rockinrob86

Stopping hum in steel chassis
« on: May 29, 2020, 12:51:43 PM »
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?


Fuzz Face

Re: Stopping hum in steel chassis
« Reply #1 on: May 29, 2020, 02:51:29 PM »
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

rockinrob86

Re: Stopping hum in steel chassis
« Reply #2 on: June 07, 2020, 03:14:11 PM »
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.

CJ

Re: Stopping hum in steel chassis
« Reply #3 on: June 10, 2020, 03:20:35 AM »
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.
If I can't fix it, I can fix it so nobody else can!
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ruffrecords

Re: Stopping hum in steel chassis
« Reply #4 on: June 10, 2020, 04:45:22 AM »
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.

Or change it to aluminium.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

abbey road d enfer

Re: Stopping hum in steel chassis
« Reply #5 on: June 10, 2020, 05:49:13 AM »
Or change it to aluminium.

Cheers

Ian
Transformer-induced hum results from a combination of magnetic field reorientation and eddy currents. Al does not reorient magnetic flux but it closes the shorted loop.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

rockinrob86

Re: Stopping hum in steel chassis
« Reply #6 on: June 10, 2020, 10:06:05 AM »
It also hummed when I put it in the rack without a top on, although the piece of gear above it is steel as well. 

abbey road d enfer

Re: Stopping hum in steel chassis
« Reply #7 on: June 10, 2020, 01:46:09 PM »
It also hummed when I put it in the rack without a top on, although the piece of gear above it is steel as well.
Does it change if teh piece of gear on top is ON or Off?
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

rockinrob86

Re: Stopping hum in steel chassis
« Reply #8 on: June 11, 2020, 01:08:11 PM »
No it didn't

12afael

Re: Stopping hum in steel chassis
« Reply #9 on: June 11, 2020, 01:25:03 PM »
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.
heavy metal is the law!!!


 

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