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Old 3rd February 2011, 11:37 PM   #1
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Default Choke orientation (Need help)

I need help figuring out which way my chokes and transformer should be placed. I have a power transformer like this:

Click the image to open in full size.

It has all wires coming out of a single opening in the case of the transformer. I'm not sure what kind of magnetic noise it makes. I also have 2 chokes like these:

Click the image to open in full size.

I need to mount all three in my chassis and I was wondering how I should place them. They can only be mounted on the same panel, but they can be rotated to reduce noise.

Thank you!
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Old 3rd February 2011, 11:44 PM   #2
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I've used an old 'trick' when positioning output transformers, and it should work for chokes as well. (Note: the component connected to the headphones is NOT wired into the circuit at all.....)
Popular Science - Google Books

Headphone trick [Archive] - The Gear Page

John
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Old 3rd February 2011, 11:51 PM   #3
Matt BH is offline Matt BH  United Kingdom
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Hey thats pretty cool

I use an old relay coil on the scope probe as a "search coil" when checking for stray fields etc. Never thought of using the choke or output tranny I was worried about as the "search coil"

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Old 4th February 2011, 04:50 AM   #4
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I was actually more concerned about their relation to each other. I've heard people say that one inductor should be rotated 90 degrees to reduce cross-talk.
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Old 4th February 2011, 05:31 AM   #5
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Quote:
Originally Posted by fingerboy21 View Post
I was actually more concerned about their relation to each other.
I thought that's what we were talking about. I guess you want an answer that doesn't require any experimentation?

"Put the laminations 90 degrees from each other".

Of course, this also applies to the output transformer. Sometimes you can put the choke under the chassis- this can help with cosmetics as well as possible interactions.

John
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Old 5th February 2011, 03:15 PM   #6
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I really enjoyed the Pop. Sci. Article. Question is, do you need to wear a coat and tie while doing the test?
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Old 6th February 2011, 02:18 AM   #7
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Thank you, I was assuming each sequential inductive divide would be 90 degrees apart. I'll do that!
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Old 6th February 2011, 03:15 AM   #8
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Mains chokes are THE WORST offender for creating fields....think about how much AC is dropped across the chokes??????? These should be located as far away as possible from anything!.......other TXs' OPTs'......signal wires , all of it.
If you can suspend these on plastic blocks at the far, far corners of the chassis.do so. Too bad we can't put them in outer space.they are that bad.

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Old 6th February 2011, 03:33 AM   #9
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Quote:
Originally Posted by Richard Ellis View Post
Mains chokes are THE WORST offender for creating fields....think about how much AC is dropped across the chokes??????? These should be located as far away as possible from anything!.......other TXs' OPTs'......signal wires , all of it.
If you can suspend these on plastic blocks at the far, far corners of the chassis.do so. Too bad we can't put them in outer space.they are that bad.

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Unfortunately they have to be relatively close to my PSU PCBs. Should I get a piece of aluminum and try to make a box around them? That would ideally reduce the transfer of magnetic interference.
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Old 6th February 2011, 04:37 AM   #10
tomchr is offline tomchr  United States
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Quote:
Originally Posted by fingerboy21 View Post
Unfortunately they have to be relatively close to my PSU PCBs. Should I get a piece of aluminum and try to make a box around them? That would ideally reduce the transfer of magnetic interference.
Not really... It would limit electrostatic fields provided that the box is grounded. But a simple 1.6 mm (1/16") sheet of aluminum does next to nothing to attenuate the magnetic field at audio frequencies. Now, if you make it several inches think, you might get enough attenuation to care. But your best bet is really to use mu-metal.

~Tom
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