

Do you think the measurements would improve if you use the settings John_Siau mentioned in post #59?
Are the measurements he posted comparable to your current AP analyzer measurements?

My testing has evolved in how I deal with varying output levels out of DACs. Can't tell you how much difference there would be without re-testing though.

 

[Silou]

My testing has evolved in how I deal with varying output levels out of DACs. Can't tell you how much difference there would be without re-testing though.

Well I think I am only one of a few people who would be interested in a re-test of the DAC1. It is probably better to focus on newer stuff anyway
I really hope John will answer the other two questions

 

[Silou]

I did some calculations and I hope they are correct. For anyone who is interested in the output power of the HPA2 headphone amp inside the DAC1, here are my results:

600 Ohm: 126mW
300 Ohm: 252mW
150 Ohm: 504mW
60 Ohm: 1260mW

I am not sure if this calculation also applies to loads under 60 Ohm, since Benchmark only listed the output level into 60 Ohm.
These wattage numbers should match the JDS Labs Atom since it has the same output level as the DAC1 into higher loads.

Only one question is left now. Is it possible to increase the output power by using one headphone output for each chanel or is the output power simply divided by 2 if a second headphone is plugged in?

 

[John_Siau]

The two headphone jacks are wired in parallel. The amplifier is designed to drive loads as low as 30 Ohms. This allows the simultaneous use of two 60-Ohm headphones. The headphone amplifier in the DAC1 is the same as the amplifier in the DAC2 and DAC3. It is our "HPA2" headphone amplifier, which, at one time, was available as a standalone headphone amplifier.