The extent of benefit when USB to DAC power output is cut?

[Rantenti]

Hello all,

My DAC does not require USB power or handshake, and I can block the power either by blocking the power pin on the USB cable, or by toggling the USB power output to "off" on my PCIe USB card.

Theoretically speaking, are both methods limited only to removing power-signal interference in the length of the USB cable only (i.e. after the USB output point), or is the output data signal produced at the USB card output also cleaner (as no power is drawn and therefore no power is running alongside the data from the motherboard to the USB ouput) ?

Thanks a lot!

 

[somebodyelse]

If it's a well designed DAC the USB power will make little to no difference. The designer should be aware of the normal variability in USB power and design to be immune to it. Measurements from the various reviews here of USB conditioning devices, and archimago's measurements of DACs powered from different USB ports and sources show only small differences similar to the usual variation between repeated measurements. The test here of one of the 'special' USB cables suggested there might be subtle measurable differences, but that they would be inaudible IIRC.

If your DAC has single ended outputs you might be better off looking at the USB ground as that can be a path for ground loops and leakage currents which can cause clearly audible noises. The modulation of leakage current or ground voltage by computer activity is often incorrectly blamed on noisy USB power.