Hi frequency noise in usb dac

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DaaDaa

Set the controls for the heart of the pun
this is the famous pcm 1704 muse dac that has been around for a long time. it shounds clean an d organic through headphones from day one that i bought it until now. but when i hook it up to my stereo amplifers there is very loud high frequency noise that is surprisingly volume independent (it is there when volume is all the way down). the noise is coming from my pc through usb. as soon as i disconnect the usb cable it goes away and then as soon as i pluf it in, it comes back

i was sure that i was gonna open it up, find a cap malfunctioning in a low pass filter on the board and it was gonna be easy. but every single componet measured extremenly well. i recapped the electrolytic caps and two ceramic caps as you see in picture and the noise is there with no change. this is becoming an annoying mystery.


as you can see i have replaced the 7 ussual caps that almost everyone replaces with nichicon and no change.

2YNRANL.jpg
 
Try a different USB cable? Turn PC volume down to about 90% and see if the noise persists.
 
the usb cable is not the problem i have tried many. cheap and expensive. it is also independed if the pc volume. it is there even if the pc is mute.

it is the ubiquitous noise from inside the pc. the problem is that through headphone it is 100% clean but through rca jacks it is so loud that it is unusable. so something in the signal path is that is supposed to suppress this noise is not doing it.
 
Dadbeh said:
the usb cable is not the problem i have tried many. cheap and expensive. it is also independed if the pc volume. it is there even if the pc is mute.

it is the ubiquitous noise from inside the pc. the problem is that through headphone it is 100% clean but through rca jacks it is so loud that it is unusable. so something in the signal path is that is supposed to suppress this noise is not doing it.
Click to expand...
I am not aware of anything in the DAC itself that would suppress any noise. I thought the reduction in noise level was merely due to remote placement of the DAC as far away from the noise generated inside the PC. :dunno:
 
im not saying it has special noise reductin curcuitry like a usb dejitter or something i just thought (guessed, hoped) a simple rc circuit. a cap and a resistor in series.
 
I would bet the noise is "there", just not audible because it's not being amplified. When I got my external USB DAC I compared the noise floor level without it, then with it. Using the external USB DAC was much quieter. There was still a low hiss, but the high pitched squealing noise, from inside the PC, was gone. The low hiss is not audible when music is playing.
 
This is probably switching power supply noise you're hearing and comes from the PC, changing caps will not fix it.

The DAC is powered through the usb plug right ?

You could try with anu usbpowered hub between the computer to see if it gets better.
There are other USB solution that are probably not worth their cost imo, better get a DAC with a dedicated power supply.
 
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If there's that much noise going out the USB port, just think of how much is going to the motherboard from the power supply. I'd try plugging the dac into a different computer, and see if it still does it. Maybe investigate whether your computer's power supply is failing.
 
i see. i tried a laptop and all the noise is gone and it sounds really good. so now i need to determine if it is a ground loop issue or the power supply in that pc is just noisy (which would be unfortunate considering that it is a new 150 dollar 850 watt unit that is powering a pc with usage under 100 watts.) i will do that by dragging down my other pc and using that to see if there is any difference. in either case the dac is not the culprit. it sounds really good for 25 bucks.
 
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Poinzy said:
It sounds like the infamous "1 kHz USB whine".
Click to expand...
I would have swear it was more like 6kHz on mine but yeah, continuous, steady whine on your speakers.

Dadbeh said:
i see. i tried a laptop and all the noise is gone and it sounds really good. so now i need to determine if it is a ground loop issue or the power supply in that pc is just noisy (which would be unfortunate considering that it is a new 150 dollar 850 watt unit that is powering a pc with usage under 100 watts.) i will do that by dragging down my other pc and using that to see if there is any difference. in either case the dac is not the culprit. it sounds really good for 25 bucks.
Click to expand...
The price of pc power supply does not matter much I'm afraid, they are made to provide powerful DC current at various voltages with a relatively good efficiency, noise filtering is not a major concern for pc parts suppliers. If you're into electronics it may be worth to try to build a low-pass RC filter and plug it into the usb power wire.
 
I went all out and ordered an isolation transformer Topaz low capacitance 1KW
 
try battery power to eliminate computer power supply. if you have scope or spectrum analyzer
look for the frequency of said noise, then look into a Zobel at the outputs or in some cases
where the PS uses a high frequency conversion then add the Zobel there.
 
I had a similar problem recently,
ended up being an issue with the screen, or its 23 volt power supply,
replaced screen, noise gone.
 
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