I absolutely love the Helix and the 4CM with the exception of one major ground loop issue that I've experienced with 2 different 2 - Channel Amplifier's. (Orange Rocker 15 and Freidman Runt 20) I've searched and read many different forums where guitarists have battled this issue. So, let me start at the beginning of what I've educated myself on from others who have shared their experience with this common grounding issue. First off, I have used the HD500 and HD500X using the 4CM and did NOT have the extreme ground loop issues that I'm having with the Helix. From what I've read, it appears that the Line 6 Helix utilizes the same grounding points for all Outputs and Aux Send/Returns. Had Line 6 isolated these different grounding points I don't believe that there would be the ground hum issues that exist. I cannot verify this personally, but it's what I've read on other forum's who had looked at the schematic and does seem to make sense.
So, in my personal experience there are two ground loop issues that I had to resolve to dramatically reduce the low end ground loop hum that I've fought with two different amplifiers. In my situation I am not only running the 4CM, but also utilizing the Helix to switch my amp channels between clean and dirty channels. When the amp switching 1/4" cable is NOT utilized, the ground hum issue is definitely still there, but dramatically less. When you plug the 1/4" amp switching cable in, (in addition to the 4CM), it more than doubles the ground loop hum (on both amplifiers). I had read on another forum that if you utilize a "ground loop isolator" on the effects loop send channel it would resolove the ground loop hum, which it does. So, that is FIX # 1. I bought a cheap Pyle 1/4" Gound Isolation box and also an expensive Lehle "P-Split" galvanic isolator. I first bought the cheap Pyle box and it did reduce the hum, but not nearly enough, so I bought the Lehle P-Splitter hoping it would reduce the hum even more down to an acceptable level. To the human ear I found that the dramatically more expensive Lehle P-Splitter ($180) did not provide any additional hum reduction over the less expensive Pyle box ($20). If you are NOT utilizing the Helix Amp Channel switching, then this should dramatically reduce your "ground loop hum" and you should only read the next section for future reference.
Before I get to this next section which will reveal the fix that worked for my situation I wanted to make sure to share one other thing. I did try and insert both the Pyle and the Lehle on my 1/4" amp switch output of the Helix, which did dramatically reduce the last part of ground hum, BUT it disabled the Helix from actually switching the amp channels back and forth.
After realizing that I still had an issue after buying the more expensive Lehle P-Splitter with no improvements I then recruited the help of my good friend and sound technician for my band. He's also has tremendous electronics background so I was hoping he might be able to help me resolve this grounding issue. We started out with all the basic trouble shooting stuff like utilizing a ground lift, etc., to no prevail. (I also have a high end ground ISO rack mount power supply in my rig.) At that point he recommended that he build an ISO-Switch Box for me to insert right out of the Helix amp switch 1/4" output and then run the cable to my Amp's 1/4" channel switch input. Well, IT WORKED!!! After weeks of struggling to figure this out it was finally resolved. So, I wanted to share my story with all of the other 4 Cable Method users and offer up a couple different options that my sound guy could help with. Not looking to make big profit off this here, but do want to make it worth his time to build these units if anybody is interested. He can build a 2 - channel ISO-Box (Clean/Dirty Switching) for $125 or he build a 3 -channel ISO-Box (Clean/Dirty/Reverb or Clean/Dirty/Lead - Tip/Ring/Sleeve) for $150. Honestly, I would have paid $300 to get rid of the ANNOYING Ground Loop Hum as it was driving me absolutely nuts.
So, for now I'll just say hit me up within this forum if you are interested and I'll connect you with my sound tech. I'm going to put a YouTube video together at some point and I will update when I do.
Peace
