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In the Forum: Audio Discussions
In the Thread: It’s mad, mad, mad... electricity.
Post Subject: MorePosted by N-set on: 11/28/2020
Adrian, I'm not yet convinced the PP is to blame. Also PP Richard is helping a lot to understand the issue (thank you Richard!). Now this f@#$%@%$ 100Hz noise stepped on my male ego - want ot understand where it comes from.
I quickly cheked the signal between the PP ground and my phono. Nothing unusual: some 50Vrms of 50Hz when the PP is online, pretty much the same as between the phono and my wall GND when the phono is connected to the wall.
Interestingly, if I connect the phono and PP GND via amperemeter, it shows an AC current diminishing practically to zero (some 0.4mA). So this 100Hz noise is not from a current loop? Or this 0.4mA rms is enough? Cap coupling GND's I might try for a test, but ultimately I want to have a DC connection for safety. I was thinking of trying this GND blocking scheme, Fig. 4: https://circuitcellar.com/resources/ee-tips/find-and-eliminate-ground-loops/
Another interesting thing I'm strugling to understand is why lifting the phono signal ground from the chassis ground has no effect on the noise. Only lifting the chassis ground from the PP ground kills it. This suggests it gets to the signal either via the air of via the supply lines (B+ and/or heater which biases the 2nd stage). I have to scope theose lines throroughly. But then again, why disconnecting GND kills it?
Pual - I checked my wall GND. First of all it is there (made tests with controlled 30mA shorts to GND - fuses worked). I was looking at the heating too but have no idea if the pipes are all metal or plastic. A bulb test will show.
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