Big hum problems

Owczar

Owczar

Member
Hi!
Recently we faced really strange problem, I hope somebody will help me out ;)
In my band we are using one big rack - we have there our monitor mixer (mackie dl32r), shure psm900 iem systems, shure qlxd wireless systems, and 2 fractals XL+.
We also have one AX8, and signal goes from wireless receiver in the rack to AX8, and from AX8 back to rack. Unfortunately there is huge issue with ground loop - or something different causing nasty hum, I don't know.
Usually, if we connect AX8 power cable to the same power strip as whole rack - everything is fine, problem occurs only if AX8 power is connected to different power strip - that's understandable.
Recently we had this hum problem even when everything was connected to one power strip, when we tried to connect ax8 to different strip for comparison, hum was louder than guitar :p Ground lift switch made things even worse. We found that eliminating wireless from the chain solved things, guitar with cable straight to AX8 - no hum at all. We tried different cables, different wireless, we swapped AX8 with XL+, using the same signal chain - wireless through the same cable into XL+, the same XLR cable to mixer - zero hum. AX8 again - hum. AX8 without wireless - no hum.
Somebody have an idea what's going on? Maybe some piece of gear like Morley Hum Eliminator will solve this problem?
 
How are you running cable from the rack receiver to the AX8? Is it an unbalanced instrument line and is it a long run?

If any longer than 25ft or so, I'd highly recommend using a Radial SGI system. It looks like a pair of DI boxes (one on either end), with 1/4" instrument cables from receiver and AX8, but a balanced XLR cable (and a ground lift option) for the distance run.

And yes, running the AX8 power on a different strip might mean it's on a different circuit or even different isolated ground, which opens the possibility of ground loops.
 
It's standard jack-jack unbalanced guitar cable. But we tried short one and it was the same. And again - on last two gigs it happened even when AX8 was connected to the same power strip as everything else in the rack. XLs were dead quiet. Only solution we found was to ditch the wireless and use cable - but it's not a solution is it? ;)

@Keg8605 You said "This has worked for me before" - You mean that You had similar problems? If putting receiver in pedalboard with ax8 can help, we will try. Any ideas for elegant solution to mount rack wireless in pedalboard? ;)

Worst thing is that we can't make this problem appear (in rehearsal room everything is fine, some gigs also were ok), so we can't be sure if any solution we applied will work on a "faulty" stage. And I can't believe that not cheap Radial SGI system is only solution for this problem. I mean I haven't seen this in any rig yet, and there was no problems like we have...

Thanks for replies guys!
 
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