Toroids and electronic radiation

[Elkaid]

Do toroids have tendencies to induce noise in components when placed too close ?.

By example, if I place an Op-Amp or a signal wire too close of a toroid transformer, will it induce noise or other indersirable things ? What are safe distances ?

I know that standard "rectangle" transformer radiate a bit (I suppose that's why aligment is so important in tube amplifier) but is it the same thing with Toroids ? R core ?

Thanks for your help !

 

[Jan Dupont]

Toroids DO induce noise in components when placed closed to them, however the induction is much smaller than for the "old" standard "rectangle" transformers.
Personally I only place non-active components near a toroid. If I have to place an active component (like an Op-Amp or a transistor) I always use a shielding metal plate to awoid induction, and never place signal wires close to the toroid.
I don't think you can "calculate" the safe distance, because this depends on many factors like the way the toroid are wounded, the internal layout of the active components, pin length etc.
You can infact hear the induction noice, by moving a signal wire over and along the sides of the toroid.
Does somebody have other experiences????

 

[Eric]

You Bet! I had to place a copper shield around my toroid because it induced hum into my signal wires that run beside it. Got some flashing from the local hardware store and cut a band to go around the outside. See photo

 

[Jan Dupont]

Hi Elkaid,
Seems very much the same as my solutions

What are your experiences with main wires around the chassis..?

 

[jackinnj]

not Cu, Fe

if you want to shield the transformer iron (muMetal) will do the trick

I believe that pot-core transformers have the lowest radiation.

 

[Elkaid]

is Fe better than Cu ?

A few month ago, we were using sheets of Cu to shield PowerLine transmitters prototypes from RF noise. It seems to work fine but that couldn't make us win the bakeoff though. (Anyway, that's another story)

So, is Fe better in shielding LF noise than Cu ? Or is it something more "subtile" ?

Thanks !

 

[Jan Dupont]

I personally don't think that there are a big difference because Cu also has a low resistance as Fe. I think that the result is determent by the actual way the schielding is made (please also renember that if you use perforated plates for shielding, that the holes are smaller than the wave lenght of the RF-signal that you wich to schield out)....

 

[Elkaid]

if you use perforated plates for shielding, that the holes are smaller than the wave lenght of the RF-signal that you wich to schield out

Uhhhh...
If I'd like to filter out 60Hz noise by example, how can you convert a frequency to a distance (diameter) ?

Also, using a non-perforated plate will block any frequencies ?

 

[peranders]

You Bet! I had to place a copper shield around my toroid because it induced hum into my signal wires that run beside it. Got some flashing from the local hardware store and cut a band to go around the outside. See photo

Did the hum go away?

Maybe you had capacitve coupling? May I ask why you have your cables so loose and near the transformer? Ground rule must be: keep away everything from the transformer. I notice also that your 115/230 volt primary is very close to one of the secondary winding.

 

[Jan Dupont]

To calculate the wave-lenght:

Wave lenght in meter = 300000 / the frequency in kHz, so you would need rather big holes to let 60 Hz pass through

Thats why you can have air circulation holes in your cabinet without problems.

In theory, all frequencies should be blocked by a massive plate. But thats theory........

 

[Shoog]

I have tried using Lead to shield my transformer because of its easy of working, but to limited success. Is lead a no brainer.

Shoog

 

[Jan Dupont]

Lead is good for magnetic/inductive shielding, not RF-signals.

Make sure to only use one electric connection to your shielding, and this should be connected the common ground junction of your supply.

 

[Elkaid]

Interesting...
http://www.diyaudio.com/forums/showthread.php?postid=206794#post206794

Looks like we're not alone discussing about those issues

Lead is good for magnetic/inductive shielding, not RF-signals.

In which category nuclear radiation is categorized ?

 

[Jan Dupont]

I have worked with isotop scanners, so I sure hope that Lead is shielding against nuclear...
No problem... It does!!!!!!!!!

Regarding Peranders. He is right in his point. Keep those wires away from the toroid!!!

 

[peranders]

Lead is good for magnetic/inductive shielding, not RF-signals.

You actually mean that lead can bend magnetic field? I thought only magnetic materials could do that, iron, nickel, crome, cobalt, more?

 

[Jan Dupont]

Peranders:
There you hit me on a soft spot
As I recall, I have seen Lead used as magnetic shielding on sensitive sensors.... But I would not bet on it......

 

[Elkaid]

Is it me Peranders or your last post has just "disappeared" ?

You were talking about high energy radiation...

It's the 3rd time that I read a post and when I hit refresh, it has disappeared...

very strange.....

 

[Jan Dupont]

Elkaid:
I don't recall anything about high energy radiation
However.... Have you got some answer to your question???
Or..............

 

[peranders]

Is it me Peranders or your last post has just "disappeared" ?

You were talking about high energy radiation...

It's the 3rd time that I read a post and when I hit refresh, it has disappeared...

very strange.....

I deleted my post since I saw Jan's post above covering the thing I mentioned.

Lead is used for shielding X-rays and for other kind of high energy radiation like alfa, beta, gamma rays, cosmic radiation (which some sensors must be protected from) nuclear stuff.

 

[Jan Dupont]

Please let me know if I was ALL wrong regarding Lead used as magnetic shielding... I'm still sure that I recall the use of Lead for this purpose....