Background:
I have a portable TV which I want to add a headphone socket to.

Plan:
Open TV.
Find wires (probably just 2, I doubt it a 14", £80 TV has stereo)
Add chassis mounted switch to the live (?) wire.
Add chassis mounted headphone socket to the casing
Wire the socket to the other 'side' of the switch

This will (I hope) leave me with a TV which I can switch between
headphone and speaker modes.

thoughts anyone?
M.

Plan:
Open TV.
Find wires (probably just 2, I doubt it a 14", £80 TV has stereo)
Add chassis mounted switch to the live (?) wire.
Add chassis mounted headphone socket to the casing
Wire the socket to the other 'side' of the switch

This will (I hope) leave me with a TV which I can switch between
headphone and speaker modes.

Be VERY careful! Lethal voltages can be present inside a TV hours after it
is turned off. Not a job for the novice.

This will (I hope) leave me with a TV which I can switch between
headphone and speaker modes.

The headphone socket will incorporate a switch. There are 4 terminals on it.

You break the speaker cable at a convenient point and reconnect them,
passing through the appropriate terminals (you may need to install
additional cable if there is insufficient slack to position the socket where
you want it. The terminals are -ve and +ve feed from the amplifier, and the
switched -ve and +ve outputs to the speaker. The internal switch disconnects
the speaker automatically when a plug is inserted.

Christian.

"Michael Murray" wrote in message
m...
Background:
I have a portable TV which I want to add a headphone socket to.

Plan:
Open TV.
Find wires (probably just 2, I doubt it a 14", £80 TV has stereo)
Add chassis mounted switch to the live (?) wire.
Add chassis mounted headphone socket to the casing
Wire the socket to the other 'side' of the switch

This will (I hope) leave me with a TV which I can switch between
headphone and speaker modes.

thoughts anyone?
M.

Hi Michael,

Buy one of these : http://tinyurl.com/mcgf then drill a hole through the
plastic casing to suit the size of socket, in an area that will not
interfere with any of the innards. Find the speaker wires and trim them
down or add to them until you have enough wire to reach the new socket. The
black wire will be connected to the outer part of the socket (the socket
casing) and the red wire will be connected through the two lugs on the end
of the socket. When you insert the 3.5 mm Jack Plug, the action of pushing
the plug in will separate the connection of the red wire from the main
circuit board and the existing speaker and will make the connection to the
headphone jack plug only.

This is really a simple enough job but as others have said in their replies
" PLEASE BE CAREFUL OF THE HIGH VOLTAGES INSIDE THE TV "
and be careful not to touch any of the capacitors on the PCB or you'll get a
shock that will badly burn on both the entry and exit points of your body.

Good luck with it.

On 5 Sep 2003 06:12:39 -0700, (Michael Murray)
wrote:

Background:
I have a portable TV which I want to add a headphone socket to.

Plan:
Open TV.
Find wires (probably just 2, I doubt it a 14", £80 TV has stereo)
Add chassis mounted switch to the live (?) wire.
Add chassis mounted headphone socket to the casing
Wire the socket to the other 'side' of the switch

This will (I hope) leave me with a TV which I can switch between
headphone and speaker modes.


*** BEWARE CHARGE IS STORED IN A TV FOR A LONG TIME AFTER IT IS
SWITCHED OFF, STAY AWAY FROM THE BACK OF THE TV TUBE ***

I did this to my cheap Matsui TV 15 years ago.
No need for a switch the headphone socket cuts the sound to the
speaker as it has 4 terminals.
My TV died 5 years ago, sound played up just before it totally packed
in, don't think it was connected with my mod.

Chris

Background:
I have a portable TV which I want to add a headphone socket to.

Plan:
Open TV.
Find wires (probably just 2, I doubt it a 14", £80 TV has stereo)
Add chassis mounted switch to the live (?) wire.
Add chassis mounted headphone socket to the casing
Wire the socket to the other 'side' of the switch

This will (I hope) leave me with a TV which I can switch between
headphone and speaker modes.

Is this just for your personal tv? If so you are probably ok with the advice
from the other posts. But I do remember the technician at my university
language lab telling me that when he did the tv's there, he had to install
isolating transformers between the headphone socket and the speaker wires (I
guess due to the possibility of live chassis).

Plus you will need a resistor to make the volume acceptable in your
headphones, otherwise it will be too loud.

StealthUK wrote:
Plus you will need a resistor to make the volume acceptable in your
headphones, otherwise it will be too loud.

....or for bonus points add a headphone volume control too.

--
jc

Remove the -not from email

In message , Tim Mitchell
writes
In article , Michael
Murray writes
Background:
I have a portable TV which I want to add a headphone socket to.

Plan:
Open TV.
Find wires (probably just 2, I doubt it a 14", £80 TV has stereo)
Add chassis mounted switch to the live (?) wire.
Add chassis mounted headphone socket to the casing
Wire the socket to the other 'side' of the switch

This will (I hope) leave me with a TV which I can switch between
headphone and speaker modes.

Beware of TVs with live chassis. This means that your headphone cable
could have 240V on it. (Found this out the painful way once)

How long ago though?

TVs have moved on a bit in the last 50 years. It's very unlikely that a
14" portable would have a live chassis nowadays

You can check for this by measuring the voltage on each loudspeaker
terminal to mains earth, should be a low voltage if any. Otherwise your
plan should work.

--
geoff

In article ,
geoff wrote:
TVs have moved on a bit in the last 50 years. It's very unlikely that a
14" portable would have a live chassis nowadays

I've heard tell some sets with a crude SMPS do still have a 'live'
chassis, although I've not come across one. I'd guess if its got any form
of AV connections it should be safe, though.

--
*Why are they called apartments, when they're all stuck together? *

Dave Plowman London SW 12
RIP Acorn

"BillR" wrote in message ...

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.

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

N. Thornton wrote:
"BillR" wrote in message
...

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

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

In article ,
Old Fart at Play wrote:
A suitable transformer would not be too expensive and would provide
isolation, especially if you add an earth wire just to the
output side.

IMHO that defeats the idea of an isolation transformer.

--
*If you lived in your car, you'd be home by now *

Dave Plowman London SW 12
RIP Acorn

In article ,
BillR wrote:
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.

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.

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

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

--
*The hardness of the butter is proportional to the softness of the bread *

Dave Plowman London SW 12
RIP Acorn

On 5 Sep 2003 06:12:39 -0700, (Michael Murray)
wrote:

Background:
I have a portable TV which I want to add a headphone socket to.

Plan:
Open TV.
Find wires (probably just 2, I doubt it a 14", £80 TV has stereo)
Add chassis mounted switch to the live (?) wire.
Add chassis mounted headphone socket to the casing
Wire the socket to the other 'side' of the switch

This will (I hope) leave me with a TV which I can switch between
headphone and speaker modes.

I did this to a small portable TV 15 years ago - I used a 5 terminal
socket ( stereo & it disconnected 2 terminals when a plug was
inserted). As other people have warned, one or more of these contacts
could be at live potential, I didn't check, because I was using an
audio isolating transformer (I think it was from Tandys).
I had to move the loudspeaker connections to the other side of the
transformer (so the cut-out would work correctly). Trouble was the
transformer lost some power, so you had the turn the volume up louder
than before, which caused it to distort if you wanted it loud (but
normal viewing was ok).

Tony.

In article ,
Tony Mudd wrote:
As other people have warned, one or more of these contacts
could be at live potential, I didn't check, because I was using an
audio isolating transformer (I think it was from Tandys).
I had to move the loudspeaker connections to the other side of the
transformer (so the cut-out would work correctly). Trouble was the
transformer lost some power, so you had the turn the volume up louder
than before, which caused it to distort if you wanted it loud (but
normal viewing was ok).

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.

--
Is the hardness of the butter proportional to the softness of the bread?*

Dave Plowman London SW 12
RIP Acorn

Dave Plowman wrote:

In article ,
Old Fart at Play wrote:

A suitable transformer would not be too expensive and would provide
isolation, especially if you add an earth wire just to the
output side.


IMHO that defeats the idea of an isolation transformer.


That depends on where you connect the EARTH wire.
I was thinking of connecting it to EARTH.
What about you? Live? Chassis? Why not be adventurous
and connect it to that thick wire that goes into the side
of the CRT?

Looking in an old RS catalogue I saw a 3W 1:1 speaker isolation
transformer for about 5 quid. Put that before the internal speaker
and you can use a switched 'phone socket.

If you're OK with a separate switch you could use a stepdown
transformer after the internal speaker and do away with the
resistors.

Roger.

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

In article ,
Old Fart at Play wrote:
IMHO that defeats the idea of an isolation transformer.


That depends on where you connect the EARTH wire.
I was thinking of connecting it to EARTH.
What about you? Live? Chassis? Why not be adventurous
and connect it to that thick wire that goes into the side
of the CRT?

Perhaps you don't understand what isolation means? Would you also earth
one side of a mains isolation transformer in a workshop?

--
*Don't use no double negatives *

Dave Plowman London SW 12
RIP Acorn

Dave Plowman wrote:

In article ,
Old Fart at Play wrote:

IMHO that defeats the idea of an isolation transformer.



That depends on where you connect the EARTH wire.
I was thinking of connecting it to EARTH.
What about you? Live? Chassis? Why not be adventurous
and connect it to that thick wire that goes into the side
of the CRT?


Perhaps you don't understand what isolation means? Would you also earth
one side of a mains isolation transformer in a workshop?


No but I'd earth the frame. Wouldn't you?
WTF does that have to do with the problem of the live chassis TV?
You can either have the headphone side of the transformer floating
at some voltage determined by the leakage capacitance, or stick an earth
lead on it (Not on the TV side!) and ensure that the sleeve is always
at 0v.

Roger.

ps. Would you like to hear the story of Big Ears and Noddy's home-made
electrostatic headphones?

Dave Plowman wrote in message ...
In article ,
N. Thornton wrote:

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.

Err, WTF do you think the purpose of a telephone line transformer is?


Load matching and isolation, or in some cases use as a hybrid. I also
dont believe you can count on such devices to have sufficient tested
breakdown voltage for this app. I haven't changed my mind any so far.

Sorry, but when you're talking about connecting mains to your head you
dont say 'well, it should be alright'. Headphones aren't insulated to
withstand mains voltage, so cant be counted on to insulate. You may
well be OK, might not tho, and thats not good enough in this case.


Regards, NT

In article , Dave Plowman
writes
In article ,
geoff wrote:
TVs have moved on a bit in the last 50 years. It's very unlikely that a
14" portable would have a live chassis nowadays

This was an el cheapo 14" colour portable, currys own brand, bought
about 5 years ago. Chassis is at 120V above ground. Such designs are
definitely still out there.
--
Tim Mitchell

Dave Plowman wrote in message ...
In article ,
N. Thornton wrote:

Err, WTF do you think the purpose of a telephone line transformer is?

Load matching and isolation, or in some cases use as a hybrid.

A hybrid transformer is used to convert a two wire into a four wire
circuit. It's a totally different device.

Its a transformer wound specifically for use as a hybrid. I excpect we
can agree there really.

The *prime* reason that BT
insist (or used to) on a transformer between external equipment and their
line is to prevent mains getting onto it.

Yup. There's a difference in consequences between mains on a phoneline
and mains thru your head. Consequently there is a difference in what
level of rish is acceptable, i.e. to what voltage the insulation
should be rated, and what other precautions should be taken.


I also dont believe you can count on such devices to have sufficient
tested breakdown voltage for this app. I haven't changed my mind any so
far.

Well, if you can't trust a device made specifically for this purpose,

wrong purpose.

then I'd suggest you only ever use a battery operated self contained
headphone system - because there's just as much chance - or more - of the
mains transformer inside an isolated chassis set breaking down and putting
mains where it shouldn't.

A fair point to consider, but I'm going to disagree. Mains stereos are
either Class I, in which case the headphone socket is safety earthed,
or theyre class II, in which case a) the insulation is very highly
rated, and b) potentially dangerous wires are tied so that if one
comes loose it still cant touch anything and electrocute.

With a live chassis TV and a phone transformer,
a) you dont have good enough insulation rating between mains and head
b) you dont have any of those backups inherent in class I or class II
either.
c) with a percentage of home installs you'll also have inadequate
precaution against EHT arcing to the socket.
The result is a much higher level of danger, too high.

Sorry, but when you're talking about connecting mains to your head you
dont say 'well, it should be alright'. Headphones aren't insulated to
withstand mains voltage, so cant be counted on to insulate. You may
well be OK, might not tho, and thats not good enough in this case.

Then, as I say, you'd never risk using them on any mains powered equipment.


Regards, NT

In article ,
Tim Mitchell wrote:
This was an el cheapo 14" colour portable, currys own brand, bought
about 5 years ago. Chassis is at 120V above ground. Such designs are
definitely still out there.

How are you measuring it? With a high impedance DVM you'll often get such
readings as there could well be will be small value resistors etc from
mains to chassis for RFI reasons. But the current they could supply is so
little as not to be a safety hazard.

--
*I will always cherish the initial misconceptions I had about you

Dave Plowman London SW 12
RIP Acorn

In article , Dave Plowman
writes
In article ,
Tim Mitchell wrote:
This was an el cheapo 14" colour portable, currys own brand, bought
about 5 years ago. Chassis is at 120V above ground. Such designs are
definitely still out there.

How are you measuring it? With a high impedance DVM you'll often get such
readings as there could well be will be small value resistors etc from
mains to chassis for RFI reasons. But the current they could supply is so
little as not to be a safety hazard.

No, it really had some umph behind it, I was trying to make an audio out
terminal. When I plugged something into it, I blew up a whole range of
audio equipment, and nearly killed myself.

I later worked out the circuit diagram, it basically involved extra
transformer windings and a 120V zener diode. The set is RF input only,
no other connections (and now I know why).
--
Tim Mitchell

Michael Murray wrote:


tonight I opened said TV, with appropriate caution, to first notice
that the wires to the speaker seemed to be hugely over-designed to
what I was expecting, looking more like the internal strands of a 5amp
lighting ring cable.

Nect I noticed the large 'Live Chassis - DANGER' sticker, and so died
my plans for a headphone socket.

Thanks to all for the posts, and I survive to plot another day,


Wimp! :-)

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

If you really think that discretion is the better part of valour,
why don't you get a second-hand stereo VCR, plug it into your hi-fi
and plug your 'phones into that?

Roger.

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 @

Dave Plowman wrote in message ...
In article ,
N. Thornton wrote:

The *prime* reason that BT
insist (or used to) on a transformer between external equipment and their
line is to prevent mains getting onto it.

Yup. There's a difference in consequences between mains on a phoneline
and mains thru your head. Consequently there is a difference in what
level of rish is acceptable, i.e. to what voltage the insulation
should be rated, and what other precautions should be taken.

Let me see. You hold a phone receiver to your ear. And you do what with
headphones?

1. A telephone is satisfactorily insulated from the head, it is
designed to safely take not just ringing voltage but also voltage
spikes resulting from switching and inductance present in phone
systems. Headphones have no such rating.

2. The telephone system is designed to protect the phone user from
lightning strikes. This was introduced in 1930 in the UK due to deaths
from lighning strikes while subscribers were using their phones.

Quite a difference.


I also dont believe you can count on such devices to have sufficient
tested breakdown voltage for this app. I haven't changed my mind any
so far.

Well, if you can't trust a device made specifically for this purpose,

wrong purpose.

Err, you'll just have to take it from me that an audio isolating
transformer designed for line isolating purposes will be perfectly
satisfactory for headphone use from the safety point of view.

If you showed you were familiar with and understood all the issues,
I'd consider it.


then I'd suggest you only ever use a battery operated self contained
headphone system - because there's just as much chance - or more - of the
mains transformer inside an isolated chassis set breaking down and putting
mains where it shouldn't.

A fair point to consider, but I'm going to disagree. Mains stereos are
either Class I, in which case the headphone socket is safety earthed,
or theyre class II, in which case a) the insulation is very highly
rated, and b) potentially dangerous wires are tied so that if one
comes loose it still cant touch anything and electrocute.

There are probably still some radios around and in use with a live
chassis, so the same would apply to modifying those.

True, only for live chassis ones. But antique radios with live chassis
are both rare and easily recognised, whereas live chassis TVs are a)
not recognisable, and b) common. Plus there is the EHT in TVs too,
circa 20,000 volts.


TVs designed to be
connected to external equipment will follow the same safety guidelines as
stereos.

yup, as far as their external ports are concerned. The big problem
comes when you start home modifying equipment that is not designed to
be so connected.


With a live chassis TV and a phone transformer,
a) you dont have good enough insulation rating between mains and head

Care to prove that? A suitable transformer is flash tested to *way* above
any likely voltage.

Agreed, but there are also many that aren't suitable. Which would the
OP end up with? Who knows.


b) you dont have any of those backups inherent in class I or class II
either.

Which is why you use an isolating transformer...

Class I and II kit has an isolating transformer in them, in the power
supply, AND those additional safety measures. An iso alone, as you
propose, is not comparable at all.


c) with a percentage of home installs you'll also have inadequate
precaution against EHT arcing to the socket.

Eh? Why do straws and clutching come to mind?

EHT arcing is a routine fault in TVs. Maybe you haven't done a lot of
work on TVs. It is not a rare event, it is a routine fault.

If you put a headphone iso in a TV it needs to be well away from the
EHT, or screened from it. Unknowing persons could end up installing it
next to the EHT lead. Cringe!

If you might get bitten via your finger, its no disaster, but if you
might get 20kV thru your head, its a whole different matter.


The result is a much higher level of danger, too high.

I wonder if you take the same precautions as you think necessary here in
everything?

Far from it, but I do take it seriously when someone discusses leading
the mains to someones head via a series of totally inadequate
insulation and safety precautions. In most other matters I wouldn't be
nearly so concerned.

If you look into medical equipment you'll find the legally required
minimum safety standards are higher than those I've been discussing
here.


If so, I wonder why you're reading a DIY group - you'd not be
able to even lift up a screwdriver.

In all honesty I dont think you really appreciate the issues. I am
qualified in this area. You have a lot to contribute, and I will be
glad to take your advice on matters you know well, just not on this
one.


Regards, NT

In article ,
N. Thornton wrote:
Let me see. You hold a phone receiver to your ear. And you do what with
headphones?

1. A telephone is satisfactorily insulated from the head, it is
designed to safely take not just ringing voltage but also voltage
spikes resulting from switching and inductance present in phone
systems. Headphones have no such rating.

And you've tested all available headphones, or have such data to hand? Or
are only guessing? And guessing what type of headphones the OP is going to
use?

2. The telephone system is designed to protect the phone user from
lightning strikes. This was introduced in 1930 in the UK due to deaths
from lighning strikes while subscribers were using their phones.

Quite a difference.

More straws. Perhaps you'd tell us all what precautions are taken with a
Hi-Fi system provided with a headphone jack where that system can be
connected to an aerial which might also be hit by lightning?


I also dont believe you can count on such devices to have
sufficient tested breakdown voltage for this app. I haven't
changed my mind any so far.

Well, if you can't trust a device made specifically for this
purpose,

wrong purpose.

Err, you'll just have to take it from me that an audio isolating
transformer designed for line isolating purposes will be perfectly
satisfactory for headphone use from the safety point of view.

If you showed you were familiar with and understood all the issues,
I'd consider it.

As oppose to thinking up the most outlandish situations possible? Do you
also think things should be proof to an invasion from Mars?


then I'd suggest you only ever use a battery operated self
contained headphone system - because there's just as much chance -
or more - of the mains transformer inside an isolated chassis set
breaking down and putting mains where it shouldn't.

A fair point to consider, but I'm going to disagree. Mains stereos are
either Class I, in which case the headphone socket is safety earthed,
or theyre class II, in which case a) the insulation is very highly
rated, and b) potentially dangerous wires are tied so that if one
comes loose it still cant touch anything and electrocute.

There are probably still some radios around and in use with a live
chassis, so the same would apply to modifying those.

True, only for live chassis ones. But antique radios with live chassis
are both rare and easily recognised, whereas live chassis TVs are a)
not recognisable, and b) common. Plus there is the EHT in TVs too,
circa 20,000 volts.

So what?


TVs designed to be
connected to external equipment will follow the same safety guidelines as
stereos.

yup, as far as their external ports are concerned. The big problem
comes when you start home modifying equipment that is not designed to
be so connected.

If it's done incorrectly. Hence the recommendation to use a suitable
isolation transformer...


With a live chassis TV and a phone transformer,
a) you dont have good enough insulation rating between mains and head

Care to prove that? A suitable transformer is flash tested to *way* above
any likely voltage.

Agreed, but there are also many that aren't suitable. Which would the
OP end up with? Who knows.

If he buys a line isolating transformer *as such* it will be fine. How
many times do you have to be told this, FFS? Not a valve filament
transformer, or an LOPT, but a line isolating transformer. It's its whole
purpose in life...


b) you dont have any of those backups inherent in class I or class II
either.

Which is why you use an isolating transformer...

Class I and II kit has an isolating transformer in them, in the power
supply, AND those additional safety measures. An iso alone, as you
propose, is not comparable at all.

Yes it is, as an interface. This is how you make safe a piece of untested
mains equipment - by using a mains isolating transformer.


c) with a percentage of home installs you'll also have inadequate
precaution against EHT arcing to the socket.

Eh? Why do straws and clutching come to mind?

EHT arcing is a routine fault in TVs. Maybe you haven't done a lot of
work on TVs. It is not a rare event, it is a routine fault.

Arcing to the audio output? You must have some very strange faults to deal
with. And you're saying that life threatening currents could be present
when this happens?

If you put a headphone iso in a TV it needs to be well away from the
EHT, or screened from it. Unknowing persons could end up installing it
next to the EHT lead. Cringe!

Sounds like you know all about this.

If you might get bitten via your finger, its no disaster, but if you
might get 20kV thru your head, its a whole different matter.


The result is a much higher level of danger, too high.

I wonder if you take the same precautions as you think necessary here in
everything?

Far from it, but I do take it seriously when someone discusses leading
the mains to someones head via a series of totally inadequate
insulation and safety precautions. In most other matters I wouldn't be
nearly so concerned.

If you look into medical equipment you'll find the legally required
minimum safety standards are higher than those I've been discussing here.

Just what has this got to do with it? Or are you suggesting that a TV
supplied by the makers with a headphone outlet is built to medical
equipment standards of safety?


If so, I wonder why you're reading a DIY group - you'd not be
able to even lift up a screwdriver.

In all honesty I dont think you really appreciate the issues. I am
qualified in this area. You have a lot to contribute, and I will be
glad to take your advice on matters you know well, just not on this
one.

I'm not going to bandy qualifications with you. but I've been around
taking audio feeds off unknown equipment for many a year with a prime
regard to the safety of those using or handling it. And if your ideas on
safety were implemented, no electrical instrument would ever be used in
broadcasting or recording.

--
*Someday, we'll look back on this, laugh nervously and change the subject

Dave Plowman London SW 12
RIP Acorn

In article ,
N. Thornton wrote:
Sometimes debate gets pointless huh.
Yup.

--
*I don't work here. I'm a consultant

Dave Plowman London SW 12
RIP Acorn