@WB6BYU - I don't happen to have any of those LDO regulators to play with. I did try a set of two 5.6V zeners in series (with a resistor) but that did not help, not sure why... maybe I would need two of those sets, one for positive going and one for negative going direction?
Where did you measure the voltage in your
test? The junction of the resistor and the
top of the upper zener should be a fairly
constant 11.2VDC in that case, assuming that
the minimum voltage of the waveform is high
enough (I can’t tell what the average voltage
is from the plots). But if you just stuck the
zeners + resistor across the power supply, it
won’t provide any filtering. And a zener
probably isn’t what you want for a 1A current
draw, since it has to pass through the resistor
to be regulated. Any resistor larger than
about half an ohm is going to drop the
voltage too much, and you will lose regulation.
And when properly implemented, the zeners
likely will dissipate a lot of heat, especially if
the current draw is intermittent.
Are you measuring the ripple voltage under
full-load conditions?
One thing you could do, of course, is to use
a much larger filter capacitor, like 30,000 uF
or so. But the supply may have problems
starting up with the capacitor attached, as
it will look like a short circuit until it charges
up.
You can make your own regulator using a
big enough PNP transistor (rated at several
amps) with the input voltage applied to
the emitter and output from the collector.
Then use an op amp to compare the
output (usually through a voltage divider)
to a reference (often a zener) and use that
to drive the base, do the base drive is
reduced when the voltage is too high.
That’s the principle of some of the low
dropout regulators, but they usually
include other protective circuitry. You
could build your own if you have the
parts handy, otherwise you may need
to start with 15+ V and a standard
7805-style regulator with sufficient
current capacity.
On the other hand, one could argue
that such an audio device should not
be sensitive to ripple on the power
input, but perhaps it cane with another
supply initially that was more quiet.