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Would USB cable carry noise from upstream to downstream?

laidick

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A friend of mine asked this, and I don't know how to answer.

Say, we have a source player, USB output to DAC.
The player is using very bad power with lot of noise, 60hz him etc etc....
And it passes the signal via USB to a very clean DAC, say if it is the Top Mola Mola DAC that amir just measured,or the topping D90.
Would that noise from upstream system being passed down the DAC and impact any sound quality ?

And how would the system as a whole perform if the digital part has noise?


Thanks.
 

solderdude

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That will totally depend on how insensitive the DAC is to common mode noise.
When it is really bad one can use USB isolators or optical data transmission.
It is all about common mode (ground loop) noises in general.

So... it could be problem free it could be problematic and all variances in between.
In general USB should not be a problem with decent to excellent DACs... but it could be in some specific cases/circumstances.
 

Severian

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Every USB audio device - including two DACs, two DJ controllers, and most recently a USB audio interface - I've connected to either of my desktop PCs has produced intolerable amounts of noise through my speakers. I use an iFi Defender to sever the ground connection and that does the trick. Using optical in lieu of USB works too, but of course that's not always an option.

There is no noise when I use a laptop as a source rather than a desktop PC.
 
OP
laidick

laidick

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How could we measure the ground loop effect from USB input ? Or is it measurable ?

Does that noise transfer from not just the USB cable but also a shared main AC socket ?

Thanks
 

majingotan

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solderdude

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Every groundloop will be different. Every circumstance will differ. So a certain measurement will not represent what might or might not be there in another situation.
So one is either plagued by noise from the speakers (or headphone) which disappears when the DAC is disconnected from the PC/source or one is not plagued in which case no heroic measures are needed.
One will always have to investigate where noises come from to find the cause and a remedy.
 

Severian

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Is there any good information out there about ways to properly ground a desktop PC chassis to address this issue? I think my PC building skills are reasonably good - it's not rocket science, after all - and I simply have no idea what I could do. I've searched for troubleshooting guides but have never found anything on point.

The ubiquity of USB audio devices suggests to me that many people don't run into these ground loop and noise issues, and that it's therefore possible to avoid them in a standard desktop PC build.
 

majingotan

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There are more well engineered DACs since ASR’s appearance which reject USB motherboard interference so this issue just mainly persists with crappy DACs on the market
 
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laidick

laidick

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There are more well engineered DACs since ASR’s appearance which reject USB motherboard interference so this issue just mainly persists with crappy DACs on the market
Yup I agree.
I am curioius technically how does the DAC achieve this USB isolation ?
 

majingotan

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There’s a post somewhere that explains how well engineered DACs reject this. One biggest example is galvanic isolation though it’s not 100% rejection of noise in itself
 
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laidick

laidick

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There’s a post somewhere that explains how well engineered DACs reject this. One biggest example is galvanic isolation though it’s not 100% rejection of noise in itself
Would you mind share it? Thanks
 

majingotan

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