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My Line 6 TonePort UX2 has suddenly started malfunctioning. It is absolutely fine for playback, but on all the inputs (Mic 1 & 2, + instrument) there is terrible digital white noise maxing out the input levels, even if I disconnect all input devices. If you plug in a guitar cable and touch the end of it you can hear that it is picking up something from the input, but and musical signal is completely drowned out by noise.

POD Farm input level

I've unplugged and replugged the device, and I've rebooted Windows (I'm using Win 7). I'm running the latest drivers and have even reinstalled them. Changing the buffer sizes in the control panel doesn't help either. Does this mean something is actually broken in the hardware? Or are there any other software troubleshooting steps I can go through?

Update I've made another discovery. The noise on the inputs only appears when I have one or the other of my monitors (Alesis M1 520s) plugged in to the UX2's outputs. If I disconnect them and work with headphones then all is fine. The thing is, they don't even have to be powered on for the noise to appear.

Update 2 I can also fix the noise by not using the HDMI output on my laptop (which is connected to an LG monitor). I'm guessing this means I have some kind of nasty ground loop going on?

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Is the noise also on the line out and headphone out? –  Friend Of George Apr 27 '11 at 20:42
    
yes, when there is noise it is on both the line out and headphone out –  Mark Heath Apr 27 '11 at 21:26
1  
I got this too, I reckon it's a design hardware fault. It only happens on mine after a while and the unit begins to heat up. I ended up changing the soundcard in the end –  Willbill Apr 28 '11 at 15:34
    
Is the HDMI connected in any way to the UX2? One thing about HDMI is that it supports DRM. Pure speculation, but the noise might be an intentional signal degradation... –  horatio Apr 28 '11 at 15:57
    
@horatio I'm pretty sure its a ground loop issue. I can fix it by unplugging my LG screen or both my powered monitors. –  Mark Heath Apr 28 '11 at 16:42
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1 Answer

up vote 2 down vote accepted

OK, I have at least discovered the cause now, which is some kind of ground loop. I had ordered a replacement power supply for my Dell XPS M1530 laptop as the old one was making funny noises and the cable sheathing was torn. However, it now appears the old power supply (original Dell) earthed the laptop, while the new one doesn't (hence the hum doesn't go away whether it is plugged in or not). I suppose it serves me right for buying a cheap replacement power supply from ebay instead of paying over 5 times more for the official Dell one (£53 for a power adaptor!).

As well as using the old power supply, I can also solve my noise issue by connecting my display with VGA instead of HDMI. Very frustrating, just have to decide if I want to shell out for the full price power adaptor.

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Thanks for following up on this. It was very interesting. Sorry for your troubles. –  Zeronyne Apr 28 '11 at 18:50
2  
+1 for a great job diagnosing the problem, never giving up, and sharing the results. –  Friend Of George Apr 28 '11 at 20:16
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