toroidal transformer distance to pcb

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JAY X

Well-known member
Joined
Jan 9, 2009
Messages
683
Hi All!

I have a 15va toroidal transformer 60mm diameter, and 31mm height.  I'm trying different placements for it.
¿What is the minimum recomended distance to place it from the pcb  audio board?

thank you for your advise!

Jay X
 

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I think it will depend on the signal levels on the audio board.
If you are running signals at microphone level on the board, there might be an audio hum when the transformer is too close.
But with line level signals, no serious problems are to be axpected.
In general: further away=better!  ;D

(Maybe just move the transformer around and find the place where the stray field of the transformer causes minimal hum.)
 
Hi RuudNL,

The board is line level. At the output section i have xlr pcb connectors and a pair of lundahl LL2811pcb transformers.

If i place the toroidal near the board, i only have  2 or 3 cm left to the board. In that case i thought to place a metal separator... but this is more cost!. So yes... i will try some experriments...

jay x
 
Toroids have little spill in general, but a tad more near or towards the leads, so you might have to play with the rotation first. I looked into R-Core Transformer once, even better, but it's probably not worth the effort., maybe nearing Voodoo territory there.

- Michael
 
I would mount it in of of these 2 positions.

pcb%20layouts2.png


Then Rotate the Toroid until you find the the position where the induced hum is the lowest.

After that I would install a trafo shieldind sheet around it:
https://www.don-audio.com/trafo-shield
 
Hi!

I tested both of my schematic positions, and in both cases there were no noise problems, all was ok. In the first case the toroidal was at 1cm from the audio board.  :)
 

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The only thing i don't like much about the toroidal i bought (RSpro)  code: 6719062. is that the secondary wires are sooo thin!! that it is a bit difficult to make a good connection...

Jay x
 
JAY X said:
Hi!

I tested both of my schematic positions, and in both cases there were no noise problems, all was ok. In the first case the toroidal was at 1cm from the audio board.  :)

Listen with good headphones the last channel/pcb the one that its closer to the toroid. Crank the gain/volume up.
You should listen to some induced hum, not saying that the induced hum is a "noise problem", just that it's there.
Listen to how that hum changes when you move the toroid closer or further away.

Then put it in the position you want, rotate it and listen for the least amount of hum.


 
Hi!,

Finally the first layout with the trafo near the audio board, gives lower noise. No hum, just ripple noise...low at low volume settings, and increasing with higher volume. Maybe a clc filter at output, with a ferrite...can help reduce ripple a bit....
 
Hi,

After surfing the web, and checking the lm317/37 datasheets,  it seems that the output ripple can be reduced increasing the value of the output capacitor. Typically it is 100uf. But 220 or 470uf may also work. As the feedback resistor is 100 ohms, the output lowpass filter may have a value of 15.91,  7,23. And 3.38 hz with the given caps. But, will these help reducing ripple output?.
 
I believe the rule is if the hum is at Mains Frequency, it is EMF from the transformer, if it is 2x M. F. it is from the secondary wires / circuit...
 

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