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Noisy USB ports?
Noisy USB ports?
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Old 10th April 2020, 01:13 AM   #1
danschy is offline danschy  United States
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Default Noisy USB ports?

Greetings. Posted a question earlier about a sound card for my budget basement sound system. I have since bought an ASUS Xonar U7, which has good specs and measured well at the audiosciencereview site. Hooked it up to an old desktop computer and power amp and was disappointed in the amount of computing noise I heard. It was down about 60dB, but extremely noticeable due to the noise characteristics. After playing around with ground loop elimination I eventually realized that the USB ports themselves seem to be noisy. If I plug my headphones directly into the sound card (no amplifier/speakers), I still hear the noise. Tried different USB ports but they all have the same issue. If I use my laptop, the card is dead quiet. Looked at some USB filters, but the commonly available ones only support 12Mbps, which is not fast enough. I have a free PCIe slot and wonder if a $15 USB card would resolve my issue. Any thoughts or other ideas? Thanks.
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Old 10th April 2020, 02:49 AM   #2
phase is offline phase  United States
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Try unplugging the (power cord) monitor and see if the noise continues.
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Old 10th April 2020, 06:20 AM   #3
phofman is online now phofman  Czech Republic
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What power amp is connected? Very likely class I device with PE wire.
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Old 10th April 2020, 07:03 AM   #4
silverprout is offline silverprout  France
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Quote:
Originally Posted by danschy View Post
measured well at the audiosciencereview site
Do you know what is the SNR and the NF ?
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Old 10th April 2020, 08:09 AM   #5
phofman is online now phofman  Czech Republic
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It is a typical ground loop.
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Old 10th April 2020, 01:48 PM   #6
danschy is offline danschy  United States
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Thanks for the responses. Audiosciencereview measured SINAD at around 102dB, and when I connect it to my laptop I hear no noise, so it is not the soundcard itself - it sounds great!

I don't see how it can be a ground loop when there is only one path - AC plug --> computer --> USB sound card --> headphones. Nothing other than the computer is plugged into an outlet. Once I hook up the amp there can of course be ground-loop issues, but right now I'm hearing noise through the headphones connected directly to the soundcard with no amp connected.

Haven't checked what happens when I unplug the monitor - I'll check later today.

A little more background - previously I had the computer connected to a TV via HDMI, with the TV return audio (toslink) driving a receiver. This setup produced no computer noise, however, the receiver has a number of functional and performance issues, so I plan to simplify things by just having computer, sound card, power amps. The setup works well with the laptop, so am hoping to resolve the desktop noise issue.
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Old 10th April 2020, 01:54 PM   #7
silverprout is offline silverprout  France
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Quote:
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laptop
Unplugged or plugged ?
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Old 10th April 2020, 02:20 PM   #8
phofman is online now phofman  Czech Republic
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Quote:
Originally Posted by danschy View Post
I don't see how it can be a ground loop when there is only one path - AC plug --> computer --> USB sound card --> headphones.
Sorry I missed that part in your description.

What happens if you hook the soundcard through a powered hub?
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Old 10th April 2020, 02:42 PM   #9
danschy is offline danschy  United States
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Didn't seem to make a difference whether or not the laptop (Dell Latitude E6410) was plugged in, which surprised me. It uses a grounded plug. When I use the laptop with a Behringer UAC222 to make amplifier measurements I unplug it to reduce measurement noise; the Asus Xonar U7 does not seem to have that issue - perhaps better filtering/isolation?

Don't have a powered hub, but maybe that would be a better option than the USB PCIe card I was contemplating. Think I'll do some loopback measurements using the Asus card on my laptop and desktop and see how they compare.
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Old 10th April 2020, 02:45 PM   #10
nigelwright7557 is offline nigelwright7557  United Kingdom
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Put a few uF across the USB power supply at the DAC end.
I run USB scopes off USB and have 100uF on the 3v3 regulator.
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