Stopping hum in steel chassis

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rockinrob86

Well-known member
Joined
Mar 9, 2015
Messages
240
Location
Tampa, FL
I have an akai/roberts open power transformer in a preamp build.  The preamp is quiet, until I put the cover on or put it in my rack, and then it hums.  I am thinking this is due to the PT radiating to the steel cover.

Any way to eliminate this?
 
rockinrob86 said:
I have an akai/roberts open power transformer in a preamp build.  The preamp is quiet, until I put the cover on or put it in my rack, and then it hums.  I am thinking this is due to the PT radiating to the steel cover.

Any way to eliminate this?
You can make a mu metal shield around the transformer
 
Thanks.  I ordered a mu metal sheet and cut a box to put around the OT.  It dropped the hum from -40 or so to around -70.  I have a hum reduction plug in that makes it silent and I don’t hear negative consequences, so I think I’m good with this one.  I think when I use the other Power transformer I will mount it in a box on the back and run wires inside rather than putting it in the chassis like I did this one.
 
when you put the lid on you complete the magnetic circuit.

you could try using the lid only insulate it from the rest  of the box somehow.
 
It is the transformer isolated from the chassis? Some amplifiers have some isolating material between chassis and the transformer and special groomets to attach the screws.
 

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