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4 cable method making hum noise to amp


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Can someone help with my noisy setup ? 
i have a helix going 4 CM with a DSL 100 h. 
it is making a big hum specifically through lead channel. ( drive from marshals own distortions)
Gtr going to helix Guitar in. 
out from send 1 to amp guitar input 

( at that stage the hum is made)

out from amp loop send to helix return 1

out from helix 1/4 output to amp return. 

Then I plug my gtr straight to amp guitar input and leave the effect loop in and out with helix ,and it’s fine ! 
So the hum is at the stage before amp input in the helix. 
Note that no block at all is in that helix patch. Totally blank patch. 
how come ? 
how could I fix this? 

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All of the audio devices should be running from the same electrical source (to eliminate ground loops).

The FX loop does add a small bit of noise. It's NBD with my Tweaker, but that's not a high gain amp.

You could try lowering the SEND level (might have to increase the Output level of prior FX), or use a "hum buster" type of device between the SEND and Amp Input.

That worked for me (the hum buster) with an Engl that I had.

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In addition to running from the same source as rd2rk suggested, I also use a transformer based AVR (Automatic Voltage Regulator) on the input power for my entire rig. Ground loops are something I dealt with before I used an AVR...1985 maybe?...I have toured globally with this approach...Hum eliminators are pretty rare for me but I always have at least one...I have had some rack rigs in the past where I had some internal ground loops, but those are usually solved with a couple of signal shield lifts to normalize the rig signal ground path...Additionally in rack rigs, all but one component electrical ground are lifted because the rack rails...I always use a "hum eliminator" but that is just a direct box connecting to other systems that are not on my source power...signal isolation...


I used a Furman AR-15 for years...These days a Tripp Lite LCR1200 is plenty and just a good as the Furman but quite a bit less $$....Power Conditioners are NOT AVRs.

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On 10/10/2021 at 11:59 AM, bobpick said:

For me the fix was to set my send block to line level. The hum instantly disappeared. It's not optimal because my Helix send is going to the amps input. I adjusted level to compensate.

You can also adjust the signal strength of your send/return. 

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