getting to the root of a ground loop problem...

J

johnnyg88

Member
I've just started using my Boss RC50 with my AxeFx. Everything works and sounds great except for this ground loop hum I'm getting. I know I could get an Ebtech this or that (which I just might end up doing) but what could the root of this problem be??

No noise until I plug my RC50 into the FX Loop:

AxeFX Output 2 --> RC50 Input
RC50 Output --> AxeFX Input 2

Most of the noise occurs whenever I connect the AxeFX Output 2 into the RC50 Input. Plugging the RC50 Out to the Axe Input 2 alone brings a little bit of barely audible noise but plugging in the Axe Out2 to the RC50 In alone brings the loudest noise. Both is worse.

The RC50's power adapter only has 2 prongs, no ground prong. I disconnected the Shield on one end of the cable connecting the Axe Out2 and the RC50 In and that made the RC50 freak out and overloaded its input (luckily I had my power amp turned down to zero). So I tried that cable to connect the RC50 Out to the AxeFx In2 and a regular cable to connect the Axe Out 2 and RC50 in. This definitely reduced the noise a bunch but it's still noticeable with my higher gain patches, especially if I'm not touching the guitar. Touching the jacks of the cables plugging into the RC50 makes it go away.

So what can I do here? I'm considering getting an Ebtech Hum X, but where in my setup would that go? I could also get the 2 channel Hum Eliminator, as I wouldn't mind if the tone going to/from the RC50 is altered a bit.

But before all that, how can I properly correct this problem? Is that even possible?

My rig:

Furman Power Conditioner
AxeFX Ultra:
- Output 1 L/R --> Carvin DCM3000L --> 2 1X12 cabs
- Output 2 --> RC50 In
- RC50 Out --> Input 2

All the rack units are mounted with shoulder washers on the front and rear of the units. There are 3 washers per screw on every unit: Shoulder washer for the screw head, shoulder washer on the front and rear of the hole (the kind that goes inside the screw hole).

Thanks guys!

jg
 
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I had a somewhat similar problem with my jamhub/art t8 setup. I had to basically ground the external ground lug from the art t8 to one of the output jacks and one of the input jacks on separate channels on the opposite side of the t8. I have my axe fx coming in and the clamp is connected to the housing of that connector. From what i read you need to have all your grounds all going to one ground to avoid a ground loop. In my situation i have all the grounds from the art t8 going to the axe fx via this special cable i made.

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johnnyg88 said:
IAll the rack units are mounted with shoulder washers on the front and rear of the units. There are 3 washers per screw on every unit: Shoulder washer for the screw head, shoulder washer on the front and rear of the hole (the kind that goes inside the screw hole).
Click to expand...
This is probably part of, if not the source your problem... what you have done here is ISOLATE each device in your rack.. as soon as you hook up an un-grounded unit to something in the rack, you may get a ground loop as the signal is searching for the lowest potential route to ground.. This can be aggravated if the devices are powered from different/multiple outlets/circuits.

Remove all the washers... this will give you a star-grounding pattern, so that each device is grounded to each other - by the rack rails front and rear... it should remove your hum.

I used to have a similar issue with my PA system, until someone told me what I jsut told you. I had rubber strips between rails/devices causing each to be isolated. Thought/read that it would work better. I now have NOTHING between amps and rails, DELIBERATELY power the rack from TWO separate circuits (rails act as common ground) and it is SO QUIET you wouldn't even know it was on!
 
Thanks guys!

I will try removing all the washers and see what happens. Everything is plugged into a Furman power conditioner which goes into a single outlet, so hopefully grounding each device to each other will help.

I was also meaning to try each unit with the ground lifting plug on each unit to see if anything changes.

jg
 
Come to think of it now i have this old peavey power amp with a broken ground plug, and i got me some of them shoulder bolts, cause like you i read that it would prevent hum, but after i put them shoulder bolts in that amp hummed like a mad ape. It must of been grounded through the rack rails. I thought you needed to have a ground that like literally went into the actual ground (dirt). Wouldnt grounding each unit to the rack and having each unit with a ground plug cause it to have two common ground points. Having to ground points isnt suppose to be good from most things that ive read?
 
torchlord said:
Wouldnt grounding each unit to the rack and having each unit with a ground plug cause it to have two common ground points. Having to ground points isnt suppose to be good from most things that ive read?
Click to expand...
No, it does not work that way. If you have one power source, ground is ground. If you have 2, like I do on my rack, it ensure that the rails act as the common ground between sources/circuits, and there is no buzz/hum.
See here for basic principle..
Poor Mans' Power Distro
 
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