[Patrick Turner]

Ian Bell wrote:


snip,


plus the five stage RC filter I am using is over
120dB down at 50Hz so even a decade or so lower I would have expected
its attenuation to be significant.
I'm sure it is 'significant', which gives you an idea of just how bad
it is on the AC mains itself. It isn't a 10mV blip out there.

Which means I could probably see it on the mains side - where's that
scope probe?

Maybe. But you don't really know what to look for nor, since you say
it's random, 'when' to look.


Indeed. I have now built a new smoothing section with a 470uF reservoir
followed by five RC stages of 1K and 470uf each and the LF noise is now
below the broadband noise.

With the pole at 0.34Hz for each section, final -3dB with 5 sections is
about 0.07Hz and attenuation at 3Hz = 75dB approx.

If the Vdc tries to rise 10% in 10 seconds, then your filter won't stop
it. If one wave takes 40 seconds its 0.025Hz,
and such LF should not affect your amp.


Patrick Turner.