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Old 27th April 2007, 03:15 PM   #1
jaycee is offline jaycee  United Kingdom
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Default 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

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:

Click the image to open in full size.

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)
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Old 27th April 2007, 06:26 PM   #2
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My guess is its the nature of the EI.You might try temporarily laying transformer on its side or....Just wait and install toroid.

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after the girlfriend endlessly nagged me about it
I really hate it when they do that.....


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Old 27th April 2007, 06:42 PM   #3
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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).

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Old 27th April 2007, 06:54 PM   #4
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Quote:
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 ?
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.

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Old 27th April 2007, 08:36 PM   #5
jaycee is offline jaycee  United Kingdom
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Quote:
Originally posted by Bama Slamma
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).
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

Quote:
Originally posted by XEAGLEKEEPER
[B] 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.
[B]
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
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Old 27th April 2007, 08:39 PM   #6
jleaman is offline jleaman  Belgium
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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.
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Old 29th April 2007, 10:35 PM   #7
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Quote:
Originally posted by XEAGLEKEEPER
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

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.
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Old 1st May 2007, 02:11 AM   #8
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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...?
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Old 1st May 2007, 04:28 AM   #9
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Put a magnetic material perimeter for the transformer core.

Gajanan phadte
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Old 1st May 2007, 01:37 PM   #10
jaycee is offline jaycee  United Kingdom
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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
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