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In the Forum: Analog Playback
In the Thread: The last phonocorrector: “End of Life" Phonostage
Post Subject: Do phonocorrector first then transformers.Posted by Romy the Cat on: 11/17/2011
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 N-set wrote:
I'm slowly getting somewhere. Disconecting transformers did bring the ham down, but to my surprise not exactly to the level where it was before-it's unfortunately stronger. And all this after my heroic removal of Holcos from the grids of V2. The ham is there, its level varies from annoying (standard) to only lightly hearable depending on the orienation of the signal and PS boxes (the PS box is closed, the signal is still open). Strangly it also decreases a bit when I touch the case, possibly indicating a poor grounding of the cases, which is not the case given my religious approach to it...the fight with ham continues, i'm still not in the position to start wityh the transformers... BTW they seem like one layer of mumetal, i glued them to the Cu plate with silicone, but the cases wanted to be grounded (at least this is what I inferred)--hence a strips of braid in the picture.
Well, you need to get rid of transformers and to make your phonocorrector to have no noise of any kind with any transformers. From MM level you need to have no more then 1-3mV AC at output and absolute not noise. After you do it, then you can add transformers to start to play with it.

Yes, one layer of mumetal is not enough. Theright configuration is 4 layers separated by space: mumetal, aluminum, copper and steel. Each of the layer works with own shielding and it is very good to give for transformers at list 2-3 inches or more of free space around them before the first internal layer. Mumetal might be eliminated if steel is very think, I would say with 1/3-1/2 inch you might stat do not worry about mumetal.

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