On Tuesday, September 27, 2011 5:16 PM, "Jacopo Monegato"  wrote:
>=20
> Yes, i was thinking about that. the 12 VDC is from a switching laptop
> power supply. Using my sound card as an "oscilloscope" i see that there
> is a LOT of hum in the ground signal, but i don't know how to remove it..

Laptop power supplies can have 100 VAC common mode hum. Yes, 100 volts.

Cheerful regards,

Bob

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