22-05-2012, 12:17 AM
Rob: with those free-standing external SMPSUs that power lap-tops, I too have found that most of the interference comes from the mains lead. Now I've never tried this, but in theory a narrow-band filter, resonant at 50 Hz, fitted at the mains input, should eliminate most of the hash. Trouble is of course that that will require very low inductance coils and quite large capacity capacitors. Nevertheless, it might be worth investigating, especially where the mains current is relatively small - as in a lap-top SMPSU.
Al.
Al.
