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Effective  toroidal transformer shielding
Effective  toroidal transformer shielding
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Old 28th May 2018, 10:00 PM   #11
MAAC0 is offline MAAC0  Portugal
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I have two mixing consoles in both of them there is a toroid inside and a metal sheet between them and the mixer up pcb enclosing the toroid. When I crank up the gains and master out there is a slight hum. When I lift the mixer boards up this hum gets quieter and if I move the board away from the case it dissapears completely towards hiss . What I've done was increasing the main supply capacitors which helped a lot. The hum is the same as You hear when You connect an 2m consumer RCA lead to an amplifier without source.
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Old 29th May 2018, 08:24 AM   #12
ctrlx is offline ctrlx  United Kingdom
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[QUOTE=tanwa;5446890
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.
Any suggestion would be appreciate[/QUOTE]


have you tried rotating the transformer?
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Old 29th May 2018, 01:56 PM   #13
Pascal Nguyen is offline Pascal Nguyen  Australia
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Try to isolate the problem by disconnect the PSU and loaded with a dummy (same impedance and wattage as your amp).
From that dummy, built a resistor divider with zener protection and connect it to your soundcard, use Any available soundcard spectrum analyzer, watch the FFT with power off, copy the spectrum as overlay, load that overlay and power on, copy both and post the photo here for further comments. If the spectrum of loaded PSU has 50Hz (60?) and its harmonics lesser than -70dB (-60, -70 is acceptable, -80, -90 excellent, -90 ...top notch...)
Almost all amps that I built never need a shield or enclosed container, with an exception, the latest one, a bi-circleton, does need a special shield.
Cheers and good luck
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Old 29th May 2018, 03:34 PM   #14
tanwa is online now tanwa  Thailand
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Quote:
Originally Posted by MagicBus View Post
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.


Perhaps all that you need is a mains DC offset blocker Mains DC and Transformers
Quote:
Originally Posted by chede View Post
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
Thank you, It also surprise me that the problem is get a lot better by adding the steel box. I am thinking about the problem from transformer itself too, cause the loud buzzing directly from transformer.
So, I manage with the transformer supplier to sent transformer back to re-check the buzzing problem, but I really not sure, the problem is from the transformer or power line DC offset.
Do you have any idea,what should I suggest the supplier to check? I afraid that the problem may not show up in the testing at the lab.

Quote:
Originally Posted by MagicBus View Post
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.
Quote:
Originally Posted by MEPER View Post
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.
Thank you, thinner steel sheet is better? or is it better to be multi layer? My transformer is mounting with the resin in the middle, bolt to the bottom plate, and floating at the top.


Quote:
Originally Posted by MAAC0 View Post
I have two mixing consoles in both of them there is a toroid inside and a metal sheet between them and the mixer up pcb enclosing the toroid. When I crank up the gains and master out there is a slight hum. When I lift the mixer boards up this hum gets quieter and if I move the board away from the case it dissapears completely towards hiss . What I've done was increasing the main supply capacitors which helped a lot. The hum is the same as You hear when You connect an 2m consumer RCA lead to an amplifier without source.
I afraid the my enclosure have not enough space already
So, I try to shield it.

Quote:
Originally Posted by ctrlx View Post
have you tried rotating the transformer?
That is what is want to try next, now the transformer wires are short. I will make it longer and try to rotate it. will see what happen.

Quote:
Originally Posted by MossFed View Post
Try to isolate the problem by disconnect the PSU and loaded with a dummy (same impedance and wattage as your amp).
From that dummy, built a resistor divider with zener protection and connect it to your soundcard, use Any available soundcard spectrum analyzer, watch the FFT with power off, copy the spectrum as overlay, load that overlay and power on, copy both and post the photo here for further comments. If the spectrum of loaded PSU has 50Hz (60?) and its harmonics lesser than -70dB (-60, -70 is acceptable, -80, -90 excellent, -90 ...top notch...)
Almost all amps that I built never need a shield or enclosed container, with an exception, the latest one, a bi-circleton, does need a special shield.
Cheers and good luck
I afraid that, I cannot find the same load as the power since my aleph5 draw 6A continuously. Is it possible to measure while I use power itself as a load?
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Old 29th May 2018, 03:55 PM   #15
tanwa is online now tanwa  Thailand
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I have also check the psu ripple. the ripple at the PSU out after CRC was less than 100 mV p-p. and the frequency was 100Hz.

An externally hosted image should be here but it is no longer accessible. Please upload images instead of linking to them to prevent this.
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Old 29th May 2018, 04:20 PM   #16
MagicBus is offline MagicBus  Greece
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Quote:
Originally Posted by tanwa View Post
...So, I manage with the transformer supplier to sent transformer back to re-check the buzzing problem, but I really not sure, the problem is from the transformer or power line DC offset.
Do you have any idea,what should I suggest the supplier to check? I afraid that the problem may not show up in the testing at the lab.
Most probably the problem is mains DC offset. Building the recomended DC blocker is easy and will save money and time to have the transformer checked by the supplier who is unlikely to accept that as defective.
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Old 29th May 2018, 05:01 PM   #17
tanwa is online now tanwa  Thailand
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Quote:
Originally Posted by MagicBus View Post
Most probably the problem is mains DC offset. Building the recomended DC blocker is easy and will save money and time to have the transformer checked by the supplier who is unlikely to accept that as defective.
Now, the buzzing sound from transformer is heard all the time. Just different level each time. Is it from DC offset? I will build the dc blocker to see what happen. But for long term use, does it has an affect to sound quality or the reliability of the components in the dc blocker itself?
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Old 29th May 2018, 05:07 PM   #18
BeardyWan is offline BeardyWan
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If itís emi then a closed copper box will do fine -just a faraday cage
If itís the magnetic field then you can play with orientation, proximity or a mu metal shield..
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Old 29th May 2018, 05:14 PM   #19
MagicBus is offline MagicBus  Greece
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Quote:
Originally Posted by tanwa View Post
Now, the buzzing sound from transformer is heard all the time. Just different level each time. Is it from DC offset? I will build the dc blocker to see what happen. But for long term use, does it has an affect to sound quality or the reliability of the components in the dc blocker itself?
DC blocker won't affect sound and it will protect the transformer in the long term. Just read Rod Elliott's article and build it according his instructions.
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Old 29th May 2018, 06:57 PM   #20
MEPER is offline MEPER  Denmark
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Quote:
Originally Posted by tanwa View Post
Thank you, thinner steel sheet is better? or is it better to be multi layer? My transformer is mounting with the resin in the middle, bolt to the bottom plate, and floating at the top.

Yes, just thin steel to shield against the magnetic field from the transformer. Mu-metal is very expensive so thin sheet steel should be a cheap alternative.
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