60-0-60 Balanced power system

[mbrooke]

Does anyone have that old Mike Holt graphic of a balanced power system? I had it on my hard drive but can't find it.

 

[LarryFine]

Sounds like a simple grounded-center-tap on a 120v transformer secondary.

 

[drcampbell]

That's what they are. They used to be common in radio, TV & recording studios to reduce 60-Hz noise. The center tap was connected to earth ground, and all the equipment grounding conductors (if used!) and the shields of the shielded analog cables were connected to it. The centertap wasn't used as a neutral; 120 volts was derived from the two 60-volts-to-ground conductors.

I don't know if this arrangement ever reduced noise, but it did make it impossible to have stray neutral-to-ground connections that you didn't know about.

 

[romex jockey]

I'm interested, but am missing the theory here, can U dumb it down? ~RJ~

 

[mbrooke]

There was a specific graphic I have in mind. Even a special receptacle I think. Google images no longer has the industry in mind.

 

[mbrooke]

There was a specific graphic I have in mind. Even a special receptacle I think. Google images no longer has the industry in mind.

Scratch that, found it.


But how does it supposedly work in limiting audio noise?

 

[pjones]

Are you going to post it so we can see too?


Sent from my iPhone using Tapatalk

 

[LarryFine]

Are you going to post it so we can see too?

He posted it in the Jenn-air plug thread.

 

[zbang]

But how does it supposedly work in limiting audio noise?

Makes the power cords & distribution behave more like a balanced line. Or that's the theory I've read about it.

 

[ptonsparky]

Pretty sure my old 120v generator was 60v L-G-L, 120 L-L. Also pretty sure it had nothing to with fancy electronics.

 

[mbrooke]

Are you going to post it so we can see too?


Sent from my iPhone using Tapatalk

Found it:

 

[mbrooke]

Makes the power cords & distribution behave more like a balanced line. Or that's the theory I've read about it.

Reactive currents maybe?

 

[Speedskater]

Makes the power cords & distribution behave more like a balanced line. Or that's the theory I've read about it.

Yes the theory was that it would act like a balanced signal interconnect system. But in an AC power system from a noise/leakage voltage/current point of view, the power transformer in an audio component is asymmetrical (mostly due to capacitance differences of the windings), so the noise voltages don't cancel out nearly as well as the proponents would have you believe. Much of the benefit comes from the it acting as an isolation transformer wired as a Separately Derived System.

 

[drcampbell]

I think some of the benefit comes from not having any neutral current flowing on ground wires and creating different voltages at different places on the "same" grounding system.

I realize that the same benefit could be derived from not installing wiring errors, but we're talking about the real world here. Any wiring error that puts return current onto the green grounding wire is going to be immediately obvious when the return wire is 60 volts above ground. Not so when the white return wire is a grounded conductor and it's only a volt or two above ground.

I suspect that isolated-ground systems sometimes reduce noise for the same reason.

 

[gar]

190411-1125 EDT

There at least three things to consider. Magnetic fields, electric fields, and conducted current voltage drops.

External magnetic fields are minimized by running forward and return current paths very close together. Twisted wire pairs help as well.

External electric fields are reduced the same way, by creating counterbalancing capacitive currents, and by shielding. Use faraday shielding in transformers.

A common grounding bus should be remote from current or voltage sources. Also design the system with electrical isolation, signal transformers or fiber optics, for examples. Two isolated twisted wires to a low impedance microphone, magnetic shielding around the microphone, electrostatic shielding the whole way, and only connect the shield at the destination to one of the signal wires.

The 60-0-60 does some of this.

.

 

[mbrooke]

I think some of the benefit comes from not having any neutral current flowing on ground wires and creating different voltages at different places on the "same" grounding system.

I realize that the same benefit could be derived from not installing wiring errors, but we're talking about the real world here. Any wiring error that puts return current onto the green grounding wire is going to be immediately obvious when the return wire is 60 volts above ground. Not so when the white return wire is a grounded conductor and it's only a volt or two above ground.

I suspect that isolated-ground systems sometimes reduce noise for the same reason.

Correct to say a 240 volt system does the same? Or a 208 volt 3 phase circuit?

 

[drcampbell]

So long as a "neutral" wire isn't used, yes.

 

[mbrooke]

So long as a "neutral" wire isn't used, yes.

Ok, now I want to know!

 

[gar]

190411-2366 EDT

Any conductor with a current flowing thru the conductor will have a voltage drop between any two non-coincident points on said conductor.

Any conductor will have an AC voltage drop between any two non-coincident points on said conductor where the space between said two points is in a changing magnetic field.

.

 

[LarryFine]

Keep in mind that every electronic device has a transformer in it, which is an isolation device.

Sometimes, the power supply is single-ended (like a DC version of 120v, with one end grounded), and sometimes, it's a dual-polarity split supply (like a DC version of 120/240v, with a grounded center tap).

Either way, it shouldn't matter whether the 120v supply is end-grounded or center grounded.