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How to affix shielding can to transformer?

eastone

eastone

pfm Member
Just a quickie: I've fashioned some steel shielding cans for the autoformers in my power amp. Can they safely be affixed with glue or double sided tape? Don't really have the option to clip to the pcb.
 
Glue is O.K. so long as it will withstand the temperature. Many glues and most double sided tape hardens and comes adrift after a period of time - you need to be sure that this will not allow the can to short something out, especially mains.

You also need to earth the can, from a safety point of view as well as stopping it acting as an aerial .
 
How would I go about earthing the can?

The autoformers are in the signal path rather than power supply, if that makes a difference.
 
You could drill the can and use a tag to connect to an earth point in the amp - possibly the chassis. Or you could solder an earth wire on if you have a decent size soldering iron.

It`s bad practice to have largish lumps of unearthed metal in an amplifier even if there is no safety implication.

The hot melt glue mentioned above will probably be a good bet and lasts well too.

How big are these transformers?
 
I would pot them with the proper epoxy resin for the job, it normally comes in a bag with both parts ready to mix.
 
Are you building or looking at a finished (factory made) amp? If the former, the key seems to be placing the mains transformer (virtically if possible) at the front of the case and the autoformer end of the pcbs at the rear. Screened mike cable for signal connections as well, obviously. Mainly for peace of mind, I found a big toroid screen for the mains transformer on Ali-express - belt and braces.
 
davidjt said:
Are you building or looking at a finished (factory made) amp? If the former, the key seems to be placing the mains transformer (virtically if possible) at the front of the case and the autoformer end of the pcbs at the rear. Screened mike cable for signal connections as well, obviously. Mainly for peace of mind, I found a big toroid screen for the mains transformer on Ali-express - belt and braces.
Click to expand...

The amp is a few years old, I'm just trying to improve the hum situation as I now listen rather closer and quieter than previously. It's laid out as you describe, with the toroid on the horizontal and the autoformers on the vertical plane. I'm adding steel enclosures on the autoformers which will be augmented with an adhesive mu-metal strip. I'll try to locate the belt and braces - hopefully cheaper than doing mu-metal on the toroid, it's big!
 
Irrc the FirstWatt products had all three transformers in the same horizontal plane, the edcors having a single square of (shielding?) material on top, so yours are presumably diy. I'd have thought that steel and mu-metal on the edcors would do the trick, but you never know - on the diy thread there are builders wrestling with the problem while others claim no pick-up at all. And mu-metal for the toroid would as you say be pricey. Best of luck!
 
Thanks David, it is DIY, you're right. I always assumed the shielding on the production version was a can but looking again it does appear just to be a square of mu-metal sheet.

I'll report back my findings...
 
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