Re: Ground Busses

Andre Jute wrote:
 snip for brevity, 
 
> Most schematics don't tell you enough about earthing. 

This is a very true statement if ever there was one.

A schematic is just how things are connected, and sure, worth a thousand
words.

But they are often utterly useless in telling folks how to layout 
the circuit and placement of parts and wiring for 
best operation, freedom from micro power supply rectifying noise
voltages in 0V wiring,
magnetically induced mirco voltages, and return current effects in load
current carying wiring 
etc etc etc. 

A lot is left for the maker to get right.

Countless times diyers construct something with the exact and right
schematic
but are left with deafening hum and noise problems, and with
maybe RF oscilations as well, all because of very poor understanding
of most basic aspects of electronics. When told to spend weeks doing
some real learning,
they just cannot do it because they don't have a questioning mind.

In a recent case a guy with an old tubes CJ preamp had me instal
a fet cascode circuit for the MC input to suit his MC cart because the
CJ
had a rather poor tubed phono rendition fit only for high output MM.
I finally got the 0V pathing adjusted after several hours to give
negligible
hum when the preamp gain was set to normal operation level 
with an average power amp connected with a speaker.
He appreciated the revaltion the MC cart gave him.
Then he wanted all the crummy old 1960s RCA sockets replaced to stop the 
intermittent noises he was getting.

My time is valuable, and too valuable to do the donkey work 
of replaceing RCA sockets, so I insisted he learn to use a drill and
make a new panel and 
pay for some Cardas sockets and do it himself.
Of course he insisted on remaining a practical klutz, and talked his dad
into 
doing this highly skilled but tedious task for nothing of course.
His dad wanted to keep the exact positions of the existing RCAs the same
so as not to 
disturb what 0V rails I had arranged initially.
But the guy had his dad change the positions to suit two different sizes
of new RCAs,
so that phono input wiring was 150mm longer, and woe, he used untwisted
1mm thick house wire type wires.

When he tried te amp, its hum was quite deafening, and ther amp
was unusable, so he comes across town to me for a fix, cheaper than
learning anything.

I re-route the cabling internally to where it was, but get him to agree
there was no difference 
in quality the two sizes of RCA sockets, so no need to make the
compromise in positioning 
just because of some wacky idea about the RCA socket quality.

He went away after $50 worth of work which stuffed my afternoon on a
saturday
but he had a Turnerized Conrad Johnson that wasn't noisy any more,
and he had some real understanding of how bleeding im****tant 
it is to consider everything about all aspects of what you're doing
when making any changes to circuits.




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.)

The schema above is fine, but has no chassis shown,
so I suggest 27ohms x 5W from star 0V point to chassis point near the 
RCA inputs and well away from the PT.

The mains green / yellow earth wire sould also be taken to a chassis
point away from the 
PT, and not necessarily to where the 27ohm is anchored, to reduce
induced chassis voltages.....

I might add that 0V rails layout is even MORE critical in high powered
SS amps...

Patrick Turner.