Dr. John or Richard re no Mains T screen wire with 300b PSE

[Audionorth]

I have two questions but I think I will post the other in a different thread so as not to confuse the issue (even though they may be related). Since I have been working to reduce the hum in my amps, I have been looking at the earthing scheme.

Below is a copy of my original e-mail with Nick Lucas (of WAD) back in 03 regarding the fact that I was confused that my mains T didn't come with a screen wire.


My question:

"I've been wiring up one of the amps according to the directions. I've reached step Route J and have run into what appears to be a problem.

My Mains Transformer primary has four wires only (red, blue, brown, orange). But the step instruction references a green/yellow wire."


Nick's response:

"Hello, we have taken off the screen, not required so pls ignor the section of the yellow/green wire. The other primary wires are correct . . .

Cheers, Nick"


Since my mains Ts didn't come with a screen wire, should I implement the star earth/ground via the instructions provided with the kit or should I be doing something else?

Thanks,
Mike

[John Caswell]

Hi Mike,
Simple answer is yes. The star earthing will not be affected by the lack of yellow/green wire which was an electrostatic scrreen between the primary and secondary windings in the Tx. It was not connected in any way to any of the windings in the power Tx.
All you have to do is ignore the instructions for this wire.
What I tend to do is provide an insulated tag or tags for the star earth and then connect them to chassis earth via a 10R/2Watt resistor in parallel with a 0.1µf/250V capacitor. The power line earth of course must go directly to chassis earth.

John aka Dr John