Re: Ground Busses

Iain Churches wrote:
> 
> "Patrick Turner" <info@[EMAIL PROTECTED]
> wrote in message
> news:47CAAC99.9BE36341@[EMAIL PROTECTED]
> >
> >
> > Iain Churches wrote:
> >>
> >> Patrick posted some interesting facts about ground buss
> >> connections, which I have extracted from another thread
> >> and pasted here, because I think the subject is im****tant
> >> enough to warrant  its own thread.
> >>
> >> He wrote:
> >>
> >> > The 0V rail of the preamp should be a short buss wire about 100mm
long
> >> > with ends connected to the RCA plug 0V bodies at inputs and
outputs.
> >> > ALL parts with OV connections should be made to this buss,
> >> > and the CHASSIS or CASE connected via a 5 watt 27 ohm R, and the
case
> >> > taken to the  green/yellow wire to the wall socket so the case
can't
> >> > become live to mains or the B+. There should be NO direct
connection of
> >> > the OV buss to the case.
> >> --
> >>
> >> I ask:
> >>
> >> In other words the mains supply case should be bonded to the case,
> >> and the 0V (signal grounds) taken to the ground point via a 27 Ohm
> >> 5W resistor?
> >>
> >> Why is this?
> >
> > Because chassis can have magnetically induced voltages in them,
> > they should never be used for the 0V rail.
> >
> And why 25W?

I said 5W, but 25W would be OK.

Because you don't want that R to go open, ever, or the whole audio
circuit 
IS NOT REFERENCED TO THE CHASSIS AND EARTH, something I feel is
im****tant.

If the B+ becomes shorted to the chassis, you want the fuse to blow
because of that short.
You DON'T want a 27 ohm x 1/4 watt R to fuse open in an instant, leaving
the 0V rail at +500V,
including the OV rail and the speaker wires....

Hope for the best with your amps, but ALWAYS prepare for the worst!

Patrick Turner.


   
> 
> Iain