A star ground is just a circular bus or a very short bus. Grounding is
is tricky and tiresome in inverse proportion to the amount of thought
you give it, so I do something between what Iain does and what Patrick
does, and I call it a "star-point". Here you can see my star point
http://members.lycos.co.uk/fiultra/K...0T68MZ417A.jpg
on my T68bis "Minus Zero" amp. It is the short piece of stiff wire
sticking up at the right hand side of the aluminium cased resistor
behind the battery boxes in the centre of the top right hand
photograph. It's the bleeder resistor to the power supply and the star
point is at its 0V end. Notice how the convenitonally drawn schematic
http://members.lycos.co.uk/fiultra/t...17acircuit.jpg
tells you nothing of this, leaving you to work it out for yourself.
All the 0V wires are dropped over this stiff wire and soldered on.
Even on such a short bus I take care of the order of the wires as I
put them on. From this point a wire is taken to main's earth. The case
is connected to mains earth by a wire from very sturdy bolt held in
with serrated washers and nuts, which is placed as near as possible to
the mains socket; unfortunately it is not too clear in the photograph,
but it is just below the switch, near the top right hand corner of the
righthand output transformer in the picture.
Most schematics don't tell you enough about earthing. Here, for
instance:
http://members.lycos.co.uk/fiultra/Jute-EL34-SEntry.jpg
I've shown the star earth being implemented but have not said anything
about connecting the case to earth. Mind you, on some of the Lundahl
Modular Series 300B schemos I showed all the 0V connections in order,
with a note saying "mind the order of the grounding connections", and
two people wrote me letters saying that DIYers are not idiots who need
their hands held. (I was, when I started, and I'm very grateful to
people who made 90 mile round trips to come check over my
constructions before I fired them up.)
Andre Jute
Visit Jute on Amps at
http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
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containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review
On Mar 2, 12:39*pm, "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 important
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?
My experience with ground buss amps is limited. I have never been
able to make them quiet enough. I found that the exact position in
which a wire was placed on the buss was critical, and that a difference
was audible.It may be there is something lacking in my implementation
of the buss.
I prefer to use a star ground, as follows. *Earth (ground) connection
from the supply - the only green yellow wire in the amplifier is taken
straight to the chassis bonding screw. *The input and output RCA
signal connectors I used are the isolated type (Neutrik NF2D)
http://www.neutrik.com/uk/en/audio/2...-0_detail.aspx
I run a separate wire (black) from each of the RCA input and output
ground tags to the star ground. Signal wires on the input side have
their shields connected at the RCA socket end only.
On the psu, I run separate grounds (heavier wire) from each cap
separately to the star. They are not linked. *The only exception to
this is the 1st (reservoir) electrolytic , which is connected directly
to the neg terminal of the FW bridge, and then to the star.
This is a topology I have seen used on amps that perform well,
and has been taught to me as a good solution.
It seems to work. My 50W power amp has only 80µV
of noise (-108dB) and no audible hum even with the ear
against the speaker (Tannoy Gold 15 inch)
Regards to all
Iain