Farady shield to power ground

[pjd3]

Hi all,
Just a couple more wires to go then done!

I'm wondering best place for the Faraday shield. Never came across that in the posts. If I didn't know better (which I don't) I would wire it to power ground.

Is that what you would do?

Thank you everyone, you've been great guidance during this venture.

Phil D

[xtian]

Are you talking about the shield on the PT? Ground that to chassis anywhere convenient.

[pjd3]

Thank xtian. Yes. Orange wire from a Mojotone Bassman PT. There is a note on the spec sheet saying simply to connect orange Faraday shield wire to ground. I just wanted to hear someone elaborate on that since ground locations for certain things have so far been something of importance.

Thank you!

Phil D

[pompeiisneaks]

Yeah anywhere will work, it just is a copper band wrapped around the transformer that, if earthed, helps control stray magnetic fields by pulling them to earth. They're not high current or problematic like some grounding stuff can be, so literally anywhere works, but it's usually just easiest to put it near the transformer that it's connected to. Simple.

~Phil

[pjd3]

Thank you guys,
I just connected it to power ground. It was there and convenient

Best,
Phil D

[pjd3]

Thank you guys,
I just connected it to power ground. It was there and convenient

Best,
Phil D

[TUBEDUDE]

Also called a flux band.

[Tony Bones]

If we're getting technical....

There's (at least) two kinds of shield that you might find on a transformer. One kind is actually around the outside of the coil and core. It goes on after the transformer is more or less fully assembled, but possibly before paint. They're sometimes called a flux band and do not have a separate wire attached to it; it's already in contact with the core anyway. It's purpose is to reduce radiated field. It works because field that makes it that far will create current that runs around the band. This current creates an equal and opposite field that essentially cancels the offending field.

The other kind is a static shield between windings. When this shield is grounded (or tied to any low impedance, steady voltage) it reduces capacitive coupling between the two windings. Usually, this is placed in a power transformer between the primary and secondary windings. A lot of HF electrical noise will enter a transformer in common mode, i.e. it appears on both ends of the primary with the same voltage (picked up while traveling through ordinary power wiring in a building.) This common mode noise gets capacitively coupled to the secondary(s) as common mode and doesn't get filtered by the PS caps. The static faraday shield reduces the capacitive coupling of the common mode noise.

It's old school but effective. The new school way is to put a tiny common mode choke in the power circuit, often built in to the IEC connector.