Ground Wire: Optimal Set Up?

[watchnerd]

Here are some real world scenarios and my hum experiences:

TT -- ground --> Devialet = no hum

TT -- ground --> SUT -- ground --> Devialet = no hum

TT -- ground --> SUT -- ground --> tube phono -- ground --> Devialet = hum

TT -- ground --> SUT -- [bypass tube phono ground wires] -- ground --> Devialet = no hum


What's going on here?

I assume it's a ground loop due to potential differences, but I'm not understanding why the tube amp seems to be the culprit.

Why does bypassing the ground connection for the tube amp make ground better?

Is the big fat tranny on the tube amp causing EM induction in the ground wire?

And is this optimal, or is there a better way to do things?

 

[SIY]

I assume it's a ground loop due to potential differences, but I'm not understanding why the tube amp seems to be the culprit.

Because most tube amps are designed by hacks with no engineering approach to grounding or layout.

 

[watchnerd]

Because most tube amps are designed by hacks with no engineering approach to grounding or layout.

So best to just bypass it entirely?

Or is there a better choice?

 

[PaulD]

The return currents all run through "ground", and it is the reference for all signals in unbalanced equipment. The attached PDF is readily available on the net, in case you have not seen it, it's well worth reading carefully. Yes, it looks like the tube amp is the culprit, who knows if it's possible to fix it...

 

[watchnerd]

The return currents all run through "ground", and it is the reference for all signals in unbalanced equipment. The attached PDF is readily available on the net, in case you have not seen it, it's well worth reading carefully. Yes, it looks like the tube amp is the culprit, who knows if it's possible to fix it...

Do I need to fix it, or is bypassing it just fine?

 

[Blumlein 88]

Is this when you could be convinced you need one of these?
https://www.entreq.com/products/ground-boxes-17667704

If bypassing ground on the tube unit fixes it, that is what I'd do. BTW, exactly what do you mean when bypassing ground? Lifting the 3rd pin on the cord or not connecting a grounding lug on the phono unit?

Without knowing the unit I couldn't know, but in some tube units you can reverse the power cord polarity and hum goes away with no bad consequences. But that depends on how your unit is made.

 

[watchnerd]

Is this when you could be convinced you need one of these?
https://www.entreq.com/products/ground-boxes-17667704
View attachment 34620

If bypassing ground on the tube unit fixes it, that is what I'd do. BTW, exactly what do you mean when bypassing ground? Lifting the 3rd pin on the cord or not connecting a grounding lug on the phono unit?

Without knowing the unit I couldn't know, but in some tube units you can reverse the power cord polarity and hum goes away with no bad consequences. But that depends on how your unit is made.

Not connecting the grounding lug on the tube phono; the grounding lug on the SUT (upstream from the tube phono) being connected to both the TT, on one side, and the amp, on the other.

If I remember right, those Entreq boxes are just filled with Swedish dirt....

 

[Blumlein 88]

Not connecting the grounding lug on the tube phono; the grounding lug on the SUT (upstream from the tube phono) being connected to both the TT, on one side, and the amp, on the other.

If I remember right, those Entreq boxes are just filled with Swedish dirt....

Oh, but such special magical dirt.

From what you describe just don't connect the tube unit ground if that makes hum go away.

 

[PaulD]

Do I need to fix it, or is bypassing it just fine?

That's impossible to answer without circuits and measurements.

 

[watchnerd]

That's impossible to answer without circuits and measurements.

I don't hear it, and can't feel it by touching the speaker cones when no music is playing; this implies to me it has dropped below the threshold of audibility (or is close to it), even if not zero.

Plus, the designer of the tube phono is deceased, so not so easy to get a circuit diagram.

 

[SIY]

Plus, the designer of the tube phono is deceased, so not so easy to get a circuit diagram.

The circuit diagram will rarely, if ever, give a hint about the grounding.

Just out of curiosity, was this one of Allen Wright's preamps?

 

[watchnerd]

The circuit diagram will rarely, if ever, give a hint about the grounding.

Just out of curiosity, was this one of Allen Wright's preamps?

No, it was designed / built by Don Garber of Fi.

 

[SIY]

No, it was designed / built by Don Garber of Fi.

Aha. He made stuff that looked really nice, but seems to not have much actual engineering to it. I wouldn't be surprised if there were issues with layout and grounding.

 

[GrimSurfer]

Plus, the designer of the tube phono is deceased, so not so easy to get a circuit diagram.

As long as the cause of death wasn't electrocution, you should be fine.

 

[watchnerd]

Aha. He made stuff that looked really nice, but seems to not have much actual engineering to it. I wouldn't be surprised if there were issues with layout and grounding.

Yeah, it gets much higher marks as a work of art than one of engineering.

It's also built in such a non-standard way it's not easy to take apart and look at (photos not mine):

 

[watchnerd]

As long as the cause of death wasn't electrocution, you should be fine.

I did blow up a tube in it, though.

About a month ago, I grabbed one of what I thought was a 6DJ8-type tube from my box. I was in a bit of a rush and didn't look at the box/tube label and stuck in a 6BZ7 that came with some mothballed Schiit thing.

Turned it on, got distracted by life, left it on but didn't use it. The next day one of the tubes was shattered with a weird white effect at the top of the tube.

 

[Cbdb2]

You say the engineerings not great but your thinking about lifting the ground pin? Hope your interconects can handle 15 amps of fault current, or you can handle 120volts.