Headless Mac Mini (2018) and Grounding - audio drop-outs

[MMMSA-10]

I trialled my MacBook with Audirvana, with an external Samsung 1TB SSD using a USB-C/USB3 hub, as a server to my DAC (SA-10). This worked well, except for QuadDSD where I experienced drop-outs - whether the file was fully loaded into memory or not. Was not able to get anyone to tell where the problem definitely was, so considered grounding issues a possibility - prompted by the not unusual 'sparking' when plugging the USB-C hub in to the MacBook.

 

Now set up a new Mac Mini (2018) as a headless server, and I experienced the same dropouts again only on QuadDSD. The drop-outs were causing the USB-DAC to click in and out of connection - suggesting that the actual comms between the two was being interrupted (as opposed to a glitch in the stream).

 

Have installed an iFI nano iGalvanic3 isolation unit and the problem is gone with the 3-position switch in the DC-RF position (which iFI claim is for hum loop situations). It reappears in either of "ISO" (full isolation) or "RF" (for non-grounded things like the Mac Mini) positions. 

 

I have tried adding a ground connection from an unused Mac Mini USB3 port (pin 4 and shield)  to the system earth on the pre-amp. Makes no difference to the drop-out behaviour.

 

So, although I am 'sorted', anyone experienced this, and or have a full explanation for the reasons behind my success? 

[Cornell77]

I have experienced the same dropouts when upsampling to DSD256 with a 2017 13" MacBook Pro and Audirvana 3.5.  The MacBook CPU runs at about 63% to perform the quad DSD upsampling, so I thought it might ba a CPU limitation.  Your post makes me think that it is not a CPU limitation, as the 2018 Mac Mini is faster than my dual core 2107 MacBook Pro.  I did find this clarification from IFI regarding the operation of the DC-RF position of their nano iGalvanic3:

 

Quote

The other options restores the Earth connection from DC to RF, and thus actually defeats the galvanic isolation for the ground connection only (power supply and signals remain galvanically isolated). This is needed if “floating” the audio system causes hum and may be needed if for example switching lights on/off trips audio dropouts.
In both cases the restored earth is a “soft connection”, not a hard safety earth connection. Generally we recommend to use the switch as a diagnostic device.

 

My DAC's USB input is self-powered, so I also defeated the power connection from the MacBook Pro, but the dropouts remain.  In any case, your experience has been valuable.  I also wonder if there is a less expensive solution to the problem.