EMI shielding suggestions?

[saildoctor]

Ok - in my Paramount / FPIII / Seduction system I've recently taken out the 3x voltage divider from input of the Paramounts and went back to a 250k tantalum resistor to ground.  Now I remember why I put that on.  The FPIII is picking up a lot of EMI - very large amounts of it!

I would like to try shielding the inside of my BH bases and was wondering if there were any tips / solutions out there already before I went and did something.  I actually already have some thick copper sheeting that I found and was thinking of cutting that to line the insides and solder some copper or aluminum mesh across the bottom.  I'm guessing it would store quite a bit more heat under the hood this way though.  Would just gluing some aluminum foil probably be just as effective you think?

 

[Grainger49]

Kerry,

Do you know if it is the tubes or the circuit that is picking up the EMI?  I ask just to keep you from doing something that doesn't help the situation.  You could try shielding the tubes with a ground on the shield.

If you have gone that route already, never mind!

 

[johnsonad]

I was thinking tube shielded sockets if you don't already have them.  Moving the preamp may be easier than the shielding rework though.

 

[4krow]

One thing that I have used in the past is a cloth made just for shielding EMI/RFI. Sorry I don't recall the name of it, but I got it from parts connexion, and it is easy to work with.

 

[saildoctor]

I don't think it's the tubes - I draped over a piece of aluminum foil tight around them making sure to close in on the top plate and couldn't hear any difference.  I did however try something I had not before - disconnecting all but one of my inputs.  Hey now - that cut what I'm hearing coming out of the speakers in half!  Must have some ground loop issues too!    I'll work on that later and see if I can find something to cut and try that copper sheet I've got.

 

[4krow]

Hum seems to end up in a search for better or worse. Good thinking you have by disconnecting all of the inputs except one. Now, you might try disconnecting it just to see if that stops your problem.

 

[2wo]

Make a pair of shorting plugs and work your way back from the amps. then swap out each interconnect, even with cheep ones that came with a VCR or whatever. before you look at shielding...John

 

[Paul Birkeland]

Hello Kerry,

So with the volume controls all the way down on the Foreplay, you have a fair amount of noise coming through the Paramounts?

The voltage divider at the input of the Paramounts is the correct implementation if this is the case.

-PB