Power transformer buzzing

[rotation]

Hi,

i'm having problems with this 230V-230V/100mA,12V/1,5A toroid. When i got it i could hear little buzzing from it, and the thing get worst when it got warmer. At that time buzzing wasn't too loud and it didn't really disturb audio (i'm using it for a tube mic pre). But now, after six months, it is buzzing even louder, warm or cold.
I thought that i'm having hum in audio because AC is entering somewhere in my circuit or maybe because of bad grounding. I tried transformer when it was several meters from the circuit with no change at all. But when i tried another similar transformer (actually several) all was quiet as it should be. So hum comes from this particular transformer.
My first thought when buzzing was getting louder was that this is what causes hum in my audio. But i don't understand how this is possible. Can someone please explain me this?

When i was ordering this transformer i explain why i need it and that it must be quiet. Also, i asked for 9V second secondary but got 12V instead. I don't mind about this 3 volts so much (at cost of 80 degrees on regulator), but i think company should take back buzzing transformer. I would return it before but from beginning it was not buzzing so loud...
Would you asked them to take it back or just buy another and forget this story?

Miha

 

[ioaudio]

i just returned one humming power transformer (out of five i costum-ordered) - they should replace it, especially if you ordered it for low noise (e.g. with shielding)
-max

 

[JohnRoberts]

Mechanical noise or electrical noise?

If electrical is the transformer torroid, EI core, or whatever? Most transformers will have a pretty well defined magnetic field but with torroids depending how the windings are overlapped the magnetic field can be affected by orientation. Perhaps experiment with transformer orientation relative to other circuitry.

JR

 

[rotation]

i just returned one humming power transformer (out of five i costum-ordered) - they should replace it, especially if you ordered it for low noise (e.g. with shielding)
-max

Well, i didn't order shielded transformer because i never really had problems without it (if it was toroid). But i did ask them for mechanically quiet transformer and also told them it will be used for a high gain tube mic pre...

Mechanical noise or electrical noise?

If electrical is the transformer torroid, EI core, or whatever? Most transformers will have a pretty well defined magnetic field but with torroids depending how the windings are overlapped the magnetic field can be affected by orientation. Perhaps experiment with transformer orientation relative to other circuitry.

JR

As i undrstand it, noise starts as mechanical and turns into electrical. I came to this conclusion by trying a few other transformers inside and outside of chasis, and all of them were electrical and mechanical quiet in any position.
But i don't really understand how can mechanical noisy (buzz) transformer make electrical noise.

Miha

 

[Kamel]

microphonics noise of the tube, the mechanical movement of the transformer is mechanically transfered to the tube, can be fix with silent block, some audioffool gear use it

 

[Winston OBoogie]

I gave up using torroids after some disastrous results with some units custom wound for valve gear I designed for a company*  
Bear in mind, they are much wider bandwidth than a standard EI and let more hi frequency mains garbage into the system.  
I personally think a nice EI with a static shield is a better solution.  Of course, you need to orient it correctly or keep it away from other coils to prevent magnetic coupling.  Sometimes, the leads on components can pick up noise too as most seem to now be magnetic for the sake of the 'pick 'n' place' machines.  I try not to use resistors and such with magnetic leads but the choices are getting slimmer by the year. 

My $0.05


*Edit: I'll add that no particular orientation of the torroid got rid of the noise in this particular case.  For the hi frequency crud, I threw in some filtering on the AC side and the company also had to have expensive custom Mu-metal shields made to fit around the transformer.  It still took some rotating and fiddling with things which added 15 minutes or so to the final test procedure.  After we'd used up about 500 of the 1000 transformers we bought, we switched to an EI and found we could eliminate the Mu shield and reduce test time by 10+ minutes.  Noise and price went down considerably.  

 

[rotation]

microphonics noise of the tube, the mechanical movement of the transformer is mechanically transfered to the tube, can be fix with silent block, some audioffool gear use it

As i already said; transformer is mechanical noisy even when i MOVE IT SEVERAL METERS from chasis. This mechanical movement of transformer somehow transforms into electrical buzzing...

I gave up using torroids after some disastrous results with some units custom wound for valve gear I designed for a company* 
Bear in mind, they are much wider bandwidth than a standard EI and let more hi frequency mains garbage into the system. 
I personally think a nice EI with a static shield is a better solution.  Of course, you need to orient it correctly or keep it away from other coils to prevent magnetic coupling.  Sometimes, the leads on components can pick up noise too as most seem to now be magnetic for the sake of the 'pick 'n' place' machines.  I try not to use resistors and such with magnetic leads but the choices are getting slimmer by the year. 

My $0.05


*Edit: I'll add that no particular orientation of the torroid got rid of the noise in this particular case.  For the hi frequency crud, I threw in some filtering on the AC side and the company also had to have expensive custom Mu-metal shields made to fit around the transformer.  It still took some rotating and fiddling with things which added 15 minutes or so to the final test procedure.  After we'd used up about 500 of the 1000 transformers we bought, we switched to an EI and found we could eliminate the Mu shield and reduce test time by 10+ minutes.  Noise and price went down considerably. 

Yeah, i have similar experiences, even cheap EI's seem to work ok. And with mu-metal shields they looks much nicer to me. The only problem is higher cost, specially if i want external mu-metal shield.

So, i will try to return this bad transformer and try to find another winder for my future projects. thanks for help guys!


Miha

 

[Jonte Knif]

Just one time I got mechanically humming and mostly buzzing toroid. It was impossible to hear from 1 meter distance but because I'm used to dead silent units I called the company and they told that the noise is caused by loose lamination end and they will of course replace the trannie.

It's a good idea to over design trannies for audio use, and the company I use does it routinely. When maximum flux density is reached the risk of mechanical noise increases because of magnetostrictive forces and temperature.

Very humble but good magnetic shield in toroids is about 3 layers of core laminate placed just outside windings and preferably under any external wrappings. This is what I get for about 3e extra. The effetc of the shield is about 10dB, so nothing to compare with mu metal shield, but OK. Every time I've had magnetically induced hum it has been Hammond filter chokes too close to signal trannies. Hmmm.

In my opinion the biggest advantage of toroids over well designed EI-cores is much smaller size.

This is my experience and I never used EI, so I can not compare.