Hi


several people write:

Modern TVs tend to have a switched mode power supply which
isolates the
chassis from the mains.
If it doesn't then headphone socket is a no-no.

Millions of sets in use today dont have that, and do run with live
chassis. It is not an outdated practice at all.

I just gave away a 10 year old JVC and that had an isolated chassis
as does
my new Sony and the two 5 year old small bedroom sets.
BTW they all had/have headphone sockets too.

right. and millions dont.


How could they run modern electronics without a transformer of some
kind?

TVs have been running transformerless for decades. There is more than
one approach to it.

If there were no external connections, you could use a form of auto
transformer which is marginally cheaper?

you dont need any transformer. There are stacks of silicon based TVs
around running mostly on HT. I have 1 right here. The few bits that
can only be LT dont eat much power, and either HT circuits produce low
voltage at various points to run them, or a low voltage loptf wind is
used to supply them.

Another option is to use a self oscillating lop stage running on HT.
That starts up with no LT and the lop produces the LT needed for the
rest of the set. The LT circuits then pull the lop into sync. Flywheel
sync has been standard for a long old time. There are many approaches.


Millions of sets in use today dont have that, and do run with
live
chassis. It is not an outdated practice at all.

I just gave away a 10 year old JVC and that had an isolated chassis
as
does my new Sony and the two 5 year old small bedroom sets.

I'd agree that all the quality makes I've played with have been fully
isolated.

does that mean all TVs are isolated? Maybe you're overlooking the
consequences of 240v to the head.


BTW they all
had/have headphone sockets too.

Most quality makes do - and also AV connections, so they'd have to
have an
isolated chassis in practice.

those kind normally are, tho again exceptions exist. If 'most' is good
enough for you to apply 240v to the head in 5% of cases, I guess
that's your funeral.


I'd say the ideal cheap transformer would be a telephone line isolating
type if quality isn't that important. A good quality audio isolating
transformer won't be cheap.

I'd say the level of advice in this thread is just plain dangerous.

To connect a headphone to a chassis thats either live, or not live but
not particularly well insulated from live, is a /really/ stupid idea.


Regards, NT