A-B-Y Box Noise:

Inspector #20

Inspector #20

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I ended up getting a new ART Cool Switch Pro Passive (unpowered) for my new board. It has a ground lift feature, phase switch and transformer isolate switch.

Trouble is, I have a noticeable hum on the slave amp (not the Origin) when using it.

I can diminish this noise to a degree via the switches, but I cannot eliminate it.

I've experienced the same noise with my 1999 Marshall MG50 and Blackstar ID-Core 100watt.

Is it time to step up to a better quality, powered box???

20211030_112945.jpg
 
you can try an adapter that doesnt have the ground lug on one of the 2 amps, with / without the ground lift.
I am not 100% sure this is safe, but think so since the ground is shared.

For a few bucks you could try it to determine if the 2nd ground path is the issue (or determine if the ABY ground lift is not actually lifting the 2nd ground path / ground loop). You might have to put tape over the green lug.

I tried this awhile back, just as an experiment with my plain old DIY ABY. I think it did work, but dont recall specifically.

1636036068665.png
 
Robert Herndon said:
I ended up getting a new ART Cool Switch Pro Passive (unpowered) for my new board. It has a ground lift feature, phase switch and transformer isolate switch.

Trouble is, I have a noticeable hum on the slave amp (not the Origin) when using it.

I can diminish this noise to a degree via the switches, but I cannot eliminate it.

I've experienced the same noise with my 1999 Marshall MG50 and Blackstar ID-Core 100watt.

Is it time to step up to a better quality, powered box???

View attachment 75256
Click to expand...
1. The slave amp is powered by a 3 prong plug - it's grounded to the power.

2. When you ground the slave amp a second time (at the input jack) it creates a ground loop.

3. Making a guitar cable with 1 end disconnected from ground will stop the ground loop.
The shield of the guitar cable is normally connected to both 1/4" plugs of the cable.
But you are making a special cable.
One plug will be connected to the wire shield as usual.
But the other plug will be isolated/ disconnected from wire shield (not grounded to cable shield wire on 1 end).

Shield = talking about the ground of the guitar cable wire.
Ground = also called "earth" in UK.
Shield = also called "screen" in UK.
We are all taking about the same thing, just to clarify.

This is a "ground lift cable." It would be common to see these type cables in studios / professional sound systems.
 
Amp Mad Scientist said:
1. The slave amp is powered by a 3 prong plug - it's grounded to the power.

2. When you ground the slave amp a second time (at the input jack) it creates a ground loop.

3. Making a guitar cable with 1 end disconnected from ground will stop the ground loop.
The shield of the guitar cable is normally connected to both 1/4" plugs of the cable.
But you are making a special cable.
One plug will be connected to the wire shield as usual.
But the other plug will be isolated/ disconnected from wire shield (not grounded to cable shield wire on 1 end).

Shield = talking about the ground of the guitar cable wire.
Ground = also called "earth" in UK.
Shield = also called "screen" in UK.
We are all taking about the same thing, just to clarify.

This is a "ground lift cable." It would be common to see these type cables in studios / professional sound systems.
Click to expand...

Both amps are plugged into my Furman Power Supply. This is the correct practice???

So, this modified guitar cable goes between the slave amp input and the ABY box???

And, to clarify...I will be unsoldering the ground at the plug on one end of this "special cable" so it will only have a single conductor???

Sorry for the questions, but I'm not as advanced as you are in this field.

Thanks...
 
Robert Herndon said:
Both amps are plugged into my Furman Power Supply. This is the correct practice???

So, this modified guitar cable goes between the slave amp input and the ABY box???

And, to clarify...I will be unsoldering the ground at the plug on one end of this "special cable" so it will only have a single conductor???

Sorry for the questions, but I'm not as advanced as you are in this field.

Thanks...
Click to expand...
Yes yes yes yes
 
jtcnj said:
you can try an adapter that doesnt have the ground lug on one of the 2 amps, with / without the ground lift.
I am not 100% sure this is safe, but think so since the ground is shared.

For a few bucks you could try it to determine if the 2nd ground path is the issue (or determine if the ABY ground lift is not actually lifting the 2nd ground path / ground loop). You might have to put tape over the green lug.

I tried this awhile back, just as an experiment with my plain old DIY ABY. I think it did work, but dont recall specifically.

View attachment 75257
Click to expand...
No you shouldn't do it that way.
You want to leave the power ground connected, that's the safety ground.
You can lift the audio ground instead. That's the better way.
 
Amp Mad Scientist said:
No you shouldn't do it that way.
You want to leave the power ground connected, that's the safety ground.
You can lift the audio ground instead. That's the better way.
Click to expand...

Not lifting the 120 VAC ground.

Yes to lifting audio shield/ground only on cable between ABY and Slave amp.

I'm building a cable right now.

@Amp Mad Scientist - Question

Any distance requirements between the two amps???
 
I suggeted above as an exploratory / troubleshooting suggestion, not a permanent solution.
The modified cable sounds like the right solution: most excellent @Amp Mad Scientist.
I would think you want to clearly label it.

So back to the ABY - the ground lift function is BS then?
 
jtcnj said:
I suggeted above as an exploratory / troubleshooting suggestion, not a permanent solution.
The modified cable sounds like the right solution: most excellent @Amp Mad Scientist.
I would think you want to clearly label it.

So back to the ABY - the ground lift function is BS then?
Click to expand...
We don't know what the ground lift is. I don't have the schematic...

But ground lifting is very widely used in any audio system, even home theaters, studios, PA systems...
I do it all the time to get rid of hum in systems.
Ground loops happen from cable TV too.

And making a ground lift cable (or adapter) is pretty basic stuff.
 
Apologies for being late to this, but AMS has answered with the correct method to use.
You want to keep the safety ground (the ground prong of the 3 prong AC mains) connected to both amps.
If you lift this safety ground at one amp, in the event that that amp develops a type of fault where the safety ground is needed (for YOUR safety), then the ground lifted amp has to rely on the signal chain connecting the inputs of both amps for it's safety ground, a less than ideal situation.
Here in Oz, the safety ground wiring must have less than 2 ohms series resistance for compliance with regulations. I imagine the USA has similar requirements. The signal chain linking the amp inputs will in all probability exceed this & is not something I'd bet my life on.
Break the audio ground (shielding braid) at one jack of one instrument cable as AMS has suggested. I have a patch cable with this done to it for when I use 2 amps in a wet/dry setup (via a stereo chorus pedal). Cheers
Edit:
A better ABY/signal splitter box will feature transformer isolation to avoid ground loop hum. Cheers
 
Last edited:
ivan H said:
Apologies for being late to this, but AMS has answered with the correct method to use.
You want to keep the safety ground (the ground prong of the 3 prong AC mains) connected to both amps.
If you lift this safety ground at one amp, in the event that that amp develops a type of fault where the safety ground is needed (for YOUR safety), then the ground lifted amp has to rely on the signal chain connecting the inputs of both amps for it's safety ground, a less than ideal situation.
Here in Oz, the safety ground wiring must have less than 2 ohms series resistance for compliance with regulations. I imagine the USA has similar requirements. The signal chain linking the amp inputs will in all probability exceed this & is not something I'd bet my life on.
Break the ground (shielding braid) at one jack of one instrument cable as AMS has suggested. I have a patch cable with this done to it for when I use 2 amps in a wet/dry setup (via a stereo chorus pedal). Cheers
Click to expand...

Thanks to both of you for the help!!!!!
 
Ok,

The noise from running two amps is overwhelming. I'm using the Cool Switch Pro Passive A-B-Y box that has a ground lift Switch, a phase switch and a transformer isolate switch.

Both my Blackstar ID-Core 100watt and my 1999 Marshall MG50 Solid State behave in exactly the same manner.

Both amps are powered from a Fuhrman SS-6B power strip.

Using a modified ground lift cable makes the noise even worse.

Here's a short video I shot today:

youtube.com

Noise From Two Amps Through Cool Switch Pro A-B-Y Box:

Ground lift feature doesn't cut the noise. I've used both a Blackstar ID-Core 100watt solid state and a Marshall MG50 Solid State with identical results. A g...
youtube.com youtube.com
 
Good tips...

Its odd that my Cool Switch Pro Passive A-B-Y Box has a ground lift, audio transformer and phase switch, but it doesn't seem to have any effect.
 
I wonder if Robert's ART amp switcher pedal is defective... :unsure:
67plexi said:
Buy a amp switcher with a audio transformer and one with a phase switch the two that work are.
I like the Radial 18db boost my friend Mark uses the Lehle,
Click to expand...
Radial Engineering (Canada) products must be good stuff. Excellent reviews on any of their stuff that I have looked into. The Radial Switchbone V2 is loaded with extra features. Maybe (@Robert Herndon) can consider the simpler and less expensive Radial Twin City as an alternative:
 
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