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In the Forum: Analog Playback
In the Thread: The last phonocorrector: “End of Life" Phonostage
Post Subject: TracesPosted by N-set on: 8/31/2011
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 Paul S wrote:
No way to guess about grounding, at least until you show the final traces.  I simply must use shielded inputs, and I bleed these "upstream" via a "dedicated" ground (and certainly NOT the "house ground"...).  Yes, I realize this is not the desired "star" grounding.  However, it was this or madness.  Also, some units require to cap any and all unused inputs, and some even the unused outputs.

BTW, I would root out that ".5m" buzz like a terrier on speed...

Best regards,
Paul S


Paul, not sure if by traces you ment what follows (if not, it may be deleted)
but below are some sample
traces of the output noise, recorded by my improvized soundblaster "scope".
The vertical scale is irrelevant as it's not calibrated, but both traces are
recorded with the same sensitivity "20mV/div" (but don't take it seriously).
The timebase is 20ms.

Channel one, which in the previous test was the problematic, now decided not to
catch so much of the 50Hz:


Channel1Noise.GIF

Channel1NoiseFFT.GIF


Channel two, which now decided to go for that free 50Hz:

Channel2Noise.GIF

Channel2NoiseFFT.GIF

This all recorded with the boxes not covered, quite close to each other
(one more fuck-up: too short umbilical at 70cm).
The interference seems to come from the PS magnetics: playing with the orientation
of the boxes changes the noise. The above traces are the "minimal" ones.




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