IIRC the shield on a DIN connector was always intended to be the chassis
connection, with pin 2 optionally being an isolated signal ground. Quad
were rather naughty when they connected pin 2 to chassis in the 303.
Keeping it separate would have allowed more flexible connection without
introducing hum loops. Linking the shield to pin 2 is fine for low level
inputs, but it shouldn't be done when linking to other equipment.

Modern electrical safety earthing might allow the 303 to be powered from
the 33 as the mains transformer appears to include an earthed shield
which would isolate the secondary from the primary. That would make it a
Class II (double-insulated) appliance. Of course, the shield would have
to be capable of carrying any fault current from the mains until the fuse
blows. Also, all mains leads (& probably internal mains wiring) would
need an outer sheath to provide double insulation.

"mick"

Modern electrical safety earthing might allow the 303 to be powered from
the 33 as the mains transformer appears to include an earthed shield
which would isolate the secondary from the primary.

** That is an electrostatic shield - it helps to eliminate mains noise.

That would make it a Class II (double-insulated) appliance.

** Absurd crap !!!

The basic principle of class II is *NOT* to rely on the mains earth for
user safety.

Two reasons:

1. If the mains earth connection is missing anywhere, the equipment still
operates ( with no warning to the user) and you have no safety.

2. If the AC outlet or equipment plug is miswired, active can appear on the
earth conductor and you have a lethal situation.

A very nasty example of scenario "2" occurs when the equipment plug has
earth and neutral wires reversed - which goes unnoticed until the day it is
plugged into an outlet that has active and neutral reversed.



..... Phil

In article ,
Phil Allison wrote:
A very nasty example of scenario "2" occurs when the equipment plug has
earth and neutral wires reversed - which goes unnoticed until the day it is
plugged into an outlet that has active and neutral reversed.


Crikey. Have you never heard of RCDs in OZ? I sort of guessed it was third
world - but not that bad.

--
*Aim Low, Reach Your Goals, Avoid Disappointment *

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (Nutcase ****head )


Crikey. Have you never heard of RCDs in OZ?


** We have plenty of Ratbag Criminal Dickheads here.

All of them ****ing, pommie ****s like you.

On Sat, 02 Aug 2014 11:24:57 +1000, Phil Allison wrote:

"mick"

That would make it a Class II (double-insulated) appliance.

** Absurd crap !!!



Ah... yes... That screen couldn't make it Class II could it? It would
need to be earthed. lol I missed that one!

I take that back, the Quad 303 definitely requires a mains earth to the
metalwork in order to comply with current UK regs. It can't rely on the
input connector as that can be unplugged while leaving the mains supply
connected. That makes it even more sensible not to connect signal earth
directly to chassis in the 303.


The basic principle of Class II is *NOT* to rely on the mains earth for
user safety.

Two reasons:

1. If the mains earth connection is missing anywhere, the equipment
still operates ( with no warning to the user) and you have no safety.

2. If the AC outlet or equipment plug is miswired, active can appear on
the earth conductor and you have a lethal situation.



The principle of Class II is that there is NO REQUIREMENT to rely on
earthing for user protection at all, as all mains-carrying wiring is
double-insulated away from the user side. Note that phone chargers etc
are virtually all Class II. In the UK these have a dummy plastic earth
pin which is only used to open the live & neutral shutters on the socket.

The mains output sockets on the 33 almost certainly wouldn't be legal now
anyway. Getting live and neutral right way round is a 50/50 guess.


A very nasty example of scenario "2" occurs when the equipment plug has
earth and neutral wires reversed - which goes unnoticed until the day it
is plugged into an outlet that has active and neutral reversed.


Agreed. It's only relatively recently that domestic wiring in the UK has
been using earth-leakage protection. Older installations (including my
own!) don't have it - in fact, I'm still on rewirable fuses here!
Consequently we tend to be careful about wiring plugs & sockets up
correctly. Even when properties are being refurbished over here, there
is no legal requirement to change any existing distribution boards etc.
unless they are damaged. Consequently there are a lot of houses in the
same condition as mine.

"mick"

The basic principle of Class II is *NOT* to rely on the mains earth for
user safety.

Two reasons:

1. If the mains earth connection is missing anywhere, the equipment
still operates ( with no warning to the user) and you have no safety.

2. If the AC outlet or equipment plug is miswired, active can appear on
the earth conductor and you have a lethal situation.


The principle of Class II is that there is NO REQUIREMENT to rely on
earthing for user protection at all,

** Not correct.

There must be NO earth connection made to the item.

The familiar notice reads:

" Double Insulated Do Not Earth. "
-------------------------------------


A very nasty example of scenario "2" occurs when the equipment plug has
earth and neutral wires reversed - which goes unnoticed until the day it
is plugged into an outlet that has active and neutral reversed.


Agreed. It's only relatively recently that domestic wiring in the UK has
been using earth-leakage protection. Older installations (including my
own!) don't have it - in fact, I'm still on rewirable fuses here!
Consequently we tend to be careful about wiring plugs & sockets up
correctly. Even when properties are being refurbished over here, there
is no legal requirement to change any existing distribution boards etc.
unless they are damaged. Consequently there are a lot of houses in the
same condition as mine.


** Much the same situation exists in Australia, though it varies from state
to state.

Interestingly, in the USA it has been compulsory to fit safety devices to AC
outlets in bathrooms for decades.

Originally they used mechanical "core balance relays" instead of the modern
electronic version.


.... Phil

In article ,
Phil Allison wrote:
The principle of Class II is that there is NO REQUIREMENT to rely on
earthing for user protection at all,

** Not correct.

There must be NO earth connection made to the item.

The familiar notice reads:

" Double Insulated Do Not Earth. "
-------------------------------------

Which means then in amplifier terms it cannot be connected to a device
where the signal ground is connected to main ground?

Something wrong there...

--
*I want it all and I want it delivered

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (Nutcase TROLL)"
Phil Allison

The principle of Class II is that there is NO REQUIREMENT to rely on
earthing for user protection at all,

** Not correct.

There must be NO earth connection made to the item.

The familiar notice reads:

" Double Insulated Do Not Earth. "
-------------------------------------

Which means then in amplifier terms it cannot be connected to a device
where the signal ground is connected to main ground?

Something wrong there...

** Absolutely correct.

Class II items should ONLY be interconnected with other class II items,
however with audio and video gear, everyone breaks the safety rule. The
hazard of doing this is an X rated topic that one must never mention.

Class II items are inherently safe until you connect them to a class I
item - so when that class I item develops a safety fault, the whole shebang
becomes a death-trap.

With a class I system, each item grounds the others so it is also inherently
safe.

In the world of live music, I have come mixed class I / II systems that are
very scary.



..... Phil

In article ,
Phil Allison wrote:

In the world of live music, I have come mixed class I / II systems that
are very scary.

In UK TV studios etc, before the days of RCDs etc, every single item of
unknown equipment - like say a guitar amp etc supplied by a musician - was
fed via a mains isolation transformer. Expensive and time consuming but
very necessary.

--
*I'm planning to be spontaneous tomorrow *

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Phil Allison wrote:
** Much the same situation exists in Australia, though it varies from
state to state.

Interestingly, in the USA it has been compulsory to fit safety devices
to AC outlets in bathrooms for decades.

In the UK until fairly recently, the *only* AC socket allowed in a
bathroom was a shaver socket fed via an isolating transformer. Also things
like light switches had either to be outside the room, or of an insulated
type like a pull cord one.

--
*If I agreed with you, we'd both be wrong.

Dave Plowman London SW
To e-mail, change noise into sound.