Helix 1/4" Output strange noise

PLOP

Hey

So I use a Line 6 Helix and recently bought a poweramp and 2x12 to play live. The setup sounds great, but I've noticed a squealing/humming sound when the guitar signal is silent or the amp is on but not being used. I have previously been using the Helix into the Effects Return of an amp (but I don't currently have access to this) and I don't recall this noise there. (Although maybe it was because I always wear ear plugs at practice).

The hum sounds almost like the standing 'hiss' from a loud amp with overdrive but no signal, but plus a tinnitus-esque electronic squeal. It persists when even the Helix is switched off, so I also don't think its a software issue on the Helix.

I've done some experimentation to isolate the Helix:

When my signal is Guitar>poweramp, or Guitar>Normal pedal>Poweramp it sounds fine.

I also tried swapping all the cables used, as well as the power supply to the poweramp (direct to wall vs extension lead), and unplugging everything except the 1/4" output on Helix (including the guitar).

I've also tried it in every other 1/4" plug on the Helix, whether its an input or output jack.

After some light searching I found a post on the Line 6 forum that details something similar, but he was "cured" by using an "impedance balanced TRS cable" I'm not even going to begin to pretend I know what that means but I'll try and read up.

Can anyone offer potential insight to the cause of my issue here? It isn't loud, and it can't be heard over playing, but I know it shouldn't be there, and it does increase in volume in line with the poweramp output so I expect at band volumes it may be noticeable.

Cheers!

PLOP

Some additional experimentation this evening:

Helix>Headphones and Helix>HiFi via Aux (via phones jack and both mono outs) have no squeal.

The issue has got to be somewhere between the Helix output and the Poweramp input, but the fact that the sound persists when the Helix is off is really weird.

PLOP

OK so I fixed this, and I always like to finish off a post I started if I find the solution.

First off, I was very new to using the Poweramp (Warwick Gnome mini bass head) and so did not really understand what my problem was.

At home I was hearing the noise at very high volume levels on the amp itself (12:00 Gain and Master). I was compensating for that by using the big volume knob on the Helix itself and keeping it pretty low. I realised instead that the better way (and the more practical way for playing live) is to keep the poweramp's volume low and the Helix on 12:00. That way I can easily reduce or increase my signal from my board, but also it stops that squeaking that I could hear from the amp because it's volume isn't despicably loud.

Next, I had a different squeal (think electronic rather than analogue) was there whenever I was using my computer with the Helix over USB. I don't know why but I had never plugged the cable direct from the Helix into my Mac, it went through a USB extension hub. Direct into the Mac, the squeal goes away. I feel like an idiot for not trying that before, but whatever. A scientist also documents his failures!

So now I've got non-squealy tones from the Helix and I've also had a number of compliments on my guitar tone, so I think I'm onto a winner!

Chris.B

That's a useful follow up - thanks for taking the time to come back and update us. 

I've had trouble with odd noises from time to time on the Helix when using some gain. The problems were caused by:

1: Dimmer switch in the same room
2: Lighting in the room below.  There is a combination of a fluorescent tube and an LED tube in the same fitting so I'm not sure which tube is the culprit