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50/60/whatever cycle hum
50/60/whatever cycle hum
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Old 2nd January 2008, 01:11 PM   #11
Richard Ellis is offline Richard Ellis  Argentina
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Join Date: Sep 2006
Location: Mar del Plata, a BIG seasonal getaway city, can see the Ocean from our residence.
Default Hmmmmmmmm..

First off... the center Transformer should be rotated 90 degrees as you look straight down from the top.
You can twist it OK but you will have "dummy" holes you can 'fill' with a nut/bolt that goes nowhere. The TX will need to go forward toward the tubes somewhat to clear the lip on the chassis.
And yes you will need to change the values on your PI filter on the PS.
The wildcard is the steel chassis...the interaction of magnetic fields is the one unpredictable variable & experimentation is the only way to nail it down.
____________________________________Rick.......... .
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Old 2nd January 2008, 02:48 PM   #12
Sheldon is offline Sheldon  United States
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Join Date: Dec 2003
Location: San Diego
Default Re: Re: Re: hum

Originally posted by janneman
putting a sheet below the xformer won't do anything.
Sometimes it does. If the chassis is steel and the core sits on the chassis, or very close, leakage inductance can be propagated through the chassis. Lifting it can reduce this quite a bit - like as gapping a transformer.

I agree that rotating the power transformer can make a big difference. Easy to try both at the same time. By the way, if the power transformer is coupling to the OPT's the transformer closest with be much more affected - one easy diagnostic.

Richard is right too, in that experimentation is the easiest way to solve the problem. I have found it most productive to just listen while things are carefully moved around. An easy test is to take a plate of steel 3 or more mm thick and place it between components on top of the chassis while listening. Thick aluminum works for this too (yes I know it's non-magnetic, but try it, it works).

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