Sheelding power transformers

[kkrafs]

If you have a ring power transformer (power supply) what would
you recommend to be the best way to screen off the magnetic flux
from other sensitive cirquits inside the box?

Is it possible to completely shield the flux off?

With a stel plate, aluminium, or perhaps
wrap in the transformer in bismuth sheets?

The box is made of steel or aluminium and im aware
that this can cause magnetic flux problems to.

Perhaps i should go plastic with the box wich
then put other problems in to day light!

kkrafs

 

[northsiderap]

A thread about xformer screening just passed by a week or two ago... Try searching recent threads.

 

[vibrolax]

In my experience, aluminum does not shield or couple magnetic flux appreciably, so aluminum boxes are good for preventing RFI.

I try for maximum distance from the TX to the high gain portion of the circuit.
100 mm is usually adequate.

Toroids produce less radiated field than E-I lam TX's.

Mu Metal is the shield material of choice, but it's expensive unless you can salvage it from some other equipment.

I find that proper attention to grounding and layout has a bigger effect on hum and noise than maximally shielding the power transformer.

Jon

 

[CJ]

You will never get rid of 100 percent hum, there will always be an audible amount, as long as you have the gain to make it heard. Its a matter of what you want your s/n ratio to be. I have heard horrendous amounts of hum not from the studio, but from the guitar amplifiers. But when it's a stack cranked to earbleed, you don't hear it.
If you record classical, you obviously need to be more quiet.
So somewhere in between there is a noise figure you can live with. Using a seperate power supply with the power trans three feet away is one way to get s/n specs down to a very usable figure. And you do not have to fish around for the best transformer location and shielding. But, I admit, it is an impratical solution for most people. The want everything in the same box.

I have a feeling that hum specs in older equipment was not always stellar.
So trying to copy a piece of vintage equipment and expecting better noise figures could lead to disappointment.
There is a lot of crap on early recordings, if you listen for it. Mostly tape hiss. But if it's Chuck Berry, who cares.

Hey I just figured out that 60's dance, "The Jerk" People wanted to dance, but if the jumped around, the record skipped. So they kept the feet planted and just used the upper half. So no vinyl, no "The Jerk" Tragic, I tell ya!

 

[bcarso]

[quote author="CJ"]
Hey I just figured out that 60's dance, "The Jerk" People wanted to dance, but if the jumped around, the record skipped. So they kept the feet planted and just used the upper half. So no vinyl, no "The Jerk" Tragic, I tell ya![/quote]

The jerk is actually the seldom-heard term for the third time derivative of position, following velocity and acceleration. It makes sense since, in rectilinear motion, if you are moving at a constant velocity there is no force felt. At a constant acceleration on the Earth you can lean into the trajectory (and compensate for the constant force using the force of gravity) and be stable.

But if the acceleration is changing you get jerked around.

When I brought this up in a high school physics class, the seemingly homespun but sly teacher said, "Well, I reckon that's when you have to lie down and take it like a man."

 

[tk@halmi]

I have used half of a bean can over a toroid transformer before. It provided no benefit whatsoever, at least none I could measure, and increased the likelyhood of an accident. So stay away from bean cans. Also, refrain from attractive looking, but perishable materials such as pineapples.