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In the Forum: Analog Playback
In the Thread: The last phonocorrector: “End of Life" Phonostage
Post Subject: ExorcismsPosted by N-set on: 1/14/2012
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Paul, after a month of vacations I've tried you advice:

 Paul S wrote:
If you can do it, try isolating both cases/chasses from your "ground plane(s)". Use one inclusive "ground plane" for both the PS and the gain/RIAA sections, and ground this "ground plane" to the house "neutral" wire. Do NOT connect any shielding to the "ground plane". Then ground the cases/chasses, all internal shields, the IC shields, TT/motor, arm and step-up ground lugs to a special, dedicated ground rod (not the house neutral or ground!). This special ground rod is the "bleeder" I keep referring to. 


but with the chasses floating (I've realized I have a two-pin instalation in my apartment and no visible pipes
to connect to). No effect.
I continued the exorcisms with "Grounding and shielding techniques in instrumetation" in one hand
and a scope in the other. After some less idiotic arrangement of transformer screens and watching the AC polarity
I got only a minor 5dB reduction in 50Hz ham, but it's still audible.
The only quiet condition still remains as before: i)the signal earth (the Cu plate) connected to the PS chassis
ii) the signal box shielded.
All the rest doesn't work, including taking the input stage out completely, disconnecting air caps, etc etc. Shit...

Disconecting the signal earth and leaving it floating results in an ugly 100Hz pickup, related to the
mains Xformers/rectification. It resists all the exorcisms, it only wants the Cu plate to be connected to
the PSU chassis, driving me crazy.
Sorry for spamming you with all this...
Cheers,
N-set

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