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Effective  toroidal transformer shielding
Effective  toroidal transformer shielding
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Old 28th May 2018, 04:25 PM   #1
tanwa is offline tanwa  Thailand
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Default Effective toroidal transformer shielding

Hello guy,

I spent a lot of time to find the source of buzzing in my DIY aleph5 in this thread
Need help! Aleph5 buzzing when introduce preamp

Finally, I found that it is the EMI from the transformer which I actually not expect that because the torroidal suppose to irradiate less noise.

The first try, I put in the 1.2 mm thickness steel box cover the transformer, it work! buzzing is reduce a lot. but if I come close to the speaker I still can hear the buzzing sound.

So, I decide to put more shielding, but what is the most effective, practical, and wallet friendly to shield the EMI from toroidal transformer? I have search several thread and found some method that might be work ex.

- Put the thin sheet of copper around circumference of the toroidal like this
Click the image to open in full size.
but I found this method with EI transformer. Is it work with toroidal?
- Or I just put more steel box in layer.
- What is the good material for shielding? steel which is quite cheap of copper /aluminium with higher cost?

one notification is my transformer generate buzzing sound that I can here from 2 m. it is not normal for sure. but it happen some time. What is it possible from? and does it relate to the EMI from transformer? The transformer is new, do you think it is fail?

Any suggestion would be appreciate

Last edited by tanwa; 28th May 2018 at 04:27 PM.
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Old 28th May 2018, 06:20 PM   #2
ColinA123 is offline ColinA123  United Kingdom
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Old 28th May 2018, 07:58 PM   #3
MagicBus is offline MagicBus  Greece
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Quote:
Originally Posted by tanwa View Post






- What is the good material for shielding? steel which is quite cheap of copper /aluminium with higher cost?
Have a look here to get an idea: Τ.Γιατράς Μετασχηματιστές - Toroidal Transformers
But it's hard to believe that EMI could be the reason itself.

Quote:
one notification is my transformer generate buzzing sound that I can here from 2 m. it is not normal for sure. but it happen some time. What is it possible from? and does it relate to the EMI from transformer? The transformer is new, do you think it is fail?

Any suggestion would be appreciate
Perhaps all that you need is a mains DC offset blocker Mains DC and Transformers
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Old 28th May 2018, 08:04 PM   #4
chede is offline chede  Germany
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Effective  toroidal transformer shielding
The intermittent buzzing sound could come from DC on the powerline. I have it sometimes for a few minutes, then it goes away again.
Though on my toroids it is not very loud, so I didn't bother with the DC blocker anymore.

You could try one of the circuits discussed here:
dc blocker test report
or here:
DC blocker diode/cap orientation
I think the "Bryston" one referenced in post #2 (or post #1 of the first thread linked above) works quite well.

Best regards, Claas
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Old 28th May 2018, 08:13 PM   #5
MagicBus is offline MagicBus  Greece
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Also, in the other thread, the picture doesn't help to understand where is the transformer. What you have to ensure is that the mounting bolt doesn't touch the chassis at both ends.
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Old 28th May 2018, 08:13 PM   #6
MEPER is offline MEPER  Denmark
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When I Picked up some transformers direct at a transformer factory I was told that thin steel does a very good job shielding against magnetic "noise". Thicker steel would be less efficient because of Eddy currents. The best solution is to have the transformer and bridge "far" away from the amp.
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Old 28th May 2018, 08:21 PM   #7
scottjoplin is offline scottjoplin  Wales
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Yes, distance is the best remedy, why do you include the bridge though?
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Old 28th May 2018, 08:32 PM   #8
MEPER is offline MEPER  Denmark
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The bridge and the first filter capacitor because of the high pulse currents which can radiate noise from the wires (wires from transformer to bridge and from bridge to first filter capacitor). A 2nd filter capacitor is probably good to have in the amp chassis to have short wires from capacitor to amp circuit. It all depends…….
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Old 28th May 2018, 08:39 PM   #9
scottjoplin is offline scottjoplin  Wales
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Gotcha, that's what I do, hadn't considered or read of radiated noise from wires, makes sense. I reckon too that the cable between the PSU and amps (I have them in separate chassis') would act as resistance in CRC filter?
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Old 28th May 2018, 08:53 PM   #10
MEPER is offline MEPER  Denmark
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Yes, some put an e.g. 0.1 ohm resistor between the two filter capacitors to reduce the current pulses to the 2nd filter capacitor. Then the 2nd filter capacitor will define the Gnd for the amp. Layout of wires is also important. Good to twist wires. The size of the R in a CRC filter depends of how much current is needed…..how much voltage drop you can afford, how much ripple you can live with.....etc.
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