I finally used couple of days to do small fixes for the first unit I put together and got first decent measurement results.

 

Results are still considered preliminary, because the DAC was measured without any shielding case, plain boards and transformers on a table, connected with open unshielded wire hassle...

 

I performed my usual set of measurements.

 

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First was 0 - 22.05 kHz linear frequency sweep (44.1 kHz 32-bit PCM source file) with analyzer set to 5 MHz bandwidth and "peak hold" mode. This is a good measurement to see any digital or analog filter leakage as well as buildup of other ultrasonic noise.

 

Sweep with DSD128 output rate:

 

 

 

...and DSD256 output rate:

 

 

 

...and DSD512 output rate:

 

 

 

As can be seen, the ultrasonic noise bump is completely gone from the figure at 22.5792 MHz output rate, and very low indeed already at 11.2896 MHz. No correlated images visible at all, as those are completely removed by the oversampling digital filter to those high rates (analog filter cuts out everything way before reaching 11.2896 MHz).

 

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Then the standard IMD measurement with 19+20 kHz tones:

 

 

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Sine wave at 1 kHz:

 

 

 

THD is predominantly friendly sounding second harmonic.

 

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24-bit J-test signal:

 

 

 

Nothing visible there...

 

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Notes and conclusions:

• Overall noise performance was better than expected, especially the audio band noise floor was lower than with couple of other DACs I compared against.
   
• Low impedance (noise) design of analog stages is pushing the active parts a bit. DIstortion figures would go down with some amount of tweaking on the analog stages. AD797 could have been better choice for the filter stages based on earlier experience.
   
• This one already sounds so good, that I probably need to make a DSC2 design this winter...