> I think that it is likely that the existing power supply can be
> optimized to achieve the desired low ripple

Getting back to the original enquiry -

A couple of s/w issues came up (which are of more importance
than the hum) so for the time being I've added a 22R series and
10,000uF cap, which has reduced the hum significantly enough
to not bother me while I sort out the s/w. I did make a start on
the other hum reducing options and should get back to it over
the weekend

> First of all, it should be verified that the input ripple never takes
> the regulator input voltage close to the dropout level

I didn't intend, or expect, the audio section to have a regulator,
although a 7812 or LM317 should work, there's a bit over 3V
excess for the input. I am keen to try Bob's idea, not least to
see what happens

Joe


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