Frightening the yaks, Robert St-Louis just had to say:

Hi all,
THis is my first message on this forum.

How-DEE!


Alternatively, if someone has suggestions for another way to get
(relatively) hum-free DC into it from house current, I'd love to hear
them.

If you don't mind a tiny bit of surgery on your current
converter....

Project requirements: electrolytic capacitor (see below); sharp
knife; voltmeter (or other polarity indicating device); soldering
iron & solder; electrician's tape.

Likely, it was designed for something that didn't care if the DC
was filtered or not. You can add in a nice electrolytic
capacitor to the cord that comes from the unit to filter the
power. You need to get a cap that's about 1000-2500 uF and rated
for at least 12 volts (35 would be more than enough.) Axial
style is best (leads sticking out of each end.)

And you'll need to know which is the positive and which is the
negative lead, so you should have some sort of voltmeter to
check.

Assuming the cord is two insulated wires laid side-by-side,
carefully cut between them to separate the two wires. This
should probably be close to the converter end. How long the
separation should be depends on the capacitor you have. Keep
reading and you'll know how to tell.

At one end of the split, carefully strip the insulation off the
wire for about 3/4" (2cm.) Temporarily wrap the bare wire around
one of the capacitor's leads. Next step is figuring out where to
strip the other wire so that the other lead can be wrapped with
the other wire. Try it and see where the wire needs to be
stripped; then go ahead and strip it.

Now, the polarity of the wired must be determined. Using
whatever means you have, figure which is positive and which
negative. The capacitor MUST be installed with its positive lead
to the positive wire. For a 9volt circuit, it wouldn't explode,
but it just wouldn't work well; with higher voltages there would
be real dangers.

Trim the leads of the capacitor to about 1/2" (1cm) then wrap the
bare lead wires around the appropriate ends of the cap and
solder. Use some black electrician's tape to completely cover
the added part.

All done!
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This calls for a careful blend of
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