Old Fart at Play writes:

Plenty of loudspeaker isolating transformers rated 1-2Kv between
windings.

In my early twenties (long, long ago, while I still knew everything) I
added a headphone jack to a mains/battery radio, and used it for some
time.

Then my father had a heart attack, and I gave him the radio so that he
could listen in hospital.

He had a second heart attack while listening to a rugby game, and died.
No suggestion that the radio had anything to do with it, but after some
time (and maybe suffering from what they now call 'survivor guilt') I
belatedly checked the insulation between the metal headband and the
headphone plug. It was quite low; long ago now, but I think around 40K.

I've never really been sure........

It's not something anyone would want to wonder about.

--
Roy Millar, Use m o u l i n e t @