USB Isolator and PC noise
Jan 10, 2013 at 12:33 PM Thread Starter Post #1 of 13
tuoppi

tuoppi

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I recently bought a tube amp for my PC (Litte Dot MKIII). I am using an USB DAC.

The problem is that there is ground loop related noise. There is a buzzing noise on high volumes. When I scroll a web page there is more noise. And when I play a game there is a lot of buzzing. Anyway, the cause is that the amp does not have isolated inputs and it's the PC's noisy ground that differs from the amps ground that is causing the noise. I tested using the amp with a cheater plug (no ground in power cable) and the noise is gone.

Since cheater plugs are not really safe, I am looking for a better fix.

Would a USB isolator work?
I found these two:

https://www.olimex.com/Products/Modules/Interface/USB-ISO/
 
http://electronicsshop.dk/isolated_usb_hub.htm?currency=EUR

Any experience on these? Which one is better?
 
Jan 12, 2013 at 2:44 PM Post #4 of 13
Quote:
tuoppi said:
I recently bought a tube amp for my PC (Litte Dot MKIII). I am using an USB DAC.

The problem is that there is ground loop related noise. There is a buzzing noise on high volumes. When I scroll a web page there is more noise. And when I play a game there is a lot of buzzing. Anyway, the cause is that the amp does not have isolated inputs and it's the PC's noisy ground that differs from the amps ground that is causing the noise. I tested using the amp with a cheater plug (no ground in power cable) and the noise is gone.

Since cheater plugs are not really safe, I am looking for a better fix.

Would a USB isolator work?
I found these two:

https://www.olimex.com/Products/Modules/Interface/USB-ISO/
 
http://electronicsshop.dk/isolated_usb_hub.htm?currency=EUR

Any experience on these? Which one is better?
Click to expand...

Pulling the ground isn't actually particularly dangerous, I had to pull the ground to my amp because of a hum, no adverse effects. Unfortunately with computers having ground loop issues is fairly common unless you have good isolation between the signal path and the computer power.
 
Jan 13, 2013 at 7:29 AM Post #6 of 13
65535 said:
Pulling the ground isn't actually particularly dangerous, I had to pull the ground to my amp because of a hum, no adverse effects. Unfortunately with computers having ground loop issues is fairly common unless you have good isolation between the signal path and the computer power.
Click to expand...
There is no adverse effects when everything works. But when something goes wrong and the amp starts looking for a ground it will most likely use the user (me) as the ground which is pretty dangerous. Seeing as the amp is sitting at my desk and I sometimes use it with headphones I rather not take that risk unless I really have to. Pulling ground is the absolute last option I will use if nothing else works.
squallkiercosa said:
Apparently Little dot have ground issues
There are a few solutions posted
http://www.compudio.ca/2007/06/little-dot-mk-iii-exclusive-review.html
Click to expand...
The recommended solution in there is an RCA isolator. However I read that those lessen the sound quality, especially those cheap ones. It makes sense too because they work in the analog domain and breaking the ground loop is not a simple task.
That's why I am looking at USB isolators so the ground loop would be broken when the signal is still digital thus leaving the sound quality intact.
 
Jan 13, 2013 at 7:45 AM Post #7 of 13
I use one of the Olimex USB isolators. For me it wasn't so much a sound issue or hum issue, there was a potential difference between the AC outlet that my PC was plugged into and where the USB DAC and other nearby USB things we connected to the AC line.  Maybe one of the outlets had ground and neutral reversed, I don't know.  (There is some dodgy wiring in my flat.)
 
What would happen is the printer and the scanner would repeatedly reset. Also, if you turned a light on it would cause the printer to reset and cycle and the scanner to home up.  Damned annoying.  So I put an Olimex isolator in line with the USB from my PC and that solved the issue.
 
So, the Olimex isolators DO work; they galvanically isolate one side from the other.
 
Jan 13, 2013 at 2:45 PM Post #8 of 13
The isolators only support full speed (12 Mbit/s) and not high speed (480 Mbit/s). Even though full speed in theory should be enough, some USB devices require high speed to function properly (eg. M2tech Hiface Two).
 
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