Isolation Transformers Used For Audio Systems and Grounding

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wmhart

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Austin
gar said:
170701-2149 EDT

wmhart:

I believe your original post was mostly about noise or interference getting into your sound equipment, and listening room. Some basic electrical principles apply.

1. Magnetic coupling. To induce a current or voltage in something requires a changing magnetic field coupled to that something. This can occur in several ways.

Move a fixed magnetic field in space relative to the something, or vice versa.

Change the magnetic field intensity produced by the source so that field intensity changes at the something. Typically from an AC current in a conductor.

A single wire with current is big problem (a large loop for the current path). Two wires with exactly the same current but opposite in direction tightly positioned together produce a much lower stray magnetic field when measured a short distance away compared to the single wire.

Romex is fairly good. A twisted pair with a short twist pitch is probably better. A steady DC current is better, but how do you make it steady.

An electrostatic shield has little effect on low frequency magnetic fields.

Magnetic materials can provide magnetic shielding.

Transformers generate leakage flux.

You can probably assume magnetic field intensity drops off at least as fast as 1/r, where r is the radial distance from the source.


2. An electrostatic shield operates by providing a conductive path physically between an electric field source and the said something being shielded.

Two conductive plates separated by an insulator creates a capacitor. A capacitor conducts an AC current.

If a transformer is built without an electrostatic shield between primary and secondary, then a capacitance exists between primary and secondary that can couple high frequency noise between the pri and sec.

Insert a shield between pri and sec and connect the shield back to the source, and little noise is coupled to the secondary

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Gar- I need to chew on this, you are taking me back to basics here, and I need to think through it. (Sometimes the simple stuff is the hardest).
 
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wmhart

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gar said:
1270702-0853 EDT

junkhound:

My comment on how do you get a constant DC current was meant to discuss current and not voltage. A variation in a DC current will induce a voltage or current in a conductor somewhere. If one uses a DC power distribution system for audio, then there will be a varying magnetic field from that distribution system from audio signal level changes.

Thus, in a DC distribution system it is important to keep the source and return conductors close together.

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Got it. I use a bench power supply with several channels to feed some small tweaks that come with switching type wall warts- the bench supply has a large toroidal and theoretically eliminates the noise of the wall warts. This gets fed from one of the regular household outlets, not the dedicated lines in the audio system. What's fascinating to me is how little current these things actually draw. The voltage fluctuates by, say, .1 or .2 on occasion- perhaps that means that whatever regulates the voltage in the supply is less than robust-- it isn't a terribly expensive supply. The voltage loss at the end of the cables for the devices it services seems to be minimal- the runs are about 12 feet (so that's calculated as 2x, right?) i have this nice Fluke meter I use to bias my amps, i believe it is pretty accurate in measuring the point of use output. The line stage, as mentioned, uses batteries. It is a thing of beauty. The designer, who knows I like to expose the internals and shield them with a really thick piece of acrylic, added a few things when he upgraded the battery system. I'd be happy to show you the inside of that thing with a photo. He's in Pa. and unlike the old school tube stuff, this thing is a work of industrial art in a totally different way.
 
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teqniqal

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Location
Fort Worth,TX
Getting some objective information to base you decision upon.

Getting some objective information to base you decision upon.

A really well-researched and objective white paper on the subject of power for audio systems can be found at:
http://www.middleatlantic.com/resources/white-papers.aspx

Look at "Power Distribution and Grounding of Audio, Video and Telecommunications Equipment" and the following Addendum to it. As Joe Friday would say: "Just the facts, ma'am".
 
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Ingenieur

Senior Member
Location
Earth
teqniqal said:
A really well-researched and objective white paper on the subject of power for audio systems can be found at:
http://www.middleatlantic.com/resources/white-papers.aspx

Look at "Power Distribution and Grounding of Audio, Video and Telecommunications Equipment" and the following Addendum to it. As Joe Friday would say: "Just the facts, ma'am".
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interesting
looks like a compilation of various available technologies
it will take some time to read
looked at the authors
looks like av equipment suppliers with support from ee's
 
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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
170707-1040 EDT

I have read some portions , and glanced thru the entire middleatlantic reference and it looks to be a very good source of information, and includes some likely useful numeric values.

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Ingenieur

Senior Member
Location
Earth
ggunn said:
Does it justify spending $1500 on a 6' power cord?

http://www.soundstage.com/revequip/audiomagic_clairvoyant.htm
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:lol:

The distortion caused by the power line, although measureable, is inaudible
after filtering/rectification, signal processing, etc, it a very small component of the delivered signal
over 110 dB down
it is the distortion on the lv signal side that may be audible
I guess if you ran the phono cable close to and in parallel with the amp power cable you could hear it, MAYBE
 
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