120 volt pedals without a ground, safe when using GFCI?

[Burstbucker]

I was wondering something and I'd like some input from some of you knowledgeable people out there.

I'm having some ground loop problems when I try to use an old Ross Phaser pedal, it's powered with 120 volt power cord which has a ground wire which is there for safety but is very noisy.  I know that there's a special adaptor made by Ebtech that'll cure it safely but I was wondering if this idea would work just as well.  

What if I were to use a two prong 120V male cord end(no ground)instead of the three prong for my Ross Phaser and then just plug this new two prong male cord end into a power bar that will also feed some 9V wallwarts and my guitar amp, then just plug this power bar that's feeding everything into a GFCI(ground fault circuit interupter)?

Wouldn't this GFCI plug offer protection even though the noisy ground wire going to the Ross pedal isn't there anymore?  I'm thinking, if this will work, it'll be cheaper than buying one of those Ebtech doodads.  Will this work or not?

[niftydog]

disconnecting the appropriately named "safety ground" is the absolute last resort in any ground loop situation!

The ground wire is not in and of itself noisy - lets be clear about that.

A GFCI will only work when a device actually has a ground. Therefore, in your described scenario, it will not work if the fault exists in the Ross.

Also, even if you disconnect this ground, that is no guarantee that the ground loop will be fixed. How have you come to the conclusion that it's the Ross at fault and not the wallwarts?

I would first be sure that it is the Ross at fault by doing some simple tests with it in and out of circuit with the other equipment. Then, if you're sure that it is the Ross, then think about disconnecting the circuit (signal) ground from the chassis (safety) ground.

[Burstbucker]

niftydog said,
"How have you come to the conclusion that it's the Ross at fault and not the wallwarts? "

Well, when the Ross pedal isn't in the effects chain everything is nice and quiet or if I lift the ground going to the Ross and put it back in the effects chain it's quiet as a mouse.  If I put that ground back on there all hell breaks loose.

I know that a GFCI receptacle measures the current flowing through both the hot wire and neutral wire and if they don't read the same, (like if you're getting shocked etc),  it'll trip.

[niftydog]

Ok, so have you tried using the Ross exclusively? without any other pedals at all. Or, have you tried various combinations to see if it's not just the Ross, but a combination of the Ross and something else that's causing it?

Again, I would first try to do something about the signal grounds before taking the risky step of disconnecting the power ground.

Seems I may have been mixed up with my statement, after some reading I've discovered that a GFCI should work on a two prong device. But, here's the catch;

Suppose the hot comes loose inside the Ross and shorts to the metal chassis (if it is metal!). The chassis is now live and the GFCI will not trip until there's a path to ground from the hot chassis. This could be your hand! Now, as long as the GFCI is working as it's supposed to, you are safe, but should it fail, you're potentially fried.

However, if the safety ground remains in place, when the hot shorts to the chassis then a circuit breaker should trip. Or, if it's shorted after the fuse, the fuse will blow. Either way, it's just that little bit safer than the previous scenario.

Again, try modifying it to remove the signal ground from the safety ground. If you cant do this, consider moving the Ross to a plastic box before disconnecting the safety ground.

[Burstbucker]

Niftydog,

I'm not 100% sure if I did tried the Ross exclusively or not.  I'm almost certain that I did try that in the past and the Ross still caused this hum.  I'll try that again tomorrow when I get a chance and I'll post a follow-up.  Thanks for your input too BTW.