Edward Bartolo <edb...@gmail.com> wrote: > Lately, I have experienced an amplifier input failure that was > supplied audio signals from a laptop powered with an AC mains power > supply.
2pin or 3pin mains input to the power supply ? > As you know, these AC power supplies are of the switching type > that use an inductance to transform voltage. The problem with these > power supplies is the fact that energising an inductance, also > energises parasitic inductances and capacitances that give rise to > transient interferences that may cause an external circuit to fail. It's not so much the transformer, but the input filtering and lack of earth on 2 pin mains inputs. In effect, the output of the supply will naturally float to around 1/2 the mains voltage (so around 115V AC on a 230V mains) with a weak driver via the filter caps. With my (metal cased) MacBook Pro I can sometimes feel this voltage as a "sensation" in my palms if using a 2 pin adapter* > Has anyone used some sort of filtering circuit to protect their > laptop/s or computer/s? For important setups and with a 2 pin mains connection, I'd suggest adding a "hard" earth connection to the laptop - find a suitable connecting point** and run an earth wire to a suitable earth. Otherwise, there's a risk that you are using your audio connection to earth this 115V signal ! The current is tiny, but when plugging in/unplugging an audio connection, it could apply a damaging voltage to your audio gear. The same applies to a lot of equipment these days - TVs, DVD players, STBs, etc - which tend to have only 2 wire leads. WHat happens in practice is that the whole lots will get earthed through the connecting leads if any one device is earthed. People sometimes report seeing small sparks when connecting things up (eg connecting antenna leads) with things powered up. * With the Mac power supplies, if you use the "duckhead" adapter then it doesn't earth the supply, but using a lead does. ** One good candidate might be a securing screw for the VGA socket (if you are't using that). _______________________________________________ Dng mailing list Dng@lists.dyne.org https://mailinglists.dyne.org/cgi-bin/mailman/listinfo/dng
