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[Nick Longden]

Ok...I’m frustrated. I’ve run three gigs now with my new DriveRack, and the problem I’ve faced each time now is interesting. I have the DR plugged into a power conditioner at the stage with my amplifiers. I’ve run at two separate venues now, and as soon as I fire up the DR, the input level meters on the front of unit start peaking. If I turn on the amps, (I only made that mistake once!) there is an awful buzz that comes through. The solution, I’ve found, is to run an extension cable all the back to my mixer.  It seems, that as long as the PA2 is on the same circuit as the FOH, it operates fine. But the minute I plug into another circuit, it goes crazy. Has anyone heard of this? I’ve decided I’m going to move the PA2 into my FOH rack, but I’m curious as to the reasoning for this. Never had this problem before the DriveRack.

Any explanation would be greatly appreciated! Thanks!

[Tim McCulloch]

Ok...I’m frustrated. I’ve run three gigs now with my new DriveRack, and the problem I’ve faced each time now is interesting. I have the DR plugged into a power conditioner at the stage with my amplifiers. I’ve run at two separate venues now, and as soon as I fire up the DR, the input level meters on the front of unit start peaking. If I turn on the amps, (I only made that mistake once!) there is an awful buzz that comes through. The solution, I’ve found, is to run an extension cable all the back to my mixer.  It seems, that as long as the PA2 is on the same circuit as the FOH, it operates fine. But the minute I plug into another circuit, it goes crazy. Has anyone heard of this? I’ve decided I’m going to move the PA2 into my FOH rack, but I’m curious as to the reasoning for this. Never had this problem before the DriveRack.

Any explanation would be greatly appreciated! Thanks!

You have a mis-wire in either your audio signal wiring, a defective device that is dumping voltage to ground, or neutral/ground swap in your electrical wiring of the amp rack.  Another possibility is that your "power conditioner" (did you use power shampoo first) has taken enough over-voltage hits that the MOV is now shunting voltage to ground.

[Mike Sokol]

You have a mis-wire in either your audio signal wiring, a defective device that is dumping voltage to ground, or neutral/ground swap in your electrical wiring of the amp rack.  Another possibility is that your "power conditioner" (did you use power shampoo first) has taken enough over-voltage hits that the MOV is now shunting voltage to ground.

You can use a clamp ammeter right around the entire XLR cable feeding the DR and see if you're getting measurable current on the shield. This is what actually causes ground loop hum. While you're at it, measure the voltage between the shield of the XLR connector and the DR without plugging it in. You're measuring open-circuit voltage in this case. Experimentally I've found that even 1/10 volt difference and maybe 100 mA can cause some gear to misbehave (the classic pin-1 problem). Since I also did a lot of gigs in places with compromised grounds, that why I've carried Ebtech Hum Eliminator or Whirwind ISO box isolation transformers. These are all just 600-ohm to 600-ohm audio transformers that allow you to break the copper path in the XLR shield, preventing any ground loop current to occur.

[Jerome Malsack]

https://www.guitarcenter.com/Ebtech/HE-2-XLR-Hum-Eliminator-with-XLR.gc 

[Tim McCulloch]

https://www.guitarcenter.com/Ebtech/HE-2-XLR-Hum-Eliminator-with-XLR.gc

His problem - full tilt meters without audio - indicates more than a simple ground loop.  I *suspect* there are a pair of failures at work here:  a hot/neutral swap, and a neutral/ground bonded (or shorted) in a major system component.

This means that there is potentially a threat to human safety.  Treat the problem, not the symptom.

[ProSoundWeb Community]