AW: To earth, or not to earth...

[Martin Czech]

> Is there any regulation (VDE or so) that says circuit ground has to be
> connected to Protective Earth? This connection is made in many devices
> and it causes trouble again and again.
Only if signal ground is connected to chasis ground.
This is not always needed.

But it is the case with all guitar tube stuff, because signal ground goes
to the strings and guts of the guitar.

In my understanding of VDE/IEC stuff, our types of DIY belong to
Protection Class I Devices. That is: Possible Hazard of dangerous
voltage at chassis, because you don't always have the right material
(trafo, mounting stuff) to get class II.  And class I means: Chassis
ground to supply earth, i.e. all conductive parts that can be touched
by the user, even potis, if there are metal.  Most industrial stuff
(19" ware) belongs to class II, because they have double insulated
trafos, special power chords etc., so there is no possibility that the
metall chasis will get hazardous voltage. In this case the chassis is
not grounded.

I think: keep all 230 Volt stuff into a separate metal enclosure.  Put
it far away.  Ground it. This way you keep also magnetic fields etc
away.  Good mixing consoles do it that way.  Use good, shielded trafos,
that is ground shield between prim. and second.  If the low voltage
side is properly mounted, so there is no possibility ever to connect to
chassis or power (carefull at chassis openings etc.) the audio device
may not be grounded. But in this case, you'll loose some hf shielding.
I'd ground the audio devic, too. But no connection to signal ground,
thus no hum.

Best connection between 2 "boxes":  Both metal enclosures to the *same*
supply earth.  Banlanced cable between, with shield to chassis at
*both* sides.  No connection between chassis ground and signal ground.

> If there is such a regulation, what about laboratory power supplies?
> They always have earthfree outputs.
They are for "expert use" only.

> If there is not, why do so many manufacturers implement this connection?
You mean class II. See above.

All tube stuff I have is properly earth grounded. I don't want to feel
500V anode suplly!

m.c.