Should I lift signal ground from chassis earth ground for all amps and Dumbleator clone?

itsGiusto

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Since working on my Revibe, I'm really intrigued by the common advice I'm seeing of separating the signal ground (Common) from the chassis ground (earth). As far as I understand, you should really only have 1 device in your signal chain that has an earthed signal ground, because otherwise, you'll get cross-talk of noise between the two earthed devices. Noise from the ground of one device will flow through the signal ground to the other, and vice versa. It seems the remedy for this in the Revibe is to lift the signal ground from the chassis, and connect the signal ground to the chassis with a 16 ohm resistor, a forward diode, a reverse diode, and a 0.047uf capacitor, all in parallel (with the capacitor specifically running from the input jack sleeve to the chassis, and the rest running from the signal ground bus to the chassis), as stated here:

Is this something that it would be good to do for all of my devices and amplifiers? For example, my Dumbleator clone could theoretically have ground loops when used with an amp. Or if I wanted to run two amps in parallel with each other, if I don't use some sort of transformer-isolation device to separate the two, then they'll have a ground loop between each other. I've experienced this before, a very bad buzz when amps are in parallel with a basic y-splitter.

If I wanted to try to spruce up my amps and Dumbleator, could it be a good idea to lift the ground like this for all of them? Could it adversely affect the sound in any way? And is the prescription for all of them the same: a 16 ohm resistor, a forward diode, a reverse diode, and a 0.047uf capacitor, all in parallel?
 
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itsGiusto

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Always have the safety earth connected.
In my post I'm not talking about disconnecting the safety earth, I'm talking about how to lift the signal ground from safety earth.

If you are using a number of amplifiers, take them from the same phase and supply point. There will be no ground or earth loops then.
What do you mean by "same phase and supply point"? Do you mean there'll be no loops if I just plug them both into the same wall socket?
 
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Jon Snell

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To lift the ground use a DI box. That is what they are designed to do.
If you take all power amplifiers from the same wall socket when using backline on a stage, the earth point comes from one point reducing the possibility of a ground hum.
I had an issue a few years ago; hum in the background on stage with a couple of national bands.
The problem was the mixing desk came from a power point from a wall socket in the main arena and the stage housed the power amps and backline that was off a 64Amp supply on stage.
The 64A supply came from the L1 phase and the desk supply from the L3 supply.
DI box between the desk and the stage cured the issue.
 

itsGiusto

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To lift the ground use a DI box. That is what they are designed to do.
Doesn't a DI box usually convert from instrument level to mic level? Do they make DI boxes that convert from instrument level to instrument level, for daisy-chaining amps?

If you take all power amplifiers from the same wall socket when using backline on a stage, the earth point comes from one point reducing the possibility of a ground hum.
I had an issue a few years ago; hum in the background on stage with a couple of national bands.
The problem was the mixing desk came from a power point from a wall socket in the main arena and the stage housed the power amps and backline that was off a 64Amp supply on stage.
The 64A supply came from the L1 phase and the desk supply from the L3 supply.
DI box between the desk and the stage cured the issue.
I get the hum when I daisy chain two amplifiers that are plugged into sockets on opposite sides of my living room. Does that sound plausible?
 

SRHmusic

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An isolation transformer is useful if you end up with a ground loop. Some DIs include an isolation transformer, and that's probably what folks are referring to. A problem, or at least a limitation, with single ended (not balanced) instrument and guitar cables is the shield is the return path for the signal. With isolation transformers at each output in the chain (e.g. fx processor, pedal board, then to the amp), each piece of equipment has its own path back to earth, and the cables between equipment have their shield tied to only one side. So this breaks the larger ground loop(s) but each segment is still earthed for safety.
Note, the isolation is between the shields of different equipment, not between an instrument and an amp if directly connected.
 

Wally

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You can simply break the ground connection at one end of an instrument cable that would then be used ONLY for connecting the Revibe to the amp. Mark this cable for this special purpose. Maintain the chassis ground to the wall on the Revibe and the amp. If one lifts the ground for one of those pieces of equipment, then the player becomes the shortest path to ground in the worst case scenario. This cable will break any ground loop while maintaining the shortest path to ground from the Revibe and the amp.
If I understand what that link shows us, that is called a partial ground lift, isn’t it? I built on of those into a Fender 6G15 a couple of decades ago to eliminate ground loops.
 

itsGiusto

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If I understand what that link shows us, that is called a partial ground lift, isn’t it? I built on of those into a Fender 6G15 a couple of decades ago to eliminate ground loops.
Yep, that sounds right. Can you do a partial ground lift for anything? Like amps and dumbleators (buffered effects loops)? And is it always implemented the same way?
 




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