Does the quality of the USB power matter

[mikemag]

I am wondering how the quality of the USB power adapter can affect the audio out from a DAC. It would seem to me that a noisy USB AC adapter would introduce noise to the output of the DAC ( the analog component of a DAC)
Am I correct ? If so how does one select a clean USB power adapter ?

 

[amirm]

If a DAC is designed correctly, it would expect USB power and data to be noisy and will take that into consideration to filter all that out. Every DAC I recommend is situated this way. I do have an old Schiit Magni DAC that is sensitive to USB noise but that is it.

 

[Doodski]

I am wondering how the quality of the USB power adapter can affect the audio out from a DAC. It would seem to me that a noisy USB AC adapter would introduce noise to the output of the DAC ( the analog component of a DAC)
Am I correct ?

Yes, it can occur but it is very rare.

If so how does one select a clean USB power adapter ?

Read the adapter specifications or check the adapter power output with a oscilloscope and look for bad stuff.

 

[dfuller]

Amir has summed it up in one.

Basically if a DAC has good enough PSRR and properly laid out and filtered analog stages it should be a non-issue.

 

[kemmler3D]

Am I correct ? If so how does one select a clean USB power adapter ?

As others have stated, you are correct, but only rarely.

There are ways to clean up USB power (sometimes people use batteries instead of AC due to paranoia on this point) but the real solution is just to buy a DAC that's designed for real-world use and not weird tweak-o audiophile money-wasting kid glove treatment.

 

[wwenze]

Am I correct ? If so how does one select a clean USB power adapter ?

Those China brandless ones, I cannot charge my phone and use the phone at the same time, they make the touchscreen go crazy.

 

[mikemag]

My DAC is Amir tested and approved so it looks like I am good to go

 

[fatoldgit]

Simple solution... only use DAC's that power the USB receiver internally and use a "data only" USB cable with the USB 5VDC lines inoperable.

Also means the DAC's source of power shouldnt be the USB audio cable.

Peter

 

[ajawamnet]

I ran into the crap USB pwr adapter thing a few times. The deal is that unless they have third prong they radiate all kindsa noise from the little cheap SMPS in them. So I just add a ground via a homemade USB feed thru. Works great. Don't know why no one makes these.

In this example I have a cheap scope I use at my desk when writing code. When on battery it's quiet. But when I plug in the charger - any of the chargers I have (and I have a ton of them in the lab) it's funky noise.

So I made these little feed thrus that just add the safety ground. Noise goes away.

See vid here:

 

[wwenze]

I ran into the crap USB pwr adapter thing a few times. The deal is that unless they have third prong they radiate all kindsa noise from the little cheap SMPS in them. So I just add a ground via a homemade USB feed thru. Works great. Don't know why no one makes these.

I actually do not recall a USB pwr adapter having a third prong, even the good ones. Unless it's those >60W stuff (high power SMPS are required to have common-mode filtering) and even then the arrangement w.r.t. secondary is a mystery.

Adding a earth where there is none can actually remove "safety via class II isolation" and in the event of a fault, kill you with secondary side loop current without triggering primary side ELCB / RCD. Probably won't happen but something to take note when the insurance inspectors come after a fire.
The solution is easy: Instead of using a wire for a straight short, use a class Y capacitor. Safety is guaranteed and choose a value where 50Hz impedance is high while still letting RF through. Parallel a high-value resistor to control the DC voltage and this is the commercial standard way of connecting secondary to primary side earth..