EI transformer in case problem
 

OK, so I finally got around to putting the lid on my amp, after the girlfriend endlessly nagged me about it :D

The problem is, I have done so, and now the lid vibrates and theres a quite but audible humming noise. I'm not quite sure why.

Here is a picture:

http://www.darkmatter.myby.co.uk/amp/S2020019-small.jpg

There is a good 2cm clearance between the transformer and the top of the case. All panels are earthed to a star earth point. There is no connection between 0V and the mains earth (yet!)

Is this simply because it's an EI transformer, or is there something stupid im missing ? Would putting some foam material between the base and the transformer help, even though no vibration happens with the lid off ?

(I plan to get a 160VA toroid to stick in there.. but at the moment... i'd like to know the problem)

My guess is its the nature of the EI.You might try temporarily laying transformer on its side or....Just wait and install toroid.

I really hate it when they do that.....


Dave

Can you hear your transformer when the lid is off? Check your mounting bolts. If they are not tight, they can rattle. Check all the bolts that hold your chassis together. What brand of transformer is that? My 100 watt per channel amp that I built has an EI transformer and you can't even hear any hum unless you put your ear on the chassis. It makes a small "grunt" due inrush at power-up. I used oversized bolts to mount it in the chassis (1/4" machine screws and nuts).

The problem is your cover is in close proximity to the EI core laminations.Possibly wedging a piece of wood or plastic or even possible a long Hex standoff from bottom cover to top cover near the transformer to stabilize the case limiting its ability to sag or flex/vibrate due to the transformers magnetic flux field.

Dave

Can't hear a thing with the lid off... the bolts are definitely tight. The case isnt really bolted together, its made from 4 sheets of 1.5mm thick steel with threaded L angle profiles on the edges, and two plastic end caps that keep everything together.

I've no idea what brand the transformer is, as it's "recycled" from something else :)

Hmm.. ok well I plan to try turning it on it's side as suggested, although I will need to get some spacers to do that. At the moment it's mounted using two PCI backplate covers that've been sawn down and had holes drilled in them :)

You can do what a friend of mine did, and soon to my self.

Take a small block of wood and line it with felt on the bottom, then bolt your transformer to it, it will cure the vibration problem. Or you can see if there is any plastics/rubber shops around and find a piece of 1/2" rubber to mount it to.

exactly, it doesn't make the noise when the cover is off, but yet still in the chassis so why would it be the chassis vibrating? The cover is definitely being effected by the magnetic flux of the transformer.

is your lid aluminum or steel? If its steel it will be affected, I have had this problem with amps as well, I just normally stick a padded peice of wood between the two and it quiets it. Maybe vent holes would cause it to have less 'grab' on the metal...?

Put a magnetic material perimeter for the transformer core.

Gajanan phadte

Thanks for all the suggestions :)

I will try turning it on its side, and if that doesn't help... well it needs the right toroidal anyway :) At the moment, I have an Arcam Alpha 7R that I am repairing (blown outputs) and will be using that for a while