Copper tape on output transformer

I've seen output trafos (like the Profile 4804 and API) that have some kind of copper tape wrapped around it.

Is there a purpose for that? Or it's just there for aesthetic reason?

Here's a sample photo of what I mean...

Hmmmm.... looks like copper shielding to me... probably grounded.  I know edcor does this with some of their tranny's

ok, copper tape always means shield, but for what?

could be between windings to minimize stray C, obviously not that, because it is wrapped around the outside.

could be to prevent noise from entering the transformer, but this 1:1 brute has zero noise floor problems, it's an output.

so, that leaves shielding, to keep the Transformer from coupling with any other output that might be nearby.
If you want 300 db seperation, there ya go.


  If you think 60 cps radiation travels into your hum box, try 20,000 cps.

the copper foil forms a shorted turn winding.  because it is around the OUTSIDE of the core (and does not go through the "window" where the windings wrap around the center leg) only the STRAY flux from the transformer couples to the shorted turn.  this can reduce radiation from the transformer which might couple into input transformers, etc, which is what CJ is getting at.  you more often see this sort of thing on power transformers.

ed

Thanks for the responses. 
Yeah, Cinemag does not do it on their output trafo, thus the curiousity on why some manufacturers have it and some don't.

I have copper tape (one sided adhesive) that I wrapped around my output trafo to "dress it up", and it does look better (must be the shiny copper).  ;D

I just don't know if it also needs to be connected to ground to properly do it's thing,
or is just wrapping the copper tape around the trafo enough?

Here's my "dressed up with copper" Cinemag output trafo.

Probably there to reduce coupling with adjacent units, like a 500 style rack where the outputs
are lined up with only a fraction of an inch separation.

you don't need to ground it, but you do need to make sure that the two ends of the tape are electrically connected where they overlap.  this can be difficult to test for since the DCR of the foil is low.  most transformers that you'll see this shielding on are soldered where the join happens.

ed

Ed, CJ, Dan, Davo... thanks for the information. Much appreciated!

i have seen that copper taped used in a grounding scheme many of times.
i always assumed it acted as a faraday shield causing a ground field around the object shielded to null out magnetic radiation.
it is only used on open frame transformers because obviously closed frame trannies are grounded through fastening.
http://en.wikipedia.org/wiki/Michael_Faraday

another reason i like to use aluminum chassis verses steel....steel may be tougher, but it is harder to drill and machine, aluminum does not rust
and most of all.....aluminum is non magnetic. Having a transformer in an aluminum case or walled away from components or on the other side of a chassis, cuts down on radiation.

On single coil pickups, i wrap some thin pipe tape around them, the a layer of copper tape...have a ground from the copper tape to the star/other grounding scheme and it breaks down much of the noise and microphonics. Usually i throw em in a wax pot right after.
Unfortunatly, i think this takes away a bit of high end, but depends on the pickup.

michael faraday...
we owe alot to him along with tesla, edison and maxwell and countless others who's tinkering and laboring led to....preamps!
oh, and electricity.
chicken, egg....i eat them both!

http://en.wikipedia.org/wiki/James_Clerk_Maxwell

before they used copper tape: